i CONTENTS CHAPTER-1 INTRODUCTION 1.1 Introduction 1-1 1.2 Arunachal Pradesh and Its River Systems 1-2 1.3 Power Potential Of Arunachal Pradesh 1-4 1.4 Project Profile 1-7 1.5 Project Developer - Bhilwara Energy Ltd. 1-9 1.6 Policy, Legal and Administrative Framework 1-10 1.7 Scope of the EIA Study 1-10 1.8 Stages in an EIA Study 1-11 1.9 Outline of the Report 1-12 CHAPTER– 2 PROJECT DESCRIPTION 2.1 Introduction 2-1 2.2 Nyamjangchhu River Basin 2-1 2.3 Justification of Various Project Alternatives 2-2 2.4 Project Details 2-8 2.5 Salient Features 2-10 2.6 Land Requirement 2-14 2.7 Infrastructure Facilities 2-17 CHAPTER-3 METHODOLOGY ADOPTED FOR THE EIA STUDY 3.1 Introduction 3-1 3.2 Study Area 3-1 3.3 Scoping Matrix 3-1 3.4 Data Collection 3-4 3.5 Summary Of Data Collection 3-8 3.6 Impact Prediction 3-9 3.7 Environmental Management Plan And 3-10 Cost Estimates 3.8 Resettlement And Rehabilitation Plan 3-10 3.9 Catchment Area Treatment Plan 3-11 3.10 Tribal Development Plan 3-11 3.11 Environmental Monitoring Programme 3-11 CHAPTER–4 HYDROLOGY 4.1 Basin Description 4-1 4.2 Water Availability Study 4-2 4.3 Dependable Flow Analysis 4-14 4.4 Design Flood Studies 4-17 4.5 Discharge data measured at site 4-19 4.6 Sediment data measured at site 4-20
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CONTENTS CHAPTER-1 INTRODUCTION 1.1 Introduction 1-1 1.2 Arunachal Pradesh and Its River Systems 1-2 1.3 Power Potential Of Arunachal Pradesh 1-4 1.4 Project Profile 1-7 1.5 Project Developer - Bhilwara Energy Ltd. 1-9 1.6 Policy, Legal and Administrative Framework 1-10 1.7 Scope of the EIA Study 1-10 1.8 Stages in an EIA Study 1-11 1.9 Outline of the Report 1-12 CHAPTER– 2 PROJECT DESCRIPTION 2.1 Introduction 2-1 2.2 Nyamjangchhu River Basin 2-1 2.3 Justification of Various Project Alternatives 2-2 2.4 Project Details 2-8 2.5 Salient Features 2-10 2.6 Land Requirement 2-14 2.7 Infrastructure Facilities 2-17
CHAPTER-3 METHODOLOGY ADOPTED FOR THE EIA STUDY 3.1 Introduction 3-1 3.2 Study Area 3-1 3.3 Scoping Matrix 3-1 3.4 Data Collection 3-4 3.5 Summary Of Data Collection 3-8 3.6 Impact Prediction 3-9 3.7 Environmental Management Plan And 3-10 Cost Estimates 3.8 Resettlement And Rehabilitation Plan 3-10 3.9 Catchment Area Treatment Plan 3-11 3.10 Tribal Development Plan 3-11 3.11 Environmental Monitoring Programme 3-11 CHAPTER–4 HYDROLOGY 4.1 Basin Description 4-1 4.2 Water Availability Study 4-2 4.3 Dependable Flow Analysis 4-14 4.4 Design Flood Studies 4-17 4.5 Discharge data measured at site 4-19 4.6 Sediment data measured at site 4-20
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CHAPTER-5 BASELINE SETTING FOR PHYSICO-CHEMICAL ASPECTS
5.1 General 5-1 5.2 Meteorology 5-1 5.3 Geology 5-6 5.4 Geomorphology of The Project Area 5-10 5.5 Seismicity 5-11 5.6 Land Use Pattern 5-15 5.7 Soils 5-17 5.8 Water Quality 5-22 5.9 Ambient Air Quality 5-27 CHAPTER-6 BASELINE SETTING FOR ECOLOGICAL ASPECTS
7.1 General 7-1 7.2 Demographic Profile of Arunachal Pradesh 7-1 7.3 Demographic Profile of Twang District 7-2 7.4 Demographic Profile of the Study Area 7-3 7.5 Socio-Economic Survey For Project Affected Families 7-8 7.6 Socio-Economic Profile of the Project Affected Families 7-9 CHAPTER-8 PREDICTION OF IMPACTS 8.1 General 8-1 8.2 Impacts on Water Environment 8-5 8.3 Impacts on Air Environment 8-11 8.4 Impacts on Noise Environment 8-13 8.5 Impacts on Land Environment 8-18 8.6 Impacts on Biological Environment 8-30 8.7 Impacts on Socio-Economic Environment 8-38 8.8 Increase Incidence of Water-Related Disease 8-39
CHAPTER-9 CONSTRUCTION METHODOLOGY
9.1 General 9-1 9.2 Basic Assessment of Construction Methodology 9-2 9.3 Pre Construction Activities 9-2 9.4 Approach Road and Bridge 9-3 9.5 Basic Considerations 9-3 9.6 Detailed Design and Construction Drawings 9-3 9.7 Basic Assumptions for Equipment Planning 9-3 9.8 Methodology of Construction for Various Activities 9-5 9.9 Equipment Planning 9-14
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Annexure Annexure-I A copy of the TOR approved by MoEF Annexure-II Drinking Water Quality Standards Annexure-III National Ambient Air Quality Standards Annexure-IV Ambient Noise Standards Annexure-V List of Plant Species (With their Family and Local Names) Found in the Study Area
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LIST OF FIGURES
Figure-1.1 Major river system of the state
Figure-1.2 Location of Tawang district Figure-1.3 Project location map Figure-2.1 Layout Plan
Figure-3.1 Study area map Figure-4.1 Satellite image of Nyamjang Chhu catchment Figure-4.2 Catchment area map showing drainage network
Figure-4.3 Rainfed and Snowfed catchment area Figure-4.4 Location of IMD stations in the region Figure-4.5 Flow duration curve Figure-5.1 Location of IMD stations at Bhalukpong and Dirang Figure-5.2 Annual rainfall at Bhalukpong and Dirang Figure-5.3 Monthly average rainfall at Bhalukpong and Dirang Figure-5.4 Seismic zoning map of India Figure-5.5 FCC image of the project area Figure-5.6 Classified image of the project area Figure-5.7 Sampling stations (Soil, Noise) Figure-6.1 Ecological sampling location (WAPCOS) Figure-6.2 Ecological sampling location (RSET) Figure-9.1 HRT Layout
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CHAPTER-1
INTRODUCTION
1.1 INTRODUCTION
India’s installed capacity in the hydropower sector is presently estimated at
around 36498 MW out of total installed capacity of 146753 MW. Only about 20%
of the economically feasible hydropower potential has been exploited. The
economic development in the country in recent times has resulted in widening of
the gap between the demand and the supply of power. In order to make power
available to all by 2012, the total installed capacity is planned to be increased to
about 210000 MW. The development of hydropower potential can significantly
help to bridge the gap between power demand and supply. The central
government alongwith various state governments have taken significant initiatives
for development of power projects in both public as well as private sectors.
Special emphasis is being made for development of hydropower potential of the
country to keep a balanced mix of thermal and hydro power generation.
Arunachal Pradesh, with an area of 83743 km2, is the largest state in the north-
east region in terms of land area. The state is endowed with mighty rivers with an
estimated feasible hydropower potential of about 57,000 MW. The hydropower
development in Arunachal Pradesh has been identified as a key area by both the
government of India and the state government of Arunachal Pradesh as one of the
key areas for meeting the country’s increasing energy requirements. Fast track
development of hydropower potential in the state both in public and private sector
is being pursued by Government of Arunachal Pradesh (GoAP). The state
government has signed Memoranda of Understanding (MoU) with 25 developers
for development of over 27000 MW of hydropower potential in the state.
The Government of Arunachal Pradesh has awarded the work of development of
the hydropower potential in the Nyamjang Chhu Basin in Tawang district to
Bhilwara Energy Limited (BEL). A memorandum of agreement in this regard was
signed between GoAP and BEL at Itanagar on the 27th October, 2006. The project
is designed as a run-of-the river scheme having a diversion barrage near the
Zimithang village with powerhouse near the confluence of the Tawang Chhu with
the Nyamjang Chhu.
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1.2 ARUNACHAL PRADESH AND ITS RIVER SYSTEMS
Profile
Arunachal Pradesh – the Land of the Rising Sun – with an area of 83,743 sq km.
is the largest state in the North Eastern region sharing international boundaries
with Bhutan in the West, China in the North and Myanmar in the East. The States
of Assam and Nagaland flank it’s Southern and South Eastern borders. The state
of Arunachal Pradesh is situated between latitudes 26° 30' N and 29° 30 ' N and
longitudes 91° 30' E and 97° 30' E. Arunachal Pradesh is divided in thirteen
administrative districts namely; Tawang, West Kameng, East Kameng, Lower
Subansiri, Upper Subansiri, West Siang, East Siang, Dibang Valley, Changlang,
Tirap, Papum Pare, Lohit and Upper Siang. The main rivers in the State are the
Siang, Kameng, Subansiri, Kamla, Siyom, Dibang, Lohit, Noa-Dihing Kamlang and
Tirap.
Forest covers about 82% area of the state and numerous turbulent streams,
roaring rivers, deep gorges, lofty mountains, snow clad peaks and rich diversity
of flora and fauna characterize the landscape. The climate varies from sub-
tropical in the South to temperate and alpine in the North, with large areas
experiencing snowfalls during winter. The heights of the mountain peaks vary,
the highest peak being Kangte (7,090m above msl) in West Kameng District.
The major rivers draining the area with their numerous tributaries from west to
east are Tawang, Kameng, Subansiri, Siang, Dibang, Lohit, Kamlang, Noa -
Dihing and Tirap.
Climate
The climate of Arunachal Pradesh varies with elevation. Areas at high elevations in
the Upper Himalayas, close to the Tibetan border are subject to a Tundra-type
climate, while areas in Middle Himalayas have a temperate climate. The sub-
Himalayan and sea-level elevation areas generally experience a humid sub-
tropical climate, along with hot summers and mild winters. The annual average
rainfall in various parts of Arunachal Pradesh varies between 2000 mm and 4000
mm. The area experiences high precipitation during the monsoon period between
May and September. The prolonged period of Monsoon has resulted in lush forest
growth over the hill slopes. The mountain slopes are covered with Alpine,
Temperate and Subtropical forest of dwarf rhododendron, Oak, Pine, Maple and
Fir. Juniper, Sal and Teak are the main economic species. During winters,
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especially months of December to February, the area experiences severe fog with
thick mist formation and occasional rainfall. The summer season is hot and humid.
Flora
Arunachal Pradesh has a rich diversity of flora and fauna and the state is entirely
covered with hills and forests. Nearly 61000 sq. km of the total land area of
83743 sq. km is covered with forests. Forest products are the most significant
sector of economy next to agriculture. These forests are home to a sizeable
population of various tribes who extract resources from them for their livelihood.
The forests of Arunachal Pradesh include some 5000 species of plants, about 85
terrestrial mammals, over 500 birds and a large number of butterflies, insects and
reptiles.
The vegetation of the state falls under four broad climatic categories and can be
classified in five broad forest types which are: tropical forests, sub-tropical forests,
pine forests, temperate forests and alpine forests.
Rivers
There are five major river basins in the State, namely Kameng, Subansiri, Siang,
Dibang and Lohit River basin. Almost all the major river systems flow from
North to South and ultimately drain into the Brahmaputra. Apart from the major
rivers, the State has many small rivulets which are perennial in nature and
provide ideal condition for developing projects in the category of micro/mini and
small HEP. The major river system of the state are shown in Figure-1.1.
Figure-1.1: Map of River Systems
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1.3 POWER POTENTIAL OF ARUNACHAL PRADESH
Arunachal Pradesh has a huge potential to generate hydroelectric power. The
state has number of large, medium, mini and micro hydel projects. The
Government of Arunachal Pradesh began planned development of the hydropower
potential of the state and invited private developers to invest in the hydropower
sector for the economic growth of the state and to decrease the energy deficit in
the country. The details of projects being developed in Arunachal Pradesh are
indicated in Table 1.1.
TABLE -1.1 BASINWISE HYDRO POWER PROJECTS UNDER DEVELOPMENT IN
ARUNACHAL PRADESH S. No.
Basin Name of Project
Probable IC (MW)
Allotted to
1 Tawang Tawang-I 750 NHPC
2 Tawang Tawang-II 750 NHPC
3 Tawang Nykcharongchu 96 SEW Energy
5 Tawang Mago Chu 96 SEW Energy
6 Tawang Nyamjungchhu 900 Bhilwara Energy Ltd.
TOTAL OF TAWANG BASIN 2592
1 Kameng Kameng-I 1120 NEEPCO
2 Kameng Kameng-II 600 Mountain Fall India Pvt. Ltd. 3 Kameng Kameng Dam 600 KSK Electricity Financing India
Pvt. Ltd.
4 Kameng Gonri 90 Patel Engineering Ltd.
5 Kameng Saskang 7 Patel Engineering Ltd.
6 Kameng Talong 160 GMR Energy Ltd.
7 Kameng Phanchung 60 Indiabull Real Estate Ltd.
8 Kameng Utung 100 KSK Energy Ventures Ltd.
9 Kameng Nazong 60 KSK Energy Ventures Ltd.
10 Kameng Dibbin 125 KSK Electricity Financing India Pvt. Ltd.
11 Kameng Khuitam 29 Adishankar Power Pvt. Ltd.
12 Kameng Pichang 31 Indiabull Real Estate Ltd.
13 Kameng Tarang Warang 30 Indiabull Real Estate Ltd.
14 Kameng Sepla 46 Indiabull Real Estate Ltd.
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S. No.
Basin Name of Project
Probable IC (MW)
Allotted to
15 Kameng Jameri 50 KSK Energy Ventures Ltd.
16 Kameng Tenga 8 ECI Engineering & Const. Company Ltd.
17 Kameng Dimijin 20 KSK Energy Ventures Ltd.
18 Kameng Dinchang 90 KSK Energy Ventures Ltd.
19 Kameng Dinen 10 KSK Energy Ventures Ltd.
20 Kameng Dikhri 15 KSK Energy Ventures Ltd.
21 Kameng Nafra 96 SEW Energy
22 Kameng Pakke Bung-I 15 Energy Development Company Ltd.
23 Kameng Pakke Bung-II 15 Energy Development Company Ltd.
24 Kameng Pachuk-I 60 Energy Development Company Ltd.
25 Kameng Pachuk-II 60 Energy Development Company Ltd.
26 Kameng Majingla 60 Energy Development Company Ltd.
27 Kameng Dengzi 18 Satyam (North East) Hydro Power Ltd.
28 Kameng Lower Ngorgum 18 Satyam (North East) Hydro Power Ltd.
29 Kameng Upper Ngorgum 9 Satyam (North East) Hydro Power Ltd.
TOTAL OF KAMENG BASIN 3602
1 Subansiri Par 65 KVK Energy & Infrastructure Ltd.
2 Subansiri Dardu 60 KVK Energy & Infrastructure Ltd.
TOTAL OF SUBANSIRI BASIN 125
1 Dikrong Pare 110 NEEPCO
2 Dikrong Turu 90 ECI Engineering & Const. Company Ltd.
economic aspects of environment. The baseline study involved data collection
using primary as well as secondary sources of data and public consultation.
Chapter-8 describes the anticipated positive and negative impacts as a result of
the construction and operation of the proposed Nyamjangchhu hydro-power
project. It is essentially a process to forecast the future environmental conditions
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of the project area that might be expected to occur as a result of the
construction and operation of the proposed project. An attempt was generally
made to forecast future environmental conditions quantitatively to the extent
possible. But for certain parameters, which cannot be quantified, general
approach has been to discuss such intangible impacts in qualitative terms so that
planners and decision-makers are aware of their existence as well as their
possible implications.
Chapter-9 gives a brief description of the methodology and schedule to adopted
for construction of the proposed Nyamjangchhu hydroelectric project.
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CHAPTER - 2
PROJECT DESCRIPTION
2.1 INTRODUCTION
The Nyamjang Chhu basin lies in the north-west area of Arunachal Pradesh
with its catchment spreading across international border covering part of Tibet.
Nyamjang Chhu originates from snow clad peaks in Tibet and flows in India
from north to south direction up to its confluence with Tawang Chhu. The total
catchment area of the Nyamjang Chhu up to the confluence with Tawang Chhu
is about 3170 km2. The catchment area up to diversion site near Zimithang is
about 2650 km2. The catchment area is mostly of tropical wet climate and
supports dense mixed forest. The area is characterized by hills with steep
gorges and deep rugged valleys with streams feeding Nyamjang Chhu River
system of which Takhsang Chhu and Sumta Chhu are major contributors.
Nyamjang Chhu Hydroelectric Project (HEP) is a run-of-the-river scheme with
reservoir having diurnal storage. The project is located in Tawang District of
Arunachal Pradesh. The project area is connected to other parts of the state
and Assam through road network and helicopter service.
The scheme envisages utilization of the available river flow at Zimithang and
gross head of about 1057.4 m between barrage and tailrace outfall near
confluence of Nyamjang Chhu with Tawang Chhu near Kumba village to
generate 780 MW in an underground power house. The Project is expected to
generate an annual energy of 3430.29 GWh, in 90% dependable year.
The diversion structure is proposed at Zimithang with FRL at El 2114.9 m.
Maximum Tail water level at the TRT outfall is El 1051.26 and the nozzle level
for Pelton turbines is proposed at El 1057.5 m providing a gross head for
power generation of 1057.4 m. The diversion of discharges from Taksang Chhu
to the water conductor system of Nyamjang Chhu HEP has been proposed at
an elevation EL.2151.4 m.
The total time schedule for the project construction is considered as 74-
months including 12-months for establishment of access roads,
infrastructural facilities and other pre-construction activities.
2.2 NYAMJANGCHHU RIVER BASIN
The Nyamjang Chhu basin lies in the north-west area of Arunachal Pradesh
with its catchment spreading across international border covering part of Tibet.
Nyamjang Chhu originates from snow clad peaks in Tibet and flows in India
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from north to south direction up to its confluence with Tawang Chhu. The total
catchment area of the Nyamjang Chhu up to the confluence with Tawang Chhu
is about 3170 km2. The catchment area intercepted up to diversion site near
Zimithang is about 2650 km2. The catchment area is mostly of tropical wet
climate and supports dense mixed forest. The area is characterized by hills
with steep gorges and deep rugged valleys with streams feeding Nyamjang
Chhu River system of which Takhsang Chhu and Sumta Chhu are major
contributors.
2.3 JUSTIFCIATION OF VARIOUS PROJECT ALTERNATIVES
Various aspects considered while selecting the scheme of Naymajangchhu HEP
are briefly described in the following paragraphs.
Topographical Aspects
Initial reconnaissance identified the suitable reach for project development
between Zimithang and Kumba villages. River bed Elevations at Zimithang and
at the confluence of Nyamjang Chhu with Tawang Chhu near Kumba village
are around El. 2106.2 m and El. 1041.4 m respectively. Topographical details
including physical features, villages, religious monuments and other structures
falling within the reach from Zimithang to the confluence were identified to
assess possible impacts of placing the project structures in development
alternatives.
Geomorphology of the area
The area is characterized by undulating dissected structural hills, which have
been denudated forming various features. The area near BTK Bridge is
characterized by massive landslides and a fault is located just upstream of the
Bridge. The area near Zimithang village is marked by flat river terraces and
flood plains. The river is about 200m wide at this location with very low
gradient making it suitable for the location of diversion structure.
Lithology
The general lithology observed in the area is as follows:
Phyllitic schist Schist with quartzitic bands Quartzite Gneiss with quartzitic bands Gneiss
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This is a metamorphic terrain and rock types are generally competent enough
for most project components. Major faults such as MCT, MBT are not traced in
the project area.
Social Aspects
The BTK Bridge is an important bridge linking the habitations in Zimithang and
other higher reaches of Lumla sub-division in Tawang district. Safety of this
bridge is required from adverse impact due to development of the project.
An important Buddhist religious site, the Gorsam Stupa (refer Exhibit-2.1), is
located about 8 km upstream of the BTK Bridge. It is a very old stupa held in
great esteem by the Buddhist Community. An annual festival attended by
Buddhists and other people from all over the state and abroad is held in this
Stupa. While formulating the project development scheme, it was ensured
that there are no adverse impacts to the Gorsam Stupa .
Exhibit – 2.1 : Gorsam Stupa
Environmental Aspects
The environmental aspects considered were:
• Minimal submergence area • Minimum tree cutting • Minimum disturbance to wildlife during construction of project and
other appurtenances including roads
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Alternatives Studied
The barrage site at Zimithang has been selected near Zimithang for the
following reasons:
provides the possibility for harnessing the highest feasible head
suitable for development in the Nyamjang Chhu.
height of the diversion structure is low as river gradient in this
reach is flat and the width of the river is sufficient to provide
peaking storage. The effect of seismicity on the diversion structure
will also be low.
minimal disturbance to the local population.
No impact on Gorsam stupa.
No adverse geological feature is observed in the vicinity of this
location.
Sufficient space for construction of barrage & desanding works
and for contractor’s facilities.
The study of geological features and field investigations suggest the depth of
rock available in this location varies from 60 to 90 m, as a result, barrage type
diversion structure is proposed.
As a part of DPR, four alternatives were studied. In all four alternatives,
barrage type diversion structure is proposed at Zimithang at river bed
elevation of 2106.2 m and Power House on the left Bank near Namstering
Village with tailrace discharging at EL. 1051.26 m.
Alternative – I
This alternative proposes the water conductor system and powerhouse on the
right bank of river Nyamjang Chhu. A Head regulator, feeder channel &
Surface Desilting Basin are planned on Right bank for diverting the design
discharge through a 31.44 km long Head Race Tunnel to a pressure shaft
leading to the turbines for power generation in underground power station.
The length of the TRT, MAT and Pressure Shaft are about 1800 m, 1090 m and
1335 m respectively.
The proposed project components on the right bank are approachable only to
the limited length of the river from the existing available road network. There
are about 11 first order streams on the right bank draining into Nyamjang
Chhu in the project reach under consideration. These further join to form
second and third order streams. It is also observed that tributaries to the
Nyamjang Chhu are more deeply incised on the right bank and therefore the
right bank alternative requires longer water conductor system and associated
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works within the development reach of the river. The length of road network
to be developed in the area for project development is about 75 km with
construction of two major bridges across Nyamjang Chhu.
Alternative – II
This alternative proposes the water conductor system and powerhouse on the
left bank of Nyamjang Chhu having the diversion structure at Zimithang and
power House near confluence of Nyamjang Chhu with Tawang Chhu. A
Barrage is proposed. The head regulator, feeder channel, surface desilting
chamber and HRT intake are proposed on left bank. Underground Power
House is proposed near Kumba Village. TRT level at the outfall is El 1045.12
m. The length of the TRT, MAT and Pressure Shaft are about 1546 m, 1080 m
and 2550 m respectively.
The HRT is aligned on left bank with 6 Nos. of adits. Surge shaft is located at
elevation El 2181.40 and is open to sky. The location of the surge shaft on the
left bank is fixed for all the alternatives due to topographical limitations. All the
main project components are approachable in this alternative. The length of
the pressure shaft in this alternative is maximum and will involve huge steel
cost. The length of HRT is 23.407km.
Alternative – III
This alternative is on the left bank of river Nyamjang Chhu, The diversion
structure is placed at Zimithang at the river bed elevation of El. 2106.20 m
and Power House on the Left Bank near Gispu Village just upstream of the
Gomkarang Chhu nala. The proposed gross storage required at Zimithang is
0.95 Mcum with FRL at El. 2114.90 m and MDDL at El. 2112.02 m
respectively. A gated barrage with overflow structure near Zimithang village
with head regulator & Surface Desilting Basin on Left bank is planned for
diverting the design discharge through a 19.607 km long Head Race Tunnel to
a pressure shaft leading to the turbines for power generation in underground
power station located near Gispu Village. The length of the TRT, MAT and
Pressure Shaft are about 5846 m, 1375 m and 1000 m respectively.
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The location of the HRT intake is near the desilting Chamber. The length of the
feeder Channel is reduced in this arrangement leading to increased length of
the silt flushing arrangement. The HRT is aligned on left bank with 5 No. adits.
Surge shaft is located at elevation El 2171.40 and is underground. All the main
project components are approachable in this alternative. The length of the HRT
and pressure shaft is minimum in this alternative; however power house is to
be located 100 m below the river bed for full utilisation of the available head
for power generation.
Alternative – IV
This alternative is on the left bank of river Nyamjang Chhu, The diversion
structure is placed at Zimithang at the river bed elevation of 2106.20 m and
Power House on the Left Bank near Kharteng Village just upstream of the
confluence of Nyamjang Chhu with Tawang Chhu. The proposed gross storage
required at Zimithang is 0.95 M cum with FRL at El 214.90 m and MDDL at El.
2112.02 m respectively. A gated barrage near Zimithang village with head
regulator, Surface Desilting Basin on Left bank is planned for diverting the
design discharge through a 23.450km long Head Race Tunnel to a pressure
shaft leading to the turbines for power generation in underground power
station located near Gispu Village. The length of the TRT, MAT and Pressure
Shaft are about 1965 m, 1010 m and 2530 m respectively.
The location of the HRT intake is near the desilting Chamber after 600 m long
feeder Channel from head regulator. The HRT is aligned on left bank with 6 No.
adits. Surge shaft is located at El 2171.40 and is open to sky. All the main
project components are approachable in this alternative. The length of the
pressure shaft and MAT is optimal in this alternative considering the overall
scheduling of the project.
Comparison of Alternatives
The selection of optimal alternatives for Nyamjang Chhu H.E. Project is based
on the comprehensive study of the four alternatives described above. The
assessment of each alternative is based on detailed investigations and studies
covering assessment of geology, topographical features, and possibility of
utilisation of maximum head, storage characteristics, alignment of water
conductor system and other relevant parameters. After considering the above
factors, alternative – IV is adopted.
The main consideration for selection of Alternative –IV included the following:
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Left bank is suitable for development of the project based on
accessibility and geological considerations.
Most of the project components are easily accessible in this
alternative.
Utilizes the total head available in the reach.
Length of the main access tunnel (MAT), Pressure Shaft is suitable
from construction point of view.
Alternative – I on the right bank requires large network of roads to
be developed besides longer length of water conductor system due
to presence of deeply incised streams. This alternative would have
some adverse impact on the old Buddhist stupa on right bank which
is held in great esteem by the local population.
Alternative – II has a very long length of the pressure shaft and
also involves heavy cutting of the river bed for the silt flushing
arrangement.
Alternative - III has the high risk of seepage problem in utilising
the full head as the power house is located about 100 m below the
river bed. The length of the TRT is also on a higher side; thus
leading to minor loss of head as well as construction problems.
As the location of the diversion structure is almost same in all the
alternatives, the considerations on the alignment of tunnel,
approach to adits, length of the pressure shaft and location of the
power house favours Alternative – IV techno-economically.
Considering complete utilisation of the drop available in the river and
economics of cost of power generation, in the DPR, scheme under Alternative –
IV has been selected.
During the project planning stage, it was earlier planned to commission the
project with a capacity of 900 MW with a rated discharge of 99 cumec. The
present proposal envisages project capacity as 780 MW, with rated discharge
as 87 cumec. The reduction in rated discharge will lead to increased flow to the
tune of 12 cumec in the river stretch between the barrage site and the tail race
disposal site. This is an added advantage of the present proposal, as it will
also increase the Environmental Flows.
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2.4 PROJECT DETAILS
Major Project Components
The project envisages construction of barrage across Nyamjang Chhu River, a
head regulator, Feeder Channel, desilting chamber with collection pool &
intake, a headrace tunnel, surge shaft, pressure shafts, underground
powerhouse and tailrace tunnel. The project layout plan is enclosed as Figure-
2.1. The project components are described in the following paragraphs.
Barrage
Average bed level at barrage site is El. 2106.2 m. FRL is fixed at EL 2114.9 m
and MDDL at EL 2112.2 m keeping in view peaking storage and the inflow of
water in Nyamjang Chhu during lean period. The top of the barrage has been
proposed at EL 2116.4 m. The barrage has been provided with spillway for
passing of Design flood with 11 bays each 10 m wide and 7.5 m high having
crest at elevation of EL 2107.4 m. The under sluice has been provided with 3
bays each of 5 m width and 6.3 m high having crest at elevation of EL
2105.9 m.
Intake and Desilting Arrangement
The head regulator, desilting basin and power intake systems are proposed on
the left bank of river Nyamjang Chhu. The Head regulator has 8 gates of 4 m x
6.5 m each. Feeder channel up to the desilting basin is 600 m long and 20 m
wide and is divided into four compartments. The flow depth in the feeder
channel is 3.55 m. Eight desilting basins are proposed each having a width of
10.5m and length of 150 m for removal of silt particle of size 0.2mm and
above. The invert level of the tunnel intake structure has been kept at
EL.2093.4 taking into consideration the water seal requirement to prevent
vortex formation and air entrainment. The intake structure has been provided
with trash racks to prevent entry of trash in the water conductor system.
Head Race Tunnel
A 23.450 km long, 6.2 m dia circular concrete lined HRT has been designed to
carry design discharge of 87 m3/sec of water. Six (6) intermediate adits are
provided to facilitate the construction of headrace tunnel.
Surge Shaft
A 240 m high, 4/10/12 m dia open to sky restricted orifice type surge shaft
has been designed to take care of the water hammer and mass oscillations due
to load variations.
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Butterfly Valve Chamber
Two (2) underground Butterfly valve chambers 12.5 m long, 12.5 m wide
and12.5 m high chambers have been provided to accommodate two Butterfly
valves of 3.3 m dia each. The chambers are inter-connected by a 5.0 m dia
connecting gallery.
Pressure Shaft
Two underground pressure shafts each of 3.3 m dia & 2103 m long steel lined
bifurcating into six shafts of 2.0 m diameter & 423 m long, are provided to
convey water to the six turbines in the power house.
Underground Power House Complex
An underground cavern of 166.3 m long x 20 m wide x 45 m high has been
provided to house 6 units of 130 MW Pelton turbines and spherical type main
inlet valves.
Transformer cavern 172.3 m long x 16.3 m wide x 24 m high has been
provided to accommodate 20 nos. single phase 13.8/ 420 kV transformers
including three spare transformers, each of 56 MVA capacity and 400 kV Gas
Insulated Switchgear (GIS).
Tail Race Tunnel (TRT)
A 1965 m long 7.0 m dia Circular shaped tunnel has been provided to carry a
total discharge from the turbines back to the river.
Transmission System
The power evacuation from the project would be carried out by the PGCIL as
per the recent regulation issued by CERC.
Project Benefits
The annual energy from the project has been assessed as 3430.29 GWh in
90% dependable year. The project would also provide peaking benefits of 780
MW round the year.
Project Cost
The Project is estimated to cost Rs 68522.8 million at December 2010 Price
Level. The details are given below:
a) Total direct charges including Civil and E&M works :Rs.5,0447.9 million b) Indirect Charges : Rs.71.1 million c) Escalation : Rs.5365.0 million d) IDC & Financial Charges : Rs.12638.8 million e) Total Complétion cost including IDC & Financing : Rs 68522.8 million
Charges
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2.5 SALIENT FEATURES
The salient features of the Project are given in Table-2.1. The project layout
map is shown in Figure-2.1.
TABLE-2.1 Salient features of Nyamjangchhu hydroelectric project
1. LOCATION State : Arunachal Pradesh District : Tawang River : Nyamjang chhu Vicinity : Tawang Longitude at diversion site : 91°43’37” Latitude at diversion site : 27°43’06” 2. HYDROLOGY
Catchment area at diversion : 2650 Sq. Km. Design Flood (50 year Return period) : 3400 Cumecs Design Discharge 87 Cumecs 3. BARRAGE
Length of Barrage : 174.50 m
H.F.L : 2114.90 m
F.R.L : 2114.9 m
Average river bed level : 2106.20 m Max. height of Barrage above Avg.
River Bed Level : 11.20 m
Bridge deck level : 2117.40 m
Max. height of Varrage above river bed levels
: 10.2 m
Design Flood (SPF) : 3400 Cumecs
3(a). SPILLWAY Type : Gated No. of Bays : 11 Nos. Length of Bay : 10.00 m
Sill level : 2107.4 m Size of gates : 7.5m(H) x 10m(W)
Type of gate : Vertical lift gates Energy Dissipation arrangement : Stilling Basin type
3(b). UNDERSLUICE
Type : Gated
No. of Bays : 3 Nos. Length. of Bay : 5.00 m.
Sill Level : 2105.9 m Size of gates : 6.3m(H) x 5m(W) Type of gates : Vertical lift gates Energy Dissipation System : Stilling Basin.
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3(c). HEAD REGULATOR
Length : 46 m HFL : 2114.90 m
FRL : 2114.9 m MDDL : 2112.2 m Sill level : 2108.4 m Bridge deck level : 2116.4 m No. of bays : 8 Nos. Length of bay : 4.00 m
Size of gates : 6.5 m(H) x 4.0 m(W) Type of gates : Vertical lift gates No. of silt excluder tunnels : 8 Nos. Size of silt excluder tunnels : 0.75m(H) x 1.5m(W)
4. FEEDER CHANNEL
Length : 600 m Total width : 20.00 m No. of channels : 4 Nos. Width : 4.25 m Height : 6.00 m Velocity of flow : 2 m/s 5. DESILTING ARRANGEMENT Type : Surface basins Hopper type No. & Size of desilting basin (LxBxH) : 8 Nos., 150m x 10.50m x
19m Particle size to be excluded : 0.20 mm and above Flow through velocity : 0.2 m/s Flushing velocity : 4.5 m/sec. Dia. of silt flushing Conduit : 2.0 m 6. HEAD RACE TUNNEL Type and Size : Concrete Lined Circular
Shaped, 6.20 m Finished Dia.
Velocity : 2.88 m/s Length : 23450.0m Design discharge : 87 cumec. Slope : 1 in 145 7. ADITS Type : D – Shaped Adit No.-1 : 7.0mx5.0m, Length
=362.0m Adit No.-2 : 7.0mx5.0m, Length
=322.0m Adit No.-3 : 7.0mx5.0m, Length
=460.0m Adit No.-4 : 7.0mx5.0m, Length
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=655.0m Adit No.-5 : 7.0mx5.0m, Length
=439.0m Adit No.-6 : 7.0mx5.0m, Length
=476.0m Adit No.-7 : 7.0mx7.0m, Length
=436.0m Adit No.-8 : 7.0mx5.0m, Length
=980.0m Adit No.-9 : 7.0mx5.0m, Length
=1088.0m 8. SURGE SHAFT Type : Open to sky, Restricted
orifice type. Size: : 4.0m, 10.0m & 12.0m Dia.,
240.0 m high.
Maximum Upsurge Level : 2165.20 m Minimum Downsurge Level : 2052.42 m Bottom Level : 1931.40 m Top Level : 2171.40 m
9. PRESSURE SHAFT Type : Steel Lined Size Main : 2 No., 3.3m dia, each
2115.0 m long. Unit
Pressure Shaft : 6 No, 2.0m dia, each
415.0 m long Velocity : 5.07 m/s Type & thickness of steel liner : ASTM-A-537, CL-II &
ASTM-A-517, Gr.-F, 20 mm to 65 mm thk.
Valve gallery : 12.5m (H) x 12.5m (W) x 69.5m (L)
10. POWERHOUSE Type : Underground Installed Capacity : 780 MW (6 x 130 MW) Size : 166.2m x 20m x44.5m Maximum gross head : 1057.40 m Max Net head : 1018.40 m Min Net Head : 1014.30 m Rated Net head : 1017.03 m C/L of Turbine : 1057.50 m Erection bay floor level : 1070.20 m Crane beam level : 1082.70 m Maximum TWL : 1054.0 m Capacity of E.O.T crane : 2 x 140 M Tons 11. TRANSFORMER CAVERN Size : 172.25m x 16.3m x 24m
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12. TAILRACE TUNNEL Type : Circular shaped Size : 7.0m Dia., 1965.0m Long 13. TURBINES No. & Type : 6 No., Vertical Shaft
Pelton. Rated Power (at generator terminal) : 780.0 MW Rated net Head : 1017.03 m Rated discharge : 87 cumec. Specific Speed : 500 rpm 14. MAIN INLET VALVE (MIV) Type : Spherical valve Diameter : 2.0 m 15. GENERATOR Type : Synchronous Type Number : 6 Nos. Rated Capacity : 144.45 MVA Nominal Active Power : 130.0 MW
16. MAIN GENERATOR STEP UP TRANSFORMER No. of Single Phase Transformer : 20 Nos. Rated Output : 56 MVA Rated Voltage : 13.8 KV/ 420 KV Frequency : 50Hz Type of cooling : OFWF 17. SWITCHYARD Area : 40.0m x 30.0m Type : Surface at EL 1131.4m 18. ESTIMATED COST Completion Cost at May, 2010 price
level : Rs. 6852.28 Cr.
19. POWER BENEFITS Energy generation in 90% dependable
year : 3430.29MU
20. FINANCIAL ASPECTS IRR : 12.80%
Average DSCR : 1.37
21. TARIFF Levelised Tariff : Rs. 4.25/Kwh First Year : Rs. 5.20/Kwh
22. CONSTRUCTION PERIOD Construction Period (including 12
months for pre-construction activities) : 74 months
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2.6 LAND REQUIREMENT
The total land required for the project is 254.5526 ha. The details are given
in Tables-2.2 and 2.3.
TABLE-2.2 Land requirement for Nyamjang chhu hydroelectric project
S. No. Component Village
Private Land (ha)
Community Land (ha)
Total Land
(ha )
1
Submergence Area ( Left Bank up to Barriage)
Soksen 4.0454 4.5961 8.6415
2
Submergence Area ( Right Bank up to Barriage)
Lumpo 0 2.9707 2.9707
3
Submergence Area ( River area up to Barriage)
Soksen and Lumpo (50 -
50) 0 27.7369 27.7369
4 Upstream Headworks Soksen
0 22.051 22.051
5
Head Race Tunnel
Soksen 0 1.079 1.079
6 Kyaleyteng 0 2.158 2.158
8 Shakti 0 8.332 8.332
9 Gispu 0 0.981 0.981
10 Sherbang 0 1.054 1.054
11 Kherteng 0 1.168 1.168
12 Phoomang 0 1.168 1.168
13 Bagar 0 1.168 1.168
14 Adits - 1 Kyaleyteng 0 0.333 0.333
15 Adits - 2 Shakti 0 0.2382 0.2382
16 Adits - 3 Shakti 0 0.3404 0.3404
17 Adits - 4 Shakti 0 0.484 0.484
18 Adits - 5 Sherbang 0 0.324 0.324
19 Adits - 6 ( equally in three villages)
Kherteng/Phoomang/Bagar
0 0.352 0.352
20 Adits - 7
Kherteng/Phoomang/Bagar
0 0.322 0.322
21 Adits - 8 Kungba 0 0.725 0.725
22 Adits - 9 Kherteng 0 0.805 0.805
23 Tail Race Tunnel Kherteng 0 1.335 1.335
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S. No. Component Village
Private Land (ha)
Community Land (ha)
Total Land
(ha )
24 G IB Kherteng 0 0.3261 0.3261
25 MAT Kherteng 0 0.5152 0.5152
26 Power House Kherteng 0 15.5618 15.5618
27
Surge Shaft (equally in three
villages)
Kherteng, Phoomang,
Bagar 0 0.5901 0.5901
28
Pressure Shaft (equally in three
villages)
Kherteng, Phoomang,
Bagar 0 2.693 2.693
29 Switchyard Kherteng 0 0.675 0.675
30 Muck disposal
Sites M-1 Muchat 0 2.6893 2.6893
31 M-2 Muchat 0 7.459 7.459
32 M-3 Kyaleyteng 0 8.659 8.659
33 M-4 Shakti 0 1.9571 1.9571
34 M-5 Shakti (BTK) 0 2.9283 2.9283
35 M-6 Shakti (BTK) 0 8.0694 8.0694
36 M-7 BTK 0 4.7789 4.7789
37 M-8 BTK 0 5.767 5.767
38 M-9 Shakti (BTK) 0 2.8847 2.8847
39 M-10 Sherbang 0 3.2569 3.2569
40 M-11 Sherbang 0 4.415 4.415
41 M-12 Sherbang 0 3 3
42 M-13 Kherteng 0 3.9238 3.9238
43 M-14 Kumba 0 6.6 6.6
44 M-15 Kumba 0 2.5898 2.5898
45 Colonies Sherbang 0 7 7
46
Labour Camps ( equally in three
villages )
Kyaleyteng, Kherteng, Sherbang
0 3 3
47
Workshop,Centerlized store and
Fabrication yard Kherteng 0 4 4
48
Explosive Magazines ( 2 nos) (50 - 50)
Sherbang / Kyaleyteng
0 1.5 1.5
49
Crusher ,Batching plant and aggregate
Storage (2 nos )(50-50)
Kerteng / Shakti
0 12 12
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TABLE-2.3
Ownership status of land to be acquired for Nyamjang chhu hydroelectric project
S. No. Type of land Area (ha) 1 Private land 10.0829 2 Community land 244.4697 Total 254.5526
2.7 INFRASTRUCTURE FACILITIES
The project area is located about 50 Km from district headquarter at Tawang.
The area is sparsely populated and lacks adequate residential and
telecommunication facilities. The project site is accessible from Guwahti via
National Highway, state highway and district level road. For construction
purpose access to various project components is required. Also, the existing
roads and infrastructure facilities need to be improved.
The total infrastructure works envisaged for permanent and temporary access
include:
Project Roads and Bridges. Construction power facilities Residential and non-residential buildings including electricity,
water supply and sanitary facilities. Telecommunication and other facilities.
2.7.1 Access Roads And Bridges
The entire project site is well approachable by road network available from
Guwahati/Tezpur to Tawang/Lumla/Zimithang via Bhalukpong, Bomdila and
Sela pass. Guwahati is connected to Tezpur by National Highway (NH-52). The
distance between Guwahati and Tezpur is about 170 km. The distance of
Tawang, Lumla and Zimthang from Guwahati is about is about 520 km, 575
km and 625 km respectively.
From Tezpur approach to the Project site is through Bhalukpong which is a
border town at Assam–Arunachal border. Bhalukpong is connected to Tezpur
by 60 km long road passing through Balipara Bhalukpong is connected to
Lumla through Bomdila, Dirang, Sela Pass and Jung. From Lumla, diversion
site at Zimithang is approachable by 40 km long road maintained by border
roads. The entire road network from Bhalukpong to Tawang/Lumla/Zimithang
is maintained by BRTF. Construction material, heavy equipment and machinery
required for the project will be brought to project site through this existing
road network. Heavy equipment, if imported from countries other than India,
would have to be transported from Kolkata to project site via Siliguri.
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While going to project site along this road network Sela Pass is to be crossed,
which is located at an elevation of 14000 ft and most of the time in a year is
covered with snow. Existing road network passes through Bomdila town, which
is very congested and has a very steep gradient. Considering the above
constraints the project area is also proposed to be approached through
Trashigaon–Lumla road via Bhutan which is under construction and is likely to
be completed by the time the project is expected to be taken up for
construction. This road network is conncted to Guwahati via Rangiga
(Assam)–Samdrup Jongkhar (Bhutan)–Trashigaon route. The total length of
this route from Guwahati to Lumla is 575 km. It might therefore greatly benefit
the project construction as the distance between Guwahati to Lumla along this
oad would be further shortened.
The nearest airport is at Tezpur and Guwahati which are about 400 km and
570 km from site. Helicopter service is also available from Guwahati up to
Tawang on daily basis.
Project Roads
A network of new roads is required to facilitate completion of the project as per
anticipated time schedule. Major components like Barrage, Power House,
Surge Shaft and Permanent Colonies for the project near village Kharteng and
Zimithang will require construction of new roads on the left bank. A bridge has
to be constructed across river Nyamjang Chhu upstream of the existing BTK
bridge to approach adits to HRT from the existing road on right bank. The total
length of new roads to be constructed has been estimated as 60.00 km as
detailed in Table-2.4.
TABLE-2.4 List of new roads to be constructed
Connecting details Length (km) Length of road to reach various adits and other project components
54.5
Length of road from existing road to Power House 2.5 Length of internal road from existing road at Barrage on Right bank and new Road on Left bank
3.0
Total 60.0
Apart from the above major roads about 40 km of road network will be
required for approach to the various muck dumping yards. About 120 km of
existing roads in the project area from tawang to Zimithang may require
strengthening and widening including bridges and cross drainage works.
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Transportation And Transport Limitation
For transporting major equipment such as turbines, generators, main
transformers, spherical valves, etc, road link is available up to project site from
other locations of India through Assam State.
The National Highway in India is designed for class 70R loading as per Indian
Road Congress standard and is capable of carrying 70 ton load. The standard
further specifies that up to 100 tons can be transported by trailors with
multiple wheels.
The existing road from Tezpur to Lumla/Zimithang is of state highway
specifications. Beyond the present road upto – Tawang is of the class 9N. The
details are as follows:
Classification - 9 N (as per BRO standards) Culverts designed for - 18/24 Minimum Radius - 12.13m Carriage way - 3.66m Formation width - 6.10 m
This road also requires significant widening and strengthening along with
construction of new bridges and culverts designed to carry the load of heavy
machinery and equipment required for the project construction.
2.7.2 Construction Power
The maximum power required for constructions activities is estimated
considering capacity of electrically driven machines/equipment and
requirement of lighting, varies during the construction schedule and also
depends on construction methodology.
It is assessed that about 10 MW of power would be required during peak
construction period. However, construction power requirements during the
initial two years would be about 5 MW. The power requirement would be met
through installation and operation of dedicated DG sets.
2.7.3 Power Supply Facilities
Presently power requirements in the project area are being met through
33/11KV lines from Tawang. The project area experiences frequent power cuts
and break-downs. Power requirement for project construction is not suitable
to meet the existing system of power supply in the region. A new single circuit
33/11KV transmission line is also proposed from Tawang to Lumla and is under
planning stage. Even after up gradation the power supply system will not be
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suitable to meet the dedicated power demand from the project during
construction stage.
2.7.4 Telecommunication Facilities
The telecommunication facilities in the project area comprise of fixed line and
WLL services from BSNL. Mobile network is not available in the area and
nearest mobile network is available at Tawang and is served only by BSNL. For
effective coordination among various work sites, workshop, colonies, stores,
design office, head office, etc. and a reliable tele-communication network is
necessary. An electronic automatic telephone exchange with a capacity of
about 100 lines is proposed at project head quarters at Lumla. The internal
telephone system would be maintained by the project. Telecommunication link
outside the project area would be provided by upgrading the existing BSNL
network. A wireless V-Sat system is also proposed for linking the project site
with Zimithang, Namestring, Lumla, Tawang, Bhalukpong, Itanagar and Noida.
After completion of construction activities, the telecommunication network is
proposed to be continued so as to serve during operation and maintenance
stage.
A VHF wireless network is also proposed to be established to connect various
project sites, Guwahati and Tezpur. This will be mainly utilized for the
construction purpose and will be scaled down after commissioning.
It is also proposed that the project area may be connected by the mobile
network as available in other parts of the state.
2.7.5 Project Colonies/Buildings
The Residential and non-residential facilities are required during construction
and O&M phase of the project. The same will be met by constructing suitable
colonies near Lumla, Kharteng,and Zimithang villages.
Total area required for the permanent buildings has been estimated as 17000
m2 and for temporary buildings as 22500 m2.
The temporary colonies would be utilized during construction of the project and
permanent colonies would be utilized for both i.e, during construction and
maintenance of the project.
The water supply requirement shall be met with from the flow of near by
streams by gravity flow. The flow requirement sufficient to meet the likely
water demand is about 50lps.
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The entire building construction program would be suitably phased to match
with the construction activities. Priority would be given to the construction of
field hostel, stores and temporary residential and non-residential buildings.
It is also planned to have liaison facilities at Guwahati, Tezpur, Itanagar,
Bomdilla and at Bhalukpong. A suitable storage area would also be made in
Bhalukpong to keep the buffer for the stock of construction materials for the
monsoon period etc. Guest Houses are also planned at Bhalukpong & Dirang.
Residential Non-residential Stores Recreation facilities Construction
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CHAPTER-3
METHODOLOGY ADOPTED FOR THE EIA STUDY
3.1 INTRODUCTION
Standard methodologies of Environment Impact Assessment have been followed
for conducting the CEIA study for the proposed Nyamjangchhu hydroelectric
project. A brief description of the methodology adopted for conducting the CEIA
study for the proposed Nyamjangchhu hydroelectric project is outlined in the
present chapter. The information presented in this Chapter has been presented
through various primary as well as secondary sources.
3.2 STUDY AREA
The study area considered for the CEIA study is given as below:
• Submergence area • Area within 10 km of the periphery of the submergence area • Area to be acquired for siting of various project appurtenances. • Area within 10 km of various project appurtenances • Catchment area intercepted at the barrage site
The study area is shown in Figure-3.1.
3.3 SCOPING MATRIX
Scoping is a tool which gives direction for selection of impacts due to the project
activities on the environment. As a part of the study, scoping exercise was
conducted selecting various types of impacts which can accrue due to
hydroelectric project. Based on the project features, site conditions, various
parameters to be covered as a part of the EIA study were selected. The results
of Scoping analysis are presented in Table-3.1.
TABLE-3.1 Scoping Matrix for EIA study for the proposed Nyamjangchhu
Hydroelectric Project Aspects of Environment Likely Impacts A. Land Environment Construction phase - Increase in soil erosion from
various construction and quarry sites - Pollution by construction spoils - Acquisition of land for labour camps/ colonies - Solid waste generated from labour camps/colonies
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Aspects of Environment Likely Impacts Operation phase
- Acquisition of land for various project appurtenances - Loss of agricultural and forest land due to acquisition of land for various project appurtenances
B. Water resources & water quality Construction phase
- Impact on water quality of receiving water body due to disposal of runoff from construction sites carrying high sediment level. - Degradation of water quality due to disposal of effluent from labour, camps/colonies
Operation phase - Modification of hydrologic regime due to diversion of water for hydropower generation
C. Aquatic Ecology Construction phase - Increased pressure on riverine
fisheries as a result of indiscriminate fishing by the immigrant labour population. - Reduced productivity due to increase in turbidity levels as a result of disposed off waste water from construction sites and labour camps/colonies.
Operation phase - Impacts on spawning & breeding grounds in the stretch downstream of dam site to fail race disposal site. - Degradation of riverine ecology - Impacts on migratory fish species - Impact on aquatic ecology due to reduction in flow downstream of the dam site upto tail race disposal site.
D. Terrestrial Ecology Construction phase
- Increased pressure from labour to meet their fuel wood requirements during project construction phase - Adverse impacts on flora and fauna due to increased accessibility in the area and increased level of human interferences - Loss of forest due to siting of
various project appurtenances Operation phase
- Impacts on wildlife movement due to the project
- Impacts on wildlife habitats due to acquisition of forest and other categories of land for various
project appurtenances.
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Aspects of Environment Likely Impacts E. Socio-Economic Aspects Construction phase
- Increased employment potential during project construction phase - Development of allied sectors leading to greater employment - Pressure on existing infrastructure facilities. - Cultural conflicts and law and order
issues due to migration of labour population
Operation phase - Acquisition of private land, home- Stead and other private properties - Loss of community properties - Impacts on archaeological and cultural monuments, if any - Impacts on mineral reserves, if any
F. Air Pollution
Construction Phase - Impacts due to emission as a result of fuel combustion in various construction equipment
- Impacts due to emission as a result of increased vehicular movement for transportation of men and material during project construction phase
- Fugitive envisions from various sources
- Impacts due to emissions from DG set
G. Noise Pollution Construction Phase - Noise due to operation of various
construction equipment - Noise due to increased vehicular
movement - Impacts due to blasting - Increased noise levels due to
operation of DG set H. Public Health Construction Phase - Increased incidence of water
related diseases - Transmission of diseases by
immigrant labour population Operation phase - Increased incidence of vector-
borne diseases
Based on the Scoping matrix, the environmental baseline data has been
collected. The project details have been superimposed on environmental
baseline conditions to understand the beneficial and deleterious impacts due to
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the construction and operation of the proposed Nyamjangchhu hydroelectric
project.
3.4 DATA COLLECTION
3.4.1 Physico-Chemical Aspects
Primary surveys have been conducted for three seasons namely, monsoon ,
post-monsoon and pre-monsoon seasons. The data has been collected for flora,
fauna, forest types and ecological parameters, geological and soil features.
During these surveys data and information was collected on physico-chemical,
biological and socio-economic aspects of the study area. In addition, detailed
surveys and studies were also conducted for understanding bio-diversity in the
study area.
As a part of the EIA study, primary data has been collected by WAPCOS Ltd. for
three seasons. However, as a part of TOR clearance, the project proponents
were asked to get the field studies conducted by another agency. The project
proponents selected RS Envirolink Technologies Private Limited as the other
agency, who collected data for three seasons.
TABLE-3.2
Details of field studies conducted as a part of CEIA studies
Agency Season Months WAPCOS Ltd. Monsoon August-September 2007
Winter December 2007 – January 2008 Summer April – May 2008
RS Envirolink Technologies Private Limited
Summer April – May 2008 Monsoon July – August 2008 Winter November – December 2008
Geology
The regional geology around the project area highlighting geology, stratigraphy,
etc. have been covered in the EIA Report, as per the available information in the
Detailed Project Report (DPR) of the project.
Hydrology
Hydrological data for river Nyamjangchhu as available in the Detailed Project
Report was collected and has been suitably incorporated in the Comprehensive
EIA study.
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Seismo-tectonics
The regional seismo-tectonics around the project area highlighting seismicity
have been covered in the EIA Report, as per the available information in the
Detailed Project Report (DPR) of the project.
Landuse pattern
Landuse pattern of the study area as well as the catchment area was carried out
by standard methods of analysis of remotely sensed data and followed by
ground truth collection and interpretation of satellite data. For this purpose
digital satellite data was procured from National Remote Sensing Agency,
Hyderabad, IRS-P6 LISS-IV. The data was processed through ERDAS software
package available with WAPCOS.
Soil
The soil quality was monitored at various locations in the catchment area. The
monitoring was conducted for three seasons as detailed in Table-3.2.
The existing data on water quality has been collected to evaluate river water
quality on upstream and downstream of the project site. The water quality was
monitored for various seasons as listed in Table-3.2. The water samples were
collected from the study area and analyzed for physico-chemical parameters
which are listed in Table-3.3.
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TABLE-3.3 Water quality parameters analysed as a part of the field studies
pH Zinc Electrical Conductivity Total Suspended Solids Total Dissolved Solids Cadmium Sulphates Magnesium Chlorides Lead Nitrates Manganese Phosphates Fluorides Sodium Hardness Potassium DO Calcium BOD Copper COD Iron Oil & grease Total Coliform
Ambient air quality
The ambient air quality was monitored at three locations in the study area.
Monitoring was conducted for three seasons as listed in Table-3.2. The frequency
of monitoring for each season was twice a week for four consecutive weeks. The
parameters monitored were Suspended Particulate Matter (SPM), Respirable
Particulate Matter (RPM), Sulphur-dioxide (SO2) and Nitrogen Oxides (NOx).
Ambient Noise level
As a part of the EIA study noise level was monitored at various locations in the
study area. Monitoring was conducted for various seasons as listed in Table-3.2.
At each station, hourly noise level was monitored during day time. Further day
time equivalent noise level was estimated.
3.4.2 Ecological Aspects
Terrestrial Ecology
Flora
Data on forest type legal status and their extent in the catchment and study
area has been collected from the forest department. The other relevant data on
bio-diversity economically important species medicinal plant, rare and
endangered species in the study area and its surroundings have been collected
from secondary sources like research institute forest and wildlife department. In
addition field studies were conducted to collect data on various aspects in the
study area. The sampling sites were selected based on topography and floristic
composition. The various aspects studied were floral density frequency and
abundance of species of trees, shrubs, herbs and grasses. Plants of economical
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species and medicinal use and endangered species were also identified as a part
of the study. The monitoring was conducted for various seasons listed in Table-
3.2.
Fauna
The faunal assessment has been done on the basis secondary data collected
from different government offices like forest department, wildlife department,
fisheries department etc. The presence of wildlife was also confirmed from the
local inhabitants depending on the animal sightings and the frequency of their
visits in the catchment area. In addition review of secondary data was another
source of information for studying the fauna of the area. In addition, sightings of
faunal population during ecological survey and then field studies were also
recorded as a part of the data collection exercise.
Aquatic Ecology and Fisheries
Water samples from river Nyamjangchhu were also collected as a part of field
studies. The density and diversity of periphyton and phytoplanktons, species
diversity index and primary productivity etc. were also studied. The field studies
were conducted for various seasons as listed in Table-3.2.
The secondary data pertaining to fisheries in river Nyamjangchhu was collected
from Fisheries Department and through literature review as well. Fishing was
done at various sites in the project area and river stretches both upstream and
downstream of the dam site of proposed hydroelectric project to ascertain the
dispersal pattern of fish species. Identification and measurements of all the fish
catch was done and an inventory of the fish species was also prepared. Various
migratory species and the species to be affected due to conversion of lentic to
lotic conditions as a result of commissioning of the proposed project were also
identified.
3.4.3 Socio-economic Aspects
Demography
The demographic and socio-economic characteristics of the submergence area as
well as the study area have been studied through primary as well secondary
sources. Detailed socio-economic census survey was conducted in the project
affected villages due to the proposed project. Collection of data was completed
at two levels - at village/ block and individual household level. The socio-
economic survey at the village/ block level was aimed at finding out the status
and extent of amenities and resources at the disposal of villages/ blocks. The
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household surveys were conducted with the main aim of evolving and preparing
compensatory and rehabilitation packages for families who would be rendered
houseless, landless and whose part of land would be acquired for various project
activities. Based on the assessment of demographic profile of Project Affected
Families (PAFs), Resettlement and Rehabilitation Plan using guidelines and
norms as per National Policy on Resettlement and Rehabilitation (2007) was
formulated.
3.5 SUMMARY OF DATA COLLECTION
The summary of the data collected from various sources is outlined in Table-3.4.
TABLE-3.4
Summary of data collected for the Comprehensive EIA study Aspect Mode of
Secondary Flow, Design hydrograph and design flood hydrograph
- Detailed Project Report (DPR)
Water Quality Primary Physico-chemical and biological parameters
Three seasons
Field studies for monsoon, winter and summer seasons by two agencies
Ambient air quality
Primary RPM, SPM, SO2, NOx
Three seasons
Field studies for monsoon, winter and summer seasons by two agencies
Noise Primary Hourly noise and equivalent noise level
Three seasons
Field studies for monsoon, winter and summer seasons by two agencies
Landuse Primary and secondary
Landuse pattern
- NRSA and Ground truth Studies
Geology Secondary Geological - Detailed Project
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Aspect Mode of Data collection
Parameters monitored
Frequency Source
characteristics of the study area
Report (DPR )
Soils Physico-chemical parameters
Three seasons
Field studies for monsoon, winter and summer seasons by two agencies
Terrestrial Ecology
Primary and secondary
Floral and faunal diversity
Three seasons
Field studies for monsoon, winter and summer seasons by two agencies Secondary data as available with the Forest and Wild life Department
Aquatic Ecology
Primary and Secondary
Presence and abundance of various species
Three seasons
Field studies for monsoon, winter and summer seasons by two agencies Secondary data as available with the Fisheries Department
Socio-economic aspects
Primary and secondary
Demographic and socio-economic, Public health cultural aspects
- Field studies for PAFs, secondary data collection from Revenue Department and literature review.
3.6 IMPACT PREDICTION
Prediction is essentially a process to forecast the future environmental conditions
of the project area that might be expected to occur because of implementation
of the project. An attempt was generally made to forecast future environmental
conditions quantitatively to the extent possible. But for certain parameters,
which cannot be quantified, general approach has been to discuss such
intangible impacts in qualitative terms so that planners and decision-makers are
aware of their existence as well as their possible implications. Impact of project
activities has been predicted using mathematical models and overlay technique
(super-imposition of activity on environmental parameter). For intangible
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impacts qualitative assessment has been done. The environmental impacts
predicted are listed as below:
- Loss of land. - Displacement of population due to acquisition of private and community
properties. - Impacts on hydrologic regime. - Impacts on water quality. - Increase in incidence of water-related diseases including water-borne and
vector-borne diseases. - Effect on riverine fisheries including migratory fish species. - Increase in air pollution and noise level during project construction phase - Impacts due to sewage generation from labour camps - Impacts due to acquisition of forest land - Impacts due to increase in terrestrial and aquatic ecology due to increased
human interferences during project construction and operation phases 3.7 ENVIRONMENTAL MANAGEMENT PLAN AND COST ESTIMATES
Based on the environmental baseline conditions and project inputs, the adverse
impacts were identified and a set of measures have been suggested as a part of
Environmental Management Plan (EMP) for their amelioration. The management
measures have been suggested for the following aspects:
- Compensatory afforestation and bio-diversity conservation plan - Catchment Area Treatment - Fisheries Management Plan - Public health delivery system - Environmental management in labour camp - Muck Management Plan - Restoration of quarry sites and landscaping of construction sites - Management of Impact due to construction of road - Greenbelt development plan - Control of Air Pollution - Measure for noise control - Water pollution control
The expenditure required for implementation of these management measures
has also been estimated as a part of the EMP study.
3.8 RESETTLEMENT AND REHABILITATION PLAN
As a part of the CEIA study, a socio-economic survey of project affected families
was conducted. As a part of the survey, information on family profile,
occupational profile, income, land holding, crop grown, assets owned, etc. was
collected. Based on the findings of the survey and the norms of outlined in
National Policy for Resettlement and Rehabilitation (NPRR) 2007, Resettlement
and Rehabilitation Plan for the project affected families has been formulated.
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3.9 CATCHMENT AREA TREATMENT PLAN
As a part of the CEIA study, a catchment area treatment plan for the catchment
area intercepted at the project site has been formulated. Various sub-
watersheds have been categorized into different erosion categories, as per Silt
Yield Index (SYI) method. For high and very high erosion categories, a
catchment area treatment plan comprising of engineering and biological
measures has been formulated.
3.10 TRIBAL DEVELOPMENT PLAN
In view of the Ministry of Tribal Affairs Strategy for development: the TSP
Approach and Plans/Programs of the ministry, various measures for Tribal
Development Plan has been suggested. These measures are in addition to the
measures outlined under Resettlement and Rehabilitation Plan and Area
Development Activities.
3.11 ENVIRONMENTAL MONITORING PROGRAMME
It is necessary to continue monitoring of certain parameters to verify the
adequacy of various measures outlined in the Environmental Management Plan
(EMP) and to assess the implementation of mitigative measures. An
Environmental Monitoring Programme for critical parameters has been suggested
for implementation during project construction and operation phases. The staff
along with necessary equipment and agencies to be involved for implementation
of the Environmental Monitoring Programme and costs have also been indicated.
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CHAPTER – 4
HYDROLOGY
4.1 BASIN DESCRIPTION
The river Nyamjang Chhu runs through north-western part of Arunachal Pradesh and flows mostly in
a North - South direction. It is a major tributary of the westerly flowing Tawang Chhu within the
State of Arunachal Pradesh. Nyamjang Chhu originates in China at an elevation of about ±6400 m
and flows through Tibet before entering India at Khinzemane. It flows southwards crossing into
Arunachal Pradesh and continues on a southerly course, parallel with the Indo-Bhutanese border, for
a distance of about 40 km to its confluence with the Tawang Chhu near Lumla, Kumba villages.
Tawang Chhu flows beyond Lumla village in a westerly direction into Bhutan as Gamri Chhu and
ultimately becomes a tributary of the Manas and Brahmaputra rivers. Major tributaries of river Manas
include Tawang Chhu, Nyamjang Chhu, Kuri Chhu, Khulong Chhu, Amri Chhu and Sheri Chhu.
Nyamjang Chhu is a perennial river with its main source of water being the south west monsoon and
snow melt contribution of Himalayan glaciers. The general pattern of river flow shows a large
variation with high flows in the months of June to September and lower flows in the remaining
months. The total length of Nyamjang Chhu from its origin in the Tibetan plateau at an elevation of
about 6400 m, to its confluence with the Tawang Chhu at an elevation of about about 1036 m is
about 125 km. The upper portion of the river, comprising about 85 km, is in Tibet and remaining 40
km is in India. In India, the Nyamjang Chhu flows through rugged mountainous terrain with an
average gradient of 1 in 30. The river enters India at approx. EL 2220 m near village Khinzemane
and covers a distance of about 10 km up to Zimithang. It meets Namka Chhu 2.41 km south of
Khinzemane and Sumta Chhu joins Nyamjang Chhu near Zimithang. The river is flat in the Zimithang
area for a stretch of almost 2.5 km. After this it again runs through steep slopes up to confluence
with Tawang Chhu. Eight nallas including Taksang Chhu and Gomkarang Chhu join Nyamjang Chhu
between Zimithang and its confluence with Tawang Chhu. These contribute to the discharges of the
Nyamjang Chhu all along this stretch.
The river bed elevation at Zimithang village is about EL 2106.0 m and that at the confluence is about
EL about 1036 m. A gross head of about 1057.4 m can therefore be exploited for development of
hydro power potential of the basin.
The total catchment area of the Nyamjang Chhu up to the confluence with Tawang Chhu is about
3170 km2. The catchment area upstream from Zimithang Village (barrage site) is about 2650 km2.
Out of this 2650 km2, about 1945 km2 of catchment area is above permanent snow line of EL 4500 m
and 705 km2 of catchment area receives precipitation in the form of rainfall. A Satellite image of the
Nyamjang Chhu catchment is shown in Figure 4.1.The catchment area map showing drainage
network is shown in Figure 4.2. The delineation of snow fed and rainfed areas in the catchment is
shown in Figure-4.3.
During its course from Zimithang to its confluence with Tawang Chhu, Nyamjang Chhu is joined by
eight major nallas. Two nallas namely Sumta Chhu and Taksang Chhu carry significant perennial
discharges and have catchment areas of 100 km2 and 154 km2 respectively. Sumta Chhu is a right
bank tributary of Nyamjang Chhu while Taksang Chhu is located on the left bank. It is proposed to
divert the perennial flow of Taksang Chhu into the headrace tunnel of Nyamjang Chhu HEP to utilise
the flow for power generation. The catchment area of Taksang Chhu upto the proposed diversion site
at EL 2156.4 m is 154 km2. Accordingly the flow in Nyamjang Chhu is computed including the
catchment area of Taksang Chhu upto the proposed diversion site. Thus, the total catchment area
including Taksang Chhu is 2804 km2.
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4.2 Water Availability Study
Hydrological data of Nyamjang Chhu is available for a period of only 18 months from December
2006. Discharge data of Tawang river located east of Nyamjang Chhu and Kuri Chhu located west of
Nyamjang Chhu is available for 7 years and 16 years respectively.
In the absence of long term discharge data for Nyamjang Chhu, the hydrological data of Tawang
Chhu and Kuri Chhu have been used in the DPR to estimate a long term flow series for Nyamjang
Chhu.
Confluence Point of Nyamjang Chhu & Tawang
Chhu
Barrage Location
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Figure 4.1 – Satellite Image of Catchment Area of Nyamjang Chu
Confluence Point of Nyamjang Chu & Tawang Chu
Barrage Location
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Figure -4.2
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4.2.1 Rainfall Data
The India Meteorological Department (IMD) has confirmed that no rainfall data
is available for the Nyamjang Chhu river catchment. Out of the available IMD
gauging sites in the region, the stations nearest to the project catchment are
at Dirang, Bomdilla and Bhalukpong. The location of these stations is shown in
the Figure 4.4.
Figure 4.4: Locations of Dirang, Bomdilla and Bhalukpong
The rainfall data of the rain gauge stations at Bhalukpong and Dirang is given in Tables-
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4.4 DESIGN FLOOD STUDIES
Estimation of design flood is one of the most important components of
planning, design and operation of various types of water resources projects.
Inflow design flood is required to finalize different design parameters of any
hydraulic structure like dam, barrage, etc. Inflow design flood is the flood for
which, the performance of the dam etc. should be safe against overtopping
and structural failure.
For a diversion structure, design flood should be considered based on following
methods.
i) Hydrometeorological approach (unit hydrograph method) ii) Flood frequency analysis
As per DPR, the design flood estimated using Hydrometeorological approach is
given in Table-4.10.
TABLE-4.10
Design Flood Values by Hydrometeorological Approach
Design Flood (m3/s)
Single Bell Storm Distribution
3487
Two Bell Storm Distribution
3392
Standard Project Flood (SPF)
3400
The estimated design flood values by frequency analysis based on the annual
peaks transposed from Kuri Chhu in catchment area proportion for various
return periods for the diversion structure are given in the Table-4.11.
TABLE-4.11
Design Flood Values by Frequency Analysis
Return Period Design Flood (m3/s)
50 year flood 1463
100 year flood 1764
500 year flood 2009
1000 year flood 2173
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From the above studies, the 100 year return period design flood value from
flood frequency analysis is 1764 cumec and by the hydrometeorological
approach SPF is of 3400 cumec.
As per the DPR, design flood value obtained by hydro-meteorological approach
is recommended for preliminary design purposes as it is on conservative side
as compared to flood frequency approach. The recommended design flood is
given in Table-4.12.
TABLE-4.12
Recommended Design Flood Values
Design
Flood m3/s
Return
Period Recommended Purpose
3,400 SPF Design of barrage and determination of free
board
4.3.2 Recommendation of Diversion Flood
Flood frequency analysis has been used for the estimation of diversion flood
during the non-monsoon season. The 25 year return period peak value for
non-monsoon period by Gumbel Distribution Method is 468 cumec say 500
cumec and by transposition of observed maximum daily non-monsoon
discharge of Kuri Chhu recorded at Kurizampa station to Zimithang is 407.57
cumec.
The inflow design flood for river diversion works is the greater of the following:
• Flood with a return period of 25 years derived with non monsoon peak
discharge values.
• Highest observed non monsoon discharge in the river.
Thus, as per the above criteria, the 25 year non-monsoon return period flood
value of 500 cumec being on the higher side as compared to highest observed
non monsoon discharge of 407.57 cumec, 500 cumec is recommended as
design flood for the river diversion works.
The percentage of risk involved based on the duration of the construction
period of the diversion structure (coffer dam) is given in Table-4.13.
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Table-4.13 Percentage of risk involved based on the duration of the construction
period of the diversion structure (coffer dam) is given in
Construction Period (n) in years
Return Period (T) in years
5 10 20 25 % Risk Involved
1 20% 10% 5% 4%
2 36% 19% 10% 8%
3 49% 27% 14% 12%
4 59% 34% 19% 15%
5 67% 41% 23% 18%
4.5 DISCHARGE DATA MEASURED AT SITE
The project proponents are monitoring discharge data at the following
locations since December 2006:
• Zimithang • BTK • Namstring
The monthly averages of the data observed at the above sites are given in
Tables-4.14 to 4.16.
TABLE-4.14
Average measured discharge data at Zimithang
Month Discharge (cumec) 2007 2008 2009 2010
January 20.13 19.30 17.22 13.81206 February 14.19 18.14 15.49 12.31263 March 20.48 21.86 16.84 22.69947 April 32.97 39.40 26.66 53.02033 May 51.95 48.62 56.55 74.8008 June 56.22 61.96 71.03 109.2776 July 124.00 80.14 88.97 139.3928 August 87.22 86.42 73.97 129.5893 September 67.95 68.39 55.22 October 45.24 38.26 27.75 November 31.17 31.47 21.49 December 20.81 19.08 17.16
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TABLE-4.15
Average measured discharge data at BTK
Month Discharge (cumec) 2007 2008 2009 2010
January 22.27 21.26 20.05 15.60 February 16.36 20.48 19.12 16.79 March 23.34 24.63 21.05 39.66 April 37.36 47.31 33.34 104.16 May 59.90 63.13 81.22 158.73 June 89.32 87.05 87.10 227.29 July 164.47 115.60 110.89 259.19 August 158.32 123.24 110.77 272.79 September 80.39 104.86 76.55 October 54.31 51.52 44.17 November 38.17 41.57 32.11 December 23.98 26.25 21.90
TABLE-4.16
Average measured discharge data at Namstring
Month Discharge (cumec) 2007 2008 2009 2010
January 29.86 27.60 32.31 26.12 February 25.53 28.62 31.72 26.68 March 31.67 33.98 36.12 84.3 April 52.03 70.10 61.82 206.48 May 96.13 112.54 151.44 284.68 June 113.90 114.36 154.36 368.8 July 220.40 197.10 186.54 409.6 August 169.30 228.60 212.31 426.21 September 141.20 193.60 141.64 October 91.62 91.20 92.04 November 64.80 83.50 68.70 December 42.60 39.20 37.90
4.6 SEDIMENT DATA MEASURED AT SITE
The project proponents are monitoring sediment level at Zimithang since
January 2009. The monthly averages of the sediment data observed at
Zimithang site is given in Table-4.17.
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TABLE-4.17
Average sediment data at Zimithang (Unit:ppm)
Year Month Block Coarse Medium Fine Total
2009
January I 0.00012 0.00014 0.0181 0.184 II 0.00014 0.00016 0.0198 0.0201 III 0.00018 0.00019 0.0179 0.0183 February I 0.00011 0.00028 0.0092 0.0096 II 0.0003 0.0029 0.0062 0.0094 III 0.0007 0.0021 0.0047 0.0075 March I 0.0016 0.0035 0.0162 0.0214 II 0.0016 0.0074 0.0148 0.0238 III 0.0019 0.0067 0.0087 0.0173 April I 0.0028 0.0053 0.0536 0.0617 II 0.0038 0.0103 0.0472 0.0613 III 0.0072 0.0115 0.0343 0.0530 May I 0.0082 0.0118 0.0159 0.0359 II 0.0089 0.0079 0.0234 0.0402 III 0.0116 0.0194 0.0300 0.0610 June I 0.0124 0.0336 0.0403 0.0863 II 0.0157 0.0523 0.0740 0.1420 III 0.0194 0.0168 0.0680 0.1492 July I 0.0163 0.0316 0.1460 0.1939 II 0.0178 0.0298 0.2172 0.2648 III 0.0315 0.0536 0.2412 0.3263 August I 0.0258 0.0214 0.1980 0.2452 II 0.0166 0.0362 0.1342 0.1870 III 0.0152 0.0279 0.1280 0.1711 September I 0.0089 0.0310 0.1162 0.1561 II 0.0108 0.0386 0.1112 0.1606 III 0.0128 0.0428 0.1212 0.1768 October I 0.0109 0.0523 0.0861 0.1493 II 0.0096 0.0672 0.0726 0.1494 III 0.0078 0.0617 0.0468 0.1163 November I 0.0062 0.0382 0.0532 0.0976 II 0.0054 0.0222 0.0288 0.0564 III 0.00093 0.0126 0.0184 0.0319 December I 0.00076 0.0122 0.0098 0.0228 II 0.00044 0.0098 0.0188 0.0290 III 0.00031 0.0082 0.0164 0.0249
2010
January I 0.00006 0.00000 0.01624 0.01630 II 0.00000 0.00000 0.02162 0.02162 III 0.00000 0.00000 0.01936 0.01936 February I 0.00000 0.00000 0.00500 0.00500 II 0.00032 0.00116 0.00306 0.00454 III 0.00065 0.00333 0.00525 0.00924 March I 0.00118 0.00500 0.01100 0.01718 II 0.00184 0.01496 0.00878 0.02558 III 0.00195 0.00509 0.00582 0.01285 April I 0.00246 0.00464 0.01596 0.02306
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Year Month Block Coarse Medium Fine Total II 0.00438 0.01158 0.02386 0.03982 III 0.00504 0.00960 0.01232 0.02696 May I 0.00640 0.01330 0.01590 0.03560 II 0.00616 0.00968 0.02336 0.03920 III 0.00711 0.01500 0.02998 0.05209 June I 0.01184 0.02532 0.04034 0.07750 II 0.00436 0.00756 0.01138 0.02330 III July I 0.01492 0.02718 0.07772 0.11982 II 0.01690 0.04172 0.23492 0.29354 III 0.02362 0.04200 0.13051 0.19613 August I 0.01980 0.02372 0.13142 0.17494 II 0.01664 0.03134 0.11880 0.16678 III 0.01311 0.02356 0.10378 0.14145 September I 0.00992 0.02704 0.11004 0.14700 II 0.01052 0.03036 0.10266 0.14354 III 0.01482 0.01804 0.04102 0.07388
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CHAPTER-5
BASELINE SETTING FOR PHYSICO-CHEMICAL ASPECTS
5.1 GENERAL
Before start of any Environmental Impact Assessment study, it is necessary to
identify the baseline levels of relevant environmental parameters which are
likely to be affected as a result of the construction and operation of the proposed
project. A similar approach has been adopted for conducting the CEIA study for
the proposed Nyamajangchhu hydroelectric Project. A Scoping Matrix as outlined
in Chapter-3 was formulated to identify various issues likely to be affected as a
result of the proposed project. Based on the specific inputs likely to accrue in the
proposed project, aspects to be covered in the EIA study were identified. The
other issues as outlined in the Scoping Matrix were then discarded. Thus,
planning of baseline survey commenced with the shortlisting of impacts and
identification of parameters for which the data needs to be collected.
The baseline status has been divided into following three categories:
• Physico-chemical aspects • Ecologcal aspects • Socio-Economic aspects. The baseline setting for physico-chemical aspects have been covered in this
Chapter.
5.2 METEOROLOGY
The climate of the project area is characterised by cool and dry climate.
Meteorologically, the year can be divided into three distinct seasons. Winter
season sets in from the month of October and continues upto February, followed
by summer season from March to June. The area receives rainfall under the
influence of south-west monsoons over a period of three months from July to
September.
The climate of the region varies with altitude. The climate of Nyamjang Chu basin
is humid in the lower elevation and cold in the higher elevations. From late
October to early March winter prevails, whereas, pre-monsoon season is from
March to April. The monsoon period extends from May to September. The
minimum and maximum temperature at Tawang, the district headquarters varies
between -2.9oC to 32oC. The rainfall varies considerably in the basin. The average
annual rainfall reported at Muruga Bridge in the adjacent Tawang Chu sub basin is
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about 1710 mm. The rainfall data available at Bhalukpong and Dirang is given in
Tables-5.1 and 5.2. The location of the stations at Bhalukpong and Dirang is given
in Figure-5.1. The annual rainfall (mm) at Bhalukpong and Dirang is given in
Figure-5.2. The monthly average rainfall (mm) at Bhalukpong and Dirang is given
in Figure-5.3.
Figure 5.1: Locations of Dirang, Bomdilla and Bhalukpong
Dirang
Not to Scale
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TABLE-5.1 Rainfall Data at Bhalukpong
Year Monthly Total Rainfall (mm) Annual
Rainfall Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
The rocks can be grouped into two main classes, viz gneiss and quartzite’s with
schist bands. While the gneisses occupy the upstream half of the site, the
quartzite’s occur in the downstream half.
The gneisses are generally medium to coarse grained and consist of quartz,
feldspar and biotite. Augen gneisses also occur occasionally. The biotite content
varies and mica rich gneisses are common.
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Quartzite is fine to medium grained and invariably contains mica that makes it
micaceous quartzite. Schist band of 1-5 m thickness are found associated with
the quartzite. There are a few exposures of carbonaceous schist in the vicinity of
the proposed area of surge shaft.
The geology of different components of the project is given in following
paragraphs.
Barrage
At the barrage site, the river is flat and very wide up to 200m, with high discharge
and low velocity. River bed exposes black fine silty sand with high content of
micaceous minerals. Boulders, composed mostly of quartzite and gneiss, and
ranging in size from a few centimeters to a few meters, are seen in the river bed
area. Gneissic rocks are best exposed on the right bank. General dip of Gneissic
rock foliation is N 009°/46°, i.e. in the upstream direction. The prominent joint set
is developed along the foliation. On the left bank, gneisses are exposed only along
the deeply incised nallahs near the Zimithang village.
Desilting Basin and Intake
The Desilting Basin is proposed to be placed over the river terrace on the left
bank of the river. Four bore holes have been drilled on the left bank of barrage
area that includes two each in desilting and intake areas at the base of the left
bank slopes. In the desilting basin holes, the top layer comprises boulders of
Biotite Gneiss of 4.5 to 7.0 m thickness, followed by 50 to 55 m thick blackish
medium to fine silty sand with bedrock of Gneiss at the base. Although the rocks
are fractured, the core recovery has been good. In the intake area holes, the
bedrock of Biotite Gneiss is encountered at shallower depth.
Head Race Tunnel
The 23.99 km long and 6.7 m dia Head Race Tunnel has been proposed on the
left bank of the Nyamjang Chu. From its intake near Zimithang Village to the
Surge Shaft, the HRT descends from El 2102m to 1940m at an average gradient
of 1 in 148. The site is located in the rugged terrain of the Nyamjang Chu valley
with ground elevations varying between El 1050m and 3800m. The site location
on the left bank has been preferred mainly on considerations of adequate ground
cover, exposed rock and development of infrastructure. The long section suggests
that the vertical rock cover along the HRT varies from 100 m to about 990 m. The
valley slopes on the left flank of the river tend to be much steeper than on the
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right side where the slopes are flatter and has number of streams cutting it
deeply. The left bank in this stretch is covered with dense forest on the left bank.
Large tracts along the HRT alignment are covered with thick overburden. These
account for about 50% of the alignment. The HRT cuts across four major
drainages, viz Taksang Chu at RD 5110m, BTK nala at RD 10810m, Shakti nala at
RD 13700m and Gomkang Rong Chu at RD 20470m. For want of adequate ground
cover, the HRT alignment has been pushed into the hill across the BTK and
Gomkang Rong Chu, more prominently for the latter where the shift has been as
much as 2.7 km leading to a rectangular kink in the HRT. Post realignment, the
available ground cover over the HRT at drainage crossings is in excess of 150m.
The area is characterized by the absence of springs. In general, entire project
area is dry excepting ground moisture in Shakti-Gispu area that is attributed to
well cultivated and irrigated landuse practices. The drilling at Surge Shaft site
down to 125m depth has not encountered water table and has seen complete
water loss during drilling.
Surge Shaft
The proposed 10/12m diameter Surge Shaft is located over quartzite with schist
bands and occasional carbonaceous schist bands. The rocks have steep dips
oriented in N178/35. The strata are highly jointed & occasionally sheared.
Foliation joints are the most prominent ones. A slide debris also occurs at the site.
Thin bands of carbonaceous schist dipping N 178/35 are found in the road cutting
near the surge shaft area. Thickness of this band varies between 1 to 2 m.
Pressure Shaft
A two steps branched pressure shaft is proposed to take water from the surge
shaft to the underground powerhouse. Three branches of the pressure shaft of
dia. 2.9 m will carry water from the surge shaft and each of these branches will be
subdivided into two branches of dia. 2.0 m to provide water to six machines in the
powerhouse. Jointed quartzite with schistose bands is exposed in the area. Rock
foliation dips N178/35. On surface, bedrock appears to be affected by closely
spaced joints, foliation joints being prominent.
As the geology of the area suggests that the zone consists of quartzite which are
highly fractured requires steel liners and adequate support for stabilization of
structure during the construction.
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Powerhouse
An underground powerhouse complex is proposed in the downstream of
Namtsering Bridge. The proposed size of the powerhouse cavity is about 20 m x
42 m x 166 m, with vertical cover of about 530 m and lateral cover of nearly 1200
m. Two parallel cavities, one for the powerhouse and one for the transformer hall
are planned. The dimension of transformer hall is 172.25m X 16.3 m X 24m.
5.4 GEOMORPHOLOGY OF THE PROJECT AREA
The project sites lie in a well dissected mountain terrain drained by the glacial fed
Nyamjang Chu and the Tawang Chu. The ground elevations range between
1030m and 3800m. The slopes are mostly steep to very steep. The Nyamjang
Chu flows at a general gradient of about 1 in 25. However, past river blockades
have resulted into silted up lakes leading to sections of the river having very
gentle gradients and wider river beds. Two such sections were found at Zimithang
and BTK Bridge.
The river section at the proposed barrage site near Zimithang is wide and
characteristically flat in a stretch of about 2.5 km. It presents a classic case of
silted up lake formed due to river blockade that, as per local reports, may not be
very old. By implication, the lake deposits may not be much consolidated. The
sudden drop in the river bed from a gradient of 1:280 at the barrage site to 1:10
immediately d/s of the lake deposit, suggests that its maximum thickness may be
about 100m. At the barrage axis, it is found to be over 91m thick. A similar type
of blockade with the presence of another lake deposit is found in BTK bridge area
that is reported to have occurred as recently as July 2006.
The drainage pattern is structurally controlled. Streams are typically seen to be
taking sharp bends. Tributary streams are meeting the main river at about right
angle. There are a number of first, second and third order streams joining the
main river. The number of first order streams on the right bank is much more
than that on the left bank. There are about 11 first order streams on the right
bank of the river to which several second and third order streams are joining. On
the left bank, there are only three major nallahs cutting across the area,
important ones being Taksang Chu and Gomkang Rong Chu.
Geomorphic Units Based on Satellite Imagery Interpretation
Geomorphologically the study area is characterized by undulating dissected
structural hills, which have been denudated and formed various features. The
dissected hills have been denudated with Intermountain valley. Different
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geomorphic units were delineated based on their denudational, depositional,
topographical and structural characteristics. The geomorphic units have followed a
standard classification scheme. Homogeneous geomorphological terrain units were
delineated and mapped as individual polygons. The main types of
geomorphological units were distinguished as following:
Highly dissected structural hill: With high density of drainage & lineaments.
Moderate dissected structural hill: With moderate drainage density.
Low dissected structural hill: With low drainage density.
Hill terraces: In the study area hill terraces are developed on the gentle slopping
area, especially nearby main river valley. These terraces are mainly under
cultivation for agricultural crops.
Flood plain: In the study area narrow floodplain is developed in upper reaches of
Nyamjang Chu river. These flood plains are occupied with agricultural field.
Sand bars: In the study area these landforms are developed near to river and
are subjected to flooding in the monsoon period due to rise and fall of floodwater.
Denudation hills: These are formed due to differential erosion and weathering.
These are low hills with sparse vegetation cover and are subjected to high erosion
rate. In the study area these landforms are found in the surge shaft area near
Lumla village as well as in between Gispu and Shakti village.
Intermountain valley: The intermountain valleys are developed in between the
high sloping hills because of structural disturbances. In the study area these are
the broad depressions between mountains normally filled with colluvial deposits.
5.5 SEISMICITY
The north eastern part of the Himalayas is seismically very active. It is located at
the junction of three tectonic plates: the Indian plate, the Eurasian plate and the
Indo-Burmese plate. These are in constant collision and thus the region is under
high tectonic stresses, which are released in the form of earthquakes. Neo-
tectonic activity has rejuvenated the existing tectonic lineaments and developed
new cross-faults. These cross-faults have controlled the sedimentation of Older
(Mid to Lower Pleistocene) and Newer (Holocene) Alluvium. This has off-set the
major thrusts (MCT, MBF, FHF). Epicenters of almost all the faults are located
along the major cross-faults, whereas no activity is observed in the above said
major thrusts. Major concentration of seismic events is restricted to north eastern
part of the area with two main clusters around Po Chu fault zone. Besides these,
some events scattered around Bame, Siang, Lohit and Tiding faults have also
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been observed indicating recent movements along these. About 87 seismic events
have been witnessed in a period of 64 years, between 1929 and 1993.
As per the Seismic Zoning map of India, the whole North East India falls in zone
V. The list of major earthquakes in the Northeastern Himalaya, Arakan-Yoma and
Shillong Plateau regionsis given in Table-5.3.
TABLE-5.3 Major Earthquakes in the Northeastern Himalaya, Arakan-Yoma and
Shillong Plateau regions Epicentral Region Date and
Time Magnitude Major Damage to
Environment Cachar March 21, 1869 7.8 Numerous earth fissures
and sand craters Shillong plateau June 12, 1897 8.7 About 1542 people died Indo-China border, Xizang China 30º N and 95º E
Feb 17, 1905 Mw=7.1 Landslides
Indo-China border, North of Itanagar 28º N, 92º E
May 12, 1906 Mw=6.5 Landslides
Indo-Myanmar border, Near Chaukan Pass 27º N 97º E
Aug 31, 1906 Ms=7.0 Landslides
Sibsagar August 31, 1906
7.0 Property damage
Myanmar, Northern Sagaing Division, 26.5 N, 97º E
December 12, 1908; 12:54:54 UTC
Ms=7.6 Property damage
Srimangal July 8, 1918 7.6 4500 km2 area suffered damage
SW Assam September 9, 1923
7.1 Property damage
Dhubri July 2, 1930 7.1 Railway lines, culverts and bridges cracked
Assam January 27, 1931
7.6 Destruction of property
Nagaland 1932 7.0 Destruction of property Indo-Bhutan Border region, 27º N, 92º E
Jan 27, 1941; 12:41:48 UTC
Ms=6.7 Landslips and damage to property
N-E Assam October 23, 1943
7.2 Destruction of property
Arunachal July 7, 1947 7.5 Destruction of property Indo-China Border north of Itanagar, 28.5º N, 94º E
July 29, 1947; 13:29:25 UTC
Mw=7.3, Ms=7.5
Landslips and destruction of property
Upper Assam July 29, 1949 7.6 Severe damage
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Epicentral Region Date and Time
Magnitude Major Damage to Environment
Upper Assam, Indo-China Border, 28.7º N 90.6º E
August 15, 1950; 19:39:28.5 IST
Mw=8.6 About 1520 people died. It is the 6th largest earthquake of the 20th Century.
Patkoi Hills, Tirap District 25º N 95.8º E
August 15, 1950; 21:42:16 UTC
8.0 Property Damage
North of Sadiya, Dihang valley, 28.6º N 94.2º E
Aug 16, 1950; 06:41:59.5 UTC
7.0 Bank collapse
NW Sadiya, Dihang Valley District (Arunachal-Assam border), 27.8º N 95.3º E
Sept 13, 1950; 11:07:34.1 UTC
7.0 Landslides and Bank failure
Indo-China Border north of Itanagar, 28.7º N 94.2º E
Nov 18, 1951; 14:52:20 UTC
6.7 Landslides
Manipur-Burma border
1954 7.4 Property damage
Darjeeling 1959 7.5 Property damage Myanmar, SE of Patkoi Hills, 26.13º N 96.94º E
Feb 20, 1962, 22:02:35 UTC
Ms=6.7 Landslides
Indo-Myanmar border
August 6, 1988 7.5 No casualty reported
Note: Mw=Moment Magnitude, Ms=Surface Wave magnitude Mb=Body Wave Magnitude, UTC: Coordinated universal time Source: Tiwari (2002) and Amateur Seismic Centre at http://asc.india.org
As IS1893:2002, , delineated as Figure-5.4, there are four zones, viz. Zone -II,
III, IV and V in the country, on the Seismic Zoning map of India. Each area is
defined by a specific zone factor listed in Table-5.4. On this seismic zoning map
the northeast India including the project region lies on Very High damage zone
(Zone V) (see Figure-5.4.) with zone factor 0.36.
TABLE-5.4 Seismic zones of India and zone factors
Seismic Zones of India Hazard Intensity Zone Factor (Z) II Low Damage Risk Zone 0.10 III Moderate Damage Risk Zone 0.16 IV High Damage Risk Zone 0.24 V Very High Damage Risk Zone 0.36
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A site specific study for design earthquake parameters for Nyamjang chhu HE
Project has been conducted by IIT Roorkee and is enclosed as Annexure-II. The
key findings of this report are given in the following paragraphs.
The project lies in seismic Zone V as per the seismic zoning map of India
incorporated in Indian Standard Criteria for Earthquake Resistant Design of
Structures (IS : 1893 (Part 1): 2002). The recommendations for the site specific
earthquake design parameters for the site are based on the studies carried out
related to the tectonics, regional geology, local geology around the site,
earthquake occurrences in the region around the site and the seismotectonic
setup of the area.
The site specific design earthquake parameter for MCE condition is estimated to
Ms=8.0 magnitude earthquake occurring at MCT. The PGA values for MCE and
DBE conditions and estimated to 0.36g and 0.18g respectively.
Data for time history of earthquake ground motion for the dynamic analysis of
the barrage was normalised to peak ground accelerations of 1.0 g. For MCE and
DBE time history analysis ground motion will have to be multiplied by 0.36g and
0.18g respectively. Vertical spectral acceleration values may be taken as two
third of the corresponding horizontal values. Similarly acceleration ordinates for
the time history of vertical ground motion may be assumed as two third of the
corresponding horizontal value. The site specific design acceleration spectra shall
be used in place of the design response spectra, given in IS: 1893 (Part 1).
The horizontal design seismic coefficient for preliminary design of Dam (primary
structure) is evaluated as
αh= (Z/6)* (Sa/g)
where,
Z is taken as the estimated PGA coefficient for MCE (0.36 in this case)
Sa/g is obtained from normalized horizontal acceleration spectra) corresponding
to the fundamental time period of the dam ‘T’. For other (secondary structures),
appropriate Reduction Factor R, as specified in IS: 1893 may be used along with
Importance factor I=1.
For calculating the horizontal seismic design coefficient as:
Ah=(Z/2)* (Sa/g)*(I/R)
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5.6 LAND USE PATTERN
Landuse describes how a patch of land is used (e.g. for agriculture, settlement,
forest), whereas land cover describes the materials (such as vegetation, rocks or
buildings) that are present on the surface. Accurate land use and land cover
identification is the key to most of the planning processes.
The land use pattern of the study area has been studied through digital satellite
dated 9th May,2007 was procured from National Remote Sensing Agency
(NRSA), Hyderabad. The data was processed through ERDAS software package
available with WAPCOS.
Multi-variate statistics have been used for the analysis of multi-spectral data. As
a first step, clustering algorithms was established to a set of multi-variate class
statistics against which each pixel measurement vector in the scene was
compared. Then a classification decision rule, such as the probability of
maximum likelihood that the pixel belongs to a particular class amongst the
statistics set was calculated and the pixel was assigned to the particular class.
The information classes most often considered include both cover type or
community type descriptors as well as limited structural categories, such as
crown cover and size class: of the trees.
Although two different approaches to the development of the multi-variate
statistics are used, unsupervised and supervised, their combination gives better
results. In the unsupervised classification, the radiance values of the image data
set were submitted to clustering algorithms that generate statistics until the
stopping rule i.e. minimum number of points per cluster, was reached and the
minimum distance between clusters and separability measure was established.
Another approach is to 'seed' spectral space with starting points to establish
candidate mean value for clusters, and then iterate the clustering procedure
until minimization criteria is achieved. In the supervised method, training sites
with known properties were used to extract spectral statistics from the image
data by interactively identifying the sites in the imagery. Ground truthing was
done for site identification. In the unsupervised method, identification of the
cluster was done after completing the classification by comparing the spatial
distribution of the mapped classes with ground reference data.
The wide geographic distribution and the range of sites and climates occupied by
forests complicates the understanding of the interaction of forests with solar
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radiation. Many forests grow in uneven mountainous terrain. The terrain relief
produces large variations in how solar radiation reaches the forests and
produces land form shadows. Terrain relief also generates large micro-climate
variations in temperature, precipitation, and soil properties that produces large
differences in forest composition and activity over elatively small geographic
areas. Vegetation indices are an aid for obtaining accurate results. The DN
values of different bands can be combined mathematically to create output
images that can be used extensively in forest analysis to bring out small
differences between vegetation classes. These mathematical combinations are
called indices and if chosen judiciously, they highlight and enhance differences,
which cannot be observed in the display of original color bands. Indices also help
in minimizing shadow effects in satellite multi-spectral images. Ground truth
studies were conducted in the area to validate various signals in the satellite
images and correlate them with different land use domains. The image obtained
after the vegetation index, enhancement becomes a single band data Le. The
grey set. The grey set was merged with the colored False Color Composite
(FCC). This image was then classified using the prominent signatures extracted
based on the past experience. However, this is only a preliminary classification
which will be refined further. The FCC and the classified image of the project and
its surroundings is given as Figures-5.5 and 5.6 respectively. The landuse
pattern of the study area are given in Table-5.5.
TABLE-5.5
Land use pattern of the study area Landuse Cover Area (ha) Percentage of Study Area (%) Dense vegetation 42010 60.27 Open vegetation 19519 28.00 Scrubs 4358 6.25 Agriculture land 2813 4.04 Water body 987 1.43 Settlement 21 0.03 Total 69708 100.00
It is evident from Table-5.5, that major land use category in the study area is
forest, which accounts for almost 88.27% of the study area. The other major
category is scrubs accounting for about 6.25% of the study area. The agriculture
land accounts for about 4.04% of the study area. The area under water body
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account for about 1.42% of the study area. The area under settlement is about
0.03% of the study area.
5.7 SOILS
Soil is the product of geological, chemical and biological interactions. The soils in
the region vary according to altitude and climate. The soil in the project area
and study area are young like any other region of Himalayas. The vegetal cover
is one of the most important influencing factors characterizing the soil types in a
region. Soil on the slope above 30o, due to erosion and mass wasting
processing, are generally shallow and usually have very thin surface horizons.
Such soils have medium to coarse texture. Residual soils are well developed on
level summits of lesser Himalayas, Sub-soil are deep and heavily textured.
The soil quality was monitored at various locations in the catchment area. The
monitoring was conducted by WAPCOS for three seasons namely Monsoon
(August 2007), Post-Monsoon (December 2007) and Pre-Monsoon (March 2008).
As a part of field studies, soil samples have been collected at various locations in
the catchment area. The sampling stations are shown in Figure- 5.7. The results
of Monsoon (August 2007), Post-Monsoon (December 2007) and Pre-Monsoon
(March 2008). seasons are given in Tables 5.6 to 5.8 respectively.
The pH of soil at various sites lies within neutral range. The levels of NPK
indicate moderate to high soil productivity. The sodium levels do not indicate
any potential for soil salinization or adverse impacts on soil productivity.
In a hydroelectric project, no significant impact on soil quality is expected
barring, soil pollution at local level due to disposal of construction waste. For
amelioration of such impacts appropriate management measures are
recommended.
R. S. Envirolink Technologies Pvt. Ltd. monitored soil quality at various locations
for three seasons namely, Pre-monsoon (March 2008), Monsoon (August 2008)
and Post-monsoon (December 2008).The results are given in Tables-5.9 to 5.11.
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TABLE-5.6
Results of soil sampling analysis of study area (Monsoon season)
5 Sirdi village 45.6 47.6 45.9 6 Sirdi, Along the river bank 49.0 50.2 59.6 7 Downstream of BTK bridge 48.6 49.1 47.4 8 Power house Site 39.5 42.5 40.5 9 Namtsering bridge 43.5 47.6 45.3
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CHAPTER-6
BASELINE SETTING FOR ECOLOGICAL ASPECTS
6.1 GENERAL
The baseline status has been divided into following three categories:
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6.2.4 FIELD STUDIES ON VEGETATION AND FLORAL DIVERSITY BY WAPCOS LTD.
The present ecological study by WAPCOS Ltd. was undertaken with the following
objectives to:
• prepare a checklist of flora in the submergence area;
• list RET, economically important and medicinal plant species;
• determine frequency, abundance and density of different vegetation
components;
• estimate density and volume of the tree component with height above 8
m;
• identify and list RET faunal species in the project area.
The field survey for all the above aspects of the ecological study pertaining to
monsoon was conducted in monsoon (August 2007), winter (December 2007)
and summer (April 2008).
6.2.4.1 Sampling Sites
The sites selected for sampling of vegetation is given in Table-6.3. The location
of sampling sites is given in Figure-6.1.
TABLE-6.3
Details of sampling sites for terrestrial ecological survey Sampling Site Location Site-1 Catchment Area Site-2 Submergence area Site-3 Dam site, near village Zimithang Site-4 Near village Shakthi Site-5 1 kmdownstream of BTK Bridge Site-6 Near village Gispu Site-7 Near Power House Site
6.2.4.2 Methodology
The sampling was carried out within 1 km of the riverbed. Considering the
difficult terrain, quadrat method was used for vegetation sampling. The
phytosociological data for trees and shrubs were collected from random quadrats
of 10 x 10 m size laid at the project site. Random quadrats of 1 x 1 m size were
laid for the study of herb component at each site. The number of quadrats used
for the study of different vegetation components at each sampling site is given in
Table 6.4.
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TABLE 6.4 Number of quadrats used for vegetation study at different sampling
sites for different vegetation components S.No Sampling Sites Tree Shrub Herb
1. Catchment Area 20 20 40 2. Submergence area 20 20 40 3. Dam site, near village
Zimithang 20 20
40
4. Near village Shakthi 20 20 40 5 1 kmdownstream of BTK
Bridge 20 20
40
6 Near village Gispu 20 20 40 7 Near Power House Site 20 20 40
During the survey, number of plants of different species in each quadrat was
identified and counted. The height of individual trees was estimated using an
Abney level/ Binocular and the DBH of all trees having height more than 8 m
was measured. Based on the quadrat data, frequency, density and cover (basal
area) of each species were calculated. The IVI values for different tree species
were determined by summing up the Relative Frequency, Relative Density and
Relative Cover values. The Relative Frequency and Relative Density values were
used to calculate the IVI of shrubs and herbs.
The volume of wood for trees was estimated using the data on DBH (measured
at 1.5 m above the ground level) and height. The volume was estimated using
the formula: πr2h, where r is the radius and h is the estimated height of the bole
of the tree. The data on density and volume were presented in per ha basis.
Two species diversity indices viz., Shannon index of general diversity (H) and
Evenness index (e) were computed using the following formula:
Shannon index of general diversity (H): - ΣPi log Pi
Where, ni = importance value for each species
N = total importance values
Pi = importance probability for each species = ni /N
Evenness index (e): H/ log S
Where, H = Shannon index of general diversity
And, S = number of species
IVI values were used for computation of both the diversity indices.
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During the vegetation survey, herbaria were prepared for the plants those had
flowers. Rare and endangered species were identified referring to the Red Data
Book of India, Flora of Meghalaya and other available literature, flora and
herbarium pertaining to the rare/ endangered species of Arunchal Pradesh.
6.2.4.3 Results
The community characteristics and species diversity indices at various sampling
sites is given in Tables-5.5 and 5.6 respectively.
Site-1: Catchment Area
There were 10 tree species recorded from this site. The tree density was 455
individuals/ha (Table-5.5). Pinus wallichiana (160 individuals/ha) and Alnus
nepalensis (125 individuals /ha) were the dominant and co-dominant tree
species in this forests. This two species together accounted for about 55% of the
total density. Ten shrubs were recorded from the site. Rhus javanica and
Eleagnus sp. were the dominant shrub species. Eighteen, Twenty three and
thirty nine herbaceous species were recorded during monsoon, winter and
summer respectively. Polygonum capitatum, Oxalis corniculata and Hydrocotyl
javanica were the dominant species.
Shannon’s diversity index ranged from 1.95 to 3.55 for tree, shrub and herb
component. The evenness index was high having values more than 0.85 (Table
5.6).
The project site was not found to have any rare and endangered plants of the
region. Plants of other economic importance such as timber, medicinal and
edible fruits were common.
Site-2 : Submergence Area
Twelve tree species were recorded from this site. The tree density was 270
individuals/ha (Refer Table-6.5). Alnus nepalensis with 70 individuals/ha was the
dominant species and alone contributed to about 26% of the total density
followed by Erythrina arboresence (45 individuals ha-1) and Macaranga
denticulata (35 individuals ha-1). Ten shrubs were recorded from the site.
Eleagnus sp. and Rubus ellipticus were the dominant shrub species. Twenty four
species of herbs were recorded during winter and monsoon and thirty nine
species during summer season. Polygonum capitatum, Anaphilis triplinervis and
Oxalis corniculata were the dominant herbaceous species.
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Shannon’s diversity index ranged between 2.18 and 3.55 for all for all three
components i.e., tree, shrub and herb. The evenness index was also high having
values more than 0.9 (Table 6.6).
The project site was not found to have many rare and endangered plants. Plants
of other economic importance such as timber, medicinal and edible fruits were
common.
Site-3 : Dam Site
Eight tree species were recorded from the dam site. The tree density was low
(250 individuals ha-1) (Table-6.5). Alnus nepalensis was the dominant species
with 137 individuals ha-1 and alone accounted for about 48% of the total density
followed by Rhododendron medini. However, the Alnus nepalensis individuals
were found as cut stumps. Seven species of shrub were recorded from the site.
Rubus ellipticus and Elaegnus sp. were the dominant shrubs. Twenty one
herbaceous species were recorded during winter and monsoon season and
twenty seven species during summer season. Galinsoga parviflora and
Polygonum capitatum were dominant during winter and Pteridium aquilinum and
Galinsoga parviflora during summer season.
In general, species diversity and the Shannon’s Index were low for the trees
(1.71) and shrubs (1.68). However, it was higher in case of herbaceous
components (2.85 - 3.17) in the forests. The evenness index was also high
having values more than 0.8 for all the three components (Table 6.6). Rare and
endangered categories of plant species was not recorded in the dam site.
However, plants of economic importance such as timber, medicinal and edible
fruits were common.
Site-4 : Near village Shakti
There were eleven tree species recorded from this site. The tree density was 475
individuals/ha (Table-6.5). Alnus nepalensis with 160 individuals/ha was the
dominant tree species followed by Schima wallichii (80 individuals /ha) were the
dominant and co-dominant tree species in this forests. This two species together
accounted for about 41% of the total density. Fourteen shrubs were recorded
from the site; Ribes glaciale and Maesa indica were dominant. Twenty eight
herbs species were recorded during winter and monsoon and thirty two herbs
species were recorded during summer. Drymaria cordata and Nicandra
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physaloides were the dominant herb species during winter and Rumex
nepalensis and Gnaphalium sp. dominated during summer season.
Shannon’s diversity index was high and ranged from 1 to 2.15 for tree, shrub
and herb component. The evenness index was also high having values more
than 0.8 (Table-6.6).
Site-5 : 1 km downstream of BTK Brridge
Nine tree species were recorded from the dam site. The tree density was low
(410 individuals /ha) (Table -6.5). Macaranga denticulata was the dominant
species with 210 individuals/ha followed by Albizzia lucida (40 individuals/ha)
constituting 61% of the total density. Thirteen shrubs were recorded from the
site and Artemesia nilagirica and Rubus ellipticus were dominant. Twenty six
herbs species were recorded during winter and monsoon season and twenty five
species during summer season. Galinsoga parviflora and Fagopurum dibotrys
were dominant during winter and Polygonum hydropiper and Galinsoga
parviflora during summer season. In general, species diversity and the
Shannon’s Index were low for the tree component (1.78) as compared to shrub
(2.33) and herb (1.28 and 1.33) components in the forests. The evenness index
was also high having values more than 0.8 for all the three components (Table
6.6).
Rare and endangered categories of plant species was not recorded in the at this
site. However, plants of economic importance such as timber, medicinal and
edible fruits were common.
Site-6 : Near village Gispu
Seven tree species were recorded from this site. The tree density was 345
individuals/ha (Table-6.5). Alnus nepalensis with 180 individuals/ha was the
dominant species and alone contributed to about 52% of the total density
followed by Schima khasiana (60 individuals /ha). Twelve shrub species were
recorded from the site. Elaegnus sp., Artemesia nilagirica, Mesea indica were the
dominant shrub species. Nineteen species of herbs were recorded during winter
and monsoon and twenty four recorded during summer season. Pouzolzia hirta
and Bidens pilosa were dominant during winter while Fagopyrum dibotrys and
Anaphalis triplinervis were the dominant herb species.
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Shannon’s diversity index ranged between 1.04 and 2.03 for all for all three
components i.e., tree, shrub and herb. The evenness index was also high having
values more than 0.7 (Table 6.6).
The project site was not found to have many rare and endangered plants. Plants
of other economic importance such as timber, medicinal and edible fruits were
common (Table-6.2).
Site 7 : Powerhouse site
Six tree species were recorded from this site. The tree density was low (355
individuals /ha) (Table-6.5). Alnus nepalensis was the dominant species with
215 individuals/ha and alone accounted for about 60 % of the total density
followed by Macaranga denticulata. Eleven shrubs species were recorded from
the site. Artemesia nilagirica and Eleagnus sp. was the dominant shrub. Sixteen
species of herbs were recorded during winter and monsoon and seventeen
species recorded during summer season. Fagopyrum dibotrys and Houttuynia
cordata were dominant during winter season while Rumex nepalensis and Rubia
cordifolia were dominant during summer season.
In general, species diversity and the Shannon’s Index were low for the tree
component (1.35) as compared to shrub (1.00) and herb (1.17 and 1.19)
components in the forests. The evenness index was also high having values
more than 0.7 for all the three components (Table 6.6).
Rare and endangered categories of plant species was not recorded in the dam
site. However, plants of economic importance such as timber, medicinal and
edible fruits were common (Table-6.2).
TABLE 6.5 Community characteristics of the vegetation at various sampling
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Ficus roxburghii 5.52 Eucalyptus sp. Schima khasiana 24.43 7.83 Toona ciliate Total 149.80 163.28
TABLE-6.8 Summary of Estimated volume of wood (m3/ha) at
different sampling sites S. No. Sampling site Wood Volume (m3/ha)
1 Catchment site 161.94 2 Submergence site 45.69 3 Dam site 21.38 4 Near village Shakti 179.49 5 1km downstream of BTK bridge
site 156.32
6 Near village Gispu 149.80 7 Power house site 163.28
6.2.4 Flora under Threatened category
No threatened category of plant species was encountered during the survey. The
area showed no rare / endangered / vulnerable plant species as per IUCN
categorization.
6.2.5 FIELD STUDIES ON VEGETATION AND FLORAL DIVERSITY BY RS ENVIROLINK TECHNOLOGIES PVT. LTD.
A systematic enumeration of plant species (trees, Shrubs/under shrubs,
Climbers, Herbs, Sedges and Grasses) based on primary field survey for project
influence and non-influence zones have been prepared and is presented below in
Tables 6.9 to 6.12 respectively. TABLE-6.9
List of Plant Species (Trees) Recorded in Project Area
S. No.
Botanical Name Family Influence zone
Non-Influence zone
1 Abies pindrow Pinaceae P 2 Aesculus indica Hippocastanaceae P 3 Albizia procera Mimosaceae P P 4 Alnus nepalensis Ulmaceae P P 5 Rhododendron
arboreum Ericaceae P
6 Cedrus deodara Pinaceae P 7 Celtis eriocarpa Ulmaceae P P 8 Cupressus torulosa Cuperassaceae P
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S. No.
Botanical Name Family Influence zone
Non-Influence zone
9 Juglans regia Juglandaceae P 10 Lyonia ovalifolia Ericaceae P P 11 Pinus wallichiana Pinaceae P 12 Populus ciliata Salicaceae P P 13 Pyrus pashia Rosaceae P P 14 Quercus semiserata Fagaceae P 15 Salix karelinii Salicaceae P 16 Toona serrata Meliaceae P 17 Engelhardtia spicata Juglandaceae P P 18 Pinus roxburghi Pinaceae P P 19 Ficus semicordata Moraceae P P 20 Larix sp. Pinaceae P 21 Myrica esculenta Myricaceae P 22 Syzygium cumini Myrtaceae P P 23 Bombax ceiba Bombacaceae P P 24 Phyllanthus emblica Euphorbiaceae P P 25 Quercus sp. Fagaceae P 26 Prunus cerasoides Rosaceae P P 27 Quercus
leucotrichophora Fagaceae P
28 Morus alba Moraceae P 29 Malotus philippensis Euphorbiaceae P P 30 Erythrina variegata Fabaceae P 31 Castanea sativa Fagaceae P 32 Mahonia nepalensis Berberidaceae P P 33 Toona hexandra Meliaceae P 34 Sapium insigne Euphorbiaceae P P 35 Albizia julibrisin Mimosaceae P P 36 Betula alnoides Betulaceae P P 37 Ficus oligodon Moraceae P 38 Ilex fragilus Aquifoliaceae P 39 Erythrina arborscens Fabaceae P P 40 Grewia optiva Tiliaceae P P 41 Brassiopsis mitis Araliaceae P P
TABLE-6.10
List of Plant Species (Shrubs) Recorded in Project Area S.
No. Botanical Name Family Influence
zone Non-Influence zone
1 Abelia triflora Caprifoliaceae P 2 Artemisia sp. Asteraceae P P 3 Asragalus
chlorostachys Fabaceae P
4 Berberis angulosa Berberidaceae P
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S. No.
Botanical Name Family Influence zone
Non-Influence zone
5 Barlaria cristata Acanthaceae P P 6 Buddleja asiatica Scrophulariaceae P P 7 Cotoneaster
accuminatus Rosaceae P P
8 Coriaria nepalensis Corariaceae P P 9 Cotoneaster
microphyllus Rosaceae P
10 Desmodium macrophyllum
Fabaceae P
11 Daphne papyracea Thymelaeaceae P 12 Desmodium elegans Fabaceae P 13 Deutzia compacta Rosaceae P 14 Elaeagnus parvifolia Elaeagnaceae P P 15 Girardinia diversifolia Urticaceae P P 16 Hypericum
oblongifolium Hypericaceae P
17 Indigofera heterantha Fabaceae P 18 Jasminum humile Oleaceae P 19 Leptodermis lanceolata Rubiaceae P 20 Lonicera sp. Caprifoliaceae P 21 Philadelphus
tomentosus Hydrangeaceae P
22 Princepia utilis Rosaceae P 23 Rubus ellipticus Rosaceae P P 24 R. prostrata Rosaceae P 25 Rabdosia rugosa Lamiaceae P P 26 Rhamnus virgatus Rhamnaceae P 27 Rosa brunonii Rosaceae P P 28 Rubus foliolosus Rosaceae P P 29 Sarcococca saligna Buxaceae P 30 Sorbaria tomentosa Rosaceae P P 31 Spiraea canascens Rosaceae P 32 Urtica dioica Urticaeae P P 33 Wikstroemia canascens Thymelaeaceae P 34 Woodfordia fruticosa Lythraceae P P 35 Zanthoxylum
nepalensis Rutaceae P P
36 Hippophae salicifolia Elaeagnaceae P P 37 Rhododendron sp. Ericaeae P P 38 Spiraea sp. Rosaceae P 39 Spermadictylon
sauveolens Rubiaceae P
40 Euonymus sp. Celastraceae P 41 Xanthium indicum Asteraceae P P 42 Eupatorium
adenophorum Asteraceae P P
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S. No.
Botanical Name Family Influence zone
Non-Influence zone
43 Flemingia alata Fabaceae P 44 Inula cuspidata Asteraceae P P 45 Punica granatum Punicaceae P P 46 Asparagus adscendens Liliaceae P P 47 Anisomeles indica Lamiaceae P P 48 Euphorbia royleana Euphorbiaceae P 49 Boehmeria platyphyla Urticaceae P 50 Buddleja paniculata Scrophulariaceae P 51 Debregeasia longifolia Urticaceae P P 52 Debregeasia sp. Urticaceae P 53 Elscholtzia sp. Lamiaceae P 54 Strobilanthes sp. Acanthaceae P 55 Arundinaria nepalensis Poaceae P 56 Baoninghausenia
albiflora Rutaceae P
57 Gaultheria nummularis Ericaceae P P 58 Gaultheria sp. Ericaceae P 59 Rhus javanica Anacardiaceae P P 60 Ribes sp. Grossulariaceae P 61 Rhus parviflora Anacardiaceae P 62 Vitex negundo Verbenaceae P 63 Rhododendron sp Ericaceae P 64 Lantana camara Verbenaceae P P 65 Randia tetrasperma Rubiaceae P 66 Caryopteris odorata Verbenaceae P 67 Murraya koenigii Rutaceae P P 68 Inula cappa Asteraceae P
TABLE-6.11
List of Plant Species (Climbers) Recorded in Project Area
S. No.
Botanical Name Family Influence zone
Non-Influence zone
1 Clematis sp Ranunculaceae P P 2 Cuscuta reflexa Cuscutaceae P P 3 Cissampelos pareira Menispermaceae P P 4 Ficus hederacea Moraceae P P 5 Hedera nepalensis Araliaceae P P 6 Rubia cordifolia Rubiaceae P 7 Smilax aspra Smilacaceae P 8 Jasminum officinale Oleaceae P 9 Vitis sp. Vitaceae P 10 Periploca calophylla Asclepediaceae P 11 Stephania glabra Menispermaceae P 12 S. biternata Menispermaceae P P
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TABLE-6.12
List of Herbs, Sedges and Grasses Recorded in Project Area
S. No.
Botanical Name Family Influence zone
Non-Influence zone
1 Aconogonum molle Polygonaceae P P 2 Agrimonia pilosa Rosaceae P 3 Alpuda mutica Poaceae P P 4 Anaphalis contorta Asteraceae P P 5 Andropogon controtus Poaceae P P 6 Androsace sp. Primulaceae P 7 Anemone sp. Ranunculaceae P 8 Aquilegia pubiflora Aquifoliaceae P 9 Arabis sp. Brassicaceae P P 10 Arctium lappa Asteraceae P 11 Arenaria sp. Caryophyllaceae P P 12 Arisaema sp. Araceae P P 13 Bergenia ciliata Saxifragaceae P 14 Campanula sp. Campanulaceae P P 15 Cerastium sp. Caryophyllaceae P P 16 Cirsium verutum Asteraceae P P 17 Cynoglosum lanciolatum Boraginaceae P P 18 Epilobium sp. Onagraceae P P 19 Euphorbia hirta Euphorbiaceae P P 20 Fragaria vestita Rosaceae P P 21 F. nubicola Rosaceae P 22 Galium sp. Rubiaceae P P 23 Geranium sp. Geraniaceae P P 24 Hypericum sp. Hypericaceae P 25 Impatiens sp. Balsaminaceae P P 26 Kylinga sp. Cyperaceae P P 27 Lespedeza sp. Fabaceae P 28 Lotus corniculatus Fabaceae P 29 Mentha longifolia Lamiaceae P P 30 Micromeria biflora Lamiaceae P P 31 Nepeta sp. Lamiaceae P 32 Origanum vulgare Lamiaceae P P 33 Oxalis acetocella Oxalidaceae P P 34 Phytolacca acinosa Phytolaccaceae P 35 Pimpinella sp. Apiaceae P
36 Plantago himalaica Plantaginaceae P P 37 Potentilla sp. Rosaceae P 38 Rumex hastatus Polygonaceae P P 39 Ranunculus sp. Ranunculaceae P 40 Rosularea sp. Crassulceae P 41 Rumex nepalensis Polygonaceae P P
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S. No.
Botanical Name Family Influence zone
Non-Influence zone
42 Salvia sp. Lamiaceae P 43 Stellaria media Caryophyllaceae P P 44 Thalictrum sp. Ranunculaceae P 45 Thymus linearis Lamiaceae P 46 Trigonella corniculata Polygonaceae P P 47 Viola betonicifolia Violaceae P 48 Verbascum thapsus Scrophulariaceae P P 49 Viola pilosa Violaceae P P 50 Bidens pilosa Asteraceae P P 51 Majus sp. Scrophulariaceae P P 52 Cynodon dactylon Poaceae P P 53 Cyperus sp. Cyperaceae P P 54 Aeschynanthus
nepalensis Gesneriaceae P
55 Sedum sp. Crassulaceae P
56 Drosera sp. Droseraceae P 57 Lecanthes sp. Urticaceae P 58 Pilea umbrosa Urticaceae P P 59 Hedychium spicatum Zingiberaceae P 60 Campylotropis speciosa Fabaceae P 61 Ainsliea aptera Asteraceae P 62 Aconogonum sp. Polygonaceae P 63 Parochetus communis Fabaceae P 64 Prunella vulgaris Lamiaceae P 65 Acorus calamus Araceae P P 66 Primula macrophyla Primulaceae P 67 P. sikkimensis Primulaceae P 68 Boerhavia diffusa Nictaginaceae P P 69 Senecio sp. Asteraceae P 70 Cicerbita sp. Asteraceae P 71 Scutellaria sp. Scrophulariaceae P 72 Polygonum sp. Polygonaceae P 73 Roscoea purpurea Zingiberaceae P 74 Leucas lanata Lamiaceae P P 75 Solanum nigrum Solanaceae P P 76 Gynura hispida Asteraceae P P 77 Cassia occidentalis Caesalpinaceae P P 78 Sida sp. Malvaceae P 79 Hypoxis aurea Liliaceae P P 80 Cynotis vaga Commelinaceae P P 81 Geranium occelatum Geraniaceae P P 82 Anemone vitifolia Ranunculaceae P 83 Lespedeja juncea Fabaceae P 84 Conyza japonica Asteraceae P P 85 Gynura nepalensis Asteraceae P P
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S. No.
Botanical Name Family Influence zone
Non-Influence zone
86 Chenopodium album Chenopodiaceae P P 87 Sida rhomboidea Malvaceae P P 88 Cymbopogon sp. Poaceae P P
VEGETATION COMMUNITY STRUCTURE
Methodology
To study community structure for terrestrial ecology quadrat sampling mode was
followed. Sampling consisted of ten randomly placed quadrats of 10m x 10m size
for trees, twenty quadrats of 5m x 5m size for saplings and shrubs and twenty
quadrats of 1m x 1m for herbs were laid. The size and number of quadrats
needed were determined using the species- area curve (Misra, 1968). The
individuals falling within the range of 10-31.5 cm cbh were designated as
shrubs. The individuals having cbh more than 31.5 cm were recorded as trees.
The data on vegetation has been analysed quantitatively for density, dominance,
frequency (Curtis & McIntosh, 1950). The Important Value Index (IVI) is sum of
relative density, relative dominance and relative frequency. The diversity index
is calculated by using Shannon-Wiener Diversity Index (Shannon Wiener, 1963). Shannon-Wiener Diversity Index (H) = - � pi ln ( pi )
Here, pi is the proportion of total number of species made up of the ith species.
Sampling Sites
The study area was divided in to following sampling sites:
1. Dam site (Right bank) - Submergence Area
2. Dam site (Left bank) - Submergence Area
3. Near Confluence of Nyamjang Chhu and Taksang Chhu
4. Near Namstring Bridge area
5. Powerhouse site
The sampling locations are shown in Figure-6.1.
Dam site (Right bank) - Submergence Area
The proposed dam site is near the village Zimithang on the river Nyamjang
Chhu. Right bank of river is composed of mixed evergreen forests with Pine
forest at higher elevation on hills. The most dominant trees are Alnus
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Sl. No. Common Name Zoological Name Family 50 Golden-throated Barbet Megalaima franklinii Megalaimidae 51 Great Barbet Megalaima virens Megalaimidae 52 Black Redstart Phoenicurus ochrurus Muscicapidae 53 Blue fronted Redstart Phoenicurus frontalis Muscicapidae 54 Blue Whistling Thrush Myophonus caeruleus Muscicapidae
55 Chestnut-bellied Rock Thrush Monticola rufiventris Muscicapidae
56 Golden Bush Robin Tarsiger chrysaeus Muscicapidae 57 Grey Bushchat Saxicolaferrea Muscicapidae
1972 Macaca assamensis Schedule II Part I [1A Wildlife Protection Act,
1972 Trachischium tenuiceps Schedule IV Wildlife Protection Act,
1972 Varanus bengalensis Schedule II Wildlife Protection Act,
1972 Source : WAPCOS Ltd. Protected Areas and Corridors for wild animals
There is no Wildlife sanctuary, National park or Biosphere Reserve present within the
study area. The project area does not come under any wildlife corridor.
6.4 AQUATIC ECOLOGY
6.4.1 Methodology
For enumeration of phytoplankton population, 100 l composite water samples were
collected from the river surface up to 60 cm depth and were filtered through a 20 µm
net to make 1 l of bulk sample. The bulk samples so collected were preserved in 2%
formalin solution and were brought to the laboratory for analysis. Ten replicate water
samples each of 15 ml were made out of the preserved 1 l bulk sample and were
centrifuged at 1500 rpm for 10 minutes. After centrifuging, the volume of aliquot
concentrate was measured. 0.1 ml of aliquot concentrate was used for enumeration
of phytoplankton population in each replicate. A plankton chamber of 0.1 ml capacity
was used for counting of plankton under a light microscope. The total number of
planktons present in a litre of water sample was calculated using the following
formula:
N = (n x v x 100)/ V
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Where, N= Number of plankton per litre
n = average number of plankton cells in 0.1 ml of aliquot concentrate v = volume of plankton concentrate (aliquot) V= volume of water from bulk sample centrifuged
Phyto and zooplankton species diversity index was calculated using Shannon’s
species diversity index (H) formula taking the density values of each phytoplankton
and zooplankton species into consideration.
Shannon index of general diversity (H): - ΣPi log Pi
Where ni = density value for each species
N = total density values
Pi = density probability for each species = ni /N
6.4.2 DENSITY AND DIVERSITY OF PLANKTONS
Field Studies by WAPCOS Ltd.
The density and diversity of phytoplankton in the river water was studied by
collecting the water samples from two sites i.e. from Dam site and Submergence site.
Samples were collected from river Nyamjangchhu for assessing the density and
diversity of phytoplanktons and zooplanktons.
The list of sampling sites covered by WAPCOS Ltd. is given in Table-6.31. The
sampling locations are shown in Figure-6.2.
TABLE-6.31
Details of sampling sites for aquatic ecological survey Sampling Site Location Site-1 River Nyamjangchhu near Dam site Site-2 Submergence area Site-3 Taksangchhu Site-4 River Nyamjangchhu, 1 kmdownstream of BTK Bridge Site-5 River Nyamjangchhu near village Gispu Site-6 River Nyamjangchhu near Power House Site
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Phytoplanktons
The results of phytoplankton density at various sampling sites for monsoon, winter,
and summer season is given in Tables-6.32 to 6.34 respectively. The species
diversity index of phytoplanktons at various sampling sites is given in Table-5.35. A
total of 7 phytoplankton species were recorded from the project site and their
population was high during monsoon season (Refer Table 6.32). The phytoplankton
communities were dominated by algae. Total population was quite low as compared
to the rivers in the plains.
TABLE-6.32
Density (No. per liter) of Phytoplankton in the study area (Monsoon season)
Dam site 59.02 42.61 59.02 38.19 17.05 38.19 Submergence area 64.58 56.82 64.58 46.87 20.83 46.87 Taksangchhu 59.02 42.61 97.22 38.19 17.05 38.19 River Nyamjangchhu, 1 kmdownstream of BTK Bridge
97.22 64.58 59.02 46.87 20.83 46.87
River Nyamjangchhu near village Gispu
59.02 42.61 59.02 38.19 17.05 38.19
River Nyamjangchhu near Power House Site
97.22 64.58 97.22 46.87 20.83 46.87
Source : Field Studies by WAPCOS Ltd.
FIELD STUDIES BY RS ENVIROLINK TECHNOLOGIES PVT. LTD.
To study various parameters for aquatic ecology, survey was conducted and sampling
was carried out at 6 different sites of the proposed hydro-electric project on
Nyamjang Chhu in April 2008 and July 2008 for summer and monsoon seasons
respectively. The samples were taken in the replicates at each site of the river. The
average value was calculated for the result. Physico-chemical and biological
parameters were analysed. The sites at which sampling was done are as follows:
N1 Submergence Area (Left bank) N2 Down Stream of Dam Site (Right bank) N3 Down Stream of Takshang Chhu (Right bank) N4 Down Stream of BTK Bridge (Left bank) N5 Down Stream of Namtsring Bridge (Left bank) N6 Down Stream of Power House Site (Left bank)
The sampling sites are shown in Figure-6.2.
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Biological Characteristics
Rock surfaces, plant surfaces, leaf debris, logs, silt and sandy sediments and all other
spaces in the stream provide habitats for different organisms. According to these
habitats organisms are divided into plankton, benthos, nektons and neuston. River
water was rich in all biotic richness. 24 species of phytobenthos were identified at
different sampling sites of the proposed hydroelectric project (Table -6.41). The
density of phytobenthos ranged from 6144 individual/m2 to112645 individual/m2 at
various sites. Macro–invertebrate fauna comprised of families Heptageniidae,
Baetidae, Epeorus, Hydropsychidae, Chironomidae and Perlidae (Table-6.42).
Diversity and Evenness Index (Shannon & Weiner 1964) for phytobenthos have been
worked out and are presented in Table -6.43.
TABLE-6.41
Phytobenthos identified at various sampling sites (summer season)
Sr. No.
Taxa N1 N2 N3 N4 N5 N6
1Achnanthedium biasoletiana v. biasoletiana
+ + + + + +
2A. biasoletiana v. subatomus
+ + + + +
3A. minutissima v. minutissima
+ + + + + +
4 A. subhudsonis + + + +
5Adlafia muscora
+ + + +
6Amphora pediculus
+ + +
7Cocconeis placentula
+ + + +
8Cymbella excisa
+ + + +
9 C. leavis + + + + 10C. tumida + + +
1Diatoma mesodon
+ + + +
12D. tenue
+ + + +
13Encyonema minutum
+ + + +
14Gomphonema + + + +
NJC Hydropower Limited EIA study for Nyamjangchhu Hydroelectric Project
As part of the comprehensive EIA study, a comprehensive assessment of socio-
economic aspects was undertaken. The objective of this study was to ascertain
the overall socio-economic conditions prevailing in the study area, as well as
among the project affected families. Further, impacts, both positive as well as
negative, that are likely to occur during the construction and operation phase of
the proposed project on the socio-economic aspects of the environment have
also been assessed, which has been described in Chapter 8 of this report. A
Resettlement and Rehabilitation (R&R) plan has been devised for the Project
Affected Families (PAFs) who are likely to lose land, homestead or both due to
land acquisition for various project appurtenances as a part of the present
studies. The same has been outlined in Chapter 13 of the Environmental
Management Plan (EMP) report, which is a separate volume of this report.
The baseline setting for socio-economic aspects are outlined in the present
Chapter.
7.2 DEMOGRAPHIC PROFILE OF ARUNACHAL PRADESH
The demographic profile of Arunachal Pradesh is summarized in Table-7.1.
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TABLE-7.1 Demographic profile of Arunachal Pradesh
Parameter Value Population Male 573, 951 Female 517, 166 Total 1, 091, 117 No. of females/1000 males 901 Density of population (Nos./km2) 13 Scheduled Caste (SC) population Total 6000 Percentage of SC population to total population 0.55 Scheduled Tribe (ST) population Total 710000 Percentage of ST population to total population 65 Literacy Literate Persons 487, 796 Total Literacy rate (%) 54.74 Female Literacy rate (%) 43.5
The total population and area of state Arunachal Pradesh are 1,091,117 and
83,743 km2 respectively. The population density of the district is 13 people per
sq. km. The number of females/1000 males in the study area is 901. The
Scheduled Caste (SC) population is only 0.55%, while the Scheduled Tribe (ST)
population is 65%. The number of total literate person is 487, 796.The overall
literacy rate is average (54.74%) while the female literacy rate is 43.5%.
7.3 DEMOGRAPHIC PROFILE OF TAWANG DISTRICT
The demographic profile of Tawang District is summarized in Table-7.2.
TABLE-7.2 Demographic profile of Tawang District
Parameter Value Population Male 21846 Female 17078 Total 38924 No. of females/1000 males 782 Density of population (Nos./km2) 18 Literacy Total Literacy rate (%) 47.3 Male 11160
Female 4177
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The total population of district Tawang is 38924. Total male and female
population is 21846 and 17078 respectively. The population density of the
district is 18 people per sq. km. The number of females/1000 males in the study
area is 782. The overall literacy rate is average (54.74%). Male literacy rate is
51.08% while the female literacy rate is quite low (24.45%).
7.4 DEMOGRAPHIC PROFILE OF THE STUDY AREA
There are 60 villages belonging to five circles falling within the study area of
proposed Nyamjang Chhu H.E. Project. The total human population of these
villages is 11,445 of which 10,515 belong to Schedule Tribes which constitutes
91.8 % of the total population. There are 2,693 household in study area with
Lumla circle having the highest number (1,216) followed by Zemithang (647),
Dudunghar (519), Mukto (195) and Tawang (116). The demographic profile of
villages in study area is given in the Table-7.3.
TABLE-7.3 Demographic Profile of Study Area Villages
Circle Village Name Households Population Sex ratio
Male Female Total
Socktsen 165 352 320 672 909
Lumpo 53 140 122 262 871
Muchut (Kharakpu) 68 171 165 336 965
Ghorsham 37 121 55 176 455
ZEMITHANG Zemithang H.Q. 63 128 103 231 805
Kharman 32 87 98 185 1126
Khelengteng 22 64 70 134 1094
Dung 8 22 26 48 1182
Khobleteng 81 165 169 334 1024
Thiksi 19 31 33 64 1065
Sirdi 8 13 11 24 846
Shakti 91 172 167 339 971
Gyangong Ani Gompa 21 0 33 33 0
TAWANG Tawang Gompa 73 316 0 316 0
Gompa Village(Basti) 22 40 55 95 1375
Lumla H.Q. 230 489 409 898 836
Lumla Village (Soleng) 91 197 199 396 1010
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Circle Village Name Households Population Sex ratio
Khozo (Melenghar)
(Tabrang) (Mayur) 50 123 126 249 1024
Mangnam 147 327 323 650 988
Thrillam 58 108 132 240 1222
Buikung 21 53 55 108 1038
Hoongla 45 96 87 183 906
Pharmey 27 68 50 118 735
LUMLA Khumithang 29 62 62 124 1000
Dugumba 15 32 39 71 1219
Suhung(Jung) 15 33 31 64 939
Sazo 53 115 116 231 1009
Kungba 53 102 125 227 1225
Kharteng 79 154 176 330 1143
Phomang 44 84 96 180 1143
Baghar 48 97 122 219 1258
Sherbang 43 95 78 173 821
Yabab 26 48 58 106 1208
Gispu 142 244 291 535 1193
MUKTO Bongleng 134 272 294 566 1081
Kharung 61 120 127 247 1058
Buri 25 60 56 116 933
Shorkimeng 2 1 5 6 5000
Bletting 53 129 120 249 930
Lumsang 21 46 44 90 957
Dongmareng 26 52 49 101 942
Marmey 18 33 48 81 1455
User 27 59 62 121 1051
Guntse 22 42 43 85 1024
Zemining 17 31 39 70 1258
Dormeleng 27 49 52 101 1061
Loudung 20 34 40 74 1176
DUDUNGHAR Chelengdung 22 36 53 89 1472
Ramyang 20 35 45 80 1286
Dudunghar H.Q. 19 49 54 103 1102
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Circle Village Name Households Population Sex ratio
Pamdung 2 6 3 9 500
Maling 17 34 28 62 824
Sanghar 36 72 79 151 1097
Namtsering 39 99 96 195 970
Narmaleng 8 15 20 35 1333
Dungser 7 17 17 34 1000
Phomghar 14 35 36 71 1029
Khokem 34 73 88 161 1205
Surbin 11 25 29 54 1160
Muktur 32 60 83 143 1383
Educational Profile
There are 25 primary schools, 7 middle schools and 2 secondary schools in the
study area. There is no senior secondary school or college in the entire study
area. Moreover, there is not even a single college in the entire district. Poor
educational infrastructure is reflected in the literacy status in the area. Average
literacy rate in the study area is 22.8%; village wise rate varies from 0 to 100%
and there are two villages (Shorkimeng and Narmaleng) in dudunghar Circle,
one village (Thiksi) in Zemithang Circle with entire illiterate population.
Gyangong Ani in Tawang circle has highest literacy rate of 100%. Male literacy
rate is fairly high as compared to that of female literacy rate. The details of
educational profile is given in the Table-7.4.
TABLE-7.4 Number of Educational institutions in the study area
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7.6.5 Housing
Information regarding Housing details was also collected from the affected
families during the socio-economic survey. It was found that no family was
houseless. Mixed layout of housing was observed in the project affected villages.
The settlement layout as observed during the survey ranged from dispersed to
compact settlements. Also linear settlement (on either sides of a village lane)
was also observed in some of the project affected villages. The residential unit
served the purpose of housing one or many families (off-spring), including their
cattle, fuel wood, and other material possessions of these families.
It was observed during socio-economic survey that 93.6% of the PAFs houses
were own house and rest were rented house. It was also observed that out of 47
houses 41 were electrified. It was observed that most of the houses were single
storey, and some houses had more than one floor. Further, it was observed that
the houses on an average had about 1 to 2 rooms. Wood and Stone were used
to build the walls of the houses, while the roof was mostly made of bamboo and
tin. It was observed that most of the houses had a defined space for housing
cattle, with about one room for housing cattle on an average. A small percentage
of the houses had provision for separate bathroom and toilet facilities.
Otherwise, it was observed that most of the residents either made use of the
rivulets and streams for washing and cleaning purposes. For sanitation purposes,
drains and other means of water outlets were absent in most of the villages. The
details of housing pattern of PAFs are described in Table-7.12.
TABLE-7.12 Details of Housing Pattern of the PAFs
Housing Details Khaleteng Kharteng Soksen Total Owned 4 12 31 47 Rented 0 0 2 2 Floors( No. of families) Ist 4 1 30 37 2nd 0 4 1 5 3rd 0 6 0 6 Av. No of rooms 1 2 1
No of Houses have electric connection 4 12 27 43 No. of houses have cattel shed 0 5 2 8
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No. of house have the store room 0 1 2 4 No. of house have the lavatory 0 0 0 1 Other(No of shops) 0 0 0 15 Wall Material used(No. of families) Wood & Stone 4 12 14 30 Stone 0 0 11 11 Semi 0 0 2 2 Kuchcha & wood 0 0 1 1 Kuchcha 0 0 1 1 Stone & Bamboo 0 0 1 1 Mud 0 0 1 1 Material Used for Roof(No. of families) Tin 2 4 12 18 Bamboo 2 2 17 21 Wood Tin & Wood 0 6 2 8
Source: Primary Survey, June 2009
7.6.6 Sources of Water
Information on sources of water for different uses by the villagers was also
collected. It was observed that river/streams are used primarily to meet the
water requirement for meeting drinking, washing and cleaning requirements. It
was observed that PAFs made use of pipe and tap which is connected to a
system of pipe network connected to taps which were either locally assembled or
provided by the government. It includes a storage tanks near a source and
connected through a network of pipelines, which is subsequently connected to
tap dispensers.
7.6.7 Material Assets Holding Pattern
Information on various material assets owned by the surveyed population was
also collected. The details of material assets and other assets are given in Table-
7.13. It is clear that many PAFs, if not all, own some material assets. These
assets include television sets, tape recorders, transistor radio, LPG cylinder,
refrigerators, bicycle, motor cycles, four wheelers, etc.
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TABLE-7.13 Possession of material assets owned by PAFs
As a part of the field studies, the information on awareness among the PAFs
about the proposed project was also collected. It was observed that more than
75% of the PAFs were aware about the proposed Nyamjangchhu hydro-electric
power project and only 11% of the PAFs were aware about the displacement of
the project. About 80% of the PAFs are interested in cash compensation and
about 75% of people are interested in jobs as compensation.
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CHAPTER-8
PREDICTION OF IMPACTS
8.1 GENERAL
Based on the project details and the baseline environmental status, potential
impacts as a result of the construction and operation of the proposed
Nyamjangchhu hydroelectric project have been identified. This Chapter
addresses the basic concepts and methodological approach for conducting a
scientifically based analysis of the potential impacts likely to accrue as a result of
the proposed project. The Environmental Impact Assessment (EIA) for quite a
few disciplines is subjective in nature and cannot be quantified. Wherever
possible, the impacts have been quantified and otherwise, qualitative
assessment has been undertaken. This Chapter deals with the anticipated
positive as well as negative impacts due to construction and operation of the
proposed project. The construction and operation phase comprises of various
activities each of which is likely to have an impact on environment. Thus, it is
important to understand and analyze each activity so as to assess its impact on
environment. The key activities have been categorized for construction and
operation phases.
Construction Phase Activities
• Site preparation • Earthwork and excavation including controlled blasting and drilling • Construction of a diversion barrage • Undersluice, head regulator, feeder channel, desilting arrangement • HRT of 23.45 km length with an underground surge shaft • Underground power house to generate (6x130) 780 MW of power • Tail Race Tunnel of 7.0 m diameter and 1965 m length to discharge flow
into river Nyamjangchhu • Construction of new roads and upgradation of existing roads • Construction of a temporary bridge over river Nyamjangchhu • Project headquarter, offices and colonies • Disposal of muck and construction wastes • Transportation of construction material • Operation and maintenance of construction equipment • Civil and mechanical fabrication works for construction of various project
components. • Operation of DG sets • Disposal of pollutants from workshops, etc. • Disposal of effluents and solid waste from labour camps and colonies
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Operation Phase Activities
• Diversion of water from river Nyamjangchhu for hydropower generation • Equipment maintenance and equipment restoration • Sewage and solid waste generation from project colonies
The various project activities and associated potential environmental impacts on
various environmental parameters have been identified and summarized in a
matrix and the same is outlined in Table-8.1.
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TABLE-8.1
Matrix for various project activities and associated potential Environmental Impact on various Environmental Parameters
S. No.
Project Activities Soil & Land
Geology
Hydrology
Water quality
Air quality
Noise
Flora/ Fauna
Employment
Socio-culture
A. Construction Phase 1. Sire preparation including tree
cutting √ √ √ √
2. Earthwork and excavation including blasting and drilling
√ √ √ √ √ √ √
3. Construction of Diversion barrage across river Nyamjangchhu
√ √ √ √ √
4. Construction of head race tunnel
√ √ √
5. Construction of underground surge shaft
√ √ √
6. Construction of underground power house
√ √ √
7. Widening of approach roads √ √ √ √ √ 8. Disposal of muck and
construction wastes √ √ √ √
9. Transportation of construction materials
√ √ √ √
10. Operation and maintenance of construction equipment
√ √ √ √
11. Disposal of sewage and solid waste from labour camps
√ √
12. Acquisition of private land √ √
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S. No.
Project Activities Soil & Land
Geology
Hydrology
Water quality
Air quality
Noise
Flora/ Fauna
Employment
Socio-culture
13. Acquisition of forest land √ √ √ 14. Acquisition of labour
population √ √ √ √ √ √ √
B. Operation Phase Activities 1. Diversion of water for
hydropower generation √ √ √
2. Equipment maintenance √ √ √ √ 3. Disposal of sewage and solid
waste from project colony √ √
4. Mushrooming of allied activities
√ √ √ √ √ √
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The impacts which have been covered in the present Chapter are categorized as
below:
- Impacts on Water Environment - Impacts on Air Environment - Impacts on Noise Environment - Impacts on Land Environment - Impacts on Biological Environment - Impacts on Socio-Economic Environment
8.2 IMPACTS ON WATER ENVIRONMENT
The various aspects covered under water environment are:
- Water quality - Sediments - Water resources and downstream users
8.2.1 Water quality
a) Construction phase
The major sources of surface water pollution during project construction phase
are as follows:
• Sewage from labour camps/colonies • Effluent from crushers • Pollution due to muck disposal • Effluents from other sources
i) Sewage from labour camps
The project construction is likely to last for a period of 6 years (74 months). The
peak labour strength likely to be employed during project construction phase is
about 3000 workers and 500 technical staff. The employment opportunities in
the area are limited. Thus, during the project construction phase, some of the
locals may get employment. It has been observed during construction phase of
many of the projects; the major works are contracted out, who bring their own
skilled labour. However, it is only in the unskilled category, that locals get
employment.
The construction phase, also leads to mushrooming of various allied activities to
meet the demands of the immigrant labour population in the project area.
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The following assumptions have been made for assessing the emigrating
population in the area:
• 80% of workers and technical staff emigrating into the area are married. • In 80% of the family of workers both the husband and wife will work. • In 100% of the family of technical staff, only husband will work. • 2% of total migrating population has been assumed as service providers. • 50% of service providers will have families. • Family size has been assumed as 5. Based on experience of similar projects and above referred assumptions, the
increase in the population as a result of migration of labour population during
construction phase is expected to be of the order of 11200.
The domestic water requirement has been estimated as 70 lpcd. Thus, total
water requirements work out to 0.78 mld. It is assumed that about 80% of the
water supplied will be generated as sewage. Thus, total quantum of sewage
generated is expected to be of the order of 0.63 mld. The BOD load contributed
by domestic sources will be about 504 kg/day. It is assumed that the sewage is
discharged without any treatment for which, the minimum flow required for
dilution of sewage is about 2.2 cumec.
Detailed DO modelling was done using Streeter Phelp’s model. The D.O. level
K2 – K1 Dt = D.O. deficit downstream at time t. K1 = Deoxygenation rate K2 = Reaeration rate LA = Ultimate upstream BOD DA = D.O. deficit upstream t = Time of stream flow upstream to point at which D.O. level is to be
estimated
The D.O. level in the river Nyamjangchhu was taken as 8.0 mg/l. The minimum
flow in the river Nyamjangchhu was taken as 12.3 cumec (minimum flow
estimated for 90% dependable year in the month of January-from Table-4.8).
The results of D.O. model are summarized in Table-8.2.
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TABLE-8.2 Results of D.O. Modelling due to disposal of sewage from labour camps
in river Nyamjangchhu Distance from outfall (km) D.O. (mg/l) 0.1 8.0 0.2 8.0 0.3 8.0 0.4 8.1 0.5 8.1 1.0 8.2
It can be observed from Table-8.2, that no impact is anticipated on river water
quality, as a result of disposal of sewage from labour camps. Even though no
impact is envisaged on water quality of river Nyamjangchhu, as a result of
disposal of untreated sewage, it is recommended to commission units for
treatment of sewage generated from labour camps. In the proposed project,
sewage is proposed to be treated, prior to disposal.
ii) Effluent from crushers
During construction phase, at least one crusher will be commissioned at the
quarry site by the contractor involved in construction activities. It is proposed
only crushed material would be brought at construction site. The total capacities
of the two crushers are likely to be of the order of 120-150 tph. Water is
required to wash the boulders and to lower the temperature of the crushing
edge. About 0.1 m3 of water is required per ton of material crushed. The effluent
from the crusher would contain high-suspended solids. About 12-15 m3/hr of
wastewater is expected to be generated from each crusher. The effluent, if
disposed without treatment can lead to marginal increase in the turbidity levels
in the receiving water bodies. The natural slope in the area is such that, the
effluent from the crushers will ultimately find its way in river Nyamjangchhu.
This amounts to a discharge of 0.0033 to 0.0042 cumec. Even the lowest 10 day
minimum flow in river Nyamjangchhu is 12.3 cumec. The effluent from crusher
will have suspended solids level of 3000-4000 mg/l. On the other hand,
suspended solids as observed at various sampling locations, during water quality
monitoring studies was observed to be <0.1 mg/l. The composite value of
suspended solids would increase by 0.05 mg/l, which is insignificant. Thus, no
adverse impacts are anticipated due to small quantity of effluent and large
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volume of water available in river Nyamjangchhu for dilution. Even then, it is
proposed to treat the effluent from crushers in settling tank before disposal so as
to ameliorate even the marginal impacts likely to accrue on this account.
iii) Pollution due to muck disposal
The major impact on the water quality arises when the muck is disposed along the
river bank. The project authorities have identified suitable muck disposal sites
which are located near the river channel. The muck will essentially come from the
road-building activity, tunneling and other excavation works. The unsorted waste
going into the river channel will greatly contribute to the turbidity of water
continuously for long time periods. The high turbidity is known to reduce the
photosynthetic efficiency of primary producers in the river and as a result, the
biological productivity will be greatly reduced. Therefore, the prolonged turbid
conditions would have negative impact on the aquatic life. Therefore, muck
disposal has to be done in line with the Muck Disposal Plan given in EMP to avoid
any negative impact.
iv) Effluent from other sources
Substantial quantities of water would be used in the construction activities. With
regard to water quality, waste water from construction activities and runoff from
construction site would mostly contain suspended impurities. Adequate care
should be taken so that excess suspended solids in the wastewater are removed
before discharge into water body. The effluent is proposed to be treated by
collecting the waste water and runoff from construction sites and treating the
same in settling tanks.
b) Operation phase
The major sources of water pollution during project operation phase include:
• Effluent from project colony. • Impacts on reservoir water quality. • Eutrophication risks • Sediments i) Effluent from project colony
During project operation phase, due to absence of any large-scale construction
activity, the cause and source of water pollution will be much different. Since,
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only a small number of O&M staff will reside in the area in a well-designed
colony with sewage treatment plant and other infrastructure facilities, the
problems of water pollution due to disposal of sewage are not anticipated.
In the operation phase, about 100 families (total population of 500) will be
residing in the project colony proposed to be developed at Lumla, Khartang and
Zimithang. About 0.23 to 0.27 mld of sewage will be generated. The total BOD
loading will be order of 68 to 81 kg/day. It is proposed to provide biological
treatment facilities including secondary treatment units for sewage so generated
from the BOD load after treatment will reduce to 10 to 12 kg/day. It shall be
ensured that sewage from the project colony be treated in a sewage treatment
plant so as to meet the disposal standards for effluent. Thus, with
commissioning of facilities for sewage treatment, no impact on receiving water
body is anticipated. Thus, no impacts are anticipated as a result of disposal of
effluents from the project colony.
ii) Impacts on reservoir water quality
The flooding of previously forest and agricultural land in the submergence area
will increase the availability of nutrients resulting from decomposition of
vegetative matter. Phytoplankton productivity can supersaturate the euphotic
zone with oxygen before contributing to the accommodation of organic matter in
the sediments. Enrichment of impounded water with organic and inorganic
nutrients will be the main water quality problem immediately on commencement
of the operation. However, this phenomenon is likely to last for a short duration
of few years from the filling up of the reservoir. In the proposed project, most of
the land coming under reservoir submergence is barren, with few patches of
trees. These trees too are likely to be cleared before filling up of the reservoir.
The proposed project is envisaged as a runoff the river scheme, with significant
diurnal variations in reservoir water level. In such a scenario, significant re-
aeration from natural atmosphere takes place, which maintains Dissolved
Oxygen in the water body. Thus, in the proposed project, no significant
reduction in D.O. level in reservoir water is anticipated.
iii) Eutrophication risks
Another significant impact observed in the reservoir is the problem of
eutrophication, which occurs mainly due to the disposal of nutrient rich effluents
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from the agricultural fields. However, in the present case, fertilizer use in the
project area is negligible, hence, the runoff at present does not contain
significant amount of nutrients. Even in the post-project phase, use of fertilizers
in the project catchment area is not expected to rise significantly. Another factor
to be considered that the proposed project is envisaged as a run off the river
scheme, with significant diurnal variations in reservoir water level. Thus,
residence time would be of the order of few days, which is too small to cause
any eutrophication. Thus, in project operation phase, problems of eutrophication,
which is primarily caused by enrichment of nutrients in water, are not
anticipated.
8.2.2 Sediments
When a river flows along a steep gradient, it could carry a significant amount of
sediment load, depending on the degradation status of the catchment. When a
hydraulic structure is built across the river, it creates a reservoir, which tends to
accumulate the sediment, as the suspended load settles down due to decrease in
flow velocity. The proposed project is envisaged as a runoff the river scheme,
with a barrage. At regular intervals, the gates of the barrage shall be opened to
flush out the sediments. Thus, in the proposed project, sedimentation problems
are not anticipated.
8.2.3 Water resources and downstream users
The Nyamjangchhu Hydro Electric Project is a run of river scheme project on
river Nyamjangchhu. The diversion of water for hydropower generation will lead
to drying or reduction of flow river stretch of about 32 km. The effect will be
more pronounced in the lean season. There are no major users of water in the
intervening stretches, as river flows through a gorge and requires pumping for
use at point of consumption. As a result, there are no major users of water of
river Nymjangchhu in the intervening stretch. Thus, no major adverse impacts
are anticipated on downstream water users. However, there will be significant
adverse impacts on riverine ecology, which needs to be ameliorated through the
release of minimum flow.
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8.2.4 Impacts on river bed stability
During the construction phase a large quantity of construction material like
stones, pebbles, gravel and sand would be needed. Significant amount of
material is available in the river bed. It is proposed to extract construction
material from borrow areas in the river bed. The extraction of construction
material will lead to formation of pits. Normally, deposition of material takes
place at sites where velocity reduces on account of flattening of slopes, increase
in cross-sectional area. Such sites are used for extraction of construction
material. The pits at sites after extraction of construction material will be under
constant action on account of erosion in high flows and deposition under low
flows. These pits with passage of time will be stabilized due to settlement of silt
and sediments in the pits created on the river bed. Thus, no major impacts are
anticipated o this account.
8.3 IMPACTS ON AIR ENVIRONMENT
In a water resources project, air pollution occurs mainly during project construction
phase. The major sources of air pollution during construction phase are:
• Pollution due to fuel combustion in various equipment • Emission from various crushers • Fugitive emissions from various sources. • Blasting Operations • Pollution due to increased vehicular movement • Dust emission from muck disposal
Pollution due to fuel combustion in various equipment
The operation of various construction equipment requires combustion of fuel.
Normally, diesel is used in such equipment. The major pollutant which gets emitted
as a result of combustion of diesel is SO2. The SPM emissions are minimal due to
low ash content in diesel. The short-term increase in SO2, even assuming that all
the equipment are operating at a common point, is quite low, i.e. of the order of
less than 1µg/m3. Hence, no major impact is anticipated on this account on
ambient air quality.
Emissions from crushers
The operation of the crusher during the construction phase is likely to generate
fugitive emissions, which can move even up to 1 km in predominant wind
direction. During construction phase, one crusher each is likely to be commissioned
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near proposed dam and proposed power house sites. During crushing operations,
fugitive emissions comprising mainly the suspended particulate will be generated.
Since, there are no major settlements close to the dam and power house, hence,
no major adverse impacts on this account are anticipated. However, during the
layout design, care should be taken to ensure that the labour camps, colonies, etc.
are located on the leeward side and outside the impact zone (say about 2 km on
the wind direction) of the crushers.
Fugitive Emissions from various sources
During construction phase, there will be increased vehicular movement. Lot of
construction material like sand, fine aggregate are stored at various sites, during
the project construction phase. Normally, due to blowing of winds, especially when
the environment is dry, some of the stored material can get entrained in the
atmosphere. However, such impacts are visible only in and around the storage
sites. The impacts on this account are generally, insignificant in nature.
Blasting Operations
Blasting will result in vibration, which shall propagate through the rocks to
various degrees and may cause loosening of rocks/boulders. The overall impact
due to blasting operations will be restricted well below the surface and no major
impacts are envisaged at the ground level.
During tunneling operations, dust will be generated during blasting. ID blowers
will be provided with dust handling system to capture and generated dust. The
dust will settle on vegetation, in the predominant down wind direction.
Appropriate control measures have been recommended to minimize the adverse
impacts on this account.
Pollution due to increased vehicular movement
During construction phase, there will be increased vehicular movement for
transportation of various construction materials to the project site. Similarly,
these will be increased traffic movement on account of disposal of muck or
construction waste at the dumping site. The maximum increase in vehicle is
expected to 50 vehicles per hour. Large quantity of dust is likely to be entrained
due to the movement of trucks and other heavy vehicles. Similarly, marginal
increase in Hydrocarbons, SO2 and NOx levels are anticipated for a short
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duration. Modelling studies for hydrocarbon emissions were conducted and the
results are given in Table-8.3.
TABLE-8.3 Increase in hydrocarbon concentration due to vehicular movement
Distance (m) Increase in HC concentration (µg/m3) 10 5 20 2.50 30 1.67 40 1.25 50 1.00 60 0.83 70 0.71 80 0.63 90 0.56 100 0.50 The increase in vehicular density is not expected to significant. In addition, these
ground level emissions do not travel for long distances. Thus, no major adverse
impacts are anticipated on this account.
Dust emission from muck disposal
The loading and unloading of muck is one of the source of dust generation. Since,
muck will be mainly in form of small rock pieces, stone, etc., with very little dust
particles. Significant amount of dust is not expected to be generated on this
account. Thus, adverse impacts due to dust generation during muck disposal are
not expected.
8.4 IMPACTS ON NOISE ENVIRONMENT
a) Construction phase
In a water resource projects, the impacts on ambient noise levels are expected
only during the project construction phase, due to earth moving machinery, etc.
Likewise, noise due to quarrying, blasting, vehicular movement will have some
adverse impacts on the ambient noise levels in the area.
i) Impacts due to operation of construction equipment
The noise level due to operation of various construction equipment is given in
Table-8.4.
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TABLE-8.4 Noise level due to operation of various construction equipment
It can be observed from Table-8.10, that noise level due to blasting operations
are expected to be of the order of 75-86 dB(A). Since, the nearest settlement
are about 0.8 to 1.0 km away, the incremental noise due to blasting is expected
to be 50-60 dB(A). As the blasting is likely to last for 4 to 5 seconds depending
on the charge, noise levels over this time would be instantaneous and short in
duration. Considering attenuation due to various sources, even the
instantaneous increase in noise level is not expected to 60 dB(A). Hence, noise
level due to blasting is not expected to cause any significant adverse impact.
8.5 IMPACTS ON LAND ENVIRONMENT
a) Construction phase
The major impacts anticipated on land environment during construction are as
follows:
• Quarrying operations • Operation of construction equipment • Soil erosion • Muck disposal • Acquisition of land
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Quarrying operations
The total quantities required for the construction of civil components of the
Nyamjang Chhu HEP are as follows:
Concrete and Shotcrete Volume : 8,75,000 m3 Fine Aggregate : 2,75,000 m3 Coarse Aggregate : 5,25,000 m3
The above construction material shall be arranged from the identified quarry site
near Gorsam and major portion from the excavated muck of the HRT between
Zimithang and BTK. The quantities from the HRT excavated muck and quarry site
is estimated to contribute about 10,00,000 m3 and 5,00,000 m3 (30% swelling
factor) respectively for the requirement of coarse aggregate. Fine aggregate
requirement shall be met locally from the river bed and crushed sand. The
quantity of aggregate in the Gneissic terrain would be more than the required
quantities and the test report also suggests the suitability of the same.
River Bed Material for Aggregates
For the construction purpose river bed materials shall be utilized and for that two
locations are identified on the downstream of the barrage. One location is near to
the Zimithang village where there is a natural blockade of river due to previous
floods. There big sized boulders of gneiss of about 30-40m length are observed.
These boulders can be used for the construction material. Another location is near
to the BTK nala and it is also a natural blockade which is formed in past few years.
The boulders are larger in the river bed and can be utilized for construction
material. The rocks from the quarries were found to be suitable for the use as
coarse aggregate and crushed sand in concrete for non-wearing and wearing
surfaces.
Sand quarries
In the project area there are few locations from where sand of coarse and fine
segments can be extracted. Tests have been done to assess the suitability of sand
in the Zimithang area, BTK area & Namtsering area. All the locations are in the
river banks and nearby. The quantity of the river borne sand is not sufficient for
the construction of the project and thus to be collected or transported from other
locations.
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Opening of the quarries will cause visual impacts because they remove a
significant part of the hills. Other impacts will be the noise generated during
aggregate acquisition through explosive and crushing, which could affect wildlife
in the area, dust produced during the crushing operation to get the aggregates
to the appropriate size and transport of the aggregates, and transport of
materials.
The quarrying operations are semi-mechanized in nature. Normally, in a hilly
terrain like Arunachal Pradesh, quarrying is normally done by cutting a face of
the hill. A permanent scar is likely to be left, once quarrying activities are over.
With the passage of time, the rock from the exposed face of the quarry under
the action of wind and other erosion forces, get slowly weathered and after some
time, they become a potential source of landslide. Thus it is necessary to
implement appropriate slope stabilization measures to prevent the possibility of
soil erosion and landslides in the quarry sites.
ii) Operation of construction equipment
During construction phase, various types of equipment will be brought to the
site. These include crushers, batching plant, drillers, earthmovers, rock bolters,
etc. The siting of this construction equipment would require significant amount of
space. Similarly, space will be required for storing of various other construction
equipment. In addition, land will also be temporarily acquired, i.e. for the
duration of project construction for storage of quarried material before crushing,
crushed material, cement, rubble, etc. Efforts must be made for proper siting of
these facilities.
Various criteria for selection of these sites would be:
• Proximity to the site of use • Sensitivity of forests in the nearby areas • Proximity from habitations • Proximity to drinking water source Efforts must be made to site the contractor’s working space in such a way that
the adverse impacts on environment are minimal, i.e. to locate the construction
equipment, so that impacts on human and faunal population is minimal.
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iii) Soil erosion
The runoff from the construction sites will have a natural tendency to flow
towards river Nyamjangchhu or its tributaries. For some distance downstream of
major construction sites, such as barrage, power house, etc. there is a possibility
of increased sediment levels which will lead to reduction in light penetration,
which in turn could reduces the photosynthetic activity to some extent of the
aquatic plants as it depends directly on sunlight. This change is likely to have an
adverse impact on the primary biological productivity of the affected stretch of
river Nyamjangchhu. Since, river Nyamjangchhu has significant flow, hence,
impacts on this account are not expected to be significant. However, runoff from
construction sites, entering small streams would have significant adverse impact
on their water quality. The runoff would increase the turbidity levels with
corresponding adverse impacts on photosynthetic action and biological
productivity. The impacts on these streams and rivulets thus, would be
significant. Adequate measures need to be implemented as a part of EMP to
ameliorate this adverse impact to the extent possible.
iv) Muck disposal
The total quantity of muck expected to be generated has been estimated to be of
the order of 4.061 Mm3. The component wise detail of muck to be generated are
given in Table-8.11. Based on the geological nature of the rocks and engineering
properties of the soil, a part of the muck can be used as construction material.
However, the balance requires being suitably disposed. Normally, muck is disposed
in low-lying areas or depressions. In the proposed project 0.4 Mm3 muck is
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S. No.
Component Village Private Land (ha)
Community Land (ha)
Total Land
(ha )
57 Access Roads to
Adits - 6 Kherteng/Phoomang/Bagar
0 5.625 5.625
58 Access Roads to
Adits - 7 Kherteng/Phoomang/Bagar
0 1.275 1.275
59 Access Roads to
Adits - 8 Kungba 0 1.62 1.62
60 Access Roads to
Adits - 9 Kherteng 0 1.65 1.65
61 Access Roads to MuckDumpng 3
Kyaleyteng 0 0.75 0.75
62 Access Roads to MuckDumpng 4
Shakti 0 4.05 4.05
63 Access Roads to
Surge Shaft Kherteng 0 0.375 0.375
64 Access Roads to
M.A.T. Kherteng 1.0875 0 1.0875
65 Access Roads to Cables tunnel
Kherteng 0.75 0 0.75
66 Access Roads to
T.R.T Kherteng 4.2 0 4.2
67 Quarry (Q -2 to
Q-7 ) 0 6 6
Total 10.0829 244.4697 254.5526
TABLE-8.15
Ownership status of land to be acquired for Nyamjang chhu hydroelectric project
S. No. Type of land Area (ha) 1 Private land 10.0829 2 Community land 244.4697 Total 254.5526
It can be observed from Table-8.15, that about 244.4697 ha of community land
and 10.0829 ha of private land is to be acquired. The community land has been
considered as the forest land for the purpose of preparation of Environmental
Management Plan. Appropriate plan for compensation of forest and private land
to be acquired for the project has been formulated and is covered as a part of
Environmental Management Plan outlined in Volume-II of this Report.
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vi) Impacts due to roads
A network of new roads is required to facilitate completion of the project as per
anticipated time schedule. Major components like Barrage, Power House, Surge
Shaft and Permanent Colonies for the project near village Kharteng and Zimithang
will require construction of new roads on the left bank. A bridge has to be
constructed across river Nyamjang Chhu upstream of the existing BTK bridge to
approach adits to HRT from the existing road on right bank. The total length of
new roads to be constructed has been estimated as 60.00 km as detailed in
Table-8.16.
TABLE-8.16 List of new roads to be constructed
Connecting details Length (km) Length of road to reach various adits and other project components
54.5
Length of road from existing road to Power House
2.5
Length of internal road from existing road at Barrage on Right bank and new Road on Left bank.
3.0
Total 60.0
Apart from the above major roads about 40 km of road network will be required
for approach to the various muck dumping yards. About 120 km of existing roads
in the project area from Tawang to Zimithang may require strengthening and
widening including bridges and cross drainage works.
The construction of roads can lead to the following impacts:
• The topography of the project area has steep to precipitatuous slope,
which descends rapidly into narrow valleys. The conditions can give rise to
erosion hazards due to net downhill movement of soil aggregates.
• Removal of trees on slopes and re-working of the slopes in the immediate
vicinity of roads can encourage landslides, erosion gullies, etc. With the
removal of vegetal cover, erosive action of water gets pronounced and
accelerates the process of soil erosion and formation of deep gullies.
Consequently, the hill faces are bared of soil vegetative cover and
enormous quantities of soil and rock can move down the rivers, and in
some cases, the road itself may get washed out.
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• Construction of new roads increases the accessibility of a hitherto
undisturbed areas resulting in greater human interferences and
subsequent adverse impacts on the ecosystem.
• Increased air pollution during construction phase.
8.6 IMPACTS ON BIOLOGICAL ENVIRONMENT
a) Construction phase
8.6.1 Impacts on Terrestrial flora
i) Increased human interferences
The direct impact of construction activity of any water resource project in a
Himalayan terrain is generally limited in the vicinity of the construction sites
only. As mentioned earlier, a large population (11,200) including technical staff,
workers and other group of people are likely to congregate in the area during
the project construction phase. It can be assumed that the technical staff will be
of higher economic status and will live in a more urbanized habitat, and will not
use wood as fuel, if adequate alternate sources of fuel are provided. However,
workers and other population groups residing in the area may use fuel wood, if
no alternate fuel is provided for whom alternate fuel could be provided. There
will be an increase in population by about 11200 of which about 9000 are likely
to use fuel wood. On an average, the fuel wood requirements will be of the order
of (1.0 x 365 x 9000 x 10-3) 3785 m3. The wood generated by cutting tree is
about 2 to 3 m3. Thus every year fuel wood equivalent to bout 1000-1500 trees
will be cut, which means every year on an average about 2-3 ha of forest area
will be cleared for meeting fuel wood requirements, if no alternate sources of
fuel are provided. Hence to minimize impacts, community kitchens have been
recommended. These community kitchens shall use LPG or diesel as fuel. The
details are covered in Environmental Management Plan covered in Volume-II of
this Report.
The other major impact on the flora in and around the project area would be due
to increased level of human interferences. The workers may also cut trees to
meet their requirements for construction of houses and other needs. Thus, if
proper measures are not undertaken, adverse impacts on terrestrial flora is
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anticipated. Since, labour camps are proposed to be constructed by the
contractor along with necessary facilities, such impacts are not envisaged.
During construction of various components of the project, e.g., road, colony,
dam axis, muck disposal, etc. trees will have to be cleared. The tree felling or
clearing shall be done by the Forest Department.
Impacts due to Vehicular movement and blasting
Dust is expected to be generated during blasting, vehicle movement for
transportation of construction material or construction waste. The dust particles
shall settle on the foliage of trees and plants, thereby reduction in amount of
sunlight falling on tree foliage. This will reduce the photosynthetic activity. Based
on experience in similar settings, the impact is expected to be localized upto a
maximum of 50 to 100 m from the source. In addition, the area experiences
rainfall for almost 8 to 9 months in a year. Thus, minimal deposition of dust is
expected on flora. Thus, no significant impact is expected on this account.
Acquisition of forest land
During project construction phase, land will be required for location of
construction equipment, storage of construction material, muck disposal,
widening of existing roads and construction of new project roads. The total land
requirement for the project is 254.5526 ha of which 244.4697 ha is the
community land. A part of the community land also includes forest land as well.
For EMP purposes, the entire community land has been considered as the forest
land.
The forest in the area has already been degraded due to a large-scale human
interference. Though the project area is located in an ecologically sensitive area,
the forests in and around the project area are quite degraded. The tree density
in the dam site and submergence area is about 250 and 270 trees/ha
respectively. Normally in a dense forest, tree density is of the order of 1000-
1200 trees/ha. Thus, in land to be acquired for the project, the tree density is
low to moderate. Likewise, no rare and endangered species are observed in the
forest to be acquired for the project. Thus, no adverse impacts are anticipated
on this account.
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8.6.2 Impacts on Terrestrial fauna
a) Construction phase
Disturbance to wildlife
The total land required for the project is 254.5526 ha of which 39.3491 ha
comes under submergence, (including river bed). The details of submergence
area are given in Table-8.17.
TABLE-8.17
Details of submergence area
S. No. Component Village
Land Classification Total Land (ha )
Private Land (ha)
Community Land (ha)
1
Submergence Area (Left Bank up to Barriage)
Soksen 4.0454 4.5961 8.6415
2
Submergence Area (Right Bank up to Barriage)
Lumpo 0 2.9707 2.9707
3
Submergence Area (River area up to Barriage)
Soksen and Lumpo
0 27.7369 27.7369
Total 4.0454 35.3037 39.3491
The balance (216.2035 ha) land is required for other project appurtenances.
Based on the field survey and interaction with locals, it was confirmed that no
major wildlife is reported in the proposed submergence area. It would be
worthwhile to mention here that most of the submergence lies within the gorge
portion. Thus, creation of a reservoir due to the proposed project is not expected
to cause any significant adverse impact on wildlife movement. The project area
and its surroundings are not reported to serve as habitat for wildlife nor do they
lie on any known migratory route. Thus, no impacts are anticipated on this
account.
During the construction period, large number of machinery and construction
workers shall be mobilized, which may create disturbance to wildlife population
in the vicinity of project area. The operation of various equipments will generate
significant noise, especially during blasting which will have adverse impact on
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fauna of the area. The noise may scare the fauna and force them to migrate to
other areas. Likewise siting of construction plants, workshops, stores, labour
camps etc. could also lead to adverse impact on fauna of the area. During the
construction phase, accessibility to area will lead to influx of workers and the
people associated with the allied activities from outside will also increase.
Increase in human interference could have an impact on terrestrial ecosystem.
The other major impact could be the blasting to be carried out during
construction phase. This impact needs to be mitigated by adopting controlled
blasting and strict surveillance regime and the same is proposed to be used in
the project. This will reduce the noise level and vibrations due to blasting to a
great extent.
Likewise, siting of construction equipment, godowns, stores, labour camps, etc.
may generally disturb the fauna in the area. However, no large-scale fauna is
observed in the area. Thus, impacts on this account are not expected to be
significant. However, few stray animals sometimes venture in and around the
project site. Thus, to minimize any harm due to poaching activities from
immigrant labour population, strict anti-poaching surveillance measures need to
be implemented, especially during project construction phase. The same have
been suggested as a part of the Environmental Management Plan (EMP).
Impacts on migratory routes
The faunal species observed in the project area are not migratory in nature. The
proposed submergence area is not the migratory route of wild animals. The
construction of the proposed Nyamjangchhu H.E. project will form a reservoir of
about 41.268 ha, which is also not reported to be on the migratory route of any
major faunal species.
Impacts on avi-fauna
The project area and its surroundings are quite rich in avi-fauna. However, water
birds are not very common in the area. The main reason for this phenomenon is
that water birds generally require quiescent or slow moving water environment.
However, in the proposed project area and its surroundings due to terrain
conditions, water flow is swift, which does not provide suitable habitat for the
growth of water birds. With the damming of the river, a reservoir of an area of
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about 39.3491 ha will be created, with quiescent/tranquil conditions. The
reservoir banks will have wet environment throughout the year which can lead to
proliferation of vegetation e.g. grass, etc. along the reservoir banks. Such
conditions are generally ideal for various kinds of birds, especially, water birds.
This is expected to increase the avi-faunal population of the area.
b) Operation phase
i) Increased accessibility
During the project operation phase, the accessibility to the area will improve due
to construction of roads, which in turn may increase human interferences leading
to marginal adverse impacts on the terrestrial ecosystem. The increased
accessibility to the area can lead to increased human interferences in the form of
illegal logging, lopping of trees, collection of non-timber forest produce, etc.
Since significant wildlife population is not found in the region, adverse impacts of
such interferences are likely to be marginal. The details of measures to improve
the terrestrial ecology of the area are covered in separate volume of this Report.
8.6.3 Aquatic Flora
a) Construction phase
During construction phase wastewater mostly from domestic source will be
discharged mostly from various camps of workers actively engaged in the
project area. Around 0.78 mld of water is required for the workers during the
peak construction phase out of which 80% (i.e. about 0.63 mld) will be
discharged back to the river as wastes, more or less as a point sources from
various congregation sites where workers will reside. The average minimum flow
during lean season is about 12.3 cumec. However, sufficient water for dilution
will be available in Nyamjangchhu to keep the DO of the river to significantly
high levels.
b) Operation phase
The completion of Nyamjangchhu hydroelectric Project would bring about
significant changes in the riverine ecology, as the river transforms from a fast-
flowing water system to a quiescent lacustrine environment. Such an alteration
of the habitat would bring changes in physical, chemical and biotic life. Among
the biotic communities, certain species can survive the transitional phase and
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can adapt to the changed riverine habitat. There are other species amongst the
biotic communities, which, however, for varied reasons related to feeding and
reproductive characteristics cannot acclimatize to the changed environment, and
may disappear in the early years of impoundment of water. The micro-biotic
organisms especially diatoms, blue-green and green algae before the operation
of project, have their habitats beneath boulders, stones, fallen logs along the
river, where depth is such that light penetration can take place. But with the
damming of river, these organisms may perish as a result of increase in depth.
8.6.4 Impacts on Aquatic Fauna
Construction phase
Impacts due to excavation of construction material from river bed
During the construction phase a large quantity of construction material like
stones, pebbles, gravel and sand would be needed. Significant amount of
material is available in the river bed. It is proposed to extract construction
material from borrow areas in the river bed. The extraction of construction
material may affects the river water quality due to increase in the turbidity
levels. This is mainly because the dredged material gets released during one or
all the operations mentioned below:
• excavation of material from the river bed. • loss of material during transport to the surface. • overflow from the dredger while loading • loss of material from the dredger during transportation.
The cumulative impact of all the above operations is increase in turbidity levels.
Good dredging practices can however, minimize turbidity. It has also been
observed that slope collapse is the major factor responsible for increase in the
turbidity levels. If the depth of cut is too high, there is possibility of slope collapse,
which releases a sediment cloud. This will further move outside the suction radius
of dredged head. In order to avoid this typical situation, the depth of cut be
restricted to:
γ H/C < 5.5
where, γ - unit weight of the soil H - depth of soil C - Cohesive strength of soil
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The dredging and deposition of dredged material may affect the survival and
propagation of benthic organisms. The macro-benthic life which remains attached
to the stones, boulders etc. gets dislodged and is carried away downstream by
turbulent flow. The areas from where construction material is excavated, benthic
fauna gets destroyed. In due course of time, however, the area gets recolonized,
with fresh benthic fauna. The density and diversity of benthic fauna, will however,
be less as compared with the pre-dredging levels.
The second important impact is on the spawning areas of fishes. Almost all the
cold water fish breed in the flowing waters. The spawning areas of these fish
species are found amongst pebbles, gravel, sand etc. The eggs are sticky in
nature and remain embedded in the gravel and subsequently hatch. Any
disturbance of stream bottom will result in adverse impacts on fish eggs. Even
increase in fine solids beyond 25 ppm will result in deposition of silt over the
eggs, which would result in asphyxiation of developing embryo and also choking
of gills of young newly emerged fry. Thus, if adequate precautions during
dredging operations are not undertaken, then significant adverse impacts on
aquatic ecology are anticipated.
Impacts due to discharge of sewage from labour camp/colony
The proposed hydro-power project envisages construction of a project colony at
village Sherbang. The labour camp and colonies are proposed at Kyaleyteng,
Kherteng, Sherbang. This would result in emergence of domestic waste water
which is usually discharged into the river. However, it is proposed to commission
appropriate units for treatment of domestic sewage before its disposal in to the
river. Due to perennial nature of river Nyamjangchhu, it maintains sufficient flow
throughout the year which is sufficient to dilute the treated sewage from
residential colonies. Therefore, as mentioned earlier, no adverse impacts on
water quality are anticipated due to discharge of sewage from labour
camp/colony.
Impacts due to human activities
Accumulation of labour force in the project area might result in enhancement in
indiscriminate fishing including use of explosives. The use of explosive material
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to kill fishes in the river in the project area would result in complete loss of
fishes and other aquatic life making a river stretch completely barren.
Indiscriminate fishing will reduce fish stock availability for commercial and sport
fishermen. These aspects have been adequately covered in the Environmental
Management Plan (EMP) outlined Separate Volume of this Report.
(b) Operation Phase
Impacts due to damming of river
The damming of river Nyamjanghhu due to the proposed hydroelectric project in
creation of 39.3491 ha of submergence area. The dam will change the fast flowing
river to a quiscent lacustrine environment. The creation of a pond will bring about
a number of alterations in physical, abiotic and biotic parameters both in upstream
and downstream directions of the proposed barrage site. The micro and macro
benthic biota is likely to be most severely affected as a result of the proposed
project.
The positive impact of the project will be the formation of a water body which can
be used for fish stocks on commercial basis to meet the protein requirement of
region. The commercial fishing in the proposed reservoir would be successful,
provided all tree stumps and other undesirable objects are removed before
submergence. The existence of tree stumps and other objects will hinder the
operation of deep water nets. The nets will get entangled in the tree stumps and
may be damaged.
The reduction in flow rate of river Nyamjanghhu especially during lean period is
likely to increase turbidity levels downstream of the dam. Further reduction in
rate of flow may even create condition of semi-dessication in certain stretches of
the river. This would result in loss of fish life by poaching. Hence, it is essential
to maintain minimum flow required for well being of fish life till the disposal point
of the tail race discharge.
Impacts on migratory fish species
The obstruction created by the dam would hinder migration of species especially
the Mahseers (from downstream to upper reaches) and Schizothorax sp. (from
upper reaches to the lower reaches). These fishes undertake annual migration for
feeding and breeding. Therefore, fish migration path may be obstructed due to
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high dam and fishes are expected to congregate below the dam wall. Under this
situation poaching activities may increase in the area. Most of the species will shift
to the section of the river where they find favourable environment for breeding
since the dam is 11.5 m high construction of fish ladders is a feasible option.
However, it is also proposed that the artificial seed production in hatchery may be
adopted which can be stocked in the river stretches downstream and upstream of
the proposed barrage.
8.7 IMPACTS ON SOCIO-ECONOMIC ENVIRONMENT
A project of this magnitude is likely to entail both positive as well as negative
impacts on the socio-cultural fabric of the area. During construction and
operation phases, a lot of allied activities will mushroom in the project area.
8.7.1 Impacts due to influx of labour force
During the construction phase a large labour force, including skilled, semi-skilled
and un-skilled labour force of the order of about 3500 persons, is expected to
immigrate into the project area. It is felt that most of the labour force would
come from other parts of the country. However, some of the locals would also be
employed to work in the project. The labour force would stay near to the project
construction sites.
The project will also lead to certain negative impacts. The most important
negative impact would be during the construction phase. The labour force that
would work in the construction site would settle around the site. They would
temporarily reside there. This may lead to filth, in terms of domestic
wastewater, human waste, etc. Besides, other deleterious impacts are likely to
emerge due to inter-mixing of the local communities with the labour force.
Differences in social, cultural and economic conditions among the locals and
labour force could also lead to friction between the migrant labour population
and the total population.
8.7.2 Economic impacts of the project
Apart from direct employment, the opportunities for indirect employment will
also be generated which would provide great impetus to the economy of the
local area. Various types of business like shops, food-stall, tea stalls, etc.
besides a variety of suppliers, traders, transporters will concentrate here and
benefit immensely as demand will increase significantly for almost all types of
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goods and services. The business community as a whole will be benefited. The
locals will avail these opportunities arising from the project and increase their
income levels. With the increase in the income levels, there will be an
improvement in the infrastructure facilities in the area.
8.7.3 Impacts due to land acquisition
Another most important deleterious impact during construction phase will be
that, pertaining to land acquisition. About 254.5526 ha of land proposed to be
acquired for the proposed Nyamjangchhu hydro-electric project. Of this about
10.0829 ha is private land. The details of land acquisition, project
appurtenances-wise and ownership-wise, are depicted in Tables – 8.14 and 8.15
of this Chapter.
It is observed that about 10.0829 ha of private land is proposed to be acquired
from -5 hamlets/villages. It is observed that about 47 PAFs are likely to lose land
in varying proportions. No family is likely to lose homestead on accouont of land
acquisition for the project. The list of Project affected hamlets/villages is
depicted in Table – 8.18.
TABLE – 8.18 Project affected hamlets/villages due to
the process of land acquisition S. No. Name of Project Affected hamlets/
8.7.4 Impacts on cultural/religious/historical monuments
Apart from village temple in the study area, monuments of cultural, religious,
historical or archaeological importance are not reported in the project as well as
the study area. Thus, no impact on such structures is envisaged.
8.8 INCREASED INCIDENCE OF WATER-RELATED DISEASES
8.8.1 Increased incidence of water-related diseases
The construction of a barrage would convert riverine ecosystem into a lacustrine
ecosystem. The vectors of various diseases may breed in shallow parts of the
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impounded water. The magnitude of breeding sites for mosquitoes and other
vectors in the impounded water is in direct proportion to the length of the
shoreline. Since, this is a run-of river project in a mountainous region, increase in
water spread area will be marginal and it would remain mostly confined in the
gorge of the river, the increase in the incidence of water borne disease is not
expected. Further, mosquitoes are normally observed upto a maximum elevation
of about 2000 m above sea level. The proposed project is located just above this
elevation. , Hence, increase in incidence of mosquitoes is not expected at the
barrage site. The power house is located at an elevation of about 1000 m above
men sea level. Thus at this site and at the location of other project appurtenances,
which are at a lower elevation could face increased incidence of malaria as a result
of various factors like aggregation of labour, formation of stagnant pools near
labour camps, colonies, etc. may lead to the increased incidence of such diseases
around the project area.
Labour camps located at lower elevations, especially close to the power house site
could be vulnerable to increased incidence of water-borne diseases, if adequate
measures are not undertaken.
8.8.2 Aggregation of labour
About 3500 labourers and technical staff will congregate in the project area during
peak construction phase. The total increase in population is expected to be of the
order of 11200. Most of the labour would come from various parts of the country.
The labourer would live in dormitories provided by the Contractor. Proper sanitary
facilities are generally provided. Hence, a proper surveillance and immunization
schedule needs to be developed for the labour population migrating into the
project area.
8.8.3 Excavations
The excavation of earth from borrow pits etc. is one of the major factor for the
increase in prevalence of malaria. After excavation of construction material, the
depressions are generally left without treatment where water gets collected. These
pools of water, then serves as breeding grounds for mosquitoes. However, in the
present case, the borrow areas are within the river bed, which in any case remain
under water. Thus, no additional habitat for mosquito breeding is created due to
excavation. The flight of mosquito is generally limited up to 1 to 2 km from the
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breeding sites. Since, no residential areas are located within 1 km from the
reservoir, periphery, increased incidences of malaria are not anticipated. However,
labour camps, etc. could be vulnerable to increased incidence of malaria, if proper
control measures are not undertaken.
8.8.4 Inadequate facilities in labour camps
Improperly planned labour camps generally tend to become slums, with
inadequate facilities for potable water supply and sewage treatment and disposal.
This could lead to outbreak of epidemics of water-borne diseases. Adequate
measures for supply of potable water and sewage treatment have been
recommended as a part of Environmental Management Plan outlined in separate
Volume of this Report.
8.9 IMPACTS ON GEOLOGICAL ENVIRONMENT
The project area lies mainly within Central Crystallines represented by Sela Group
of rocks (Palaeoproterozoic) that are dominated by coarse grained quartz biotite
gneiss. The Main Central Thrust (MCT), separating Sela Group from the Lesser
Himalayan formations is disposed 60 km to the south, but, the Lumla Window (Yin
et al. 2006) comprising the interbedded biotite schist and quartzites of Lumla
Formation (Mesoproterozoic) lies 15 km south of the barrage site. In general the
strata have gentle dips that are northwesterly in upstream area (N330/30),
northeasterly in central area (N020-060/30) and southerly dips in the downstream
area (N170/30). A maximum of four joint sets have been identified separately for
upstream, central and downstream areas of the project.
The site for the proposed barrage across the River Nyamjang Chhu is located over
a major lacustrine deposit formed within the gneissic terrain of Central
Crystallines. The general foliation dip of the rocks, that also represents the main
joint set, is towards right bank, viz N 240-300/15-40. The set of sub-vertical
transverse joints, striking across the river, constitutes the other important and
conspicuous feature at the site. The Zimithang Fault Scarp, a conspicuous +25m
high feature, also strikes sub-parallel to the transverse set of joints.
The lacustrine deposit is dominated by fine and medium sand and is characterized
by complete absence of pebbly horizons. 3-7.5 m thick coarser river borne material
comprising sand, gravel and pebbles overlies the lacustrine deposit. The
investigations by drilling have confirmed the interpreted thickness of the lacustrine
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deposit that is as much as 91.5m. The overall grain size distribution pattern in the
barrage area reveals dominance of fine sand that ranges between 44% and 91%.
This is followed by medium sand that is in proportions of 4% to 41% and silt in the
proportions of 7% to 38%. The coarse sand is limited to stray pockets in low
proportions. Clay fraction is not found.
The depth of SPT ‘N’ value of 20 or less is found varying between depths 10.5m
and 22.5m, and is nil in one hole. The average depth works out to be 13.25m.
Along the barrage axis, the SPT ‘N’ value of 20 or less is restricted to a maximum
depth of 15m, and an average depth of 9m. In general, the permeability of the
material ranges between 1.01x10-3 and 4.5x10-3 cm/sec with lower values
ranging between 1.7x10-4 and 9.13x10-4 cm/sec. The material, therefore, is
generally having medium permeability, and low permeability zones are limited to
insignificant pockets, like in BH-5 and BH-5A. The barrage is accordingly to be
founded on material with medium permeability. Atterberg’s Limit indicates the
material to be non-plastic. The seismic velocities of the deposit vary from 380 to
4000 m/s and have been related to unconsolidated and consolidated material.
Seismo-tectonic evaluation of the site has revealed that the area falls in the most
seismically susceptible regions of the Himalaya, viz Zone-V of the Seismic Zoning
Map of India (Anon. 2002). It also falls within the Isoseismal-IX of the Assam
Earthquake of 12 June 1897 (Anon. 2000). The site specific design earthquake
parameter studies have been conducted by the University of Roorkee and, for MCE
condition, is estimated to be Ms=8.0 magnitude earthquake occurring at MCT
(Anon. 2009). The PGA values for MCE and DBE conditions are estimated to be
0.36g and 0.18g, respectively.
The investigation results, in particular SPT and permeability, present the risk of
liquefaction (Seed and Idriss 1971). In the foundation area of the proposed
barrage, the average depth of material susceptible to liquefaction is about 9m.
However, detailed palaeo-seismic studies at the site reveal that the lacustrine
deposit and the recent river terraces are intact and completely devoid of any
feature like sand dyke, neo-tectonic activity, etc. This feature may be considered
as indicative of reduced risk of liquefaction at the project site.
For design purpose, it is proposed to excavate potentially liquefiable material down
to the maximum depth of about 14m from the ground level, i.e. El 2100m, all
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along the structures at the diversion site. The area under the barrage would be
covered with geo- membrane to restrict the upward movement of underneath soil
particles to the treated surface and at the same time it could also be ensured that
pore pressure shall be released out by allowing seepage of water through
membrane and thus safeguard the barrage structure from uplift pressure. The
excavated zone is proposed to be back-filled with well graded and compacted
material. The particle size of the back-fill shall be within the range of 0.1 mm to
150 mm for ensuring that the GSD curve shall lie out of the region which is more
susceptible to liquefaction (Tsuchida 1970).
It has been proposed that prior to placing the back-fill, dynamic compaction and
vibro-floatation techniques shall be used to treat the foundation strata. The graded
back-fill shall be compacted using vibratory roller to achieve a relative density of
more than 80%. The degree of compaction shall be based on minimum SPT
resistance requirements which could be related to relative density in the manner
suggested by Gibbs & Holtz (1957).
The foundation excavation area is expected to be saturated. For controlling
seepage in the excavation area, a plastic concrete cut-off wall is proposed in the
upstream of the barrage.
The 23450 m long Head Race Tunnel is to be excavated for a length of 11316m
through quartz-biotite gneiss in the upstream side and remaining length of
12134m through inter-bedded quartzite and schist in the downstream side. The
contact between these two formations is represented by Lumla Thrust that is found
to be tight in the project area. The entire powerhouse complex including surge
shaft, pressure shafts, underground powerhouse cavern, transformer cavern, etc.
are located within the inter-bedded sequence of quartzite and schist. The portals of
the tunnels and the adits are mostly located in rock.
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CHAPTER - 9
CONSTRUCTION METHODOLOGY
9.1 GENERAL
The project envisages construction of barrage, a head regulator, Feeder
Channel, desilting chamber, collection pool & intake, Head race tunnel, surge
shaft, pressure shaft, underground power house, tail race tunnel and all
infrastructure works. The construction methodology and equipment planning
for various works is based on the site conditions prevailing in the project area.
Construction activities are planned in such a way that the project will be
completed in the shortest possible time period. The following assumptions
have been made for construction methodology and equipment planning of the
project.
All the pre-construction activities like land acquisition, infrastructure works
and government approvals are completed before the start of construction
works on main components of the project. All civil, hydro-mechanical and
electro-mechanical works are executed in following main packages :
CIVIL WORKS Package I : Barrage and Desilting works Package II : Head Race Tunnel from RD-0.00m to
RD-8,400.00m Package III : Head Race Tunnel from RD-8,400.00m
to RD-16,875.00m Package IV : Head Race Tunnel from RD-
16,875.00m to RD-23,450.00 m Package V : Civil works for Surge Shaft and
Pressure Shaft Package VI : Civil works for Power House, Transformer Cavern, Tail Race Tunnel and Switch Yard.
HYDRO-MECHANICAL WORKS Package VII : Hydro Mechanical works comprising of
gates, hoists and Pressure Shafts steel liner Electro-Mechanical Works
Package VIII : Generating Units (Turbine & Generator), Cooling Water System, Drainage/ Dewatering System, Unit Control & Automation, Bus duct.
Package IX : Valves-MIV& BFV Package X : EOT Crane, Package XI : Air Conditioning, Ventilation etc. Package XII : Fire Fighting, Package XIII : Transformers(Generator Transformer),
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Package XIV : 415 V Switchgear & 11 kV Switchgear Package XV : Illumination Package XVI : DG sets (construction power) Package XVII : Cable &Cable Trays Package XVIII : Switchyard & Protection metering Package XIX : Transformer (Dry Type UAT SST), Package XX : DC System (Battery & Battery
Charger), UPS Package XXI : Miscellaneous and finishing works
9.2 BASIC ASESSMENT OF CONSTRUCTION METHODOLGY
The project involves execution of large quantities of excavation and concreting
for surface and underground structures. Considering the magnitude and nature
of construction activity, mechanized construction has been considered for all
type of construction job so as to achieve consistent quality at a faster rate for
timely completion of the project. Special attention has been paid to the
equipment planning for underground works as the restricted work space and
constraints of geology make this exercise very critical.
The construction of the project will involve simultaneous works on all the
packages for civil, hydro-mechanical and electro-mechanical works for various
project components. Tunneling in Head race Tunnel & underground excavation
for power house and transformer cum GIS-Cavern is one of the most critical
activities for the project and accordingly, the work is assumed to continue
uninterrupted till its completion.
9.3 PRE CONSTRUCTION ACTIVITIES
The activities proposed to be undertaken during Pre-construction work include
the following:
Detailed Topographical Survey and marking the Layout at site, Pre- construction geotechnical investigation
Clearance from Government agencies like Pollution control board, Public health, Irrigation and Forest Clearance
Acquisition of Land Financial closure Detailed design and preparation of tender documents for Civil,
Electro-mechanical, Hydro mechanical works Award of Contracts Setting up of Site office Arranging of construction power Construction of approach roads/ paths Route survey of Transmission line Mining Licence for construction materials Formation of project team
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9.4 APPROACH ROADS AND BRIDGE
Transportation of heavy machines and equipments will be required for
construction purpose. Construction of new access roads and bridges, widening
of existing roads and improvement in grade of existing roads shall be
undertaken before starting construction of main project components. These
roads would be connected through an extensive network of project roads to
various colonies, workshop, quarries etc.
9.5 BASIC CONSIDERATIONS
Construction methodology and equipment planning has been carried out
separately for execution of all project components. The types and sizes of
equipment to be used have also been indicated while describing the
construction methodology for each of the components under relevant subhead.
The number of Machines/Equipment required for construction of each
component has been worked out and their size and capacity has been arrived
at after drawing the deployment schedule matching with the construction
schedule.
Most of the construction work shall be executed through contractors. The
requirement of equipment as marked out herein has been utilized for analysis
of rates and Cost Estimates. The prices of construction equipment are based
on the prevalent market prices in India as on May, 2010.
The project area is situated in a region where extensive rainfall occurs during
monsoon. The working season is, therefore, limited to 9 months, beginning
from October to June for open works. The underground works being critical are
proposed to be carried out in two shifts of 20 hours/day.
9.6 DETAILED DESIGN AND CONSTRUCTION DRAWINGS
The detailed design will be done in parallel with the Pre-construction works. It
is envisaged that the design will be started soon after the preliminary works
are completed. During Tender engineering, detailed design work will be
started and construction drawings will be available by the time contracts are
awarded.
9.7 BASIC ASSUMPTIONS FOR EQUIPMENT PLANNING
“Guidelines for preparation of Detailed Project Reports of Irrigation and
multipurpose Projects” issued by Central water Commission have been used
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for the planning of equipments. Basic assumptions made for the planning of
equipment for various construction activities are enumerated below:
9.7.1 Working hours of equipment
All works are proposed to be done in two shifts and the scheduled working
hours have been taken as 20 hours per day. 26 days/month have been
considered on an average in a month.
9.7.2 Densities of Materials
The calculations have been based on capacity of hauling units without
considering the densities of different types of materials for excavation and the
fill material.
9.7.3 Earth Volume conversion factor
Suitable standard norms have been adopted for conversion of volumes in
natural, loose and compacted state.
9.7.4 Operating Efficiency
The operating efficiency of different types of equipment has been taken as 50
min per hour.
9.7.5 Muck Dumping Lead
A lead of 15 km has been considered for dumping of muck that would be
generated from Head Race Tunnel and a lead of 5 km is assumed for the
dumping of muck that would be generated from Power House, TRT,
Transformer Cavern, Barrage, Feeder Channel, Desilting Chamber and
Collection Pool works. A lead of 10 km is assumed for the muck dumping of the
material generated from Surge Shaft and Pressure Shaft works.
9.7.6 Concreting Lead
A lead of 10 km is considered for the concrete works in Head Race Tunnel and
5 km is assumed for the concrete works in Power House, TRT, Transformer
Cavern, Barrage, Feeder Channel, Desilting Chamber, Collection Pool, Surge
Shaft and Pressure Shaft works.
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9.8 METHODOLOGY OF CONSTRUCTION FOR VARIOUS ACTIVITIES
9.8.1 River diversion during construction
River diversion works has been planned for construction of Barrage and Head
Regulator. The construction of Barrage has to be taken up during non monsoon
months of relatively low flow. The river will be diverted along one side of the
river by construction of temporary cofferdams for the construction of the
upstream works. The cofferdam will be made of river bed material properly
compacted to the required level to prevent overtopping. An impervious layer
of geo-membrane will be provided to prevent seepage through the body of the
dam. To avoid puncturing, fine materials are placed below and over the
impermeable layer. Rip rap protections will be provided on the river side to
prevent scouring of the dam. It is expected that the cofferdam will be
damaged during the monsoon season which will be repaired for the dry
season.
The construction of Barrage structures will be done in two stages and
cofferdam will be provided accordingly. In the first stage, the river will be
diverted towards the right bank. During the period, construction work on the
left bank will be done. The work includes construction of Spillway (5 bays),
Undersluice, Head Regulator, Feeder Channel, Desilting Chamber, Reservoir,
intake structures and flood walls, upstream and downstream aprons and
stilling basins. Likewise, the remaining bays of spillway and Earthen Dam that
are on the right bank will be constructed during the second phase. During the
period, the river will be diverted through the Undersluice and gated Spillway.
The cofferdam will create the dry space in the right bank during this period.
9.8.2 Civil works
Upstream works
The deposits on the river bank shall be removed to have enough space for
construction activities. The deposit will be used for the river diversion work
and for rip rap protection works. The construction of cofferdam will be taken
up parallel with the removal of deposits. The construction of Coffer dam would
be taken up with 2 Nos of Dozers (200 HP), 2 Nos of Hydraulic Excavators of
1.5 cum bucket capacity, 2 Nos of Vibratory Rollers and sufficient number of
20/25 T Dumpers. The Coffer Dam is planned to be completed in three
months.
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Phase-I
Construction of 5 bays of Spillway, Undersluice and Head Regulator will be
taken up in the first phase of Barrage works. Total of 3.0 lacs cum of
earthwork is involved in these structures and by providing 3 Nos of Hydraulic
Excavators of 1.5 m3 capacity working round the clock (with stand bye
equipment) and fleet of dumpers, daily progress of 3,000 m3 is expected.
Therefore, the excavation gets completed in 4 months. Adequate dewatering
arrangements would be made during the excavation in foundation at Barrage
complex. Dynamic compaction will commence immediately after the necessary
excavation at Barrage site. The excavation for cut-off wall will commence
immediately after dynamic compaction/compacted backfill at Barrage site. The
deep excavation for cut-off wall will be done with Hydraulic Excavator BC-
30. Bentonite solution will be used during excavation of cut-off wall so as to
avoid the side wall collapses. The excavation of cut-off wall up to the required
level will be done and plastic concrete will be poured in the excavated trench
by using a tremmie. The concrete work for Barrage base slab and other
superstructure works will commence immediately after the completion of
plastic concrete in cut-off walls. Concreting in the river bed, pertaining to
under sluice, 5 bays of spillway and head regulator and adjacent structures will
be taken up on priority in full swing by 2 nos. 30 m3 Batching plant and 2
Stationery 1 m3 Capacity Mixers, placement of concrete is planned by Transit
mixers and Cranes with suitable Concrete Buckets. The concreting of under
sluice, 5 bays of spillway and head regulator up to sill level will be completed
in 2 months before onset of monsoon. The superstructure works of these
structures will commence immediately after the concreting of the base slab.
The Hydro-Mechanical works for these structures will be executed in parallel to
the civil works of these components. All civil and hydro mechanical works for
these components will get completed in 27 months after the start of work at
Barrage site.
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During planning it is assumed that all the structures on the left bank that will
be affected by the river flow will be completed in two seasons. Structures like
floodwalls and the intake will be completed within the first eight months. The
upstream and downstream apron, stilling basin and the rip rap protections will
be completed within 27 months. After completing the First Phase works on the
left bank, the river will be diverted through under sluice and the construction
for Phase-II Barrage works will be taken up.
Phase-II
Construction of Earthen Dam and 6 bays Spillway will be taken up in this phase
of Barrage works. 1.2 lacs cum of earthwork is involved in these structures and
by providing 2 Nos. of Hydraulic Excavators of 1.5 cum capacity working round
the clock (with stand bye equipment) and fleet of dumpers, daily progress of
2,000 m3 is expected. Therefore, the excavation gets completed in 3 months.
Adequate dewatering arrangements would be made during the excavation in
foundation at Barrage complex. Dynamic compaction will commence
immediately after the necessary excavation at this phase of Barrage
construction. The excavation for cut-off wall will commence immediately after
dynamic compaction/compacted backfilling at this front. The deep excavation
for cut-off wall will be done with a Hydraulic Excavator BC-30 and Bentonite
solution will be used during excavation of cut-off wall so as to avoid the side
wall collapses. The excavation of cut-off wall up to the required level will be
done and plastic concrete will be poured in the excavated trench by using a
tremmie. The concrete / earth filling work for this phase will commence
immediately after the completion of plastic concrete in cut-off walls. Concreting
in the river bed, pertaining to remaining bays of spillway will be taken up after
necessary excavation / dynamic compaction. The concreting of remaining bays
of spillway up to sill level will be completed in 2 months. The superstructure
work of this structure will commence immediately after the concreting of the
base slab. All civil works for these components will get completed in 18
months.
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The structures like Desilting Basin and Feeder channel can be constructed
throughout the year. The excavation of the Desilting Basin will commence
after the completion of flood wall beside the Desilting Basin. Work at Reservoir
just downstream of Desilting Basin would be taken up simultaneously with the
Desilting Basin. Excavation and backfilling at Desilting Basin, Reservoir and
Feeder Channel would be taken up with 4 Nos. of Hydraulic excavators of 5.0
lacs cum bucket capacity and sufficient nos of 20/25 T Dumpers. Therefore,
total earthwork of 5 lacs cum involved in these structures is planned to be
completed in 6 months. Adequate dewatering arrangements would be made
during the excavation at these fronts. The concrete work will commence
immediately after the completion of excavation/backfilling work at these
fronts. Concreting of the structures will be taken up on priority in full swing by
Table I Peak ground horizontal acceleration from various sources around Nyamjang Chhu HE Project site, Arunachal Pradesh.
16
Table II Values of various parameter for response spectra for various values of percentage of damping for Nyamjang Chhu HE Project site, Arunachal Pradesh.
21
Fig. 1. Seismotectonic setup around the Nyamjang Chhu HE Project site, Arunachal Pradesh (Modified after Seismotectonic Atlas of India, Geological Survey of India, 2000)
11
Fig. 2. Seismicity map of the region around Nyamjang Chhu HE Project site showing the line AB considered to plot the depth section as given in Fig. 3.
20
Fig. 3. Depth section across the seismogenic features around the Nyamjang Chhu HE project site for line AB as given in Fig. 2.
20
Fig. 4. Time history of horizontal ground motion for Nyamjang Chhu HE Project site, Arunachal Pradesh (Normalised to 1g).
24
Fig. 5. Normalised horizontal acceleration spectra for various conditions Nyamjang Chhu HE site, Arunachal Pradesh.
24
Annexure I Occurrence of Earthquakes around the Nyamjang Chhu HE Project site, Arunachal Pradesh.
29
Annexure II Ground motion acceleration time history for Nyamjang Chhu HE Project site, Arunachal Pradesh (normalised to 1g) at 0.01 sec interval.
46
iv
EXECUTIVE SUMMARY Bhilwara Energy Ltd., (BEL) has been entrusted with execution of Nyamjang Chhu H.E.
Project in Tawang district of Arunachal Pradesh. The project is located (Latitude 270 43’06” N
and Longitude 910 43’37” E) on the river Nyamjang Chhu. BEL referred the study for site-
specific earthquake parameters to the Department of Earthquake Engineering, Indian Institute
of Technology Roorkee.
The Nyamjang Chhu HE Project site lies in seismic Zone V as per the seismic zoning map of
India incorporated in Indian Standard Criteria for Earthquake Resistant Design of Structures (IS
: 1893 (Part 1): 2002). The recommendations for the site specific earthquake design parameters
for the site are based on the studies carried out related to the tectonics, regional geology, local
geology around the site, earthquake occurrences (Annexure I) in the region around the site and
the seismotectonic setup of the area (Fig. 1).
The site specific design earthquake parameter for MCE condition is estimated to Ms=8.0
magnitude earthquake occurring at MCT. The PGA values for MCE and DBE conditions and
estimated to 0.36g and 0.18g respectively.
Data for time history of earthquake ground motion for the dynamic analysis of the barrage are
given in Annexure-II normalised to peak ground accelerations of 1.0 g. For MCE and DBE
time history analysis ground motion data as given in Annexure-II will have to be multiplied by
0.36g and 0.18g respectively. The corresponding response spectra are given in Fig. 5 and Table
II. Vertical spectral acceleration values may be taken as two third of the corresponding
horizontal values. Similarly acceleration ordinates for the time history of vertical ground
motion may be assumed as two third of the corresponding horizontal value.
The site specific design acceleration spectra shall be used in place of the design response
spectra, given in IS: 1893 (Part 1). The horizontal design seismic coefficient for preliminary
design of Dam (primary structure) is evaluated as g
Zh
aS.2
.31
=α where, Z is taken as the
estimated PGA coefficient for MCE (0.36 in this case) and g
aSvalue is obtained from Fig. 5
(normalized horizontal acceleration spectra) corresponding to the fundamental time period of
the dam ‘T’. For other (secondary structures), appropriate Reduction Factor R, as specified in
IS: 1893 may be used along with Importance factor I=1. for calculating the horizontal seismic
design coefficient as: RI
gZAh .S.2
a=
1
SITE SPECIFIC DESIGN EARTHQUAKE PARAMETERS FOR
NYAMJANG CHHU H.E PROJECT, ARUNACHAL PRADESH
1.0 INTRODUCTION
1.1 Bhilwara Energy Ltd., (BEL) has been entrusted with execution of Nyamjang
Chhu H.E. Project in Arunachal Pradesh. The project is located (Latitude 270 43’06” N
and Longitude 910 43’37” E) in Tawang district of Arunachal Pradesh on river Nyamjang
Chhu. BEL referred the study for site-specific earthquake parameters to the Department of
Earthquake Engineering, Indian Institute of Technology Roorkee. Accordingly the studies
related to site specific design earthquake parameters was taken up.
1.2 The proposed dam site lies in seismic zone V as per the seismic zoning map of
India as incorporated in Indian Standard Criteria for Earthquake Resistant Design of
Structures IS:1893-(Part I) 2002 : General Provisions and Buildings. It is usually
presumed that in design of normal structures adequate safety would be attained if
structures were designed as per Codal recommendations. The probable intensity of
earthquake in seismic zone V corresponds to Intensity IX on comprehensive intensity
scale (MSK64). The structures designed as per recommended design parameters for this
zone would generally prevent loss of human life and only repairable damage could occur.
However, the recommended design parameters in IS: 1893 are for preliminary design of
important structures and it is desirable to carry out dynamic analysis for final design of
important hydraulic structures in order to estimate stresses and deformations in probable
future earthquakes. IS code, therefore, recommends that for such structures detailed site
specific investigations be carried out for estimating the design earthquake parameters.
1.3 The site specific studies related to the local and regional geological conditions,
earthquake occurrences and seismotectonic set up of the region were carried out. The
earthquake catalogue containing the location, time of occurrence and the size of
earthquakes (provided by India Meteorological Department to the BEL project authorities)
was made available to DEQ by the BEL and the same has been used for this study.
Maximum Considered Earthquake (MCE) has been evaluated on the basis of above studies
2
using deterministic approach and the same is recommended for consideration in the design
of structures.
1.4 Recommendations have been given in the form of smoothed design acceleration
response spectra for different values of damping. A time history of strong ground motion
and the acceleration spectra along with recommendations for consideration of vertical
component of earthquake motion/spectra are also included.
2.0 REGIONAL GEOLOGY AND TECTONIC SETUP
2.1 The Nyamjang Chhu H.E. Project site on the Nyamjang Chhu river is located in
the Lesser Himalayan region of Arunachal Pradesh and located 50 km north from the
surface trace of MCT. Geologically, the project area is represented mainly by the
quartzite-biotite gneiss rocks. Numerous tectonic features are present around the site and a
6° X 6° degree area bounded by latitudes 24.75°N and 30.75°N and longitudes 88.75°E
and 94.75°E around the site (Fig. 1) has been considered for the study of regional
geotectonic set up of the region.
2.2 The northern part of the study area is occupied by the Himalayas followed
southward by the narrow Brahmaputra River basin/ Assam basin, covered by alluvial fill,
and then by the Shield area i.e. Shillong Plateau. Whereas, the southeastern part of the area
is occupied by the part of Indo-Burman fold belt. Small part of the Mishmi geotectonic
unit occurs in the northeastern side of the study area. The Shillong Plateau is mainly
represented by oldest Archean landmass with Precambrian deposits. The Extra Peninsular
belt is mainly occupied by low grade complexes of the Lesser Himalaya tectonically
reworked during the Himalayan Orogeny. The foothills Himalaya, south of the MBT
exposes cover sequence of the frontal belt (Siwalik) affected by the terminal phase of
Himalayan Orogeny.
2.3 The Himalayan mobile belt forms the main and prominent geotectonic block of the
study area. The regional structural trend of the Eastern Himalayas is mostly E-W to ENE-
WSW from Bhutan to the northeastern Arunachal Pradesh, which changes gradually to
3
NE-SW near the Siang valley and terminates against the Siang fracture (Nandy, 1976).
This block is bordered by the Central Burmese Plate towards east. The prominent tectonic
feature Indus-Tsangpo Suture Zone (ITSZ) separating the mobile belt from the Indus-
Shyok Belt of the Tibetan Plateau defines its northern limit. Along ITSZ, the river
Tsangpo (Brahmaputra) flows remarkably in an E-W rectilinear valley. The ITSZ marks
the collision boundary of the Indian and Tibetan Plates. The Main Central Thrust (MCT)
separates the rock units south of ITSZ, the highest-grade metamorphites and gneisses of
the axial belt, from Precambrian sedimentary sequence and its equivalents. The Main
Boundary Thrust (MBT) separates the Siwalik rocks from the pre-Tertiary rocks. Beyond
MBT, different stratigraphic units are disposed in intricate thrust slices. Since the rocks of
this segment range in age from Proterozoic to Cenozoic, it has undergone different stages
of crustal evolution and has been subjected to orogenic movements of varying intensity
from time to time, the imprints of which are identifiable in different deformational
structures, major unconformities or discontinuities (Kumar, 1997).
2.4 The northernmost tectonic feature of the study area is Indus Suture Zone (ISZ)
trending E-W and marks the boundary between the Indian and Tibetan plates and south of
this, litho-units of the main Himalayan belt are exposed. This zone is represented by the
obducted materials of the Neotethyan oceanic crust together with deep marine Triassic to
Eocene sediments. Main Central Thrust (MCT) is a regional tectonic feature that traverses
the whole length of Himalayas has developed in response to intensive and extensive
operative compressional tectonics. This feature is a north dipping thrust fault with initial
steepness and marks the tectonic boundary between the high-grade metamorphites of the
Se La Group and low to medium-grade metasediments of the Dirang Formation in the
Diggin Valley, in upper reaches of the Kamla river and near Taliha in the Subansiri river
section (Kumar,1997). Further in east, the Dirang Formation apears to get eliminated and
it marks the tectonic boundary with the Bomdila Group. The MCT has been traced to
Arunachal Pradesh through Nepal, Darjeeling-Sikkim and Bhutan (Ravi Shanker et al.,
1989), which abuts against the Tidding Suture in the Siang Valley.
2.5 Main Boundary Thrust (MBT) is another regional tectonic feature of the
Himalayas, which demarcates the tectonic boundary between the Main Himalayan Belt
4
and the Frontal Folded Belt forming the Sub-Himalayas. It is also a north dipping thrust
fault with ENE-WSW trend from the border with Bhutan in the west to Roing in the
Dibang valley and does not continue southeast to join the Mishmi Thrust as visualized by
Ranga Rao (1983). According to Sinha Roy (1976) the MBT flattens at depth, as indicated
by the absence of Gondwana rocks in southern Bhutan and in the west-central Arunachal
Pradesh. This is possibly due to the fact that the MBT merges at depth with some
dislocation zones in the inner belt.
2.6 In the region of foothills of the Arunachal Himalayas, south of MBT, a thick pile
of molassic sub-greywacke representing the Siwaliks are exposed. This belt is continuous
all along the Himalayan foothills from Kashmir to Arunachal Pradesh. The Siwalik
sequence was deposited during the Mio-Pliocene in an unstable sinking basin, developed
on the downward bending plate north of the Shillong Plateau and south of rising
Himalayas. The Siwaliks, are folded and thrust over by the older rocks from the north
along the MBT. The lithological assemblages of the Siwaliks were also controlled by the
vigour of tectonism in the source area of the rising Himalaya. The Main Frontal Thrust
(MFT) marks the southern fringe of the Siwalik belt, bordering the Brahmaputra basin.
2.7 Towards northeastern part of the study area the geotectonic block is represented by
the Mishmi Hills which does not belong to the Indian plate and considered to be part of the
Central Burmese Plate. This block comprises of metasediments, which had undergone four
phases of deformation and had been intruded by granites/granodiorites and abuts against
the Indian Plate along the Tidding Suture. The Mishmi Hills massif is comprised of
diorite-granodiorite crystalline complex (Nandy, 1976) and the southwestern boundary of
this is marked by high angle NW-SE trending Mishmi Thrust (MT) along which this block
is thrust on the adjoining rocks. In this region, the NW-SE trending metamorphic belt is in
direct contact with the Brahmaputra alluvium. This massif acts as a linkage between the
Himalayan and Indo-Burman structural and stratigraphical trends in north and east
respectively.
2.8 The region south and southwest of the above geotectonic blocks is occupied by the
Brahmaputra River basin that has formed over the basement revealing some structural
5
features through geophysical surveys. The basement rocks are exposed to the west of the
basin and the basement has northeastward slope which reaches up to a depth of 7 km near
Mishmi foothills (GSI, 2000) as indicated by basement configuration. Whereas, near
Guwahati the alluvial cover is only of the order of 0.34 km (Barooah and Bhattacharya,
1981) where the gneissic rocks of Shillong massif are exposed on surface as hills and
ridges in the river channel and on both banks of the river. Similar hills and ridges are also
exposed at the western most side of the Assam basin. In this part of the Assam basin the
basement lays at shallower depth due to undersurface extension of the Shillong massif
rocks. Here, the basement has been affected by various faults, highs and lows, upwarps
and downwarps as revealed by seismic survey in the upper Assam (Barooah and
Bhattacharya, 1981). Most of these basement faults trend NE-SW but some are having E-
W trends. The most striking fault of the Brahmaputra river basin is the NW-SE trending
Dhansiri-Kopili fault which runs between the Shillong and Mikir Hills Massifs in the
Kopili Gap and extends across the Brahmaputra River. In this region the morphology of
the basement is represented by bowl shaped basin with thickest sediments in the area north
of Nowgang (Nandy, 2001).
2.9 This Brahmaputra Basin is bordered by the Archean landmass, the Shillong Plateau
towards south. It is interesting to note that the Shillong Plateau has witnessed prolonged
crustal deformation since Archean time. The E-W trending Dauki Fault (DF) forming
steep scarps is a very prominent linear feature marking the southern edge of the Shillong
Massif. The basement rocks of the Shillong Plateau had faulted downward along the DF
for around 13 km. In Bangladesh, the basement rock is overlain by thick sediments. This
neighbouring part of Bangladesh also has suffered intense earth movements.
2.10 The Shillong Plateau is comprised of the Shillong Massif (SM) and Mikir Hills
Massif (MHM). The MHM is separated from the SM by an alluvial tract, which is located
in the central part of Northeast India. A large part of the shield area of Northeast India
exposes Archean folds. These zones show schistose tracts grading into vast stretches of
granitic gneisses incorporating metasedimentary and metavolcanic rocks within the
gneissic complex. A major part of this complex has apparently been formed by
6
metasomatism of these sediments and volcanics. Intrusive augen gneisses occur within the
Archean and these could possibly mark late-tectonic magmatic episodes of older orogenies
(Mazumdar, 1978).
2.11 The Archean rocks of the Shillong plateau have been subjected to polycyclic
folding and metamorphism. The Shillong Group was deposited in central parts of the
plateau, as this area developed into a trough. The post-Precambrian landmass experienced
peneplanation till Jurassic, resulting into the formation of a flat-leveled surface, which is
preserved over the plateau till today (G.S.I., 1974). The MHM, with an average elevation
of 1,000 m, represents a peneplaned surface of predominantly gneissic rocks. The
sedimentary rocks are exposed along the southern and eastern flanks.
2.12 By the end of Jurassic, the southern margin of the Shillong Plateau experienced
eruption of Sylhet Traps through E-W trending fissures (Murthy, 1970; G.S.I., 1974).
Around 150 Ma, carbonatite complex was emplaced along an N-S trending fault in the
eastern part of the Shillong massif (Sarkar et al., 1992). The Cretaceous sediments got
deposited along the subsiding southern block. Towards the Paleocene-Eocene, the plateau
attained a stable shelf condition due to lower subsidence rate. The eastern and western
parts of the Shillong massif remained landmass till mid-Eocene and experienced
progressive down-sinking which initiated the deposition of coal-bearing sandstone
(G.S.I., 1974).
2.13 Shillong Plateau represents a unique structural unit in the area, as it is block-
uplifted to its present height (Murthy, 1970; G.S.I., 1974). The southern margin of
Shillong Plateau is marked by the remarkably linear E-W trending Dauki Fault. Evans
(1964) gave detailed geological and tectonic set up along the Dauki Fault Zone and
suggested that this zone is essentially a tear-fault with a lateral movement of over 200 km.
Even though presence of slickensides on a fault surface shows horizontal E-W movement,
extent of movement was not possible to be estimated. Similarly, due to lack of evidences
on the extension of this zone below the alluvial gap between Shillong Plateau and
7
Rajmahal Hills, its westward continuation can not be ascertained. Later, Murthy (1970),
Desikachar (1974) and G.S.I. (1974) have suggested vertical movements along the Dauki
Fault, as it is evidenced by the extrusion of lava through the deep-seated vertical fracture
system. Also, Murthy (1970) has reported evidences to indicate activity along a number of
E-W, N-S and NW-SE basement faults throughout the Tertiary period. It seems that the
fault zone is characterized by uplift and down-sinking of adjacent basement blocks along
the fractures.
2.14 In the western part of the Shillong Massif, NW-SE trending high-angle Dapsi
Reverse Fault upthrust the Tura range southward. This fault forms the boundary between
the Precambrians in the north and Tertiary rocks in the south. The depositional sequence
was affected by this reverse fault, which probably demarcated the northern boundary of
the sedimentary basin from Mid-Eocene through Miocene (Murthy, 1970). The Shillong
Plateau shows a criss-cross fracture pattern and marked by sharp and prominent Dudhnoi
and Kulsi faults affecting the ancient basement. Further the basement is also affected by
NE-SW trending Barapani Shear zone. Towards west, the Shillong Plateau is bordered by
the N-S trending Jamuna/ Dhubri Fault, which is indicated by the difference in basement
levels and linear north-south Brahmaputra River course for about 150 km to 200 km. The
eastern part of the Shillong Massif is marked by the NW-SE trending Dhansiri-Kopili
Fault. This fault separates the SM from MHM, which may be connected with each other at
depth. A graben-type of structure is responsible for the down-sinking of this region.
2.15 Whereas, in the southeastern part of the study area part of the Indo-Burman
tectonic belt occurs which has a regional N-S trending arc of mountain ridges extending
from Mishmi Hills through the Patkai, Naga, Chin and Arakan-Yoma Hills and is
genetically linked with the Andaman-Nicobar ridge and Sunda belt. Very prominent
eastward dipping Eastern Boundary Thrust delimits this mobile belt from the Central
Myanmar basin (Nandy, 2001). The Indo-Burman tectonic belt has formed due to
subduction of the Indian Plate beneath the Burmese Plate in geological past.
2.16 Geologically, the hill ranges of this tectonic belt are mainly formed of thick
8
turbiditic Cretaceous to upper Eocene shales and sandstones (Brunnschweiler, 1966). This
belt has been folded more intricately in Nagaland and the NE-SW trending Naga Thrust
traverses the whole of Nagaland and then verges with the Dauki Fault after taking a swing
towards southwest to west near Haflong. The anticlines, close to the Naga Thrust, show
reversal in topography with anticlines forming sites of valleys and synclinal hills (Nandy,
2001). These anticlines appear like upwarps on the edge of the moving Naga slice with
gently eastern limbs and steep, much sheared western limbs. Remarkably, most of the
thrusts in the region of Belt of Schuppen diverge from northwest and then unite with the
Naga Thrust. Thrust shows successive increase in magnitude of overriding movement
towards north. This zone has undergone large dislocation, as is indicated by enormous
variation in lithotectonic associations and attributes on either side of the Naga Thrust.
2.17 The belt of Schuppen in the Naga hills is a narrow linear belt of imbricate thrust
slices adjacent to the Assam valley and runs for 350 km (Mathur and Evans, 1964). This
belt comprises eight or possibly more overthrusts along which Paleogene rocks of Indo-
Myanmar mobile belt have moved northwestward. These thrusts define various
lithotectonic blocks and the thrusts have monoclinal dip towards southeast. As a result of
large scale thrusting in the schuppen belt the total horizontal movement that occurred is
estimated to be over 200 km (Nandy, 2001).
2.18 Towards south in the state of Mizoram and Tripura, the folded belt is represented
by high anticlinal ridges and synclinal valleys of Surmas and Tipams (Miocene) having
major N-S trending strike faults. The Oligocene rocks (Barail) consist of a series of N-S
trending marginal to basin faults. The intensity of fold movements and amplitudes of
folded layers are higher in the eastern part than in the western part of the basin. In the
Tripura and adjacent Bangladesh area, the folds are characterized by compressed
anticlines alternating with broad, very gently depressed synclines which, becomes more
compressed towards east. The Plio-Pleistocene beds in Bangladesh plains just west of
Tripura folded belt are also affected due to folding. Both anticlines and synclines are
traversed by sub-parallel and sub-vertical regional strike faults adjacent to the crestal
region of the folds. One of the significant tectonic features of this region however, is the
region of Barak-Surma valley which is bounded by hills on three sides with opening to the
9
plains of Bangladesh through Sylhet. The valley appears to have affected by tearing and
the valley trend coincides with the well known Sylhet fault. The prominent Sylhet Fault
has long been recognized in this region which trends NE and truncates the N-S trending
fold belt of Bangaldesh and Tripura region. These fold ridges exhibit eastward dragging
affect along this fault, as these folds take eastward swing. This fault extends for about 140
km and the Kusiyara River flows along this lineament for 35 km. Study of a 1968
earthquake indicated thrust faulting along this feature (Tandon and Srivastava, 1975).
However, Dasgupta and Nandy (1982) suggested deep-seated high angle reverse fault,
having a dip of about 700 towards southeast along this lineament.
2.19 To the south of the Dauki Fault of the Shillong Plateau, the plains of Bangladesh
are covered by enormously thick alluvium. The Bengal Basin is bordered on its west by
the Precambrian basement complex of crystalline metamorphics of the Indian Shield and
to the east by the frontal folds of Tripura. The basement below the basin is marked by the
Hinge zone, a high and a trough. Differential thickening and subsidence of the overlying
Oligo-Miocene sections between the shelf on the northwest and deeper basin to the
southeast has occurred in the region of EHZ. The Bengal basin basement steeply plunges
from 4 to 10 km or even further across the EHZ (Mukhopadhyay and Dasgupta, 1988).
This extends for at least 500 km from the Dauki fault on the north and Kolkata on the
south with probable extension into the Bay of Bengal having varying width from 25 km in
the north to 110 km in the central part and 35 km in the south.
3.0 SITE GEOLOGY
3.1 The geology of the project site is represented by quartz-biotite gneiss (QBG)
belonging to Precambrian Sela Group towards upstream and an interbedded sequence of
quartzite (IQS) and schist of Precambrian Lumla/Rupa Group towards downstream. The
QBG is a fairly uniform, medium to coarse grained, well foliated rock. It shows gneissose
texture with alternate bands of mainly quartz feldspar and micas aong with accessories.
The IQS are 10m to over 40m thick and are associated with thin interbands of grey
quartzite. Occasionally, thin bands of carbonaceous schist and calcitic marble also occur.
10
A limited occurrence of granitic gneiss is also found.
3.2 At the barrage site, the river is flat and very wide up to 200m. River bed exposes
black fine silty sand with high content of micaceous minerals. Boulders composed mostly
of quartzite and gneiss and ranging in size from a few centimeter to a few meters are seen
in the river bed area. Gneissic rocks are best exposed on the right bank. On the left bank,
gneisses are exposed only along the deeply incised nallas. River bed bore hole (98m deep)
information indicate presence of overburden consisting of boulders of biotite, gneisses
with quartz content and blackish medium to fine silty sand up to a depth of 7.5m and
followed by only sand without boulder up to a depth of 91.5m. Rocks consisting of biotite
gneisses with quartz content have been encountered after the depth of 91.5m. Whereas, in
the other bore hole in river bed rock were encountered at a depth of 49m overlain by
blackish medium to fine silty sand and then boulders.
11
Fig.1 Seismotectonic around the Nyamjang Chhu HE project site.
Vertical spectral acceleration values may be taken as two third of the corresponding
horizontal values. Similarly acceleration ordinates for the time history of vertical ground
motion may be assumed as two third of the corresponding horizontal value.
5.3.5 Safety Criteria
Where the structure is checked for MCE either the response spectra or time history
analysis of the structure could be carried out.
5.3.5.1 Factor of safety against sliding and overturning for MCE condition should not be
less than 1.0.
5.3.5.2 For concrete barrage the maximum tension under MCE may be allowed to exceed
50% more than those specified for DBE.
5.4 Estimation of Design Basis Earthquake
5.4.1 Earthquake Parameters
Having obtained spectra and time history for Maximum Considered Earthquake conditions
the Design Basis Spectra is evaluated by using appropriate reduction factors. A scaling
factor of 2 with respect to MCE values is recommended for obtaining Design Basis
Earthquake (DBE) values.
5.4.2 Ground Motion Characteristics
The horizontal ground acceleration values for this condition shall be derived by
multiplying the values as given in Annexure-II by a factor of 0.18g.
5.4.3 Acceleration Response Spectra
The normalised smoothed acceleration spectra are given in Table II and Fig. 5.
23
Accordingly, these are to be multiplied by 0.18 to obtain DBE spectral acceleration values.
For estimating the design seismic coefficient, hα for the preliminary design of barrage
(primary structure) is obtained as:
gZ
h aS.
2.
31
=α
where, Z is the estimated PGA coefficient for MCE (0.36 in this case). For other
(secondary structure), appropriate Response Reduction Factor R, as specified in IS: 1893
may be used along with I=1 for calculating horizontal seismic design coefficient as:
RI
gZAh .S.2
a=
5.4.4 Vertical Acceleration Vertical spectral acceleration values may be taken as two third of the corresponding
horizontal values. Similarly acceleration ordinates for the time history of vertical ground
motion may be assumed as two thirds of the corresponding horizontal values.
5.4.5 Safety Criteria
5.4.5.1 Factor of safety against sliding for DBE condition should not be less than 1.5.
Factor of safety against overturning should not be less than 1.5.
5.4.5.2 For concrete/masonry barrage the maximum tension under DBE may be allowed
to exceed upto 12.5% of the ultimate compressive strength.
5.5 For design of other relatively less important and less hazardous structures/systems
the value of acceleration history/spectra could be further reduced by 50% with respect to
DBE values. Forces obtained in this manner are to be considered as working seismic loads
and may be combined with other loads as specified in the relevant codes along with
permissible stresses.
5.5.1 The reduced spectra concept mentioned in 5.4 above is based on assumption of
ductile behaviour of structures. Hence structures must be appropriately detailed for
achieving such ductility. In case of reinforced concrete structures such details are included
in IS: 13920-1993.
24
Fig. 4 Time history of ground motion for Nyamjang Chhu H.E. Project site
Fig. 5 Normalised horizontal spectral acceleration for various conditions for Nyamjang Chhu HE project site.
25
6.0 RECOMMENDATIONS
6.1 The site specific design earthquake parameter for MCE condition is estimated to be
magnitude 8.0 earthquake occurring at MCT.
6.2 The PGA values for MCE and DBE conditions and estimated to 0.36g and 0.18g
respectively.
6.3 The design acceleration response spectra is obtained by multiplying the normalized
horizontal acceleration spectra as given in Fig. 5 by the corresponding PGA values.
6.4 Vertical acceleration spectral values shall be taken as 2/3 of the corresponding to
horizontal values.
6.5 Data for time history of earthquake ground motion for the dynamic analysis of the
barrage are given in Annexure-II normalised to peak ground accelerations of 1.0 g.
For MCE and DBE time history analysis ground motion data as given in
Annexure-II will have to be multiplied by 0.36g and 0.18g respectively. The
corresponding response spectra are given in Fig. 5 and Table II.
6.6 Safety criteria as indicated in Sections 5.3.5 and 5.4.5 as applicable may be
followed in design of the Barrage.
26
REFERECES
1. Abrahamson N. A. and J. J. Litehiser (1989) Attenuation of vertical peak
accelerations Bull. Seis. Soc. Am. 79 549-580.
2. Barooah BC, Bhattacharya SK. 1981. A review of basement tectonics of the
Brahmaputra valley, Assam. Geological Survey of India, Miscellaneous
Publication No. 46: 123-128.
3. Brunnschweiler, R. O. (1966). On the geology of the Indoburman ranges. J. Geol.
Soc. Aust., 13, 137-194.
4. Campbell K. W. (1997) Empirical near source attenuation relationships for horizontal and vertical components of peak ground acceleration, peak ground velocity and Pseudo-Absolute acceleration response spectra, Seis. Res. Let. Vol. 68, 154-179
5. Campbell, K. W. (1981), Near source attenuation of peak horizontal acceleration,
Bull. Seis. Soc. Am., 71, 2039-2070.
6. Desikachar, S. V. (1974). A review of the tectonic and geological history of eastern
India in terms of plate tectonic theory. J. Geol. Soc. India, 15, 137-149.
7. Evans, P. (1964). The tectonic framework of Assam. J. Geol. Soc. India, 5, 80-96.
8. G. S. I. (1974). Geology and mineral resources of the states of India, Part IV,
Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura.
Geol. Surv. India, Misc. Publ., 30, 124 pp.
9. GSI (2000) Seismotectonic Atlas of India and its environs, Geological Survey of
India.
10. ICOLD Bulletin (1989), Selecting seismic parameters for large dams, Guidelines, Bulletin 72, International Commission on Large Dams
11. IS : 1893 (Part-1) - 2002, Criteria for Earthquake Resistant Design of Structures; General Provisions & Buildings, Bureau of Indian Standards, New Delhi
12. IS:13920-1993, Ductile detailing of reinforced concrete structures subjected to seismic forces - Code of Practice, Bureau of Indian Standards, New Delhi.
13. Joyner, W. B. and D. M. Boore (1981), Peak horizontal acceleration and velocity from strong motion records including records from the 1979 Imperial Valley, California earthquake, Bull. Seis. Soc. Am., 71, 2011-2038.
14. Kanamori, H (1983) Magnitude scale and quantification of earthquakes, Tectonophysics 93, 185-199.
15. Kumar, G. (1997) Geology of Arunachal Pradesh. Geological Society of India,
27
Bangalore, 217pp.
16. Mathur, L.P. and Evans, P. (1964). Oil in India. 22nd Int. Geol. Congress, India,
New Delhi, 85pp.
17. Mazumdar, S. K. (1978). Morphotectonic evolution of the Khasi hills, Meghalaya,
India. Geol. Surv. India, Misc. Publ., No. 34, 208-213.
18. Murthy, M. V. N. (1970). Tectonic and mafic igneous activity in Northeast India in
relation to upper mantle. Proc. Symp. Upper Mantle Project, Hyderabad, 287
19. Murthy, M. V. N., Mazumdar, S. K. and Bhaumik, N. (1976). Significance of
tectonic trends in the geological evolution of the Meghalaya uplands since the
Precambrian. Geol. Surv. India, Misc. Publ, 23, 471-484.
20. Nandy, D. R. (1976). Geological set up of the Eastern Himalaya and the Patkoi-
Naga-Arakan-Yoma (Indo-Burman) Hill Ranges in relation to the Indian Plate
movement. Geol. Surv. India, Misc. Publ., 41, 205-213.
21. Nandy, D.R. (2001) Geodynamics of Northeastern India and the adjoining region.
ACB publication, Kolkata, p209.
22. Ni, J. and Barazangi, M. (1984) Seismotectonics of the Himalayan collision zone:
geometry of the underthrusting Indian Plate beneath the Himalaya. J. Geophys.
Res., 89, 1147-1163.
23. Ranga Rao, A. (1983). Geology and hydrocarbon potential of a part of Assam-
Arakan Basin and its adjacent regions. Petroleum Asia Jour., 6(4), 127-158.
24. Sarkar, A., Datta, A.K., Poddar, B.C., Kollapuri, V.K., Bhattacharyya, B.K. and
Sanwal, R. (1992). Geochronological studies on early Cretaceous effusive and
intrusive rocks from Northeast India. (Abstract). Symp. on Mesozoic Magmatism
of the Eastern Margin of India, Patna University, 28-29.
25. Seeber, L. and Armbruster, J. G. (1981). Great detachment earthquakes along the
Himalayan arc and long term forecasting. In: Earthquake Prediction (edited by
D.W. Simpson and P.G. Richards), Am. Geophys. Un., 259-277.
26. Shanker, R., Kumar, G. and Saxena, S.P. (1989). Stratigraphy and sedimentation in
Himalaya: A reappraisal. In: Geology and Tectonics of Himalaya. Geol. Surv. Ind.
Spl. Pub. No. 26, pp. 1-60.
27. Sinha Roy, S. (1976). Tectonic elements in the eastern Himalaya and geodynamic
model of evolution of the Himalaya. Geol. Surv. India, Misc. Publ., 34, 57-74.
28
28. Tandon, A. N. and Srivastava, H. N. (1975). Focal mechanism of some recent
29. Wells, D. L. and Coppersmith, K. J. (1994), New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement, Bull. Seis. Soc. Am., Vol. 84, No. 4, 974-1002.
Appendix I
29
Occurrence of earthquakes around Nyamjang Chhu H.E Project Site, Arunachal Pradesh from historical times to 2007 between latitude 25.00° - 31.00° N and longitude
for Nyamjung Chhu HE Project site Arunachal Pradesh (Normalised to 1 g) at 0.01 sec interval
Read horizontally
64
ANNEXURE-III Drinking water quality standards
Characteristics *Acceptable **Cause for Rejection
Turbidity (units on JTU scale) 2.5 10 Colour (Units on platinum cobalt scale) 5.0 25 Taste and Odour Unobjectionable Unobjectionable PH 7.0 to 8.5 <6.5 or >9.2 Total Dissolved Solids (mg/l) 500 1500 Total hardness (mg/l) (as CaCO3) 200 600 Chlorides as CD (mg/l) 200 1000 Sulphates (as SO4) 200 400 Fluorides (as F) (mg/l) 1.0 1.5 Nitrates (as NO3) (mg/l) 45 45 Calcium (as Ca) (mg/l) 75 200 Magnesium (as Mg) (mg/l) If there are 250 mg/l of sulphates, Mg content can be increased to a maximum of 125 mg/l with the reduction of sulphates at the rate of 1 unit per every 2.5 units of sulphates
Notes :- *1. The figures indicated under the column `Acceptable’ are the limits upto which water is generally acceptable to the consumers
**2 Figures in excess of those mentioned under `Acceptable render the water not acceptable, but still may be tolerated in the absence of alternative and better source but upto the limits indicated under column “Cause for Rejection” above which are supply will have to be rejected.
*3. It is possible that some mine and spring waters may exceed these radio
activity limits and in such cases it is necessary to analyse the individual radionuclides in order to assess the acceptability or otherwise for public consumption.
ANNEXURE-IV
National Ambient Air Quality Standards (Unit: µg/m3)
S. No.
Pollutants Time Weighted Average
Concentration of Ambient Air Industrial, Residential Rural and other area
Ecologically Sensitive area
(notified by Central Government)
1 Sulphur Dioxide (SO2) , µg/m3
Annual* 24 hours **
50
80
20
80
2 Nitrogen Dioxide (NO2) , µg/m3
Annual*
24 hours **
40
80
30
80
3 Particulate Matter (Size less than 10, µm) or PM10 , µg/m3
Annual*
24 hours **
60
100
60
100
Note: * Annual arithmetic mean of minimum 104 measurement in a year at a particular site taken twice a week 24 hourly at a uniform intervals. ** 24 hourly or 08 hourly or 01 hourly monitored values, as applicable, shall be complied with 98% of the time in a year. 2% of the time, they may exceeded the limits but not on two consecutive days of monitoring.
ANNEXURE-V
Ambient Noise Standards --------------------------------------------------------------------------------------Area Category Limits in dB(A)Leq Code of Area ---------------------------------- Day time Night time -------------------------------------------------------------------------------------- A. Industrial Area 75 70 B. Commercial Area 65 55 C. Residential Area 55 45 D. Silence Zone 50 40 -------------------------------------------------------------------------------------- Note : 1. Day time 6 A.M. and 9 P.M.
2. Night time is 9 P.M. and 6 A.M. 3. Silence zone is defined as areas upto 100 meters around such
premises as hospitals, educational institutions and courts. The silence zones are to be declared by competent authority. Use of vehicular horns, loudspeakers and bursting of crackers shall be banned in these zones.
4. Environment (Protection) Third Amendment Rules, 2000 Gazette notification, Government of India, date 14.2.2000.
ANNEXURE -VI
LIST OF PLANT SPECIES (WITH THEIR FAMILY AND LOCAL NAMES) FOUND IN THE STUDY AREA