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Chapter I
INTRODUCTION
1.1 INTRODUCTION
Rivers are the most prolific land surface sculptors. A variety of aweinspiring landforms
are thus evolved under fluvial processes (river). One of the most dynamic of these
landforms is the floodplain which responds directly and abruptly to the changes
whatsoever to the flow regime of the river. Floodplains are studied for acquiring the
understanding of surface form that affects the passage of flood water as well as ground
water management. Floodplains are a resource of immense value. These are the sites of
most of the settlements and also provide natural resources to support the rural industries.
Floodplains are capable of preserving records of past climatic change. In addition, any
morphological changes in the floodplains due to channel processes have direct bearing on
the land and land use pattern thereof.
Floodplain is defined as the smooth strip of land bordering the river channel, embracing
the river pattern and inundated at the times of high stage (Gregory and Walling, 1973).
In other words, floodplains are prone to inundation. These are best understood in the
context of meandering streams and shifting meanders, which work over the valley
alluvium and erode its outside bends. But deposition of sediments take place only along
the inside bends of the meander. In this way a smooth depositional strip of land is formed
along the length of valley (Dury, 1969).
Processes involved in floodplain evolution and modification are channel aggradation and
degradation (or scour and fill), combined with shifting of a meander. Sediments eroded
from a concave side of meander tend to get deposited on point bar along the convex side
of the next meander downstream. This process is known as lateral accretion. The result of
such type of process is a cross-stratified deposit, with a subdued relief of low ridges and
intervening swales that may record many episodes of meandering channel migration.
Apart from channel deposit, floodplain is produced by over bank deposition i.e. vertical
accretion. The suspended sediments are deposited on the floodplain when the river water
is out on the plain during floods. In such flood condition, the velocity in the over bank
water is very low and the flood waters take long time to recede back into the channel.
1
Deposits precipitated from such type of flooding are usually sand or mud, although splays
from breached channel banks may bring coarse sediments too. The abrupt loss of velocity
at the edge of the flooded channel and the abundant sediment supply commonly cause
coarser deposition on the natural levees, which grade laterally into finer back-swamp
deposits. Thin vertical accretion of alluvium may accumulate slowly on a flood plain if
the river is constrained from migrating laterally. The predominance of either of these two
kinds of depositional environments (lateral and vertical deposit) is dependent upon the
frequency of discharge that inundates the floodplain.
The most significant and characteristic features of the floodplain are the dynamic nature
of both channel and floodplain morphology. Since floodplains are by and large the
product of fluvial processes of channel, any change in these may bring about significant
morphological changes to the floodplain. This also has a direct bearing on the human
activities along the riverbanks. Considering the fact that bordering plains of most of the
rivers often form the fertile agricultural land, the modification and alteration in the
floodplains may affect the livelihood of the region. Therefore, a detailed survey of these
changes and the processes involved therein are essentially needed.
In the tropical region, seasonal inundation of the floodplains is apparent which results in
severe bank erosion as well as large scale vertical and over bank deposition. Floods cause
permanent loss of land, life, property and cause deterioration of land due to erosion, sand
casting and water logging.
This study is oriented towards developing a better understanding of the fluvial processes,
and the hazards precipitated in the flood plain of the lower Rapti river basin in Uttar
Pradesh. This includes the study of alluvial forms of the floodplain and processes that
have brought about changes through sediment deposition, bank erosion and water
logging. Impact and aspects of management and planning is addressed alongside.
2
1.2 FLUVIAL PROCESSES IN LOWER RAPTI FLOODPLAIN
The Rapti river is a typical meandering stream. The most prominent features of the lower
Rapti floodplain are ox-bow lakes, alternative channel bars, flood chutes, point bars, swirl
pit, swamps or marshes, natural levee, dry channel and anabranching streams. The
presence of ox-bow lakes (chute and neck cut offs) and the anabranching stream are
indicative of a low surface gradient.
Broken ground and bank slumps are generally determined by a combination of factors i.e.
shearing away of bank materials, variability in bank sediments and the lack of cohesion.
Material slumping into the bed due to caving of bank is more common in meandering
channel just downstream from the axis of the concave bend. The Rapti riverbed has
become shallow due to siltation. Deforestation in the tarai region has increased the
sediment load in these rivers. Sediments get deposited in the riverbed making it shallow
and convert agriculture fields into culturable waste land.
1.3 GEOGRAPHICAL PERSONALITY OF STUDY AREA
The entire Rapti river basin extends from 26° 18' 00" N to 28°33'06" Nand 81 °33'00 E to
83°45'06" E and covers an area of 25793 km2 out of which 44 % (11401 km2) lies in
Nepal and 56% (14392 km2) in Uttar Pradesh. The Rapti river flows in the sub-humid to
humid monsoon region of the middle Ganga plain. It is the largest tributary of River
Ghaghra, which in tum, is a major constituent of the Ganga. It flows through the districts
of Rukum, Salyan, Rolpa, Gurmi, Arghakhanchi, Dang, and Banke of Nepal territory;
and Bahraich, Shrawasti, Balrampur, Siddharthnagar, Santkabimagar, Gorakhpur and
Deoria districts of Eastern Uttar Pradesh (Figure 1.1 ). The SRTM elevation data has been
used to delineate the Rapti river basin with the help of ARC GIS-9.2 watershed
delineation tool. The processed basin boundary is verified using the Landsat TM data of
2005. The division ofRapti river basin is based on the Watershed Atlas of India (1990).
3
8 1°20'0"E 82°0'0"E
z b p ~
z b
~ N
z b
~
Upper
Middle
500 0 SOO Kilometers E3 E'="=3
82°0'0"E
Figure 1.1 Location map of the study area.
Lower
82°40'0"E
83°20'0"E
83°20'0"E
84°0'0"E
N
A
- -- Drainage Network
International Boundary
c:J Rapti River Basin ,------- ~
~ ___ ___ : District Boundary
- Lower Rapti Floodplain
10 20
84°0'0"E
40 Kilometers I
z b
~ N
1.3.1 Physiographic Region
The Rapti river basin is diverse in its physiography. The lofty mountain, inner and outer
tarai and undulating plain regions constitute the topography of the entire basin. On the
basis of relief, the physiography ofbasin can be divided as:
I. The Mountainous Region
II. The Inner Tarai Region
III. The Outer Tarai Region and
IV. The Plain Region or Lower Rapti River Basin (Saryupar Plain)
I. The Mountainous Region
This region consists of the Lesser Himalayas. It extends from the Mahabharat range in
the south to the Lesser Himalaya in the north. To the north, its altitude varies from 1830
m to 401 Om above mean sea level ( amsl). This region is called the Midlands (Sharma,
1974). The mountains run parallel from east to west. It consists of the Rapti, Madi,
Jhimruk, and the Lungri valleys (Figurel.2).
The Mahabharat Range
This chain of mountain runs parallel to the lesser Himalaya from west to east direction.
Altitude varies from 1520m to 3660m (amsl). Some tributaries such as Banganga,
Kunhara and Rohini of the Rapti rise from springs in this range (Sharma, 1974).
II. The Inner Tarai Region
The term 'tarai' literally means moist or wet land (Sharma, 1991). This region is called
the 'Bhitri Madhesh ',which lies, between the Mahabharat mountain in the north and the
Churia hills in the south. Altitude varies from 610m to 1830m (amsl).These mountain
ranges are separated by wide valleys called 'dun', which is a wide and elevated valley.
The Rapti Dun is important which contains alluvial soil but has harsh climate due to the
high level of humidity.
5
28°0'0"N
27°0'0"N
82°0'0"E
Legend
--- Drainage Network
-- Mountain Range
c==J Rapti River Basin
Physiographic Region
~ Mountain
t:.O. :."'<_.J inner Tarai
L~~~d Rapti Dun
~ Outer Tarai
-.:}~ Plain 0
82°0'0"E
25 50
Figure 1.2 Physiographic region of the Rapti river basin.
83°0'0"E 84°0'0"E
Upper
28°0'0"N
27 °0'0"N
Lower
83oo:o"E 84°0'0"E
The Churia Hills
These lie south of the Mahabharat range. These are the foothills of the mighty Himalayas.
Altitude varies from 610 m to 1220m (amsl). These are called the Siwalik range in India.
Landslides are frequent in these hills.
IV. The Outer Tarai Region
The outer tarai region lies between the plain region in the south and Churia hill to the
north, with altitude below 300m (amsl). The tarai is drained by the rivers such as, the
Rapti, Kain, Gholia, Dangmara, Bhainbar, Banganga, Arrah, Ghonghi and Rohini, from
west to east, respectively. A strip of the tarai in the north consists of sandy soil and
pebbles. It is called the Bhaber interspersed by marshes and forests. Due to fall in
gradient from north to south, a number of terraces of alluvial fan origin are found
between the plain and the Siwalik foot hills (Yadav, 1999).
The Dundwa Range
This range lies south of the Rapti dun. It is a longitudinal spur of the Siwalik range (Bose,
1972).
V. The Plain Region (Saryupar Plain)
The plain region is a part of the Saryupar plain which lies south of the tarai region. The
general elevation is 80m (amsl) and generally slope towards the east (Yadav, 1999).
Physical landscape is produced actually by local eminences such as river levees and
bluffs or sand features like Dhus, oxbow lakes, Tats, Chaurs, dead arms or remnants of
the river channels and frequently perceptible notches and slopes carved by the rivers at
the outer edge of the Bhangar tracts (Singh et al., 1971).
7
1.3.2 Geology
Geologically, the Rapti river basin may be divided into three zones: I. the northern
mountain zone, II. the tarai zone, and III. the plain zone.
I. The Northern Mountain Zone
The rocks of this zone are tertiary in age and highly folded. The mountain ranges such as
the Lesser Himalaya and the Mahabharata range consist of hard granite and crystalline
rocks and are somewhat older than the Churia hill, which consists of sand, clay and soft
rocks (Sharma, 1974). Thus, the hardness of rocks also varies from north to south.
II. The Tarai Zone
In the northern part of the tarai zone, the alluvial architectural studies on exposed Siwalik
section reveal that the major sandstone bodies are 1 OOOm thick (Khan et al., 1997).
These sandstone bodies are underlain by a major erosional surface and generally are
capped by a palaeo sol. These sandstone bodies are separated by 1OOm thick mudstone
dominated palaeosol bounded sequences, which contain minor sandstone bodies (one to
few meters thick). These sequences are the over bank deposits formed by filling of local
low-lying area through small channels and crevasses followed by progressive shifting
through avulsion (Willis and Behrensmeyer, 1994). This depositional environment is
analogous to the modem interfan areas in the Rapti river basin.
III. The Plain Zone
The large trough called Gorakhpur trough in the southeastern part of the basin is over
8000m deep. It indicates that the entire region has suffered great down warping due to
Himalayan upheaval (Singh et al., 1971). It is formed of sand, silt and clay materials
mostly deposited by the Rapti river and its tributaries. The surface (about 30m) of region
can be divided into two sub zones as:
8
A.Bhangar
This zone is formed by the old alluvium. It covers upland tracts beyond the annual flood
limit. It is generally below 1OOm from msl.
B.Khadar
It is formed by new alluvium soil that annually replenishes deposits through overbank
flow. The nodular limestone conglomerate known as Kankar is more abundant in the
Bhangar than in the Khadar alluvium because of riverine character of the Khadar.
1.3.3 Soil
There are five factors such as parent material, climate, topography, organism and time
involved in the soil formation. These factors vary across the Rapti river basin. Thus, the
major soils of the basin are as:
A.Red Soil
In the northern part (mountainous area) of basin the soil is mixed with limestone, granite,
sand, clay etc in some places. Red soil is mainly composed of hard stone, limestone and
mica.
B.Tarai Soil
The tarai soils are found in the inner and outer tarai regions. This type of soil covers the
Rapti Dun and northern part of Bahraich, Gonda, Basti, Sarawasti, Maharajganj and
Siddharthanagar districts of the plain region. These are poorly drained and receive
seepage water continuously from the upper Bhabhar Zone. Soils are highly leached. Clay
soils are suitable for rice cultivation in this zone. The pH value ranges between 6.6 and
7.2 (Yadav, 1999).
9
C. Alluvial Soil
On the basis of inundation, alluvial soils of the plain region are divided into two
categories: I. Khadar soils and II. Bhangar soils.
I. Khadar Soils
These are newer in age and cover the flood plains in the vicinity of rivers. Khadar soils
do not have any characteristics soil profile (Singh et al., 1971). They are suitable for the
Bhadai and Zaid crops. Silt is prominent in these soils. The soil of Rapti flood plain
(Khadar) is dated back to <500 years B.P. (Mohindra and Parkash, 1992).
II. Bhangar Soils
These are old alluvium and cover the upland tracts beyond the annual flood limit. These
soils are rich in lime content and suitable for rice cultivation, being sticky and well
drained. The soil of Rapti flood plain (Bhangar) is dated back to 2500 years B.P.
(Mohindra and Parkash, 1992).
Apart from the above classification, the soils of the basin are grouped into three
categories as A. Bhur soil, B. Dumat soil and C. Mattiyar on the basis of the sand, silt
and clay content (U.P. District Gazetteers, Gorakhpur, 1987).
A. Bhur soil: It is grayish in colour. The proportion of sand (65%) is very high as
compared to silt (20%) and clay (15%). It is moderately alkaline and deficient in
organic matter. Jowar, Tarbooj, Sakarkand and Kodon are the typical agricultural
products. These are generally grown near the river.
B. Dumat soil: It is grey to brown in colour. The proportion of silt and sand (40%) is
high as compared to clay (20%). This soil is suitable for wheat, paddy and
sugarcane cultivation.
C. Mattiyar soil: In this soil, the proportion of clay (70%) is very high in comparison
to sand (15%) and silt (15%). It is appropriate for intensive Rabi crop cultivation.
10
On the basis of above details, it can be concluded that the soil structure facilitates good
subsurface flow in the plain region. Poorly drained tarai soil causes considerable seepage
of water, whichjoins the subsurface flow in the plain, resulting in return flow, and during
floods resurges on the surface, thereby, expanding the flooded area.
1.3.4 Climate
Due to difference in altitude, the Rapti river basin has two distinct climatic regions, the
temperate climate prevails in the mountainous region while the plain has subtropical
climate.
1. Temperate climate: The area between the Mahabharat range and the Lesser
Himalayas has a temperate climate. Summers are warm and winters are cool to
severe (Thapa and Thapa, 1969). Temperature varies between 0°C to 37.7°C.
Average annual rainfall is about 170cm (Yadav, 1999).
2. Subtropical Climate: The inner Tarai, the outer Tarai and the plain region
experience typical monsoon type of climate with dry winter season. The weather
is very hot in summers. Daily maximum temperature goes upto 46.5°C. The
western part is hotter than the eastern part. The subtropical climate has four
distinct seasons that are as follows:
A. The Winter Season
The easterly humid winds are replaced by the dry north-westerly winds. The region
receives small amount of rainfall from the western disturbances. Normally, temperature
ranges from TC to 29°C (Yadav, 1999).
B. Summer Season
In this season, the pressure gradient becomes steeper from west to east and wind blows
with increasing velocity (6.4 Km!hour in March to 10 Km/hour in mid-June), with
decreasing humidity and increasing temperature. Wind velocity leads to the formation of
hot winds in this region called 'Loo' (Yadav, 1999).
11
C. Southwest Monsoon Season
The southwest monsoon season begins in the middle of June and ends in the middle of
October. The region gets 75% of annual rainfall in this season alone. The average rainfall
of the plain region is approximately 11 Ocm. Rainfall decreases from the northern part to
the west-central part of the basin (Yadav, 1999). These rains are caused by the passage of
low pressure system along the monsoon trough.
D. Post Monsoon Season
This season begins in the middle of October and ends in December and is generally
characterized by decreasing temperature and rainfall.
1.3.5 Vegetation Cover
Different types of vegetation are found in the basin due to variation in climate and
altitude from north to south. The major categories of the vegetation are as:
1. Temperate Coniferous Forest
This type of vegetation is found in the upper northeastern part of the basin i.e., north of
the Mahabharat range. The major tree species of Sallo, Dhupi, Deodar, Gojan, Kalikath,
with Rhododendrons are found at higher elevations (Sharma, 1974).
2. Temperate Deciduous Forest
This type of vegetation is found between the Mahabharat and the Churia ranges. These
trees have broad leaves. Sal, Bamboo, Walnut, Chestnut etc. are the major tree species of
the deciduous forest (Sharma, 1974).
12
3. Tropical Forest
This monsoon forest consists of evergreen trees because of heavy rainfall. It is found in
the southern part of the basin. Most of these forests have softwood, while some have
hardwood. Hardwood trees like Sal (Shorea robust) Shisam (De iberia sisso ), Sankhuwa
etc. and softwood trees like Pipal, Mahuwa, Khair etc. are found in this forest. At some
places, bamboo trees and cane reed are found. In drier parts of the tarai region, Elephant
and Sabai grass are found. The forest in the Bhaber region is very thick.
Some grasses like Bher (zizyphus glaberrima), Moonj (Erianthus moonja), Kans
(Saccharum spontaneum), Jhau etc. are found in Diaras (Yadav, 1999). Babul tree is
found both in Bhangar and Khadar regions.
1.3.6 Population
Figure 1.3 shows the block wise population density (2001) ofNepalese and Indian part of
the basin. Generally it varies from south to north due to variation in physiography,
climate, and soil. In the south-east part of outer tarai of Nepal, the population density
varies from 367 to 2445 personlkm2 while the very low density (16-187 personlkm2) is
observed in the mountainous and Rapti Dun region due to harsh climate.
In the Indian part of the basin, population density generally varies from NW to SE. In the
north-west part, the population density ranges from 339 to 526 personlkm2• This region is
mainly covered with reserved forest of the outer tarai region. In the south-east part, very
high population density (818 to 1240 person/km2) is observed because of mild climate
conditions and availability of arable land as compared to rest of the area.
1.3. 7 Economy
The economy of the basin is based on agriculture. A three-harvest system is prominent.
The major crops of the basin are wheat, paddy, sugarcane, barley, jawar, oilseeds, pulses
etc.
13
z 0 ~ 00 N
z 0 0 0 \0 N
Legend
D Rapti River Basin
- International Boundary
-------- District Boundary
Population Density ( Person/sq.km)
Nepalese Part of Basin
.. 1139-2445
- 574 - 1138
367 - 573
187 - 366
16 - 186
82°0'0"E
Indian Part of Basin
- 990 - 1240
- 818 - 989
- 670 - 817
527 - 669
D 339 - 526
20 40
Figure 1.3: Population density (2001) in the lower Rapti river basin.
80 Kilometers
z 0 0 0 00 N
z 0 0 0 .... N
1.3.8 Flood Prone Area in Rapti River Basin
The flood prone area in the basin was delineated using the Dartmouth atlas of global
flood hazard (2006 and 2007), Landsat TM (2005), Landsat ET~ (2002) satellite
imageries, SRTM elevation data (2000), NATMO maps of Balrampur (2004),
Siddharthnagar (2004), Basti (2001), Gorakhpur (2001) and Deoria (2007) and the
Survey of India topographic sheets (1916-21). Floodplain along the lower Rapti river
were delineated using steady flow data of 100 years return period. HECRAS and
ARCVIEW 3.2a GIS software were applied for the delineation.
Table 1.1 shows the area wise break up of flood prone area in the upper, middle and
lower Rapti river basin. The flood prone area covers 20 per cent of the entire basin area.
The flood prone area covers 38 per cent in the lower Rapti basin while it occupies only
19 and 3 per cent area of the middle and upper basins, respectively. Table 1.2 shows the
break up in district wise flood prone area. Flood prone area covers 49 per cent of
Gorakhpur district (Figure 1.4).
1.4 SELECTION OF STUDY AREA
The study mainly deals with fluvial process and related aspect of arable land in the lower
Rapti floodplain which largely comes under the administrative limits of Gorakhpur
district. This district is one of the worst flood affected district of the basin. The Rapti
river in this particular stretch is very dynamic and frequently inundates considerable area.
As discussed earlier, this part of the basin is densely populated. Area along the river is
extensively cultivated. Therefore, the lower Rapti floodplain is an appropriate area for the
study of fluvial processes and impact of these processes on the arable land. Apart from
this, other factors such as knowledge of regional dialect, availability of data and
conducive working conditions also have played an important role in selecting the area for
this study.
15
Legend
International Boundary .---------,
.__j Rapti River Basin
CJ District
- Flood Prone Area
0 20 40 80 Kilometers
84°0'0"E
Figure 1.4: Hood prone area in the Rapti river basin.
Table 1.1: Flood prone area in Rapti river basin (in km2).
Basin Flood Prone Area Basin Area Percentage of Basin Area to the total Percentage of Flood prone Area to Basin Area Upper 204 6594 26 3 Middle 2441 12959 so 19 Lower 2388 6241 24 38 Total 5033 25793 100 20
Table 1.2: District-wise flood prone area (in km2).
District Country N arne Total District Area District area under Basin Flood Prone Area Percentage Flood Prone Area to District Area Under Basin Gorakhpur India 3321 2944 1437 49 Siddharthnagar India 2895 2839 1171 41 Deoria India 2538 719 271 38 Sant Kabir Nagar India 1646 943 339 36 Shrawasti India 2458 1553 503 32 Balrampur India 3394 2650 741 28 Basti India 2688 182 39 22 Bahraich India 4420 64 12 19 Maharajgan,j India 2952 2210 303 14 Banke Nepal 1477 1428 150 11 Kushinagar India 2906 287 23 8 Dang Nepal 1976 1783 44 2
Source: 1. NA TMO, Dtstnct planrung map of Balrnmpur (2004 ), Stddharthnagar (2004), Basti (200 1 ), Gornkhpur (200 1) and Deona (2007), 2. Census of lndta,
2001, Administrative Atlas of Uttar Pradesh, Vol.II, and 3. The Dartmouth Atlas of Global Flood Hazard, 2006-2007.
1.5 LITERATURE SURVEY
The dynamics of river and associated problems like floods in particular have been studied
extensively by scholars all over the world. Physical based research in the area of fluvial
geomorphology has pointed out the historical trends in fluvial processes and flooding.
Objective of the present study was developed upon previous literature on similar lines.
Pioneering study in fluvial geomorphology by Leopold and Wolman (1957) is the most
noteworthy along with the work of Chorley (1969), Gregory and Walling (1973),
Schumm (1977), Brice (1981) and Hooke (2006). The following section deals with the
literature survey to streamline the present research.
A. Flood Plain Morphology and Sediment Characteristics
Leopold and Wolman (1957) had grouped the alluvial rivers into braided, straight and
meandering on the basis of planform and formulated the characteristics of each of these
patterns. Braided river was found to be the one that flows into two or more anastomosing
channels around alluvial island, and in a winding course.
Chorley et al., (1969) included some consideration of the physical geography of rivers
and drainage basins together with assessment of their significance in socio-economic
framework in geographical analysis.
Bose (1972) the physical, cultural, and economic geography of the Himalaya, had
explained in the backdrop of a detailed account on the Rapti river.
Gregory and Walling (1973) were first, to measure the basin characteristics and runoff,
sediment and solute dynamics, and secondly, with morphology of floodplain, evaluation
of basin form and changes in time and space.
Schumm (1980) while discussing the 'planform of alluvial rivers' he concluded that the
alluvial channels are dynamic and subject to change and suggested that the classification
of alluvial channels should not only be based on channel pattern but also on the variables
that influence channel morphology.
18
Beven et al., (1989) had discussed the areas of flood runoff production, flood hydraulics
and sediment transport, the interpretation of flood sediments and the geomorphological
implications of floods world wide.
Mohindra et al., (1992) had covered the historical geomorphology and pedology of the
Gandak Mega fan. The Gandak mega fan lies in eastern U.P. and northwestern Bihar. The
Gandak river has shifted 8 km to the east in last 5000 years due to tilt in the block
bounded by the Rapti and the Gandak river. Flood plain of the major Rivers such as the
Gandak, the Rapti, the Ghaghara and the Ganga has been demarcated using remotely
sensed satellite data. The soil of Rapti and Gandak flood plains is dated back to <500
years B.P., while the soil of older Gandak flood plain is dated as 2500 years B.P. On the
other hand, the age of soil of oldest Gandak Plain is dated as 5000 years B.P.
Nagarajan et al., (1993) identified the land cover such as ox- bow lakes, high moist area,
arable land, and vegetation cover. Black and white stereo aerial photographs on a scale of
1: 15000 were interpreted to demarcate the water bodies, palaeo channels and floodplain
deposits. A tangent at the point of higher curvature was drawn to get relative angle of
rotation of curvature or meander of two time periods. Based on the angle of rotation and
probability of channel migration, the flooding has been inferred. The Rapti is
characterised by frequent channel avulsion and shifts towards the east.
Simon and Downs (1995) dealt with the modular procedure to assess the magnitude,
distribution and potential for channel instabilities at a large number of sites. The
procedure, based on diagnostic interdisciplinary criteria of alluvial channel morphology
and associated riparian vegetation was presented. The modules include (1) initial site
evaluations, (2) GPS and GIS-based data input and management, (3) ranking of relative
channel stability, (4) identification of spatial trends, (5) ranking of socio-economic
impacts and identification of most "critical" sites, and (6) collection of additional field
data for more detailed evaluation of the magnitude and type of future instabilities and the
effects of proposed mitigation measures.
19
Chen et al., (1996) elucidated on evolution of the palaeochannels on the North China
plain. The palaeochannels were geomorphological expression of abandoned river channel
caused either by human or natural factors based on arial photos and satellite imageries.
These were broadly classified into two categories i.e. surface palaeochannels and
shallow-buried palaeochannels.
Gupta (1998) found the effects of high magnitude floods on the channel forms, erosion
of bed and bank materials and transfer and storage of sediments. The work highlights the
importance of flood studies and records the morphological studies in Indian rivers and
points to the areas that need further studies.
Sinha and Jain (1998) examined the flooding behaviour of rivers draining the plains of
north Bihar. Gemorphological characteristics ofthe Gandak, the Kosi, the Burhi Gandak,
the Bagmati and the Kamla-Balan rivers have been broadly interpreted in order to
develop a better understanding of flooding characteristics of these rivers which record the
highest and frequent flooding in the country. Along with a detailed analysis of
hydrological data, geomorphological factors influencing the overbank spilling of these
rivers have been discussed. Other fluvial processes such as bank erosion, channel
morphological changes and sediment load variation have been also interpreted in relation
to overbank flooding.
Higgit and Waburton (1999) highlighted the applications of DGPS in fluvial
geomorphology. Geomorphic mapping, channel pattern change, bank erosion and
ephemeral flood mapping have been done using DGPS. Ephemeral flood mapping is
based on small scale geomorphic indicators like vegetation trash lines, over bank
sedimentation, flattened vegetation and standing water.
Surian (2002) attempted to analyse the changes of bed material size along the
downstream profile of the Pi ave River (Eastern Alps, Italy) to explain changes in the light
of both natural and anthropogenic factors. Surface material was sampled using the grid
by-number method. Natural (lateral sediment sources) and anthropogenic factors (e.g.
barrages) were found significant in this river system, which provided explanation for
20
-
most of the observed discontinuities. The barrages produce important changes in
sediment texture. Fining processes of sediments were investigated in the lower part of the
study reach where the lateral sediment sources and the barrages have minor effects on the
bed material.
Jain and Sinha (2003) reviewed the geomorphic setting, fluvial processes and sediment
pattern in the Gangetic plains and illustrated the hydrological and physical characteristics
of the major rivers of the plain as the Gandak, the Ghaghra, and the Kosi, together with
the Rapti river.
Srivastava et al., (2003) studied the late Pleistocene-Holocene hydrologic changes in the
interfluve areas of the Central Ganga plain. Abandoned channel belts, ponds and point
bar deposits of palaeochannels in the region suggest changes in the morphohydrologic
conditions during the late Pleistocene-Holocene period. Oxidised aeolian sand of point
bar deposits of palaeochannel indicates that the channel abandonment possibly occurred
due to the desiccation and aridity. The ponds formed around 8-6 Ka when the channel
activity increased due to tectonic warping and higher rainfall.
Ghosh et al., (2004) studied the spatio-temporal changes in the wet lands ofNorth Bihar
for the period 1984-2002 using satellite data. Surface water bodies including tals were
seen to have decreased in both Ghaghara-Gandak and Gandak-Kosi zones due to massive
sedimentation which probably obliterated the surface waters. On the other hand, there
was a marginal increase in surface water bodies in the western Kosi fan due to west-ward
shifting and frequent spilling of the Kosi river. They conclude that the tals and marshy
lands were the remnants of the active channels in the region.
Kemp (2004) elaborated the flood plain geomorphology and sediment characteristics of
flood plain features of the Lachlan river (southeastern Australia). Both the erosional and
depositional effects of regular large flooding are on the flood plain. The alluvial facies
model shows the variation in sediment size with height and distance from the active
channel. At some distance from the channel, the flood plain is subject to cut and fills by
flood chutes, stripping and swirl pits with fills of mixed textures including coarse flood
21
deposits. The fine flood deposits are deposited in chute bars and crevasse splay during
shallow over bank flooding.
Leece and Pavlowsky (2004) examine the vertical, lateral, and downstream variations in
the grain-size characteristics of historical (post-1830) over bank deposits in the Blue
River watershed, Wisconsin, USA where high rate of accelerated flood plain
sedimentation occurs. Overbank deposits exhibit a coarsening-upward sequence
attributed to historical changes in the sand content of source materials. The average sand
content of near-channel cores increases moderately downstream along two of the reaches
because sandy source materials are increasingly exposed in larger main valleys in the
northern part of the watershed. The two northernmost reaches were coarser overall, but
do not display significant downstream trends. The sand content of surface and early
historical overbank deposits generally decrease laterally as an exponential function of
distance from the channel, suggesting transport by turbulent diffusion.
Sarma (2005) discussed the fluvial processes and morphology of the Brahmaputra River.
The slope of the river decreases suddenly in front of the Himalayas and results in the
deposition of sediment and a braided channel pattern. The Brahmaputra channel is
characterised by mid-channel bars, sidebars, tributary mouth bars and unit bars. The
geometry of meandering tributary rivers shows that the relationship between meander
wavelength and bend radius is linear. The Brahmaputra had been undergoing overall
aggradation by about 16 em from 1971 to 1979. The channel of the Brahmaputra River is
migrating because of channel widening and avulsion. The meandering tributaries have
changed because of neck cut-off and progressive shifting at the meander bends. During
the twentieth century, the total amount of bank area lost to erosion was 868 km2•
Maximum rate of shift of the north bank towards south resulted in an erosion of 227.5
m/year. Maximum rate of shift of the south bank to north resulting in accretion was
331.56 m/year. Shear failure of upper bank and liquefaction of clayey-silt materials were
found to be two main causes of bank erosion.
22
Sinha et al., (2005) attempted, to explain major hydrological and geological controls of
aggradation and degradation in river systems of the Gangetic plains. Stream power and
sediment supply are the two main fluvial parameters that govern the aggradation and
degradation in river systems, which are controlled by the inherent catchment parameters
such as rainfall and tectonics. Aggradation and degradation are the inherent
characteristics of eastern and western Gangetic plains, respectively.
Marren et al., (2006) studied the mud and sand-dominated meanders developed in
close proximity within a floodplain wetland of the Klip River, eastern Free State, South
Africa. They divided the entire reach into three geomorphological zones on the basis of
floodplain gradient (obtained using DGPS) and dealt with the morphological and
sediment characteristics in each zone.
Chabaux et al., (2006) discussed the transfer time of sediments in the Gangetic plain
using 238 U- 234 U- 230 Th disequilibrium in the bank sediments of mountain fed and foot
hill fed rivers. Sediment transfer time of mountain fed rivers like the Ghaghara and the
Gandak are slightly short (100 ka) as compared to foot hill fed river like the Rapti (160-
250 ka). This time scale variation is found to be only due to difference in mineralogical
and chemical sediment evolution in these river systems.
Chandra et al., (2007) discussed the fluvial history of lower Rapti river. Systematic
dating of fluvial sediments from active point bar and occasionally flooded floodplain has
been done using OSL dating technique. The Rapti has had a post-glacial history of
aggradation and avulsion. Aggradational phases were characteristics of the Rapti river
between 11,500 to 5500 years ago, and culminated after 5500 years B.P. by migration of
the river i.e. degradation.
B. Meandering Pattern, Channel Shift and Meander Dynamics
Tower (1904) was first to elucidate the development of cut off meanders. The variables
such as gradient change in water current, disequilibrium between cut and fill were found
to be responsible for the evolution of meander cut-off.
23
Brice (1981) dealt with the meandering pattern of three reaches of the white river system
in Indiana between 1937 and 1968. Centroid of each bend was demarcated in order to
find out the movement in the meanders. Angular movement of centroids versus meander
length was then plotted to find out the potential of erosion in each meander bend. Further,
the eroded area and the meander length were plotted on a scatter diagram to fmd out the
average meander length which triggers erosion. He concluded that the erosion along
straight segments of a highly sinuous channel was negligible.
Thorne (1991) illustrated the bank erosion and meander dynamics of the Red and
Mississippi river in U.S.A. The stability of bank, bank properties and bank failure due to
erosion and mass failure were addressed at length.
Singh et al., (1996) dealt with the neotectonic control on the Gangetic river system of
Uttar Pradesh. LANDSAT MSS (Band 5 and 7) satellite imageries and Sol topographic
sheets were used to identify the lineaments controlling drainage networks. These
lineaments controlled the slope of the region and direction of drainage networks. The
drainage of the north and central part of Gangetic plain was found to be controlled by
newly developed lineaments which formed due to compressional stress of the Himalaya.
While the drainage in the southern part was governed by the reactivated basement
lineaments.
Goswami et al., (1999) covered sequential changes in the position of bank lines of the
Subansiri river using Sol topographic sheets (1920 and 1970) and satellite imageries
( 1990). The entire reach of the river was divided into 10 equal transverse cross-sections
for analysis. The lateral shift in bank line towards east-west direction and the erosion
along cross-section was identified and quantified between 1920 and 1990.
Swamee et al., (2003) discussed the changes in channel pattern of the Ganga between
Mustafabad and Rajmahal. The causes of variation in sinuosity and meanders have been
explained for both the areas i.e. upland and low land.
Raj et al., (2004) analysed the channel shifting of highly sinuous meandering
Vishwamitri river of Gujarat. Satellite, topographic, stratrigraphic, sedimentology and
24
sub surface structural data were used to understand the controls over channel morphology
of the river. The asymmetry of the drainage basin, high sinuosity and entrenched nature
of meander suggested that the tectonics mainly influence channel morphology of the
river.
Mitra et al., (2005) found the channel avulsions in the Sarda river system. Floods
triggered the process of avulsion in this channel. The eastward lateral migration of Sarda
river was found to be related to tectonic tilting of the area during early Holocene.
Sinha and Roy (2005) have attempted to understand the geomorphologic processes in
the Gangetic plain (Farrukhabad-Kannauj area). Detailed geomorphic mapping of the
area suggests that the confluences of the Ganga-Ramganga-Garra rivers had moved both
upstream and downstream between 1970 and 2000, in response to river capture, local cut
offs and aggradation. Movement of confluence points both upstream and downstream
was mainly caused by local gradient and hydrological fluctuations over a longer time
scale. They found remarkable difference in the fluvial dynamics of this region compared
to the eastern Gangetic plains, where rapid and frequent avulsions were predominant.
They also cited the example of the Rapti river which captured the Bakla river between
1959 and 1974 due to a large scale avulsion upstream.
Hooke (2006) elaborated the spatial pattern of instability and the mechanism of change in
an active meandering river, the Dane. Nearly 100 meandering bends of the Dane river
have been analysed using historical maps and aerial photographs for the period 1981-
2002. More than 20 years of monitoring of these bends provided a unique insight into the
link between erosion, deposition and maximum discharge.
C. Floods, Flood Plain Risk Zoning, Flood Management, DEM and
Land Use
Sears (1957) dealt with the natural and cultural aspects of floods. To him, nature made
floods but man made the flood hazards. The safe evacuation of people from low lying
flood plain to natural levee during rainy season was suggested.
25
Lacewell and Eidman (1972) developed a model to estimate the incidence of
agricultural flood damages in a small watershed of Oklahoma, USA. The model contains
a series of computational steps such as calculation of elevation along a cross-section,
flood depth for specified flood sizes, damage factor as for each sample point in the flood
plain and flood damages. The flood insurance and the optimum cropping pattern were
also discussed.
Rao (1979) elucidated on water resources and floods in India and discussed the causes
and management of floods in the Rapti river basin. The Rapti river which flows in a very
sinuous course with shallow depth and causes heavy flooding in the districts of Eastern
Uttar Pradesh. He suggested that the raising of the villages above the annual flood level
can reduce the severity of floods in the region.
Kayastha and Yadav (1980) elucidated on the impact of flood on socio-economic
development of Mubarakpur village of Deoria district lying in the Ghaghara flood plain,
based on a primary survey.
Kayastha (1983) examined the causes of the floods in India. The flood damage during
1953-69 is discussed and interpreted at length. The flood forecast system and the flood
management measures were also covered in detail.
Kochel and Barker (1982) described carbon dating of slack water flood deposits to
tmderstand the long term flood frequency in the lower Pacos and Devils river. The
physical conditions of slack water deposits have been discussed in detail.
Paul (1984) explained the respondents' perception of floods and agricultural adjustment
which were normal and abnormal. In this study, he observed that normal floods are
beneficial because it enables the harvesting of both aus and aman rice which are major
subsistence to farmers of the Jamuna floodplain of Bangladesh while during abnormal
flood situation, widespread destruction to crops and properties occurred due to high
magnitude of the inundation.
26
Newson (1992) reviewed the evolution of river management and the history of applied
hydrology to contextualise a global study of river basin system and their management
within both physical and social framework.
Kumar and Ram (1995) discussed the synoptic analogue method for semi-quantitative
precipitation forecast (QPF) for the Rapti catchment. They tested the synoptic analogue
of QPF of 1993-flood season with respect to the seven years rainfall data from 1986 to
1992 and found that the systems far away from the catchment predominantly, produce
low rainfall and systems near the catchment areas or active monsoon trough had a
tendency to move towards foot hills producing heavy rainfall in the catchment. On the
basis of this information, fairly accurate QPF could be issued by the forecaster in advance
for the Rapti catchment.
Penning-Rowsell (1996) demonstrated the context of flood hazard reponse is complex
mixture of physical, demographic, political and economic variables. He has discussed
how implementation of sustainable flood alleviation strategy was complicated by the
increase in population and economic restructuring in Argentina.
Miller (1997) explained the cause of floods, flood plain management through structural
counter measures and non-structural flood defence, dam safety and emergency responses,
together with the floods in Bangalesh, China, Mississipi and Central Europe.
Dogra (1997) discusses the flood and water logging problems in east Uttar Pradesh and
north Bihar. He further stated that expenditure on flood control had been increasing
rapidly; the area affected by floods also increased accordingly. Deforestation in Nepal
hills was found to be an important cause of the worsening floods. Haphazard construction
of roads and other development works, which did not provide enough room for drainage
of water, were other important causes. He also addressed the limitation and problems of
embankment in east U.P. and north Bihar.
Kale (1999) discused the temporal patterns of monsoon floods in five large rivers i e,
Mahanadi, Godavari, Narmada, Tapi and Krishna of the Deccan Peninsula. The study
revealed non-random behaviour with respect to distinct periods of high and low floods.
27
The normalized accumulated departure from mean (NADM) plotting methods was
applied to identify the below average (low) and above average (high) floods. NADM also
showed the association between monsoon rainfall and maximum water level.
Yadav (1999) provided a detailed appraisal of floods and flood problems of Eastern Uttar
Pradesh. He illustrated drainage and flood characteristics of the region where due to
highly erratic nature of the southwest monsoon rainfall, all the streams are characterized
by exceptionally high seasonal floods. Both the magnitude and frequency of the floods
had increased due to ecological degradation in the upper reaches of the river. Damage
due to flood, impact of floods on flood plain dwellers and floods management measures
have been discussed in detail.
Parker et al (2000) synthesized research articles on floods and their management, impact
of floods on society, flood plain management of the various countries such as
Bangladesh, U.K., U.S.A., Europe and the Netherlands.
Sinha and Bapalu (2000) attempted to prepare a flood hazard map of Kosi river basin.
They provided flood hazard index using data on population density, distance from active
channels, DEM, land use/land cover and geomorphic features. The river basin has been
classified into low, medium, high and very high flood hazard based on flood hazard index
values. The MODIS flood inundation map wasused for the validation of each flood
hazard zone.
Sarma (2000) attempted the flood risk zoning along the Dikrong river (north tributary of
the Brahmaputra river). DEM, maximum gauge level, agricultural, socio-ecomonic,
communication, population and infrastructure data were used for this analysis. Flood
damages to population, agricultural land and infrastructure at each return period i.e.2, 5,
10, 25, 50, 100 and 200 years have been worked out.
Sivasami (2001) explained the causes of floods in India and its management through
structural and non-structural measures. The flood damage analysis has been worked out
through three years cumulative value for the years 1957 to 1997. The environmental
effect of floods and reservoirs has been discussed in the light of Indian conditions.
28
Thapa (2003) discussed the flood problem of West Rapti river. The 1974 flood of
Gorakhpur is also elaborated. He further remarked that the construction of detention
reservoirs on the Rapti river can protect the life and property of innumerable people
living in the Eastern U.P. Saryu canal controversy and the locational characteristics of
West Rapti high dam were also addressed in the study.
Haq and Bhuiya (2004) had aimed to delineate the flood zones of tangail District of
Bangladesh using Radarsat-WIFS and satallite imageries of 1:50,000 scale. Three types
of flood zones were demarcated and the flood plain morphology, flood intensity,
periodicity, seasonality and its spatial-temporal variations and flood damages in each
zone also analysed.
Trinh et al., (2005) Studied the land use dynamics and soil degradation in Tamduong
District of Vietnam using landsat images (Landsat MSS in 1984 (4 bands), TM 1992,
1996 and 2000 (6 bands) were used for creating maps of the color composite and band
ratios. From these images, bare and degraded soils were identified and extracted.
Classified maps of the Band Ratios G/R and R/NIR for the year 2000 were established on
the basis of new soil maps and ground data. The best band ratio, R/NIR, was selected for
further processing and classification base on visual interpretation. The classified map of
degraded soils, based on the RINIR band ratio, matched well with the soil survey map
and the field checks.
Wang et al., (2005) analysed the water volume, length, total area and inundation area of
the three gorges reservoir of China at different gauge level using the Shuttle Radar
Topographic Mission Digital Elevation (SRTM DEM) data. The voids of the DEM were
removed through void-removal method.
Chandran et al., (2006) attempt to prepare the flood map of 2004 flood in Baghmati
river (Bihar) using Airborne Synthetic Aperture Radar (ASAR) images. Land use map
(LISS III) and DEM data were used to calculated flood affected agricultural area.
Sanyal and Lu (2006) used the GIS based hazard mapping at block and revenue village
level in the Gangetic West Bengal. They used number of flood occurrences, population
29
density, road density and access to safe drinking water for flood hazard mapping at block
level. While number of flood occurrence, population density and highest elevation of
each village were used at revenue village level. A knowledge based hazard ranking
method was applied to achieve a rational scenario of flood hazard in the study area.
1.6 OBJECTIVES
In the light of above research themes the following objectives have been drawn to:
1. Study the occurrence of floods, and to delineate the floodplain of lower Rapti
River Basin.
2. Map the flood plain morphology of the lower Rapti river.
3. Study the dominant processes viz. Channel shift, Meander dynamics, lateral and
over bank deposition which collectively modify the flood plain and flow pattern.
4. Study the impact of fluvial processes on arable land.
5. Study the trend in flood damages.
6. Analyse human adjustment and response to flood and associated problems.
1.7 DATA BASE
The secondary data base used in this study are:
o National Atlas oflndia, Vol. II, 1981.
o Watershed Atlas of India, 1990.
o Monthly Rainfall data ofGorakhpur (1901-1970), Bansgoan (1901-1968), Basti
(1901-1968), and Gonda (1901-1967) obtained from: http://www.ngdc.noaa.gov
o Monthly Rainfall data (1971-2000) of Gorakhpur, Bansgoan, Basti, and Gonda
were obtained from the National Data Centre, IMD, Pune.
o Monthly rainfall data of Gorakhpur, Bansgoan, Basti, and Gonda, (2000-2006)
were collected from IMD, Lucknow.
o Monthly data (1901-2006) of All-India and East Uttar Pradesh Region were
obtained from the Indian Institute ofTropical Meteorology, Pune.
30
o Flood Appraisal Report, Monsoon Season-2002, 2003 and 2008, Govt. of India,
CWC, Lucknow.
o Flood Report, 2008, Irrigation Department of Uttar Pradesh.
o District Disaster Management Plan, Gorakhpur, 2001 and 2009-10.
o The Dartmouth Atlas of Global Flood Hazard (2006 and 2007), E80N30 obtained
from http://www.dartmouth.edu/~floodslhydrography/E80N30.jpg
o Regional Divisions of India: A Cartographic Analysis, Census of India, Uttar
Pradesh Series-1, Vol. XXII, 1989, p.29.
o Estimated discharge and sediment load data (2006-2007) of Rapti river were
collected from CWC, Gorakhpur.
o Estimated Monthly Runoff data of Rapti River at Gorakhpur is obtained from:
http://www.dartmouth. edu/-jloods/AMSR-E%20Gaging%20Reaches/209.htm
o HMG of Nepal, Ministry of Science and Technology, Hydrological Records of
Nepal Stream Flow Summary, Kathmandu, Nepal, April1998.
o Census of India 2001, Primary Census Abstract, Gorakhpur, Santkabir Nagar,
Maharajganj, and Deoria 2001.
o Population Census 2001- VDC Municipalities, Central Bureau of Statistics
Thapathali, Kathmandu, Nepal.
o Block wise population data, 2001 was obtained from Jila Sankhyikik Patrika
(District Statistical Bulletin), Bahraich, Balrampur, Siddharth Nagar, Basti,
Santkabir Nagar, Maharajganj, Deoria and Gorakhpur, 2007.
o Topographical Sheet Nos. 63J/13, 14, 63Nil, 2, 5, 6, 7, 9, 10 and 11 on a scale
1:50,000 published by Survey oflndia, 1916-21.
o Topographical Sheet No. NG44-8 on a scale 1:250,000 prepared by Army Map
Service (RMBM), Corps of Engineers, U.S. Army, Washington, D.C, 1955.
o Landsat MSS P153/R041, 16th December, 1972.
o Landsat MSS P 153/R041, 25th February, 1975.
o Landsat TM Imageries, P142/R041 and P142/R042, lOth November, 1990.
o Landsat ETM+ Imageries, P142/R041 and P142/R042, 4th February, 2002.
31
o Landsat TM P142/R04I and P I42/R042, 19th November, 2005.
o Landsat TM PI42/R04I and P 142/R042, 5th October, 2006.
o Aster Data, 3I st July, 2008. Scene description is given as:
AST _LIB_ 003021 0200405I25I_ 2008073I074125 _24744.hdf
AST LIB 00303I5200805I759 20080731074105 23332.hdf - - - -
AST LIB 00303I5200805I808 20080731074205 26036.hdf - - - -
AST LIB 00304092008051204 2008073I074205 26038.hdf - - - -
AST LIB 00304092008051213 2008073I0742I5 26370.hdf - - - -
o Landsat TM P142/R041 and P I42/R042, 27th September, 13th October, and 16th
December, 2009.
o The map of Saryu command area was accessed on 8th July, 2010 from
http:/ /irrigation. up .nic.in/ptr/ saryu.htm
o SRTM data 03 Arc Second, February 11-22, 2000 was accessed on 24th
September, 2008 from http://srtm.csi.cgiar.org.
o GEOTOP030, 30Arc Second, 1996 was accessed on 24th September 2008 from
http://eros.usgs.gov/#/Find Data/Products and Data Available/gtopo30/e060n4
Q
Primary data used for this study are:
o Ground verification of floodplain features was done using Garmin hand held
GPS-76CS.
o Lagging exposed section along the bank was done using measuring tape and
ranging rode.
o Human response to fluvial processes and adjustment to agriculture were executed
through inventory and questionnaire survey in November and December 2008.
32
1.8 METHODOLOGY
a The normalized accumulated departure from mean (NADM) plotting method was
used to filter short-term fluctuations and to highlight the long range variability in
maximum water level and annual monsoon rainfall. The NADM is the
accumulated departure from mean (ADM), divided by the largest number
(absolute) in order to plot between -1 and + 1.
a The Pearson correlation coefficient ( r ) was used as an index to show the degree
of correspondence between two or more different NADM curves.
a Log Pearson Type III method was used for recurrence Analysis
a Floodplain along the Rapti river was delineated using HECRAS and HEC
GEORAS software.
a Ground verification and Visual interpretation of topographic maps and satellites
imageries were done to identify the floodplain features such as ox bow lakes, clay
plugs, point bars, swales, Channel bars, natural levee, crevasse splay, abandoned
and anabranching channels.
a The entire stretch of the channel was divided into 8 reaches on the basis of
curvature to calculate the sinuosity index (SI).
a
a
a
a
a
SI = (Channel length I Straight line valley length)
Midpoint of the axis of meander was defined as centroid to analyse the channel
shift.
Lithologs along the Rapti river bank were prepared to know the composition of
the bank materials using ranging rode and measuring tape.
The trend in flood loss was interpreted by three years cumulative value.
Land use classification was done using supervised classification of satellite
imageries.
The Historical Migration Zone (HMZ) of the selected reach was demarcated using
ARC GIS 9.2 software. This migration zone covers the collective area of the
channel occupied in the historical records (1916-21 to 2009). The section of
33
HMZ, where embankment physically controls channel migration, has not been
considered in HMZ.
a Data logger and channel migration predictor extension of ARC VIEW 3.2a GIS
software were applied to predict the future channel course.
a Visual interpretation of the satellite imageries (1972-2009) has been done to map
and identify the sand casting and waterlogged areas.
a Width and length of gullies were directly measured during the field surveys
(November-December 2008).
a The size composition of soils was done by 'texture by feel' analysis as elaborated
by Northcote (1979).
a On the basis of the water depth associated with the 100 years return period,
selected part of the lower Rapti floodplain was divided into three classes i.e.,
high, medium, and low flood depth zone. Subsequently, proportionate random
stratified sampling was applied for collecting data for each zone.
a Special Package for the Social Sciences (SPSS-14.0) software was used to cross
tabulate different variables and analyse the frequency of different variables.
a Knowledge based risk ranking method was applied to prepare the composite
index of flood risk.
In addition, a detail description of methodology used for the analysis has been given in
each chapter.
1.9 ORGANISATION OF MATERIAL
The entire work has been organized into seven chapters. First chapter is the introduction
that includes geographical personality of the study area, literature survey, objective, data
base, methodology and practical utility of the study. Second chapter discusses drainage
pattern, flow characteristics and floodplain delineation. Third chapter covers the analysis
of floodplain morphology and channel characteristics. Fourth chapter dealt with the
channel shift and meander dynamics. Fifth chapter covers the impact of fluvial processes
on arable land. Sixth chapter contains the human responses to fluvial processes and
34
aspect of management. Seventh chapter summarizes the entire work along with
conclusion of the study.
1.10 APPLIED ASPECT OF THE STUDY
The present study has high degree of practical utility as it takes into consideration both
fluvial processes and human adjustment. This study would provide basic guidelines for
administrators and planners to:
• Access to flood risk map for any eventuality.
• Mobilise the people living along the shifting river bank in the face of any flood.
• Raise the villages located in the high flood risk zone and connect them to nearby
Highway (State and National) in order to evacuate the people prior to
exceptionally high flood.
• Have a provision for quick availability of sand and cement bags to villages
located near the embankments which are vulnerable to breaches.
• Introduce appropriate paddy varieties which are best suited to certain flood water
depths.
• Devise the mechanism for crop insurance when and where affected, based on
flood risk map.
35
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