Performance Evaluation of Pekua Rubber Dam at Cox’s Bazar S.M. AZIZUL HOQUE March 2010 Department of Water Resources Engineering Bangladesh University of Engineering and Technology Dhaka, Bangladesh
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Performance Evaluation of Pekua Rubber Dam at
Cox’s Bazar
S.M. AZIZUL HOQUE
March 2010
Department of Water Resources Engineering
Bangladesh University of Engineering and Technology
Dhaka, Bangladesh
Performance evaluation of Pekua Rubber Dam at
Cox’s Bazar
A project submitted to
The Department of Water Resources Engineering
of
Bangladesh University of Engineering and Technology
In partial fulfillment of the requirement
for the degree
of
MASTER IN WATER RESOURCES ENGINEERING
by
S.M. AZIZUL HOQUE
ROLL NO : 040416045(P)
March 2010
Department of Water Resources Engineering
Bangladesh University of Engineering and Technology
Dhaka, Bangladesh
i
BANGLADESH UNIVERSITY OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF WATER RESOURCES ENGINEERING
CERTIFICATE OF APPROVAL
We hereby recommended that the M.Engg. Research work presented by S.M. Azizul
Hoque, Roll No. 040416045(P), session April 2004 entitled “Performance evaluation of
Pekua Rubber Dam at Cox’s Bazar” be accepted as fulfilling his part of the requirement
for the degree of Master of Engineering in water Resources Engineering.
Dr. Md. Sabbir Mostafa Khan Associate Professor, Department of Water Resources Engineering, BUET, Dhaka
.Chairman (Supervisor)
Dr. Umme Kulsum Navera Associate Professor, Department of Water Resources Engineering, BUET, Dhaka
Member
Jalaluddin Mohammad. Abdul Hye
Ex. Director General, WARPO, Dhaka
Member
ii
DECLARATION
This is to certify that that this project work entitled “Performance Evaluation of Pekua
Rubber Dam at Cox’s Bazar” has been done by me under the supervision of Dr. Md.
Sabbir Mostafa Khan, Associate Professor, Department of Water Resources Engineering,
Bangladesh University of Engineering and Technology, Dhaka. I hereby declare that this
project or any part of it has not been accepted elsewhere for the award of any degree or
diploma from any other institution.
Signature of the candidate
…………………………..
S.M. Azizul Hoque
iii
iv
TABLE OF CONTENTS Page CHAPTER -1 INTRODUCTION 1.1 Background 1
1.2 Objectives of the Study 4
1.3 Scope of the Work 4
1.4 Significance of the Study 5
1.5 Conceptual Framework of the Study 5
CHAPTRER -2 LITARATURE REVIEW 7
2.1 General 7
2.2 Review of Related Study 7
CHAPTRER -3 THE RUBBER DAM TECHNOLOGY 15
3.1 The rubber Dam Technology 15
3.2 What is a Rubber Dam 15
3.3 Use of Rubber Dam 16
3.4 Material of Rubber Dam 16
3.5 Life of Rubber Dam 17
3.6 Advantages of Rubber Dam 17
3.7 Disadvantage of Rubber Dam 19
3.8 The Design principle 19
3.9 Component of Rubber Dam 24
3.10 Salient Consideration for Construction of a Rubber Dam Body 26
3.11 Fitting and Fixing of Rubber Dam 27
3.12 Filling and Emptying System 29
3.13 Durability and Maintenance 31
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Page
3.14 Foundation 31
3.15 Flexible Control 32
3.16 Oscillation 32
3.17 Side slopes 33
3.18 Specification of Rubber Dam 34
3.19 Physical Property of Rubber Dam 34
3.20 Types of Rubber Dams 35
CHAPTER- 4 PEKUA RUBBER DAM PROJECT 41 4.1 General 41
4.2 Background of the Project 41
4.3 Dimension of Pekua Rubber Dam 44
4.4 Project Concept 45
4.5 Components of the Matamuhuri Irrigation Project (Pilot Project) 45
4.6 Purpose of Pekua Rubber Dam 46
4.7 The Project Implementation Time and Expenditure 46
CHAPTER-5 METHODOLOGY
5.1 General 48
5.2 Research Design 48
5.3 Research locale 48
5.4 Sample and Sampling Technique 48
5.5 Data Gathering Techniques and Tools 48
5.5.1 Primary Data Collection 49
5.5.2 Secondary Data Collection 49
5.5.3 Indicators 49
5.6 Data Processing and Analysis 50
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Page CHAPTER- 6 RESULT AND DISCUSSION 51
6.1 General 51
6.2 Assessment Result of the Technical Aspect of Design of Pekua 51
Rubber Dam and Its Constructional Problems and their Mitigation
6.2.1 Water Retention Level 52
6.2.2 Length of the Rubber Dam 52
6.2.3 Height of Rubber Dam 53
6.2.4 Thickness of Rubber Sheet and Geometrical Shape of 54
Water filled Rubber Dam
6.2.5 Site Selection of the Pekua Rubber Dam 55
6.2.6 Floor Length of Pekua Rubber Dam 55
6.2.7 Foundation Design 56
6.2.8 Assessment of Construction Problems and its Mitigation 58
6.2.9 Fitting Fixing of Rubber Sheet 60
6.2.10 Fixation of Level of Over Flow Pipe and Procedure of 62
Commissioning Work
6.3 Assessment Result of Operation and Maintenance of Pekua 63
Rubber Dam
6.3.1 Operation System of Pekua Rubber Dam 63
6.3.2 Institutional Aspect of Operation and Management of Pekua 65
Rubber Dam Project
6.3.3 Operation and Management System of Pekua Rubber Dam 67
6.3.3.1 Damage and Repair of Rubber Dam Body 68
6.3.3.2 Disorder and Repair of Pump 69
6.3.3.3 Deposition of Silt over Rubber Bags and over U/S and D/S 70
Stilling Basin
6.3.3.4 Clogging of Foot Valve 71
6.3.3.5 Safety Device of Rubber Dam and Bed Level of Rubber Dam 71
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Page
6.3.3.6 Problem in Boat Communication 71
6.3.4 Stakeholders’ Participation in the Management of Pekua Rubber Dam 72
6.4 Impact of the Pekua Rubber Dam Project 74
6.4.1 Impact on Socio-economic Status 75
6.4.2 Impact on Agriculture 78
6.4.3 Impact of Environment 79
6.4.3.1 Impact on Draught 79
6.4.3.2 Impact on Ground Water Table 80
6.4.3.3 Impact on Water Logging 80
6.4.3.4 Impact on Fisheries 80
CHAPTER- 7
CONCLUSION AND RECOMMENDATIONS 83
7.1 Conclusion 83
7.2 Recommendations 85
References 87
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LIST OF FIGURE Page Figure 1.1 Conceptual Framework of the Study 6
Figure 3.1 Shape of Rubber Bag 23
Figure 3-2 3D view of Rubber Dam 24
Figure 3.3 Long section of Rubber Dam 25
Figure 3.4 Rubber Layers 27
Figure 3.5 Anchorage system of Rubber Dam 28
Figure 3.6 Anchorage system of Rubber Dam 28
Figure 3.7 Steel Clamps with Anchorage Bolts 29
Figure 3-8 Concrete Wedge Blocks 29
Figure 3-9 Filling and Emptying system of rubber dam 30
Figure 3.10 Cushioning system of rubber dam. 31
Figure 3.11 Flexible control 32
Figure 3.12 Oscillation Reduction 33
Figure 3.13 Variable side slope 33
Figure 3.14 Air-filled dam 36
Figure 3.15 Water-filled dam 36
Figure 3.16 Multiple Span of Rubber Dam 37
Figure 3.17 Layout of Multiple Bags Rubber Dam with dividing Pier 37
Figure 3.18 Pillow like dam 38
Figure 3.19 Inclined dam 38
Figure 3.20 Structural sketch of seamless rubber Bag 39
Figure 3.21
Figure 4.2 Location of Pekua Rubber Dam in Matamuhury 44
Structural sketch of traditional seamed rubber dam 39
Figure 3.22 Irrigation purpose served by rubber dam 40
Figure 3.23 Hydro power produced by rubber dam 40
Figure 3.24 Rubber dam used as reservoir 40
Figure 4.1 Project map of Matamuhury Irrigation Project 42
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Page
Irrigation Project (Pilot Project)
Figure 4.3 Pekua Rubber Dam 47
Figure 6.1 Driving of sand pile of Pekua Rubber Dam 57
Figure 6.2 Driving of sand pile of Pekua Rubber Dam 58
Figure 6.3 Details of anchoring plate and anchoring bolt for 61
fitting & fixing rubber sheet for rubber dam
Figure 6.4 Commissioning of Pekua Rubber Dam 62
Figure 6.5 Inflated Pekua Rubber Dam for retention of U/S water 64
Figure 6.6 Deflated Rubber Dam 65
Figure 6.7 The Organization Chart of BWDB for Operation and 66
Maintenance of Pekua Rubber Dam
Figure 6.8 Special cushion system of Rubber Dam 69
Figure 6.9 Repair and Cleaning Work of Pump and its Accessories 70
LIST OF TABLE Table 4.1 Physical Features of Pekua Rubber Dam 45
Table 4.2 Implementation Schedule and Expenditure of 46
Pekua Rubber Dam Project
Table 6.1 Impact on Annual Income 75
Table 6.2 Amount of Annual Income Increase due to Construction of 76
Pekua Rubber Dam Project
Table 6.3 Poverty alleviation 76
Table 6.4 Impact on Employment due to Rubber Dam Project 77
Table 6.5 Impact of Agricultural Production 78
Table 6.6 Amount of annual agricultural production due to 78
rubber dam project:
Table 6.7 Amount of annual crop and fish production by stake holders 79
before and after implementation of the rubber dam project.
Table 6.8 Impact on Fish production 81
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ABBREVIATIONS AND ACRONYMS
ADG Additional Director General
BMC Bloc Management Committee
BUET Bangladesh University of Engineering and Technology
BWDB Bangladesh Water Development Board
CE Chief Engineer
CMC Central Management Committee
DG Director General
D/S Down Stream
DPEC Division of Project Evaluation Committee
EE Executive Engineer
EPDM Ethylene Propylene Diene Monomer
ECNEC Executive Committee of the National Economic Council
FCDI Flood Control, Drainage and Irrigation
GO Government Organization
GL Ground Level
IFMD Inflatable Flexible Membrane Dam
IMED Implementation, Monitoring and Evaluation Department
IWHR Institute of Water and Hydro-power Research
LGED Local Government Engineering Department
LLP Low Lift Pump
MPO Master Planning Organization
NGO Non government Organization
O & M Operation and Maintenance
OMC Operation and Maintenance Committee
PRA Participatory Rural Appraisal
PCP Project Concept Proforma
PWD Public Works Department
QHEPIL Qingdao Huahai Environmental Protection Industry Co. Ltd. China
xi
Q Discharge
RCC Reinforce Cement Concrete
SDE Sub-Divisional Engineer
SAE Sub-Assistance Engineer
SO Sectional Officer
TNO Thana Nirbahi Officer
USA United States of America
U/S Up Stream
WRS Water Retention Structure
WRE Water Resource Engineering
WRL Water Retention Level
WUA Water User Association
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ACKNOWLEDGEMENT The author acknowledges his indebtedness and sincere gratitude to his supervisor Dr. Md.
Sabbir Mostafa Khan, Associate Professor, Department of Water Resources Engineering,
BUET, Dhaka, for his continuous guidance, assistance and spirited encouragement
through the entire course of this research work.
The author is extremely grateful to Dr. Umme Kulsum Navera, Associate Professor,
Department of Water Resources Engineering, BUET, Dhaka, for being the member of the
examination board and for her valuable suggestions in writing this project.
The author is also grateful to Mr. Jalaluddin Mohammad. Abdul Hye, Ex. Director,
General, WARPO, Dhaka for being the members of the examination board and for
spirited encouragement and suggestions in completing this project work successfully.
The author is also grateful to all the teachers of the Department of Water Resources
Engineering for their cooperation and guidance for completing the research work.
The author is grateful to the librarian and the support staff of the library of Water
Resource Engineering Department, BUET, Dhaka.
The author wishes to express his sincere thanks to his friends and colleagues of
Bangladesh Water Development Board for their support, encouragement and co-
operation at various stages of doing this project work.
The author also express his gratitude to the anonyms respondents of the study as well as
the personnel who were contacted and discussed for collection of data for their valuable
contribution in providing the data and information.
Finally, the author is extremely grateful to his wife Dr. Selina Akhter for her continuous
support, encouragement and suggestions to complete the study.
xiii
ABSTRACT
This study was conducted to evaluate the performance of the Pekua Rubber Dam
constructed over the Matamuhury River in Pekua upazila of Cox’s bazaar district. It was
implemented by BWDB as a pilot project. The objectives of the study were to evaluate
the technical status of the Pekua Rubber Dam in terms of its design and construction
aspects; To evaluate the operation and maintenance system of the dam in the light of
institutional provision and stakeholders’ participation in management process and to
evaluate the impact of the Pekua Rubber Dam Project on socio-economic life of the
stakeholders, local agricultural and environment.
Both primary and secondary data were collected to conduct the study. Primary data were
gathered by using a questionnaire from a sample of 50 stakeholders of the dam and
conducting focus group discussions with the design engineers; people in charge of
operation, maintenance and management of the dam; beneficiaries/stakeholders of the
project and people of relevant local organizations. For gathering secondary data, relevant
books, reports, articles, etc. on rubber dam as well as on the Pekua Rubber Dam Project
were consulted.
Major findings show that the rubber dam is functioning well since it implementation in
June 2004. The length, height, shape, site selection, foundation design, floor length, depth
of cut-off wall, fitting-fixing of rubber sheet, fixation level of overflow pipe, etc. of the
dam were ok in terms of the design parameters consideration. Besides, an increasing
trend of irrigated land and yield, yearly income of the stakeholders, employment
opportunity as well as socio-economic status of the stakeholders was observed. The local
environment also improved due to rise in underground water level and removing water
logging. This helped to decline drought in the area and increase fish production. The dam
also has some other strength in terms of implementation time, cost incurred and
simplicity of construction. However, the dam has minor maintenance problems, like
repair of pump machines, removal of clogging of foot valve and removal of silt from the
xiv
dam body, U/S stilling basin & D/S stilling basin. Some other significant limitations as
detected are absence of any safety devise for automatically inflating and deflating the
dam body in case of emergency; too deep floor level of the pump house which incurs a
huge operation cost; interruption in boat communication; absence of any full time pump
operator; absence of local management committees and stakeholders’ formal
participation in management process. Another significant to mention limitation is lack of
coordination between BWDB local office and other local relevant organizations.
Based on the finding, this study suggests for some recommendations. They are: appoint
full time pump operator(s); form different kinds of local bodies/committees with
participation of the stakeholders; establish formal coordination system between BWDB
local office and local relevant organizations and implement more rubber dams to support
irrigation in other areas of Bangladesh. In doing so some change in technical aspects are
recommended. For example, introducing a safety devise for automatic inflation and
deflation of the dam body in case of emergency; a modified design of inlet and outlet
pipe so that the mouths of the pipes can not be blocked with silt deposition and a
submergible pump to curtail the huge costing of pump house.
Chapter 1
Introduction
1.1 Background
Bangladesh is one of the densely populated countries in the world. To keep pace with
the rapid growth of population, it has to produce increased amount of food grain every
year. The additional food production comes mostly from high yielding variety (HYV)
of rice, production of which largely depends on surface water irrigation as well as
ground water irrigation. In the National Water Plan Project-II (MPO, 1991) a medium
term strategy for development of surface water irrigation system was undertaken to
utilize main river water with the help of pumps. This surface water irrigation is
generally done by means of various water control structures such as barrage, regulator,
drainage sluice, earthen dam, weir, inlet, outlet, inflatable rubber dam, etc. However,
choosing an appropriate and sustainable structure, as per need of local topography, for
irrigation is important to derive maximum benefits from an irrigation project.
Bangladesh is situated in the delta of the three major rivers of the world (the Ganges,
the Brahmaputra and the Meghna). Apart from these three major rivers, there are so
many small and medium size rivers, khals and chara distributed all over the country. In
the district of Chittagong Hill Tracts there are so many chara, khals and medium size
rivers, which originate from hills, carry fresh water and fall into the Bay of Bengal. The
people of these localities usually build earthen dams in these streams to retain perennial
water for winter season irrigation for Boro and Rabi crops (EPC, 1996; LGED, 1994;
Hossain, 1992). In the monsoon period flash flood washes away these earthen dams or
in some cases these earthen dams need to be removed for easy flood flow through these
streams. So, these dams need to be reconstructed every year, which is not cost effective
as well as not supportive of providing a sustainable irrigation mechanism for the people
of Chittagong Hill tracts . The people of these localities, therefore, felt the need for a
permanent solution of this unsustainable financial investment for irrigation purposes.
In the hilly areas, there are so many surface water sources which can not be utilized in
effective way due to lack of required and sustainable water retention structures for
2
which people have to suffer a lot of problems in irrigating their cropland. To overcome
this financial loss as well as troublesome winter season irrigation, people in the hilly
areas were in a great demand of a permanent, sustainable and effective mechanism to
retain fresh water for irrigation purpose, especially during dry season. In response to
these difficulties mentioned above, Bangladesh Water Development Board (BWDB)
has been entrusted with the task of managing the water resources of this region by
means of conducting studies as well as implementation, operation and maintenance of
water resource development projects to boost up agriculture of the area and improving
the local environment.
Besides the earthen dams some traditional RCC or brick structures were generally
constructed and practiced for irrigation purpose in these areas. These traditional water
control structures are generally provided with steel gate and wooden stop log.
Traditional water control structures with the steel gate and wooden stop log have some
disadvantages with their operation and maintenance. Operational difficulty of manually
operated gate and stop log is due to failure of the operator to remain present and
remove the stop log from the structure slot or open the gate at the time of occurrence of
sudden flash flood. Estimation of peak flood discharge is also difficult due to inaccurate
demarcation of hydrological boundaries in the ungaged hilly rivers (Hossain, 1992). To
overcome the problems mentioned above regarding the earthen dam, built by local
people, and concrete or brick water control structures, a rubber dam was introduced by
BWDB, under the Matamuhury Irrigation Project in Chittagong Hill Tracts, as an
alternative mode to support the local irrigation system.
Rubber Dam, a kind of fabric dam is now being practiced many countries of the world
according to their variety of uses (IWHR, 1994). It is an advanced technology; it is
made of high strength synthetic fabrics, supported by frame and prefabricated rubber,
anchored on RCC base. Rubber dams are cylindrical rubber fabrics placed across
channels, streams and weir or dam crests to raise the upstream water level when
inflated. The membrane is a multi-layer fabric made of synthetic fibre (usually nylon)
and rubberised on one or both sides. The fabric is quite flexible and yet exhibits good
wear-resistance characteristics. The inflatable flexible membrane dams (IFMD, or
rubber dams) were developed in the early 1950 (Flexidam – Imbertson). They are used
to divert water for irrigation, temporarily raising existing dams, flood control, water
3
retention for aquifer recharge, reducing or preventing salt water intrusion into fresh
water areas, protect low-lying coastal areas from tidal flooding, enabling fish
passage(Wikipedia) The construction cost and construction time of rubber dam are less
than those of traditional RCC or brick structures. Rubber dam structures also have
certain advantages over conventional water control structures. Water conservation is
effective as the raising or lowering of the retained water level as per requirement. Less
operation and maintenance (O&M) problems are encountered and better navigation
facilities can be provided by the rubber dams. Additionally, it seems to be
environmentally sound and friendly. It has a design life of approximately 20 years
(IWHR, 1994; SEIL, 1985).
Considering the advantages of rubber dam, Local Government Engineering Department
(LGED) first time in the history of Bangladesh introduced two rubber dams as pilot
projects in 1995. One is Idgoan Rubber Dam and the other one is Bakkhali Rubber
Dam (Raquib, 1999). So far LGED has constructed about 12 rubber dams. In line with
this BWDB implemented its first rubber dam project over the Bhola Khal, a branch of
the Matamuhury River, in Pekua upazila of Cox’s Bazar district under the Matamuhury
Irrigation Project. This was introduced as a pilot project. The major goal was to give a
sustainable solution of water retention in the area instead of temporarily made earthen
dam. Some other objectives of construction of this Pekua Rubber Dam was to provide
irrigation facility to Boro crops during dry season (Nov-April) through retention of
sweet water in the upland river system and prevention of ingress of saline water from
downstream. The irrigation was provided by LLP which were installed on both banks
on the ponded river and channel systems (BWDB, EPC, 1996).
The project was implemented with a cost of Tk.1991.08 lakh. It included the cost of
construction of the dam and development cost of some other infrastructure directly
related with the functioning the dam. The benefited area at the 1st stage is gross 14000
ha and cultivable net area 5000 ha.
The project started its functioning in 2004 and as reported by the relevant people
contributing to the local irrigation system well without any apparent disruption. At this
stage an evaluation of this pilot project has become important to look into its efficiency
in terms of the project goals and objectives. It is particularly important to look into the
4
performance of a pilot project in order to make a rational decision about its future
functioning and management as well as in replication of such project in other areas. So,
the researcher decided to conduct this study to assess the performance of the Pekua
Rubber Dam Project, which has already passed more than five years since its
implementation.
1.2 Objectives of the Study The specific objectives of this study were:
1. To evaluate the technical status of the Pekua Rubber Dam Project in terms
of its design and construction aspects;
2. To evaluate the operation and maintenance system of the rubber dam project
in the light of institutional provision and stakeholders’ participation in the
management process; and
3. To evaluate the impact on the Pekua Rubber Dam Project based on the
following aspects:
i. Socio-economic life of the stakeholders
ii. Local agricultural
iii. Local environment
1.3 Scope of the Study
The scope of the study included assessment of the technical status and operation and
maintenance aspects of the Pekua Rubber Dam. It also assessed the impact of the dam
on social-economic life of the local people as well as on agriculture and environment of
the catchments area of the Rubber Dam.
The technical performance was assessed based on the design parameters of Pekua
Rubber Dam and its constructional strengths and weaknesses. The operation and
maintenance (O&M) status were analyzed in the light of institutional aspects,
management aspects and stakeholders’ participation in management process. The other
points of evaluation of design were the sustainability of the dam during operation and
the sustainability of the bags during inflating them by injecting water into the bag. The
technical evaluation aspects included the constructional problems and the mitigation
measures as well as O&M problems. The agricultural impact due to construction of the
5
dam were assessed in terms of various indicators, like area of pre and post project
irrigated area, crops and vegetables yield before and after the project implementation,
etc. To study socio-economic impact, indicators like change in life style of the
stakeholders, poverty level decrease, increase in annual income, employment
opportunity, etc. were assessed. To assess the impact on environment, indicators like
draught, water retention level, water logging, fish production were investigated. Thus,
based on the assessment result of all the above mentioned indicators the performance of
the Pekua Rubber Dam project was determined in this study.
1.4 Significance of the Study
The Pekua Rubber Dam is the first rubber dam constructed by BWDB. The history of
implmenting rubber dam also is a recent phenomenon in the country. In recent years
LGED has built a significant number of rubber dams. As a new technology, introduced
in the country, construction of the rubber dam should be subjected to evaluation to look
into its efficiency in terms of its construction, operation, maintenance as well as its
impact on different aspects of life, locality and environment. The Pekua Rubber Dam,
therefore, needs to be evaluated in order to investigate its performance in terms of the
abovementioned aspects. So, a decision was made to conduct this evaluative study on
the Pekua Rubber Dam Project. The findings of this study has provided some lights on
its effectiveness, impact as well as some of its limitations. The findings from this study
will hopefully be helpful in making rational decisions in desigining, implementing,
maintaining and managing any such project by BWDB or any other Organization. Also
the findings will be conducieve in improving the internal and external efficiencies of
the Pekua Rubber Dam Project.
1.5 Conceptual Framework of the Study
The study as was conceptualised is presented in the next page through a schematic
diagram. The performance of the dam was assessed based on three aspects- technical
efficiency, O&M and impact on some aspects. Technical status was evaluated based on
design and constructional aspects. Institutional provision to manage and operate the
dam as well as locals’ participation in it was considered to evaluate the dam’s operation
and maintenance status. Besides, the dam’s performance was assessed based on its
impact on the socio-economic life of the stakehoders as well as local agriculture and
6
environment. The findings helped to identify specifically some strengths and
weaknesses of the project in terms of the abovementioned aspects. Finally, some
recommendations were made, implementation of which can help to improve the overall
performance of the Pekua Rubber Dam Project.
Performance
of
Pekua
Rubber
Dam
Technical Status • Design • Construction
O and M • Inst. Provision • Stakeholders’
participation in management
Impact on- • Socio-economic
status • Agriculture • Environment
Findings
Recommend-ations
Figure 1.1: Conceptual Framework of the Study
7
Chaptrer 2
Literature Review
2.1 General
This chapter deals with literature review of performances evaluation of rubber dams
conducted by three researchers in Bangladesh and some other research conducted
abroad related with inflatable rubber dams. Efforts have been given to collect the
reports of different study related to these topics. A synopsis of some of the study report
is discussed in this chapter.
2.2 Review of Related Studies
Local Government Engineering Department (LGED) has constructed two rubber dams
for the first time in Cox’s Bazar district as pilot projects. One is in Idgoan khal and the
other is in Bakkali River (LGED, 1994). Another 10 rubber dams were constructed by
the year 2003. The performances of the Idgaon and Bakkhali rubber dams were
evaluated through a study conducted by Raquib (1999). The title of his study was
“Performance evaluation of rubber dam projects in Bangladesh”. In his study the
aspects of evaluation were engineering, agriculture, environmental and organizational.
Engineering evaluation involved identification of construction, operation and
maintenance problems and mitigative measures. Agricultural evaluation involved
assessment of impacts on irrigated area, cropping intensity and yield. Environmental
evaluation involved evaluation of impact on fisheries, drought, water logging, and
ground water level and boat communication. Organizational evaluation involved
evaluation of organizational set-up including people’s participation and operation and
maintenance cost recovery of the project.
The evaluation was carried out through collection of data and information after proper
discussion with the respondents using required checklist, making field visits and study
of relevant documents. Data and information were gathered from the project
beneficiaries, adversely affected local people and the service givers and the result were
verified with the relevant experts at the thana level.
8
Major findings of his study were that the rubber dam project had no major problems in
construction, operation and maintenance. Moreover implementation period was short
due to simplicity in the construction work. Development cost was low compared to
traditional water retention structures. Construction work of the rubber dam had some
limitations as implementation work required special supervision and the rubber bag
were not manufactured in Bangladesh. There were no major operation and maintenance
problems. However, some minor problems such as leakage of rubber bags, disorder of
pump machine, siltation over the rubber bags, and clogging of foot valves were
encountered which could be mitigated easily at local level through participation of the
beneficiaries and the service givers. The project had positive impact on agriculture. An
increasing trend in irrigated areas and yield was observed. He concluded in his study
that this was mainly due to improved water management in the project area and
people’s confidence in project operation. It had good impact on environment except
little disruption in boat communication during irrigation period. Informal organizational
set up was there during the operation of the rubber dam. But, the organizational set-up
was weak and the people’s participation and operational and maintenance cost recovery
were not adequate. The existing organizational set-up was strengthened through
institutional intervention. Present organizations were operating satisfactorily in respect
of proper water management, resolution of conflicts, operation and maintenance and
cost recovery of the rubber dam.
It had no adverse environmental impact except little disruption in boat communication
during irrigation time.
Another study was conducted by Saleh and Mondol (2000) to evaluate the performance
of the same pilot projects of rubber dam of LGED in terms of some selected standard
indicators. The tile of his study was ”Performance evaluation of rubber dam porojects
in irrigation development” The performances indicators used in his evaluation have
been broadly classified in to three groups: hydraulic indicators, agriculture indicators
and non agriculture or socio-economic indicators. For the qualitative and quantitative
assessment of the indicators, field measurements and questionnaires surveys were
carried out during the study period. He mentioned that due to lack of basic data on the
targets or goals and designed values, evaluation of some of the selected indicators was
not possible. The water discharge at Bakkhali Rubber Dam Project (98%) is
satisfactory. The relative water supply of Bakkhali is adequate (1.21) but at Idgoan
9
Project it is inadequate (0.8). The computed water delivery performances are very low
for both the project (0.19 and 0.38 for bakkhali and Idgoan project respectively)
because the targeted available volumes of water were overestimated in the feasibility
reports.
The total water used in irrigation for growing HYV Boro rice at Bakkhali and Idgoan
projects are 1133 and 819 mm respectively. The irrigated area performances of both
the projects are very poor (0.22 and 0.46 for Bakkhali and Idgoan projects
respectively). The yield performances of both the projects during 1998-99 are
satisfactory (0.90 and 0.88 at Bakkhalki and Idgoan projects respectively). The average
irrigation fee collection is excellent (97%), but at Bakkhali project it is only about 62%.
The O & M cost of both the rubber dams are very low (about Tk 100/ha). Growing
HYV Boro rice with irrigation is very profitable. The calculated potential command
area of Bakkhali project is 1320ha and the actual command area in 1998-99 was
1315ha. Thus the Bakkhali project is probably operating at its optimum level and
further increase in command area is not recommended unless the farmers resort to
improved irrigation management.
A study by Nahar (2004) was conducted in the field of rubber dam project to evaluate
the feasibility of rubber dam construction in Bangladesh with locally available material.
The title of her study was “Preliminary study on design of rubber dam in Bangladesh
with special reference to the use of locally available material. The major findings of
Nahar’s study were some significant and satisfactory findings. The study shows that
there is no problem in implementation of rubber dam in Bangladesh. Moreover it was
found that the time required for implementation of the rubber dam was relatively short
and the development cost was relatively low mainly due to simplicity in construction.
However, implementation of rubber dams required special supervision and rubber bags
are not manufactured in Bangladesh. The rubber dam projects did not have any adverse
environmental impact except minor disruption in boat communication. There was a
negative impact on communication due to construction of the rubber dams in place of
the earth dams. The laboratory investigation result shows that the elongation of rubber
increases with the increase of tensile strength. Therefore, actual strength of rubber
cannot be used for thickness calculation. She concluded that there is a good possibility
of use of locally made material and technology in designing and construction of rubber
10
dam in the country. She further revealed that the local production of rubber bag will be
at cheaper cost and the rubber bags can easily have their recycle value.
Fahmida Khatun (Fahmida, K) Assistant Professor, Dept. of Water Resources
Engineering Bangladesh University of Engineering and Technology, Bangladesh,
developed a research proposal as group organiser on evaluation of Rubber Dam
Technology as an alternative to Traditional Dam Projects for sustainable development.
A number of global reports have documented the dramatic impact of human induced
water withdrawa1s. Incidentally, social, environmental, governance and compliance
aspects have been ignored in decision-making about the construction of a dam in the
past. The proposal incorporates the views of World Commission on Dams (WCD),
International Commission on Large Dams (ICOLD) and IUCN- World Conservation
Union about dams and development. The commission’s observations are based on the
emerging principle that the traditional concept of a balance sheet, that is calculating
costs and benefits, is no more acceptable.
A paper entitled as Aquifer Recharge Enhanced with Rubber Dam Installations
[(Michael R. Markus, Curtis A. Thompson, and Matt Ulukaya (From Water & Waste
Digest) 1995] is published by Water Engineering and management. In this paper it is
described that artificial recharge of groundwater has become a necessity in Orange
County, California, where natural recharge is insufficient to satisfy water demands. The
area is part of a semi-arid coastal plain with fewer than 20 in. of rainfall each year, and
the Orange County Water District is supplementing nature with artificial recharge to
supply 70 percent of the water needs of its more than two million residents. As part of
the program, the District has expanded its recharge capabilities with the Santa Ana
River Inflatable Rubber Dam Project.
Two inflatable rubber dams with bypass facilities to divert river flows to off-river
recharge basins have been constructed. These dams, both of which are 2.1 meters in
height and stretch 97.5 meters across the Santa Ana River, are among the largest single
span systems of this type in North America. They allow the District to recharge as
much of the river flows as practically possible by capturing excess flows that would
otherwise be lost to the ocean.
11
Nearly 25 million cubic meters of storm water captured annually for recharge will
supply the water needs of 100,000 of the population within the service area. In the first
operating year (1993), with only the first dam completed, almost 17 million cubic
meters of water with an estimated value of $2 million, were saved. The cost to
construct the dams and appurtenant facilities was $4.7 million. Design work included
comparison of technologies previously used to control headwater surface levels, and
evaluation of design considerations for debris control, metering, flow control, hydraulic
conveyance, and energy dissipation.
The District extracts groundwater from an extensive aquifer below a rapidly developing
urban area. To replenish the reserves, it uses over 1,500 acres of land along the Santa
Ana River for percolation basins. These are maintained in the river itself, and several
off-river basins also are in use for retention and recharge. The off-river basins have a
combined volume of over 33 million cubic meters.
Sand levees in the river are used to create a serpentine path for the water, as well as
providing sufficient head to divert approximately 7.1 cubic meters per second (cms) of
water to the off-river basins. When flows in the river exceed 14.2 cms, however, the
sand levees collapse and are scoured away and the water flows unimpeded to the ocean.
It was envisioned that inflatable rubber dams could replace some of the sand levees to
increase the diversion capacity to 14.2 cms into the off-river basins. This would
increase the capture of the larger flows and reduce the time and effort needed to replace
the sand levees after storm flows have receded.
The project consists of one inflatable rubber dam (the Imperial Highway installation)
and bypass facilities at the head works of the recharge basins, and a second similar
installation (known as Five Coves) located approximately three miles downstream.
In addition to the use of the rubber dams, two other aspects of this project are
significant. First, the bypass at the Imperial Highway dam incorporates a relatively new
trashrack design with self-cleaning debris removal equipment. Second, since space for
the bypass facilities was limited, complex hydraulic problems for bypass flow control,
metering, and energy dissipation had to be solved.
12
Structural design of the rubber dam foundation and anchoring system is
straightforward, with one caveat: the seepage and related uplift pressures created by the
new reservoir must be reviewed for their effect on the stability of the riverbed and local
riverbed structures. A typical rubber dam foundation has upstream and downstream
cutoff walls to increase the ground water seepage path and reduce uplift pressures
exerted by the ground water. Seepage analyses for the Santa Ana dams indicated that
the structural stability of river drop structures near the proposed dams could be
adversely affected. The locations of the foundations were adjusted to allow relief of the
The multiple uses of the Santa Ana River required the evaluation of several diversion
structure alternatives for the river. This is the largest river in southern California and
urban development along its course has made it an important water supply resource and
flood control channel. The U.S. Army Corps of Engineers has been engaged in a flood
control improvement project on the river since 1989, and reviewed the preliminary and
final designs to ensure compatibility between water diversion and flood control
activities on the river. The simplicity of the rubber dam concept, along with its proven
reliability, were key considerations in evaluating its suitability as a diversion structure.
Alternatives investigated included steel gates with variations on the operating
mechanism. Conditions that inhibited the use of steel gates were the corrosive
environment at the sites (approximately 19 kilometers from the ocean with the major
component of the base river flows being wastewater effluent); the high sediment
transport capability of the river (silt could clog gate operators and abrade steel gates
and hinges); additional maintenance (compared to rubber dams); and cost. While
inflatable rubber dams also have deficiencies, including increased exposure to
vandalism and a limited history (the oldest example in North America is less than 25
years old), their advantages justified their selection.
A typical rubber dam installation consists of a reinforced concrete foundation
constructed across a riverbed with a rubber bladder anchored to the foundation. In the
Santa Ana River project the two bladders extend 97.5 meters across the river bed
without need for intermediate piers or abutments. The bladder is inflated and deflated
through connected air piping. Most contemporary rubber dams use air for inflation, but
water may be suitable where hydraulic conditions are more demanding.
13
uplift pressures upstream of the drop structure, however, and structural stability was
maintained.
A key benefit of this type of dam is the ability to serve as a reliable, low-maintenance
adjustable-crest weir. In the Santa Ana project the dam/weir creates a shallow diversion
pool that provides a hydraulic gradient to convey the water into the adjacent off-river
recharge basins. Each dam can be fully inflated or fully deflated to completely block, or
completely open, the flood channel-or can be set to operate at intermediate heights.
When a dam is inflated, river flows are diverted to the off-river recharge basins, or
bypassed around the dam and back into the river. If the flow is such that the water level
is rising and will overtop the dam, the bladder will automatically deflate. (These dams
are capable of withstanding overflows up to 0.6 meters above the top). Internal air
pressure is relatively low, and associated operating equipment is minimal. Redundant
electrical and mechanical controls ensure virtually failsafe operation under emergency
conditions-a capability essential in gaining approval from the Corps of Engineers.
A secondary benefit is the adaptability for automation. The labor intensive efforts of
constructing and maintaining sand levees and diversion dikes have been replaced by a
30-minute inflation task that can be performed by a local or remote push-button. Design
provisions were made to permit future installation of telemetry equipment for remote
monitoring and operation of the dams and most of the related ground water recharge
facilities. However, the District intends to gain practical experience with this flood
control system before getting into automation.
Two major manufacturers of inflatable rubber dams were consulted throughout the
design process (Bridgestone and Sumitomo). While their operating schemes appeared
virtually identical, there were differences in the fabric, anchoring systems, hydraulics,
and equipment costs. Key considerations in determining suitability of one type versus
another included the operational hydraulics (e.g., depth and frequency of dam
overtopping, trailrace depth on the downstream face, adjustment range for the dam
crest); potential for in situ dam fabric repairs; and the need for special coatings to
protection against vandalism, caustic conditions, or overflow of potentially damaging
debris.
Both designs were found to be acceptable for this project, and the specifications written
allowed competitive bidding between the two manufacturers. Each was selected as low
14
bidder on one of the two facilities, and their products have improved the reliability and
safety of the river diversion facilities. Earth moving equipment works the river bed to
rebuild levees and diversion dikes less frequently. Also, the District can improve the
quality of diverted water by deflating the dams and allowing the silt- and debris-laden
"first flush" of storm water to bypass the recharge basins.
A study was conducted on Construction, Operation, and Maintenance of Rubber Dams
by Zhang X. Q., Tam, P. W. M., and Zheng, W (Zhang X. Q., Tam, P. W. M., and
Zheng, W. 2002).Rubber dams are inflatable and deflatable hydraulic structures.
Thousands of rubber dams have been installed worldwide for various purposes:
irrigation, water supply, power generation, tidal barrier, flood control, environmental
improvement, and recreation. Furthermore, rubber dams have been used in cold areas
where the temperature is as low as 40°C. The simplicity and flexibility of the rubber
dam structure and its proven reliability are key considerations in its wide scope of
applications. Based on the management practices of 20 rubber dams in Hong Kong in
the past 35 years, interviews with rubber dam experts and practitioners, and the
investigation to the construction of a recent rubber dam, this paper provides a detailed
discussion on various issues related to the construction, operation, maintenance, and
repair of rubber dams.
15
Chapter 3
The Rubber Dam Technology
3.1 The Rubber Dam Technology
This sub-section gives an overview of what a rubber dam is? What technology is
applied in it? What are the advantages and disadvantages of rubber dam? What are the
materials used for rubber dam construction? And What are the design considerations?
Etc.
3.2 What is a Rubber Dam?
An inflatable and movable weir made of rubber cloth and installed on the river bed or
slope of banks across a river or a canal and work as a dam to control the flow of water
is called rubber dam. It is a kind of a large bag which is inflated or deflated by injecting
and discharging air or water. It is constructed across the river to retain water. Rubber
bags are used for blocking to prevent water flow. It is practically used to prevent
upward and downward flow of water. It is a new type of hydraulic structure compared
with steel sluice gate and it is made of high-strength fabric adhering with rubber, which
forms a rubber bag anchoring on basement floor of dam. (Geosynthetica.net)
Rubber dam construction is a relatively recent technology. It was developed in the USA
in the early 1960s. China constructed the first rubber dam in 1966 and since then China
developed its own expertise on designing, manufacturing and construction of rubber
dam. More then 2000 rubber dams have been constructed worldwide including
Australia, Japan, Taiwan, Hong Kong, China, Indonesia and Thailand (Nahar, 2004).
The present trend suggests an increased use of air-filled membranes because they can
be deflated or inflated more rapidly. The rubber dam is usually deflated for large
overflows. It is however common practice to allow small spillages over the inflated
dam. During overflows greater than 20% over-topping, vibrations might result from
fluid-structure interactions and the instabilities might damage or destroy the rubber
membrane (Ogihara and Maramatsu, 1985). In practice, a deflector (i.e. fin) is installed
on the downstream face of the rubber dam to project the nappe away from the
membrane, hence preventing rubber membrane vibrations. The inflatable flexible
membrane dams (IFMD, or rubber dams) were developed in the early 1950s (Flexidam)
16
3.3 Use of Rubber Dam
Rubber dam has various uses. The main purpose of its use in our country is to provide
irrigation facilities of boro crops (one kind of paddy) during dry season (Nov-April)
through retention of sweet water in the upland river system and prevention of ingress of
saline water from downstream. Besides these, the broad use of rubber dam is as
follows:
• The dam is used as flood control structure
• Water retention for irrigation
• Water retention for aquifer recharge
• Water retention for fish production
• Reducing or preventing salt water intrusion into fresh water areas
• Protect low-lying coastal areas from tidal flooding
• Enabling fish passage past diversion works by deflation of dam
• Sewage retention/separation during flood events
• In rainy seasons, water contained in dam shall be discharged to help release
flood water from the river course.
• Intake Gate
a) Hydropower
b) Irrigation
c) Domestic water supply
d) Industrial water supply
• River Estuary Barrier
a) Tidal barrier
b) Storm surge barrier
c) Sand barrier
d) Wave barrier
3.4 Materials of Rubber Dam
The membrane is a multi-layer fabric made of synthetic fibre (usually nylon) and
rubberised on one or both sides. The fabric is quite flexible and yet exhibits good wear-
resistance characteristics (Chanson, H; 1996). A synthetic fibre, such as nylon is used
for tensile strength for fabric while the synthetic rubber coating provides high reistance
to weather, ozone and abrasion. Layers of rubber-coated fabric are bonded together in a
17
sandwich construction to provide the required tensile strength. Chloroprene rubber is
employed for its known resistance to climate condition, ozone, wear etc. A layer of
stainless steel mesh or ceramic chips can be embedded in the surface layer to reduce or
prevent vandal damage (SEIL, 1985; Chanson, H, 1996). The layers of rubber coated
fabric are joined together in the longitudal dirrection. The actual number of layers of
rubber coated fabric for each rubber body depend on the gate height and the tension.
The rubber sheet may be of single layer, double layer and multi-layer as per its height
and strength. The fabric-bag should be water tolerant, water resistant, corrosion
resistant and durable in atmosphere. But now for better protection of the dam materials
against weathering and for operating over large temperature variation chloroprene and
ethylene propylene dyne monomer are being used as the dam material.
3.5 Life of Rubber Dam
Durability of rubber bag is excellent. Recently, a 35 year old dam in eastern Ontario,
Canada was replaced and was still functional in both freezing winter conditions when it
was air filled, and water filled in summer. It was deemed to have served its useful life.
The design life of rubber dam is approximately 20 years (IWHR, 1994; SEIL, 1985;
Raquib, 1999).
3.6 Advantages of Rubber Dam
The rubber dam has several advantages over its use as mentioned below.
• It replaces heavy gates, hoisting gears and piers of conventional structures by
light rubber-nylon shell body. It saves huge amount of steel, cement, timber and
other construction materials. Thus, it has been proved to be a cost effective
technology.
• The dam body can be fully deflated to lower it to flat level on base floor so that
flood flow passes without any obstruction. This provides rubber dams a
dominant position over conventional gated regulating structures.
• Rubber dams can have spans as long as 100 meters without dividing piers. This
provides full width of active cross-section of the river channel to release flood
flow. (Nahar, 2004)
• Load of dam body is evenly distributed on foundation. This lessens treatment
of foundation soil to a nominal or almost none.
18
• Construction and installation are quicker compared to conventional gated
regulating structures.
• Total investment cost is approximately 30% lower than that of conventional
gated regulating structures.
• No gates and hoisting gears required. So it makes operation of the structure
simple. The dam bag needs very little maintenance. Repair to damages of the
dam bag is simple.
(geosynthetica.net; International Water Power and dam construction)
Cost benefit
• Capital Cost: Inflatable dams can be more cost effective compared with steel
gates.
• Installation Cost: Inflatable dams are quick and easy to install and can be
attached to existing dam crests at marginal extra cost. Minimal skills and
personnel are required to embed the anchorage system and pipe work into the
foundations and to attach the rubber membrane. Quick installation is an
advantage when considering the possibility of fluctuating water levels
interrupting completion.
• Operating Cost: Inflatable dams are economical to operate. The only significant
running costs are power requirements for the air blower or water pump during
bag inflation.
• Maintenance Cost: Inflatable dams are not subject to corrosion compared with
steel shutters that require periodic shutdowns for grinding and painting (with the
possible installation of coffer dams).
(geosynthetica.net; International Water Power and dam construction)
• The rubber dam technology compared to the traditional earthen cross dam, as
opined by the beneficiaries, are reliability and timeliness. The technology is
reliable as it can withstand the flash floods, high tides and surges without being
washed out. The easy inflation- deflation characteristic has resulted in timely
farming activities and also increased the reservoir storage compared to the prior
earthen cross dams.(Saleh, M, A and Mondol, 2000)
19
3.7 Disadvantages of Rubber Dam
Despite the advantages mentioned above, it has some disadvantages.
• The soft rubber-nylon made shell of the dam body needs careful operation and
maintenance. Large floating materials like logs, trees, bamboos etc. may be
harmful to the dam body.
• Repair to dam bags is done only in dry condition. Underwater repair is not
possible.
• Service life of dam bags is about 20-30 years. Replacement of the dam bag may
be needed if design life of the dam is longer.
• During operation period, boat communication is hampered.
3.8 The Design Principle
For designing a rubber dam basic data shall be collected, processed, analyzed and
studied on the topography, meteorology, hydrology, engineering geology, hydrological
geology, traffic and transportation, comprehensive water conservancy utilization
planning, socio-economic status and environmental appraisal of the area of river basin
where the rubber dam is to be built. Topographic data shall include topographic maps
for the planned project area, the dam site and back water areas, longitudinal and lateral
profiles of the river course, etc.
The design principal of rubber dam is similar to that of any kind of hydraulic structure.
The forces involved in hydraulic structure construction are:
• Surface flow-which causes scour and erosion
• Sub surface flow- which causes seepage, piping, soil boiling.
As hydraulic structure is founded on a permeable foundation, so both the above forces
have to be considered during designing of hydraulic structure. When flow is controlled
by the hydraulic structure then surface flow governs and when flow is stopped then sub
surface flow governs. For designing different components of hydraulic structure
different physical conditions are have to be considered. Such as hydraulic jump height,
hydraulic jump length and hydraulic gradient which determines the floor thickness,
floor length and depth of cutoff wall. The design of rubber dam involves hydrologic
and structural design (super structure & sub-structure). Before designing of the rubber
dam, it is very much important to select the dam site at first.
20
Selection of Dam Site
Dam site shall be determined after conducting comparative technical and economic
investigations according to rubber dam features and its operation requirements in
consideration of the factors, such as topography, geology, water flow, silt deposition
and environmental protection. The dam should be built preferably on relatively straight
river or channel segment with smooth water flow and stable bank slopes. It is
unsuitable to choose the dam site located on the river segments where scouring and silt
deposition as well as profiles are changing greatly and frequently. Rubber dam site
should be selected on the following considerations:
• The site should be such that the dam at that location can command the
maximum cultivated land.
• The beneficiaries have to be consulted and the site of proposed dam will
provide them the desired benefits of irrigation of the neighboring lands.
• The site should be easily approached by road
• The channel reach should be relatively straight and smooth water flow
• Bank of the river/channel should be stable one
• Land should have uniform slope.
• Optimum utilization of scarce water to derive maximum benefits.
• Canal network should be such that water can flow by gravity.
• When gravity is not possible, water is withdrawn by LLP.
Hydraulic Design
The design data/parameters required for hydraulic design of a rubber dam are as
follows:
Design Data/Parameters:
Design discharge (1:20 year)
Design water level (1:20 year)
Average LWL (March-April)
Average lowest bed level of the river
Water retention level of the project
Soil information
Embankment crests Level.
Cross section of the river up to 7-10 Km U/S and up to 2 Km D/S
Long section of the river
21
Slope of the water surface of the river
Catchments area of the project ( command area of the dam)
Dam Height
The standard state of the rubber dam should be such that its upstream water level
corresponds to the dam height and its downstream water level is zero and the dam
height under this condition is used as standard dam height and the internal pressure at
this time is used as the standard internal pressure. The standard internal pressure is
usually about 1.5 times as high as the head pressure of dam height for water filled
rubber dam. The dam height is selected from the necessity of the purpose. If the rubber
dam is used as irrigation purpose, the dam height is selected as water retention level of
the project. The water retention level is again selected from land elevation of the
project. As for example the dam height of Pekua Rubber Dam is fixed as four meter
and water retention level is fixed as 3.00 m (PWD).
Length of Rubber Dam
The length of rubber dam shall be so fixed that the sectional area at dam section nearly
equals the average sectional area of the existing river. If the river is flashy, existing
waterway should not constrict for easy passing of maximum flood flow. When the dam
will be in inflated position, design flood for pre-monsoon season should pass over the
dam without causing spillover of the existing bank and shaking of the dam. Maximum
design discharge for 20 year flood is to be considered. Clear water way is determined as
L=4.83Q1/2
, where Q is design discharge. Considering the existing waterway and
considering cross sections of the channel or river at different U/S locations, the length
of the dam is to be fixed.
U/S & D/S Apron Level
U/S & D/S apron level of the dam structure has to be fixed in such a way so that there
will be no appreciable afflux and there by high velocity of flow necessitating energy
dissipation device. However, considering probable adverse situation which occur
during life time of structure, the U/S apron level has been set in average lowest bed
level of the river while D/S apron level is set at less than U/S level as per the necessity
of stilling basin design.
22
Depth of Cutoff Wall
Depth of cutoff wall is fixed based on design of scour depth which is 1.25 times the
Laceys regime scour depth at upstream of the structure and that of 1.50 times at down
stream. A silt factor of 0.40~0.60 is assumed. Floor length is fixed on the basis on exit
gradient of 1/7 for seepage head equal to the difference of upstream retention level and
design tide level or difference of downstream maximum tide level and upstream
drawdown level whichever is higher during irrigation season.
Floor Thickness
Floor thickness at various parts of the structure is selected considering uplift pressure
computed by Khosla’s theories of independent variable for seepage head as considered
for finding the floor length above. Protective works comprising cutoff wall, inverted
filter and launching apron are designed based on design scour depth.
Strength of Rubber Dam
The main design loads acting on the dam bag are the static hydraulic pressure from
outside the dam bag and the pressure inside it caused by the filled water or air.
• =Design ratio between internal and external water pressure shall be chosen first with
value 1.25~ 1.60 for water filled rubber dam and 0.75~ 1.10 for air filled rubber dam.
Design factor safety is used as not less than 6.00 for water filled rubber dam and that
for air filled not less than 8.00 ( QHEPIL, 1999). Various design parameters for this
kind of dam bags is used from mathematical analysis by using the formulae given
below.
Radial strength of dam bag:
Radial strength Where unit wt. of water Kn/m3
=α Internal pressure ratio= H0
Design height of dam in m
Design tensile strength of rubber bag per meter strip width is
= internal pressure water head in m
=wγ
1H
Ho
=1H
212
1
2
1HT w
−= αγ
( ) KTwarpT = ( ) ( )warpTweftT3
2= 8~5== FSK
23
The radial strength of rubber Dam is required for determination of the thickness of
rubber sheet and tensile strength of rubber sheet.
Shape of Rubber Bag
The shape of dam bag after inflation is divided into four parts: (1) length of curved
segment of dam surface in the upstream direction S1; (2) length of curved segment of
dam surface in the downstream direction S; (3) length of ground touching segment in
the upstream direction N and (4) length of ground touching segment in the downstream
direction X0.
Effective Circumference (excluding the distance between two anchorage) of the dam
body is L0 = S1+S
Effective length of bottom pad is D= N+X0
Equation of calculation of N, S1, S & X0
••
•
••
••
• • •
• •
•
•
•
are as follows:
Figure 3.1: Shape of Rubber Bag (QHEPIL, 1999)
)1(2
1
−∂=N H1 S1 θR = if 5.1≤∂ , =θ sin R
N-1 5.1≥∂ , if ,
−= πθ Sin R
N-1
∂−
2
11 S= H1 . ( )2/,πkF
X0
∂+−∂
2
11= H
•
2,π
kF1 ∂− H
•
2,π
kE1 ( )14
12
−∂−∂
R= H1
U/S D/S
•
24
k2 2
12
∂−∂
=
From this equation the parameters are calculated.
3.9 Components of a Rubber Dam
Rubber dam is mainly divided into four parts. They are:
• Dam body or dam bag
• Anchorage system
• Control system (including water or air filling and emptying system, monitoring
system and safety control system)
• Foundation (including base floor, abutment and side walls etc.).
3D view and schematic diagram of a rubber dam is shown in Figure 3.2 and long
section of Pekua Rubber Dam is shown on Figure 3.3 below.
Figure 3.2: 3D View of Rubber Dam (Nahar, 2004)
25
25500
56000
80000
5600083000
22000
11000
SECTION S-S (From sheet no. )
4500019000
EL.(-) 1.50
SECTION P-P (From sheet no. )
13500
4000 11000
EL.(-) 1.00
EL.7.50
3000
OVER FLOW PIPE
EL.3.50
CL. OF PUMP HOUSE
10500
PUMP HOUSE
600EL.4.00
450x450x300 CC BLOCK
350x350x350 CC BLOCK(2 layers)
SHEET PILE(4000)
1000
1500
RUBBER BAG ( Inflated position)
GRADED FILTER
4450
EL.(-) 1.00
15000
EL.3.50
6100
SECTION A-A (From sheet no. )
4450
EL.(-) 4.00
500
RUBBER DAM
50040003000500
32001200
EL.(-) 2.00750 EL.(-) 1.00
4000
FOOT BRIDGE
U/S
EL.400
EL.6.00EL.7.00
2250EL.3.50
CL OF STORAGE
2250
WATER STORAGE
EL.4.00
EL.3.00
PUMP HOUSE
EL.7.50
EL3.00
13500
27500
Details "A"1000
SM.AZIZUL HOQUECHECKED
DATE : 16-10-2002S. M. AZIZUL HAQUE
DESIGNED
DRAWNSM.AZIZUL HOQUE
1500
EL.3.00
GEOTEXTILE
450x450x300 C.C BLOCK
60006000
SHEET PILE (8000)
SAND FILTER
EL.(-) 1.00
EE
( MD. MOZAMMEL HOQUE)CHIEF ENGINEER, DESIGNDWG. NO.MIP-RDP- 3147-36
EE
(KAZI GOLAM MUSTOFA)SUPERINTENDING ENGNEERAPPROVED
RECOMMENDED
EE
EL.3.50
400x 400x 200 CC BLOCK
D/S
SHEET NO 36
Figure 3.3: Long Section of a Rubber Dam (Design Catalogue, BWDB, 2003)
Some other Components of Rubber Dam
Besides the four main components, there are some other components, which are
mentioned below.
• U/s and D/s massive concrete floor(Apron)
• Massive concrete base (Dam Base)
• Slope wall
• Inverted filter at river bed
• Filter material
• Bank protection Work
Dam Body
Dam body is made of rubber reinforced by woven synthetic fabric that provides the
tensile strength with rubber acting as the adhesive and water proofing elements. The
fabric reinforcement is used in layers. The layers depend on the design strength
requirements.
26
3.10 Salient Consideration for Construction of a Rubber Dam Body
The following aspects should be considered during construction of a rubber dam.
• The material should be strong, resistant to tearing / puncturing and should not
deteriorate with exposure to sunlight. It is recommended to use of Ethylene
Propylene Diene Monomer (EPDM) compounded rubber with nylon
reinforcement.
• The body of the dam should be supplied in one unit to avoid the need for site
welding of seams.
• Rubber dam tube is made of high strength canvas and rubber layer that convey
the assurance of airtight.
• Rubber layer include outer layer, middle layer and inner layer.
• Outer layer is the rubber with characteristic heat-resisting, wearing-resisting and
ozone-resisting.
• Middle layer have the function to defend the canvas and joint canvas layers.
• Inner layer defend the canvas and keep watertight and airtight. The layer of
rubber dam is shown in the following
27
figure
3.11 Fitting and Fixing of Rubber Dam
Anchorage of Dam Bag with Concrete Base
Many types of anchorage system are generally used. Major types are stated below.
Steel Clamps with Anchor Bolts
For fitting and fixing of rubber sheet on the bed, steel clamp elements and stainless
steel anchor bolts and nuts are used. Stainless steel ensures against reduction of strength
of threads of the nuts and bolts by rusting. This arrangement has been shown in the Fig
3.5. Fitting and fixing of rubber sheet are not as simple as like as other construction
work of the rubber dam project. At first, the anchoring slot is kept open for second
stage concrete for positioning and fitting and fixing the anchor bolt with dowel bar of
the slot. Then lower anchoring plate is fixed with the help of anchor bolt and the anchor
bolt is fixed with dowel bar with welding work. The design level of lower plate is done
with the help of level machine and this level is adjusted with the help of bottom nut of
Figure 3.4: Rubber Layers (SEIL, (1985)
28
anchor bolt. Then second stage concrete is cast up to bottom level of lower plate. The
thickness of lower and upper plate is designed with the height of rubber dam. The
details of fitting and fixing rubber sheet are shown in figure 3.5 & figure 3.6. The
works are done very carefully with maintaining proper alignment of the anchor bolt,
because any deviation of anchor bolts will create problems in fitting of anchor plate.
800
POLYTHINE CAP ON NUT-BOLT AFTER APPLYING GREESEFILLER RUBBER(TH=10mm)
150
500
165
150FILLER RUBBER (TH=10mm)
DOUBLE NUT
BOTTOM PLATE(TH=16mm)
ANCHOR BOLT-25mm Dia
325
200
UPPER PLATE(TH=25mm)30
100
81
RUBBER BAG (TH=12mm)
Figure 3.6: Anchorage System of Rubber Dam (QHEPIL, 1999 )
Figure 3.5: Anchorage System of Rubber Dam (Design Catalogue, BWDB, 2003)
Upper Plate
Lower plate
Anchor bolt
Rubber sheet
29
Figure 3.7: Steel Clamps with Anchorage Bolts (QHEPIL, 1999)
Concrete Wedge Blocks
This system of anchoring the rubber sheet is old system. It was practiced in China. This
system does not work properly. Slots are provided in the base slab and the ends of the
rubber sheet are anchored by two sets of pre-cast concrete wedge blocks; the front
wedge blocks pressing the rubber sheet against the face of floods and the back wedge
blocks hammered into position ensuring the grip. The slots and the blocks should be in
accurate dimension and sharpness for quality work. For low height dams of simple
hydraulic forces, wooden anchorage blocks may also be used. This arrangement is
shown in the following figure (Figure 3.8)
back wedge Front wedge Wooden blocks Dam bag
Figure 3-8: Concrete Wedge Blocks (QHEPIL, 1999 )
3.12 Filling and Emptying System
The dam bag can be inflated either by filling with air or water. Water filling method
requires fresh water and normally a reservoir is provided with the dam. Where silt or
any foreign suspended materials present in water, then instead of water reservoir a deep
tube well is used for dam body for fresh water filling. Air filling is quicker but it needs
30
relatively sophisticated pumping and pipe-valve system. Water filling is relatively slow
but ordinary pumps can be used with less complicated pipe-valve system. A centrifugal
pump is used for water filling purpose. Shorter and smaller pumps are used for the
longer filling/emptying time. Generally the dam bag is filled water from the U/S of the
dam. This water is filled through some device in order to avoid silt. To avoid silt, a wire
mesh frame wrapped with geo-textile filter is used on the mouth of the intake pipe.
Filling system also usually includes safety measures against overfilling through
overflow outlets and pressure manometers. A typical filling system is shown in the
following figure (3.9).
DEFLATING BY PUMP
DEFLATING BY GRAVITY
INFLATING
MODE
Pressure pipe
Pump House
EL. 4.00
(-) 4.00
(-) 3.00
(-) 0.65 Pump well
BA
CD E
F
OTHERS CLOSEDE, C, F OPEN
PIPE JOINTREDUCING PIPE
OTHERS CLOSED
OTHERS CLOSEDOPEN VALVES A, C, D, E
OPERATION
E, D, F OPEN
VALVE OPERATION SEQUENCE
REGULATING BALVE
Inlet/Outlet water cap
LEGENDGATE BALVE
7.50{200Ø}
90° BendOverflow pipe
EL. (-) 1.50
Downstream flowOutlet end
90° Bend
3.50
Figure 3.9: Filling and Emptying System of Rubber Dam (Design Catalogue,
BWDB, 2003)
The procedure for operation of the system is as follows:
1) Filling water from upstream into dam bag by pump:
Open valves A, C, D & E and all others will be closed.
2) Emptying water from dam bag to downstream by pump:
Open valves E,C & F and all others will be closed;
3) Draining out of water from dam bag to downstream by gravity:
Open valves E,D & F and all others will be closed at same time.
31
3.13 Durability and Maintenance
The required strength can be achieved by using materials of varying thickness.
However, practice has shown that using thicker cover has undoubted advantages with
respect to durability. Thinner cover are particularly susceptible to puncture and tearing
damage from hydraulically transported materials. Durability is also improved by use of
best quality of rubber sheet and strong nylon fabric. The nylon gives the fabric its
tensile strength while the synthetic rubber coating provides a resistance to weather,
ozone and abrasion. Layers of rubber coated fabric are bonded together in a sandwich
construction to provide the required tensile strength. Durability also can be enhanced
by providing a special type of cushioning system. This protects the rubber sheet from
tearing and puncturing the rubber bag. A special type of cushioning system is shown in
Figure 3.10. This provides minimum resistance against the current and maximum
protection against damage. Maintenance of rubber dam should be minimal. It should
be easy to repair in case of puncture or tear.
Figure 3.10: Cushioning System of Rubber Dam (SEIL, 1985)
3.14 Foundation
Foundation includes base floor, apron, stilling basin and slope protection. Except base
floor all other components are designed like conventional regulators or barrage.
32
The width of the base floor should be considered for the requirement of the additional
deformation in dam body. The stability analysis has been made taking into account all
horizontal and vertical loads for the following conditions.
a) Full Operation Condition: Dam bag fully inflated to the design level and full
storage to dam height.
b) Dam Test Condition: Dam fully inflated without upstream storage.
3.15 Flexible Control
Inflation & deflation can be manual or automatically controlled. The automatic control
system can monitor the upstream water level and adjust the air pressure in the dam to
maintain a prescribed water level in the upstream pool.
Figure 3.11: Flexible Control
3.16 Oscillation
The early experience using air filled dam were unsuccessful owing to oscillation caused
during heavy flow because they did not have the ballast that water provided. Also, these
dams suffered excessive premature wear owing to oscillation included abrasion.
Bridgestone provide and answer to this by introducing the “:FIN” into the design.
Oscillation Reduction
When inflated, the FIN structure works as a deflector to create aeration below the fin.
This effectively reduces the phenomenon of oscillation up to a 50% overflow when
compared to FIN-LESS bladders.
33
Figure 3.12: Oscillation Reduction
3.17 Side Slopes
There are two types of side slope. One type is vertical side slope and the another one is
variable side slope.
Vertical Side Slope
Dams with vertical side slopes have natural disadvantages:
a) Disruption of the natural water flow when opened altering the downstream
movement affecting river bed condition, especially during flooding,
b) Vertical side walls require more supporting members, more reinforcement and
more difficult construction than sloping side walls.
c) Vertical side slopes are less in harmony with the aesthetic of river and thereby
unnatural and
d) Experience has shown that rubber dams with vertical sided are more susceptible
to damage.
Variable Side Slope
Rubber Dams can be installed in rivers with any side slope angle, eliminating the necessity of
modification to river bank, unlike steel gates which can only be installed on vertical side slopes.
Figure 3.13: Variable Side Slope (Nahar, 2004)
34
3.18 Specification of Rubber Dam
The specification of rubber dam is very much important. Before ordering the rubber
dam body from foreign country, the concerned supplier has to know the specification of
the rubber dam. This specification is made as per design consideration of that rubber
dam. The following specification with respect to stress is mentioned below.
Allowable Stress
• The thickness of the rubber dam body should not be less than 10.00mm and to
be reinforced by not less than 2 layers of nylon canvas.
• Tensile strength in water course direction shall have a safety factor of 8 under
loading condition. The tensile strength in longitudinal direction shall be more
than 2/3 of that water course direction.
• Tensile strength in watercourse direction after heat aging at 1000
• Tensile strength in watercourse direction after hot water aging at 70
C for 4 days
shall be more than 80 % of initial strength and safety factor shall be more than 8
under normal loading condition. 0
• Adhesion between nylon canvas and rubber shall be more than 6 and 4 kg/cm
for 4 days
shall conform to the requirement of tensile strength in watercourse direction. 2
at initial property and under hot water resistance test at 700
• The clamping materials and anchoring bolts shall be of either galvanized steel
or stainless steel material and shall have at least two ridges to form dual sealing
line to prevent any leakages.
C for 4 days
respectively.
• Dual anchoring line is required to cater for the situation when upstream water
level is higher than down stream water level or visa versa.
• Safety factor of clamping bolts shall be more than 3 times against tensile
strength of materials used under normal loading condition.
3.19 Physical Property of Rubber Dam
The dam body shall be of ethylene propylene diene monomer (EPDM) compound or
chloprene rubber or equivalent with nylon reinforcing fabric. An external surface shall
be abrasion resisting nature. The external rubber cover thickness shall not be less than
4.0 mm which forms part of the rubber body ( total thickness shall not less than
10.0mm) and the surface must be textured to reduce the possibility of the debris
35
dragging across the surface of the rubber body during the fully deflated stage. It should
gain high water resistance for tropical area, high durability and capable of operating in
accordance with the specified conditions, abrasion resistance, tear resistance, impact
resistance, ultra violet resistance. The body shall use water as inflating media. Fin or
deflectors shall be formed as an internal part of the rubber body during manufacturing
of the rubber body, lamination to the rubber body after manufacturing is not allowed.
The clamping plates and anchor plates shall be designed to fix uniformly the body and
transmit hoop tension of the body to the concrete foundations. The clamping plates and
anchor plates shall have complete water and air tight construction at both inflated and
deflated conditions of the body. It shall be liable for deterioration of the rubber
materials throughout the life of the rubber dam.
3.20 Types of Rubber Dams
The rubber dam can be divided into three types. They are:
• Sail type
• Mixed type
• Bag type
Sail type fabric-dam belongs to open category known as sail gate for which the gate-
lifting device is necessary. The mixed type fabric-dam is composed of soft and rigid
structures. The bag type structure is often used for most of the soft-shell hydraulic
structures.
Classification based on the Filling Media:
Based on filling media, rubber dam is of three types:
1. Air filled dam
2. Water filled dam
3. Combined air and water filled dam
Recently air inflated dams are generally constructed. This type of dam is superior to
water inflated dam in terms of the ease of inflation and maintenance but needs
sophisticated pumping unit. But, due to the passage of water over the dam body, air
inflated dams have vibration problems, water filling is relatively slow but ordinary
pumps can be used for filling and emptying.
36
Air Filled Rubber Dam: Filling media is air. In Thailand this type of rubber dam is
seen. In small stream or small channel, this type of rubber dam gives a good result.
Figure 3.14: Air-filled Dam (Yantai C.S.I. Rubber Co. Ltd)
Water Filled Rubber Dam: Filling media is water. The Pekua Rubber Dam is an
example of water filled rubber dam.
Figure 3.15: Water-filled dam (Yantai C.S.I. Rubber Co. Ltd)
Classification Based on the Number of Bags
In one rubber dam structure there may be single bag (single span) or multiple bag
(multiple span). Multiple bag rubber dam is divided by RCC pier. Figure 3.16 and
Figure 3.17 show Multiple Bags Rubber Dam with dividing Pier.
37
SECTION S-S (From sheet no.14)
56000
52000
60000
159000
159000186000
12000
60000
13500
600
1000
43000Details "A"
95001000
1500
RUBBER BAG (Inflated position)EL.3.50
2000 1200060000
13500
4300095001000
1500
2000
2950
EL.3.002000
400
SECTION B-B
46000
Details "A"
EL.(-) 1.00
2950
1500
EL.3.50
400
Figure 3.17: Layout of Multiple Bags Rubber Dam with Dividing Pier
(Nahar, 2004)
Figure 3.16: Multiple Span of Rubber Dam (Design
Catalogue, BWDB, 2003)
38
Classification based on the Form of Dam Tube:
Pillow-like dam:
Figure 3.18: Pillow Like Dam (Yantai C.S.I. Rubber Co. Ltd)
Inclined dam:
Figure 3.19: Inclined Dam (Yantai C.S.I. Rubber Co. Ltd)
Classification based on the Seam of Rubber Bag:
Rubber dam may be another two types, depending on the seam of rubber bag.
• Seamless Rubber Dam
• Seamed Rubber Dam
Seamless Rubber Dam
Seamless rubber dam is mainly used on slope dam over 4 meters high when water
filling is up to certain height, dams over 4 meters high will not only bear lateral strain
39
on its slope but also form rather great longitudinal strain and cutting force, which will
get the dam bag under complicated supporting-power state.
Seamless rubber dam is formed once for all by the heat presser in the factory, so the
problem of seam joining part will not occur (Nahar, 2004).
Figure 3.20 and Figure 3.21 shows seamless and seamed rubber dam.
Figure 3.20: Structural Sketch of Seamless Rubber Bag (Nahar, 2004)
Seamed Rubber Dam
Seamed rubber dam is formed by adhesion of pieces of adhesive rubber after grinding.
Due to human factors and the limitation of technology, the seam joining part usually
has defects and is easy to be damaged if under complicated supporting-power condition
in the section of slope, which will affect the life of dam bag and will cause the tearing
of the dam bag if under serious condition.
Figure 3-21: Structural Sketch of Traditional Seamed Rubber Dam (Nahar, 2004)
Classification based on the Purpose Served by the Rubber Dam:
Rubber dam can also be classified depending on the purpose of use. Rubber dam can be
used for irrigation, hydro power generation, reservoir etc. Some examples of the use of
rubber dam for irrigation purpose are shown in the Figures 3.22, 3.23 and 3.24.
40
Figure 3.22: Irrigation Purpose Served by Rubber Dam (Nahar, 2004)
Figure 3.23: Hydro Power Produced by Rubber Dam (Nahar, 2004)
Figure 3.24: Rubber Dam Used as Reservoir (Nahar, 2004)
41
Chapter 4
Pekua Rubber Dam Project 4.1 General
This chapter gives a brief description of the Pekua Rubber Dam Project, performance of
which was evaluated in this study. It focuses on some salient features of the project,
such as background, concepts, components, purpose, implementation schedule and
expenditure of the project as well as the physical dimensions of the rubber dam.
4.2 Background of the Project
The Matahmuhuri is a hilly and trans border river. It originates from hilly region of
Myanmar and after flowing about 110 km through Myanmar hill tracts and Chittagong
hill tracts of Bangladesh (Figure 4.1), it takes meandering shape near Champabati. At
Champabati it has narrowed down and flows about 37km over the low lying coastal
zone and falls into the Bay of Bengal near Moheskhali-Kutobdia channel. The
Mathamuhuri River then flows to the west from the east under the Chirringa Bridge at
Chittagong- Cox’s Bazar highway and splits into the three branches as the
Mathamuhuri River, the Manikchari River and the Bhola Khal. During the past 30
years, the people of this locality were suffering from scarcity of irrigation water during
dry season. They used to get limited dry season irrigation water by building temporary
earthen dam every year, on their own initiatives, over these three rivers and retained
sweet water with the assistance of local administration. The earthen dam had to be built
in several times in a year. It created several problems in the locality like unplanned
irrigation, water logging, etc. So the local people felt a need of a comparatively better
and sustainable solution of their irrigation problem. In response to the demand of the
local people and on the basis of reality, BWDB took initiatives to implement a full
stage FCDI project on the three branches of the Mathamuhuri River. This project is
known as Mathamuhuri Irrigation Project. The figure 4.1 shows the project map of
Mathamhuri Irrigation Project. Accordingly the final feasibility study on the
Mathamuhuri Irrigation Project was prepared in 1996 with an aim of a detail study on
the technical, economical, social and environmental aspect of the project (IMED,
42
2007). The project from the beginning emphasized on twin objectives of alleviating the
two most frequently articulated problems of the local people namely:
• A permanent solution of water retention structure instead of temporary earthen
dams on the three rivers which are washed away during monsoon.
• Providing unhampered navigation obstructed by earthen cross dams.
Figure 4.1 Project map of Matamuhury Irrigation Project (BWDB, EPC, 1996)
The project concept focused on these two issues mainly by improving the existing
system of water retention earthen dams the farmers were constructing for last 20 years.
There were a number of additional factors which also came to light due to the
emphasis given in the feasibility report to carryout the inventories of embankments,
structure, irrigation/drainage channels and river training works of the existing polder of
Pekua Rubber Dam
43
the project and recommendation for further development.(BWDB; EPC, 1996). These
have affected the design of the scheme which could not be kept limited to only the
above mentioned objectives but to some other issues. These issues came out from local
participation program carried out in the field. These were:
• Dissatisfaction among the local people with the way influential people were
able to change the location of earthen dam when it was constructed.
• Failure of local people to construct earthen dam on the Kataferry khal due to
high torrential current compelling them to shift the site to Pekua on the Bhola
Khal.
• Resectioning of deteriorated embankment for prevention measure against flood
and saline intrusion.
• Maitigation of crop failure by removing drainage congestion by re-exavation of
drainage channels.
• Improvement of drainage system by rehabilitation/replacement and
construction of new drainage sluices.
• Improvement of drainage sluices to irrigation inlets modifying the flap gate
lifting system.
• Control of river erosion by river bank revetments.
• Removal of flood detention by loop cut of river.
• Redress of conflict between agricultural farmers and shrimps / salt farmers.
• Poor maintenance of infrastructure.
Considering the above aspects the major highlights of the Matamhuhuri Irrigation
Project were to build a permanent dam instead of earthen dam over these three rivers to
overcome the problems. This permanent dam may be any water retention structure like
Rubber Dam or Barrage (BWDB; EPC, 996). On the basis of recommendation of the
Feasibility Study Report, the main PCP of the Mathamuhuri Irrigation Project with
estimated cost of Tk.8929.357 lakh was prepared during March/1999. The main works
of the project were to construction of rubber dams and development of some other
infrastructure which were directly related to the project. But the Pre-ECNEC meeting,
held on 07/09/1999, considered the project as an expensive one and found that the
whole project was not possible to implement at a time. So, it was decided to primarily
construct a Rubber Dam over the Bhola Khal named as the Mathamuhuri Irrigation
44
Project (Pilot Project) with an estimated cost of Tk.2243.70 lakh, which was approved
on 20/06/2000. To carry on the decision of the meeting of ECNEC, held on 20/06/2000,
the project of estimated cost of Tk. 2062.27 lakh was recommended for approval in the
meeting of DPEC and accordingly implementation of the project started. But the
project was again revised through the DPEC meeting held on 18/05/2003 with a revised
cost of Tk.2012.88 lakh and its implementation time was extended upto June/2005. The
final cost incurred for this pilot project was Tk.1991.08 lakh (IMED, 2007). The
Figures 4.2 shows the location of Pekua Rubber Dam in Matamuhury Irrigation Project
(Pilot Project).
Pekua Rubber Dam
Km.63.00
P-64/2A
Km.59.00
Km.54.00Km.55.00
Km.60.00KM.61.00
Km.62.00
Km.65.00
Ch. at Km. 55.00....................57.50 mCh. at Km. 56.00....................65.00 mCh. at Km. 57.00....................61.00mCh. at Km. 58.00....................59.00mCh. at Km. 59.00....................54.00mCh. at Km. 60.00....................42.00mCh. at Km. 61.00....................36.00mCh. at Km. 62.00....................39.00mCh. at Km. 64.00....................31.00mCh. at Km. 65.00....................35.00mCh. at Km. 66.00....................65.00mCh. at Km. 67.00....................78.00m
P-65
Bhol
a Kh
al
PEKU
A
MAN
IK C
HARI
RIV
ER
Figure 4.2 Location of the Pekua Rubber Dam in Matamuhury Irrigation Project (Pilot Project) (BWDB, 2004)
4.3 Dimension of Pekua Rubber Dam Project
The physical feature of the Pekua Rubber dam is given in Table 4.1. The dam is 83
meter long and 4 meter in height. It is a single span dam where centre to centre distance
N
45
is 6.1 meter. It can provide irrigation facilities to grossly 1400 ha of land and its net
coverage of area is 5000ha.
Table 4.1: Physical Features of Pekua Rubber Dam
Length 83 meter
Height 4 meter
Span Single
Distance between centre
to centre of slot
6.1 meter
Area coverage Gross 14000 ha, net 5000 ha
4.4 Project Concept
The overall approach to development of the Matamuhuri Irrigation Project (Pilot
Project) was based on a number of concepts, which were as follows:
• The operation of the scheme should be as simple as possible with minimum
interventions required for satisfactory operational functions.
• Optimum utilization of scarce water to derive maximum benefits,
• Proper water distribution at minimum structural cost so that operation and
maintenance cost may be brought down to minimum taxation limit when
management and supervision can be taken up by the Water User Association
(WUA).
4.5 Components of the Matamuhuri Irrigation Project (Pilot Project)
The feasibility report of the Matamuhuri Irrigation Project included a number of
components like barrage/rubber dams for gravity flow with water distribution by
gravity from canals system or Low Lift Pumps (LLP) with unhampered navigation. The
consultants proposed for options of barrage or rubber dam. These were proposed to be
constructed at Pekua on Kataferry khal, at Chowdhury Hat on Manikchari River and at
Palakata on the Matamuhuri River in consideration of public demand (BWDB; EPC,
996). Finally on the basis of the PCP approved by ECNEC a rubber dam was built on
the Bhola Khal near Pekua upazilla, considering the following aspects (IMED, 2003):
• Command of maximum cultivable land
46
• Strong Public demand
• Easy approachable road to and from the dam site
• Easy construction opportunity with keeping the river flow as it
• Minimum land acquisition
• Cost effectiveness
4.6 Purpose of the Pekua Rubber Dam
The main objective of this project was to control the flood, drainage improvement,
provide irrigation facilities to boro crop cultivation during dry season (November to
May) through retention of sweet water in the upland river system and prevention of
ingress of saline water and improve fisheries by providing proper irrigation in the area
of Pekua under Cox’s Bazar District. The benefited area of implemented 1st stage of
this Project is gross 14000 ha and net 5000 ha.
4.7 The Project Implementation Time and Expenditure
Table 4.2 shows the expenditure and time line of the Matamuhury Irrigation Project
(pilot project).
Table 4.2: Implementation Schedule and Expenditure of Pekua Rubber
Dam Project
Estimated Cost ( in Tk.Lakh)
Real Expenditure
( in Tk.Lakh)
Planned Implementation Time
Real Implementation
Time Main Last
Revised
Main Last Revised
1 2 3 4 5 6
2062.27 2012.88 1991.08 2000-2003 2000-2005 2000-2005
Initially plan was made to implement the Pekua Rubber Dam Project in a three years
time period spanned over 2000 to 2003. Later on the project implementation time was
revised and extended up to June/05. The actual construction of the rubber dam
commenced in November 2003 and was completed in June 2004. The Pekua Rubber
dam started its functioning from November 2004. The total time for construction of the
47
dam was eight month (field data). Figure 4.3 in shows a picture of the Pekua Rubber
Dam during its construction period.
Figure 4.3: Pekua Rubber Dam (BWDB)
48
Chapter 5
Methodology
5.1 General
This chapter describes the research methodology followed in the present study. It
includes the description of research design, research location/area, population, sample
and sampling technique, data gathering techniques and tools, data analysis procedure,
criteria/indicators of evaluation, etc. as adopted in this study.
5.2 Research Design
This study made use of a descriptive research design to evaluate the performance of the
Pekua Rubber Dam in terms of its design, operation and maintenance aspects as well its
impact on socio-economic life of the people, local agriculture and environment of the
project area of the rubber dam. To this end this study used the procedures of both
quantitative and qualitative analysis to determine the efficiency of the project.
5.3 Research locale
The study was conducted in the catchments area of the Pekua Rubber dam located in
the Pekua upazila of Chittagong Hill Tracts. The people live in that catchments area
served as the population of this study.
5.4 Sample and Sampling Technique
The sample size, who responded to the questionnaire, of this study was 50. The
respondents were selected from among the beneficiaries and stakeholders of the project
living in the project area. Besides, groups of stakeholders, BWDB officials and staff
(design, operation and maintenance officers and staffs), NGO people, agriculture
extension department people and people related with fisheries were consulted and
discussed to get qualitative data for conducting the study. Purposive sampling
technique was employed in selecting the sample and others.
5.5 Data Gathering Techniques and Tools
Data gathering process involved collection of both primary and secondary data. For this
a list of indicators was identified first. Based on the indicators a questionnaire was
49
developed for primary data collection. The secondary data were also collected based on
the identified indicators. The procedures followed in primary and secondary data
collection are described below.
5.5.1 Primary Data Collection
Primary data were collected through a questionnaire administered on 50 respondents. It
included both quantitative and qualitative types of inquiry for assessment of the impact
of the Pekua Rubber Dam on socio-economic status of the stakeholders as well as local
agriculture and environment. Data on the technical status of design, operation and
maintenance were collected through discussion with the stakeholders and related people
like designers, local BWDB office staff, concerned BWDB Executive Engineer and
concerned Sectional Officer of Pekua Rubber as well as through field visit and
observation. Besides, discussion was made with local agriculture extension officer and
concerned staff of that office. The researcher himself collected the data through field
visit and with the help of local people and field officials.
5.5.2 Secondary Data Collection
Secondary data were collected through literature review of IMED report, design report
of the Pekua Rubber Dam, other related reports and feasibility study of the Matamuhuri
Irrigation Project.
5.5.3 Indicators
The criteria/indicators selected as the basis for data collection were as follows:
• Yearly income increase of the people
• Range of yearly increase
• Employment opportunity
• Poverty level
• Agricultural production before and after the project
• Boat Navigation
• Movement of people
• Fish and fisheries activities (production, migration, biodiversity).
• Changes in amount of cultivable land
50
• Vegetation coverage and other natural resources.
• Water retention, water supply to the agricultural land.
• Local weather
• Upstream water retention level maintenance.
• Design parameters of Pekua Rrubber Dam.
• Constructional aspects of Pekua Rubber Dam project.
• Institutional aspect, such as water user group formation (WUG).
• Management of operation and maintenance of Pekua Rubber Dam.
• Maintenance of the Rubber Dam.
• Stakeholders’ participation in maintenance of the project.
5.6 Data Processing and Analysis
Both the primary and secondary data were processed based on the indicators and
inquiries of the questionnaire. In analysis of data simple descriptive statistics like
frequency and percentage distribution were used. Details of the data and their analysis
and interpretation are presented in the following chapter (Chapter 6).
Chapter- 6
Result and Discussion
6.1 General
This chapter presents, analyzes and interprets the data collected against the research
objectives of this study. They are discussed under three major sections (6.2, 6.3 and
6.4). Section 6.2 deals with the findings on the technical aspect of design of the Pekua
Rubber Dam as well as its construction problems and their mitigation. In section 6.3 the
operation and maintenance aspects of the rubber dam has been described. Section 6.4
presents the findings and analysis of the data collected for evaluation of the impact of
the rubber dam on socio-economic life of the people living in the project area as well as
on local agriculture and environment.
6.2 Assessment Result of the Technical Aspect of Design of Pekua
Rubber Dam and Its Constructional Problems and their
Mitigation
Technical aspect of design considered for any construction has important implication
on the durability and functionality of that project. The Pekua Rubber Dam was
designed by Design Circle-2 of Bangladesh Water Development Board. It was
constructed by Cox’s Bazar Division of BWDB and is being operated and maintained
by that division. In designing the Pekua Rubber Dam various design parameters, such
as design water retention level, discharge were considered. On the basis of these design
parameters, the dam height, length of the dam, the total floor length, the depth of cut-
off wall, the detailing of rubber dam body, the geometric shape of dam, etc. were
computed by the concerned design engineers (Design Report, 2003). Whether these
design parameters were properly selected by the design engineers in the light of
technical aspect were evaluated as part of this performance assessment study. This was
done by reviewing the design report of the Pekua Rubber Dam Project and by
conducting discussions with various groups of people, like the design engineers, field
engineers and technicians, pump operator, stakeholders, NGO people, BWDB staff, etc.
involved directly and indirectly with design, implementation, operation and
maintenance of the dam. In the following paragraphs, the design parameters, considered
for design, and their assessment results are discussed briefly.
52
6.2.1 Water Retention Level
One of the major design parameters was consideration of water retention level of Pekua
Rubber Dam. The water level was considered from the project land elevation. The land
elevation varies from + 1.80 m (PWD) to 2.0 m (PWD) near the dam site, +2.00 m
(PWD) to 2.50 m (PWD) in the middle part of the project area and 2.50 m (PWD) to
3.00 m (PWD) on the U/S area of the project. The U/S part of the project area is higher
elevation. The average elevation of the whole project is 2.50 m (PWD). In order to get
available water to the whole project area, the proposed water retention level was
selected by the designer as 3.00 m (PWD) (Design Report, 2003). The criteria of
selection of this water retention level were made through open discussion with various
groups/levels of beneficiaries or stakeholders of the project by the field office. The
objective of this water retention level was to supply irrigation water to cultivable land
of the U/S area of the project by LLP and near the dam site area with simple gravity
system. On the upper part of the project area, water is supplied to the intake channel
through inlet structure. Stakeholders/beneficiaries irrigate their lands by using LLP
installed on both of the banks on the main channel (Bhola khal) as well as intake
channel in this area. On the other hand, stakeholders/beneficiaries of the dam site area
used irrigation water by simple gravity system by cutting earthen drain from the
distributor channel system with controlling the flow of water through gated inlet/outlet
structures whenever needed. Through open discussion with the stakeholders and other
groups of beneficiaries as well as the groups of people involved in operation and
maintenance of the project no problem was found regarding irrigation of their own
lands, in terms of water retention level. From the above discussion it is clear that the
design water retention level of Pekua Rubber Dam i.e. +3.00 m (PWD) is quite satisfied
for their irrigation scheme. So, the consideration of design parameter in the light of
technical ground for keeping water retention level +3.00 m (PWD) could be considered
as ok.
6.2.2 Length of the Rubber Dam
The length of the Pekua Rubber Dam was fixed on the basis of some criteria. Since the
Bhola Khal is flashy river, the design engineers decided not to constrict the existing
waterway for easy passing of maximum flood flow. The design discharge was also
considered for deciding the length. The maximum design discharge for 20 year flood
for this structure was considered as 306 cumec. Clear water way was determined as L=
53
4.83Q1/2 = 4.83x3061/2= 84.49m (Design Report, 2003). Considering the existing
waterway and considering cross sections of Bhola Khal up to 8-10 Km of U/S at
different locations and keeping the existing conveyance of the Bhola Khal
uninterrupted, the length of the dam was fixed as 83.00m (Design Report, 2003). As till
to date no morphological change at dam site (erosion / deposition) was seen and no
protective work was needed at the dam site. So, this length of the Dam satisfies the
design parameter consideration for design work (These information is collected from
filed office). These findings support that the design parameters for designing of Pekua
Rubber Dam (Discharge and cross section) for determining the length of dam are ok.
6.2.3 Height of Rubber Dam
The height of the Pekua Rubber Dam was fixed on the basis of necessity of Water
Retention Level (WRL). WRL was fixed as 3.00 m PWD on the basis of project land
elevations. This WRL was selected by field office through open discussion with various
groups of people living in the project area. Before construction of the Pekua Rubber
Dam, local peoples used to build earthen cross dam on this point every year. These
cross dam levels were reviewed by the field office for selection of the dam height. In
this area ground level (GL) varies between. 2.00m ~3.00 m PWD, so irrigation to the
cultivable land by means of gravity flow or LLP installed on both banks of ponded
channel. Keeping WRL as 3.00 m (PWD), dam height was fixed as 4.00m with top
elevation 3.00m (PWD). Dam height is directly related for storing water in the channel
and which is also responsible for supplying of irrigation water to the cultivable land.
Through open discussion with beneficiaries/stakeholders of the project and concerned
field officials, it was found that the height of Pekua Rubber Dam was ok in respect to
supply of irrigation water to the cultivable land through maintaining desired water level
in Bhola Khal and other branches of the khal. This satisfies the design parameters
consideration for planning concept of the project. Because, there raised no problems
regarding supplying irrigation water to the cultivable land. So, it can be assumed that
the design dam height with respect to the water retention level (design parameter) is ok
(Design Report, 2003)
54
6.2.4 Thickness of Rubber Sheet and Geometrical Shape of Water
filled Rubber Dam
Various design parameters for determining the thickness and shape of the Pekua
Rubber Dam bags were used through the use of the formulae given in the chapter-3
(Para 3.2.7, the design principle). Radial strength of dam bags was calculated as 560
Kn./m of rubber dam. From this radial strength the design thickness was calculated as
12mm.The shape of dam bags after inflation was divided into four parts as mentioned
in the figure 3.1 in chater-3. Length of curved segment of dam surface in the upstream
direction S1=6.41m, length of curved segment of dam surface in the downstream
direction S=6.80m, length of ground touching segment in the upstream direction N and
length of ground touching segment in the downstream direction X0 were determined
considering the design parameters. Effective Circumference (excluding the distance
between two anchorage) of the dam body was decided as L0 = S1+S=13.21m.
Effective length of bottom pad was calculated as D= N+X0=6.10m (Design Report,
2003). Calculations of N, S1,S & X0 were taken from the equations mentioned in the
formulae in the chapter-3 (Para 3.2.7, the design principle).
From these equations the above parameters were calculated as follows:
D= 6.10m, H1= 4.00m (dam height), H0= 5.80m, Radial Strength = 76 Kn/m with FS
5~ 8 it was designed T(warf) = 560 Kn/m, • = 1.45 was considered. S=6.80 m S1=
6.41m (Design Report, 2003).
Here design parameters like, water retention level which again related to dam height
was considered for calculating the rubber thickness of rubber sheet.
Through open discussion, on functioning of the rubber bags, with the concerned field
officials of BWDB and the beneficiaries of the project, it was found that till to date
there did not happen any puncture of the rubber bag body. It was also learnt from the
concerned field officials that during commissioning of the dam, the geometrical shape
dimensions of the bags were measured and found ok. These assessment results of the
parameters reveal that the design parameter as selected by the design engineers in
respect to determine the thickness of rubber dam body as well as its geometrical shape
was appropriate. So, it was ok with respect to technical aspect of the design.
55
6.2.5 Site Selection of the Pekua Rubber Dam
In designing and construction of the Pekua Rubber Dam, proper selection of the
location/site was considered with due importance. This was done in consideration of
the points mentioned in the feasibility study report of the dam. For example, the site
should be such that the dam at that location can command the maximum cultivated
land. The beneficiaries should be consulted and the site of proposed dam will provide
them the desired benefits of irrigation of the adjacent lands. The site should be easily
approached by road. The channel should be straight reach and stable channel. Land
should be uniform sloping for optimum utilization of scarce water to derive maximum
benefits. Canal network should be such that water can flow by gravity. When gravity is
not possible, water will be withdrawn by LLP. Lastly, considering all the parameters
and through open discussion with all beneficiaries residing in the project/dam the site
was selected at ch. 53.881 km on Bhola Khal of Pekua, location of which could be seen
in figure 4.2 in Chapter 4. Through open discussion with various levels of beneficiary
groups and NGO and GO officials and staff it was clear that until now no problem with
respect to supplying of irrigation water to the whole project created. So the selection of
site could be termed as proper and suitable for achieving the project objectives. In other
words the selection of site was appropriate in terms of the parameters considered during
selection as well as from the technical background.
6.2.6 Floor Length of Pekua Rubber Dam
The total floor length was computed based on Exit Gradient of 1/7 for seepage head
equal to the difference of upstream retention level and design tide level or difference of
down stream maximum tide level and upstream drawdown level whichever is higher
during irrigation season. By using Khosla’s theory
Where
Where H = Design head.=4.50m (dam height+ spillover) D = Length of cut-off wall.
b= floor length. Depth of cut-off wall was selected as 8.00m at D/S and 4.00m at U/S.
From this formulae and considering some additional factors of safety the total floor
λπ1
.d
HGE =
.2
11 2αλ
++=
d
b=α
56
length was computed as 45.00m (Design Report, 2003). Here design parameter like
design head, which comes from water retention level was considered for determining
the floor length.
There was no reported sign of seepage under the foundation of the dam during
maximum head difference. This head difference was created in the time of rubber dam
commissioning (U/S fully ponded and D/S was remained dry). This maximum head
difference was the critical condition of WRS. In this situation as there was no sign of
seepage under the foundation it may be concluded that the design floor length was ok
with respect to design computation and in consideration of the design parameters.
6.2.7 Foundation Design
In the soil test as well as during foundation work of the dam the soil below the
foundation of the rubber dam was found very weak. From bore log it was explored that
up to 37 feet from the existing bed level of the channel, the N value was 0 to 1. Type of
soil was clay traced silt (Soil Investigation Report, 2002). Due to the weak soil the
foundation treatment was needed for construction of the dam. Acute problems during
construction of foundation were faced by the site and construction engineers. Soil was
found very weak to bear the foundation of the dam. To avoid seepage flow due to high
head difference under the foundation no RCC pile was used (Design Report, 2003) in
foundation construction. This was done based on an experience of a hydraulic structure,
done by BWDB, located at Borguna and Patuakhali, where RCC pile was used under
the drainage sluice and after some years of construction, seepage flow was seen below
the foundation of this sluice. As a result of this problem presently the sluices are not
working at all and are standing above the RCC pile. From this experience and
considering a big head difference, the concerned design engineers decided to use sand
pile instead of RCC pile under the foundation (Design Report, 2003). Sand pile of this
site also faced some problems. As the soil was clay and the site was on the river bed,
the rate of pore water release was slow. After sand piling, soil test was done and
foundation soil was found improving (SPT value range 4-10). Under this situation the
allowable bearing capacity of soil under the foundation was computed by using
empirical bearing capacity equation with one inch tolerable settlement (Terzaghi and
Peck, 1948).
57
Terzaghi & Peck Equation For 25 mm settlement
Where qa
Figure 6.1: Driving of sand pile of Pekua Rubber Dam (Design Catalogue,
BWDB, 2003)
= Allowable bearing capacity of soil below foundation of dam body.
N = SPT value (From Soil Investigation Report, 2002)
The construction of dam was completed in June-2004. Till now no sign of seepage
under the foundation or any crack on foundation was reported by the concerned field
office. So, the foundation design could be considered as ok with respect to the design
parameter considerations. Some procedures of sand piling are shown as steel pictures in
figures 6.1 and 6.2.
( )
+
−=B
BNqa 2
13720
58
Figure 6.2: Driving of sand pile of Pekua Rubber Dam (Design Catalogue,
BWDB, 2003)
6.2.8 Assessment of Construction Problems and its Mitigation
The construction process including the period of implementation, problems faced
during construction and the ways of mitigation have been presented in the following
paragraphs.
The construction work of the Rubber Dam was started during November - 2003 and
completed in June - 2004. As reported by the field office, at the beginning of the
construction work, two earthen cross dams were built on both the U/S and D/S of the
dam. During construction, the U/S cross dam was damaged due to flash flood. First
time the cross dams were built near to the main structure. The seepage water was
continued to flow from the cross dams. Second time the cross dams were built 50
meters away from the dam structure site. These dams were successfully implemented.
Some acute problems were faced during the foundation works. As the dam had to
construct on the existing river bed, a huge amount of water had to be bailed out. The
bed materials were very soft clay with traced silt. The SPT value was 0 to 1. The
foundation treatment was needed. As mentioned in para 6.2.7 RCC pile for hydraulic
structure was not good and faced seepage problems, it was decided by the design
engineers to provide sand pile instead of RCC pile for the foundation work (Design
Report, 2003). Sand piling also faced some problems. As the soil was clay, and the site
59
was on the existing river bed, the rate of pore water release was slow. Result of the first
time sand piling was not satisfactory. Second time modified design of sand pile was
done. According to the modified design sand pile was executed with the supervision of
expert design engineers. After execution of sand piling work, foundation soil was found
improving and the SPT value range finally reached at 6 to 8. This SPT value was
satisfactory for this raft foundation.
There are also some other limitations in case of construction of a rubber dams. The
construction of rubber dam is not so simple as it requires some special supervision by
the foreign experts during fitting and fixing of the rubber sheet and commissioning of
the rubber dam. Moreover, the rubber sheets are not manufactured in Bangladesh and
need to import from foreign countries, whereas the construction materials of water
retention structure (regulator, barrage) are available in the local market in our country.
However, these construction problems could easily be minimized through a time bound
work plan as was done for Pekua Rubber Dam Project. Besides, the need of foreign
experts could be supplemented by developing expert people in the country.
Despite some construction problems, rubber dam construction has some positive
aspects in terms of construction time and cost. For example the actual construction time
of the Pekua Rubber Dam was from November-03 to June-04 i.e. only eight month was
needed for construction of this structure. But, if a barrage was constructed in that place
instead of the rubber dam, this short time (eight months) would never allow
constructing a barrage. It would have taken at least two years to complete the
construction. The reason for lesser time for construction of a rubber dam is that there is
no need of construction of any RCC super structure as well as additional structure like
piers, installation of steel angles and channel in piers and bed, vertical lift gate
assembly of the gated water retention structures which are time consuming and
laborious. In the rubber dam only RCC work in foundation is needed, which was done
in a month. In respect to costing, the construction cost of a rubber dam is much lesser
than a conventional RCC barrage. A comparison of the cost between a rubber dam and
a RCC barrage at Pekua was made in the feasibility study report of Matamuhuri
Irrigation Project, Vol-2, page 11-20) by BWDB through a consulting firm EPC
(BWDB, EPC.1996). In this comparison, the costing of rubber dam was found
60
Tk.6,21,40,830/ and the costing of RCC barrage was Tk.11,35,45,000/, almost double
of a rubber dam cost.
From the above findings and analysis it is clear that despite some constructional
problems, rubber dam is less costly and time saving irrigation structure than traditional
irrigation structure. This finding also found supported by the discussions included in
literature review and in technical aspects of rubber dam. For this rubber dam is being
implemented in many countries (China, Korea, Canada, etc.) by replacing barrage and
other traditional kind of irrigation structures for irrigating agricultural land. So,
Bangladesh can effectively make use of rubber dam as a cost effective and short term
technology for solution of its irrigation problem, particularly in the hilly regions.
6.2.9 Fitting Fixing of Rubber Sheet
Fitting and fixing of rubber sheets is not as simple as like as other construction work of
the rubber dam project. At first, the anchoring slot is kept open for positioning, fitting
and fixing of the anchor bolts with dowel bar of the slot. Then lower anchoring plate is
fixed with the help of anchor bolt and the anchor bolt is fixed with dowel bar with
welding work. The design level of lower plate is done with the help of level machine
and this level is adjusted with the help of bottom nut of anchor bolt. Then second stage
concrete was done up to bottom level of lower plate. The thickness of lower plate of
Pekua Rubber Dam was designed as16mm. The thickness of upper plate was designed
as 25mm. The details of fitting and fixing rubber sheet are shown in figure 6.3 (Design
Report, 2003). The fitting fixing was done with the help of foreign experts. The works
were done very carefully with maintaining proper alignment of the anchor bolt, because
any deviation of anchor bolts can create a problem for fitting anchor plate. This work
was done successfully by local experts with the help of foreign expert. During
commissioning of the Pekua Rubber Dam, a sign of water leakage was noticed. Then
the rubber dam was deflated and the top nut of the bolt was tightened. When the dam
was inflated again, no water leakage was noticed. It was learn from field officials that
after commissioning of the rubber dam, no problem related to fitting & fixing of the
dam was noticed. So this procedure of work could be considered as ok with respect to
technical ground.
61
600
63
98 400 98400
DETAILS OF 25mm DIA ANCHOR BOLT
996
TYPE 'D' PLATE (UPPER & LOWER PLATE)
325
6320
0
200
D10 MS plain bar welded to upper plate
D10 MS plain bar welded to lower plate
200
SECTION A-A
200
ANCHOR BOLTMaterial : AISCA 325
325
UPPER PLATE(TH=25mm)
POLYTHINE CAP ON NUT-BOLT AFTER APPLYING GREESE
200
30
100
RUBBER BAG (TH=12mm)
FILLER RUBBER(TH=10mm)
81
BOTTOM PLATE(TH=16mm)
ANCHOR BOLT-25mm Dia
DOUBLE NUT
LEAN SAND CEMENT(1:6) MORTAR
Figure 6.3: Details of anchoring plate and anchoring bolt for fitting & fixing
rubber sheet for rubber dam (Design Catalogue, BWDB, 2003)
62
6.2.11 Fixation of Level of Over Flow Pipe and Procedure of
Commissioning Work
The fixation of level of over flow pipe was done through trial and error method. First
from the design calculation, the design level was fixed. With this level water was filled
in the bags. The level of height of bags was measured. If desired height was not found,
then the level of over flow pipe was adjusted until getting the desired level of the dam
body. After getting the desired height of the dam body, the over flow pipe was
permanently fixed. This work was done at dry condition as well as in water retained
position (Commissioning of the pipe is shown in the Figure 6.4). This was successfully
done as per field report. Through the open discussion with the beneficiaries/
stakeholders of the project and also with concerned filed officials of BWDB, there
found no problem for irrigation water supply to the cultivable land. As the water supply
by this dam is directly related with its height and the dam height is controlled by this
over flow pipe, so from the findings it is concluded that the level fixed for over flow
pipe and the procedure of fixation were done properly from technical viewpoint.
Figure 6.4: Commissioning of Pekua Rubber Dam (BWDB, 2003)
63
6.3 Assessment Result of Operation and Maintenance of
Pekua Rubber Dam
The state of operation and maintenance of the Pekua Rubber Dam was assessed on the
basis of various aspects related to their operation, maintenance and management. The
assessment findings have been furnished in the following paragraphs under three sub-
headings, namely (1) Institutional aspects of operation maintenance of Pekua Rubber
Dam (6.3.2), (2) Operation and management system of Pekua Rubber dam (6.3.3), and
(3) Stakeholders’ Participation in the management of Pekua Rubber Dam (6.3.4). In
addition, a brief theoretical and functional description (6.3.1) of the operation system of
Pekua Rubber dam has been attached at the beginning of the following discussions.
6.3.1 Operation System of Pekua Rubber Dam
Operation of a rubber dam means inflating and deflating of the rubber bags. Inflating of
rubber bags means, increase the height of rubber dam body by filling the rubber bags
with water or air for water retention during irrigation season. Deflating the rubber dam
means decrease in the dam height by taking out air/water from rubber dam bags. For
operation of the Pekua Rubber Dam, a centrifugal pump has been installed for both
inflation and deflation of the rubber bags with water. This pump has been installed in
the pump house built near the rubber dam site. Water is drawn from the channel bed
through the intake pipe lines from water storage. The inlet and outlet PVC pipes and
other accessories which are used in inflating and deflating the rubber dam are shown in
Figure 3.9
The inflating & deflating position of the Pekua Rubber Dam have been shown in
Figures 6.5 & 6.6. Figure 6.5 also shows a water retained condition of the dam for
irrigation in the catchments area of Bhola Khal, on which the dam is located. Deflating
is also required partly to release major flash floods and to remove inundation in the
depression areas in the upstream of the dam during irrigation period. Deflating is
required fully during the monsoon when the empty dam bags lie flat on the foundation
level to allow free flood flow and boat communication when there is no more necessity
of water retention for irrigation purpose. Outlet valves are opened to deflate the rubber
dam when water comes out of the rubber bag automatically by gravity. When water
does not come out of rubber bag by gravity system, then pump is to be operated for
64
outing the water from bag by manipulating the valves (Fig. 3.9). The pump operator
operates this pump when necessity. The rubber dam is inflated in the month of
November to close Bhola Khal for water retention and deflated to bed level to open the
channels for navigation in late May every year.
Figure 6.5: Inflated Pekua Rubber Dam for retention of U/S water (BWDB, 2003).
65
Figure 6.6: Deflated rubber dam (BWDB, 2003)
6.3.2 Institutional Aspect of Operation and Management of Pekua
Rubber Dam Project
The Pekua Rubber Dam has been constructed by Bangladesh Water Development
Board. This Project is under the jurisdiction of Bhadarkhali Water Development Sub-
Division under Cox’s Bazar Water Development (WD) Division. Cox’s Bazar WD
Division is under the jurisdiction of Chittagong Operation and Maintenance Circle. One
Superintending Engineer (SE) is posted in this circle. Again this circle is under the
jurisdiction of Chief Engineer, South Eastern Zone, Chittagong. The Chief Engineer is
under Additional Director general (ADG), O & M-1 and the ADG is under the Director
General (DG) of BWDB. There are three Section Officer’s Office under the
Bhadakhali Sub-Division. One of the Section Offices of this sub-division is located at
Pekua Up-Zilla. The Rubber Dam is under the jurisdiction of this office. The primary
responsibility of O & M of this dam is lying upon this Section Office. All activities
concerned to the operation and maintenance of the dam are done through the concerned
Division Office. The span of organizational chart of BWDB related to the Pekua
Rubber Dam is given below as Fig. 6.7.
66
Figure 6.7: The organizational chart of BWDB for operation and maintenance of
Pekua Rubber Dam (BWDB)
There is a pump operator under Pekua SO office to operate the pump machine of the
dam. The pump operator is not a regular employee of BWDB. In the standard set up of
BWDB there is provision of some permanent posts for pump operator. Despite this
provision, no permanent pump operator was appointed for running the pump machine
of the dam. The practice as found is that the concerned BWDB officials hired pump
operator(s) from the local area of the project on master role basis. He received some
training in respect to the operation of the pump machine of the rubber dam. Thus the
dam is being operated by temporarily appointed operator(s). As quoted by the field
officials, this irregular system of operator appointment creates some problems. As the
pump operator is not a regular employee, he may escapes or remains absent for some
days during the irrigation period. Then a crisis may occur in absence of a permanent
pump operator. A sense of job insecurity also prevails in him. This creates mental in
him, which may create some other irresponsibility. So, there is a need to resolve this
situation with required departmental initiative.
All operational and maintenance activities of the Pekua Rubber Dam are performed by
the concerned SO office with maintaining proper official communication and
coordination with the Divisional Office of Operation and Maintenance. Any problem or
dysfunctionality of the rubber dam during operation and maintenance as well as
Cox’s Bazar WD Division
HQ Sub-Division Badarkhali Sub-Division Kutubdia Sub-Division
HQ SO office Chiringa SO office Pekua SO office
Pekua Rubber Dam Project
67
resolving the problems lie on the SO and Divisional Office. But as found through the
discussion with the Divisional Engineer and SO, no mentionable problem created
regarding operation and maintenance of the dam, which means the institutional
arrangement of BWDB was supportive to proper functioning of the rubber dam. But
one finding, significant to mention, came out of the discussion was that in absence of
appointment of any full time pump operator, the operation of the pump might suffer in
the long run. It may affect both the internal and external efficiency of the functioning of
the dam.
6.3.3 Operation and Management System of Pekua Rubber Dam
The Pekua Rubber dam project has no local level operation and management
committees like Block Management Committee (BMC), Operation Management
Committee (OMC) and Central Management Committee (CMC). Operation of the
project is done in coordination between the BWDB local officials and the local
administrative unit [Thana Nirbahi Officer (TNO)]. When the stakeholders are in need
of water for irrigating their land during dry season, they make contact with the local
TNO and concerned BWDB officials for operation of the rubber dam. Then the TNO
makes request to the BWDB field officials to operate the dam. As per the request from
the TNO the concerned BWDB officials takes initiative to activate the pump.
Thereafter the stakeholders start to irrigate their farmlands through the khals and
channels. For this irrigation purpose they do not need to pay any charge or fees. The
Rubber Dam is kept in inflated position at starting time of irrigation and is deflated as
per requirement of the stakeholders during monsoon period. The main purpose of this
dam is to provide irrigation facilities to boro crops during dry season (Nov-May)
through retention of sweet water in the upland river system (Bhola Khal) and
prevention of saline water intrusion from downstream.
During the functioning of the Pekua Rubber Dam Project, as was reported, a number of
aspects related to its operation and maintenance occurred. They were: damage and
repair of rubber dam body, disorder and repair of pump, silt deposition over dam body,
over U/S and D/S stilling basin, clogging of foot valve, etc. How were the magnitudes
of these problems and what measures were needed to be taken to mitigate the problems
68
were assessed also as part of this evaluative study. Findings from this assessment are
presented in the following subsections.
6.3.3.1 Damage and Repair of Rubber Dam Body
Damage of any material is a common phenomenon. It can happen any time from any
reasons over time and use. The Pekua Rubber Dam has possibility of damage of rubber
bags from many reasons such as trespassing of the local people over the rubber dam
area, walking over the rubber bag and throwing of brickbats on the rubber bag. There
also have the tendency of cuts and leakage in the rubber bag. As the Pekua Rubber
Dam has been declared as a Key Point Installation (KPI), some precautionary measures
have been taken by BWDB. For examples, seven (7) guards have been appointed by
BWDB on full time basis to prevent local people from entering into the rubber dam site
to avert any such man made damage. Their duty is maintained as roaster duty. To
avoid free passing over the dam body, which may create possible damage of rubber
bag, a foot bridge has been built over the upstream stilling basin so that people can
easily cross the Pekua Khal without creating any harm to the dam. The bridge, in
addition to creating a safety measure to the dam, is playing a vital role in local people’s
physical communication process. There is another possibility of damage of rubber bag
by floating wood, bamboo raft, debris and other type of floating materials which may
be responsible for puncturing the deflated rubber dam. This type of damage can lead to
malfunctioning of the dam and decrease the resistance of rubber layer. To avoid such
damage, a precautionary measure was included in the design of Pekua Rubber Dam
which is shown in Fig. 6.8. In this figure it is seen that a special type of cushion
materials has been used inside the bag so that when debris pass over the dam body it
shocks the pressure of the debris or any other materials like this, which may cause
damage of the dam body. Through open discussion with stakeholders of the project and
concerned filed office it was found that till to date no puncture or crack on the rubber
bag was noticed. It is possibly due to number of precautionary measures, mentioned
above, as taken by the concerned authority during, implementation and post
implementation period of the dam. Despite this precautionary measures if any puncture
or crack is identified that can be easily repair/solve by BWDB through applying a
special type of gum and spices of 12mm thick rubber sheet as like as repairing of
puncture of tyre and tube of motor vehicle.
69
Anchor bolt
CUSHION MATERIALS
RUBBER COATED FABRIC
RUBBER BASE COVER SHEET
Figure 6.8: Special cushion system of rubber dam (Design Catalogue, BWDB,
2003)
6.3.3.2 Disorder and Repair of Pump
Disorder of pump machine involves electro-mechanical trouble of pump machines.
Through discussion with concerned field officials it was learnt that a little disorder of
pump machineries were detected in the Pekua Rubber Dam sites. The pump operators
were reported to be capable of doing the minor repair works of the pump machines. In
the case of the major repair, the local technicians were called for and the said repair
works were accomplished at the rubber dam site with locally available materials. There
was no need of sending the pump machines to the workshops for any significant repair
work. From this experience, it could be said that disorder of the machine is easily
repairable with local technicians and without any major cost and manpower
involvement. One of the repairing processes of the pump is shown Fig. 6.9.
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Figure 6.9: Repair and cleaning work of pump and its accessories (Field office,
BWDB)
6.3.3.3 Deposition of Silt over Rubber Bags and over U/S and D/S
Stilling Basin
Through open discussion with field office it was learnt that deposition of silt of about
200mm-300mm depth was detected over the deflated dam bag as well as at upper
stream (U/S) and down stream (D/S) of stilling basin of the dam. This silt was removed
from the top surface of the bag by using water injector. A huge amount of silt was also
deposited in the water storage well. As quoted by the field office 200mm~300mm silt
was deposited every year on the stilling basin. So, before inflating the rubber dam these
silt were to remove every year by the concerned filed office of BWDB. Another major
problem created every year was clogging of inlet and out let pipe fitted on U/S and D/S
stilling basin of the dam by silt deposition. These were also needed to be removed
every year for opening the mouth of inlet and outlet pipe. From the above findings it is
clear that clogging due to silt deposition is a big operation and maintenance problem of
the Pekua Rubber Dam site which happens every year. Though this problem is solved
by BWDB local office every year by removing the silt before inflating the dam body
however recurrent siltation of every year and its removal is troublesome. Therefore,
71
there is a need of exploring an alternative/modified design or mechanism of inlet and
outlet pipe so that the problems mentioned above could be removed or reduced.
6.3.3.4 Clogging of Foot Valve
The field officials and staff reported that clogging of foot valve of the intake pipe of the
dam by silt was sometimes detected in Pekua Rubber Dam. When it happened the foot
valve was cleaned by the pump operator with the help of skilled laborers engaged by
BWDB field office before raising the rubber bag every year. Every year a big amount
of silt also was deposited in the water storage well. So, before inflating the rubber dam,
this huge amount of silt was to remove with the help of ordinary laborers under
departmental arrangement. Before pump operation, every valve of the pump house was
cleaned by departmental people assigned for operation and maintenance of the pump. It
is clear from the above findings that despite recurrent clogging of foot valve and
removal of it was not so difficult and could easily be done under departmental initiative
with the help of local laborers and departmental peoples.
6.3.3.5 Safety Device of Rubber Dam and Bed Level of Rubber Dam
As found from the discussion with the people engaged in operation of the dam, there is
no safety device for automatically inflating or deflating the rubber dam body. In case of
flash flood, emergency deflating of the bag requires for easy flood pass over the dam.
In this case safety device automatically works, in absence of pump operator, to control
the situation. So it was suggested by the field people to provide safety device for auto
inflation and deflation of the Pekua Rubber Dam.
Another significant finding was that the bed level of the pump house is as the same
level of the bed of rubber dam. It is too deep to work. So, costing of the pump house
was very high with respect to the overall project. This costing can be reduced by
introducing a submergible pump instead of centrifugal pump.
6.3.3.6 Problem in Boat Communication
Through the open discussion with the concerned field office of BWDB and local
people, it was learned that in the Pekua Rubber Dam Project boat communication
remains stopped over the inflated rubber dam during the irrigation season (November-
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May) every year. During irrigation period the inflated dam works as a barrier to boat
movement from one side to another side of the dam. So, boatmen have to station their
boats on either side of the dam from where boats ply outwards. Boats are only allowed
to pass over the lowered position of rubber bag if enough water depth, not less than 1.5
meter, is attained. Boat movement activity starts only when irrigation period is ended
and monsoon starts, when the depth of water is sufficient. In this respect, it could be
said that the dam has little negative impact on water communication system. However,
considering the overall benefits of the dam on people’s life, economy, agriculture,
environment, etc. the stakeholders were found to exhibit a positive perception with
regard to usability of the dam. However, any solution to the problem will definitely
enhance the efficiency of the dam.
6.3.4 Stakeholders’ Participation in the Management of Pekua
Rubber Dam
One of the aspects of evaluating the performance of the Pekua Rubber Dam was
assessing the stakeholders’ participation in the operation, management and maintenance
of the dam. The information collected in this regard show that there was satisfactory
participation of the stakeholders’ in the planning, design and construction of the project
(BWDB & EPC, 1996). However, they were found lack of formal participation in
operation, maintenance and management of the rubber dam. Neither BWDB nor the
local administration took any initiative to involve them formally in the management
process, which could easily be done through forming different
management/implementation committees with practical participation of the
stakeholders.
The users of the dam have some potential role to play in connection with the
management and implementation of the dam facilities, such as operation and
maintenance of intake channel and other distributaries channels system, delivery of
irrigation water by LLP, delivery of irrigation water as per roster, preparation of the list
of the irrigated area, maintain the inlet/outlet gate operation during the irrigation period,
maintaining the field drains for proper irrigation, resolving the conflicts among the
water users, etc. The findings show that the users of the dam were not involved
institutionally in these activities.
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As mentioned before, when the inflating time comes the stakeholders contact with the
TNO for inflating the rubber dam. Then the TNO requests the concerned BWDB
officials for taking initiative. Similarly, after the irrigation period, the stakeholders
make request for deflating the rubber dam for free flood flow and navigation of the
Khal through TNO. The desired water level is maintained through open discussion with
stakeholders. Throughout the process different problems arise. For example, during the
irrigation time the users sometimes become involved in disputes over the distribution of
water for irrigation. Sometimes the beneficiaries show irresponsibility in maintaining
the channels and controlling the gates. After inflation of the dam different stakeholders
make different opinions in regard to maintaining the water level. This makes conflict
among the stakeholders. The stakeholders of upstream want the water level at their land
elevation. This higher elevation of water level may cause inundation of lands owned by
the stake holders residing near rubber dam. Therefore, the stakeholders residing near
rubber dam want the water level at their land level, which make problem of supplying
water to U/S area. These problems need to be solved properly for efficient
management of the dam without which overall impact of the project may suffer. It also
might affect fulfillment of the project goals and activities in terms of proper and desired
usability of the irrigation facilities, agricultural productivity, environment, fisheries,
etc. One of the possible reasons for these shortcomings may be absence of different
management committees with the participation of the stakeholders and institutionalized
responsibility of them in settling the issues and problems.
But, active involvement of the beneficiaries/stakeholders in running and management
of the projects is very much important. It can help to develop a mentality of shouldering
various responsibilities for running the project well and thereby create a sense of
oneness in them with the project. Considering the issue importantly, the Ganga
Kapotakho (G.K.) Project and the Pabna Irrigation and Rural Development Project of
BWDB and the Eidgah and Bakkhali Rubber Dam Projects of LGED formed different
implementation and maintenance committees of the stakeholder. For example, Block
Management Committee (BMC), Operation Management Committee (OMC) and
Central Management Committee (CMC) have been formed in the LGED projects. In
Pekua Rubber Dam Project formation of these kinds of implementation committees is
necessary for its proper and democratic management. Moreover, it is a recognized fact
that villagers in Bangladesh have extensive knowledge of the behavior of water on the
74
flood plane and its use for agriculture. Indeed they have a vested interest in
understanding the problems and the benefits of that water holds for them since their
lives depend upon this knowledge. So it is very much necessary to formally involve
them in management process of the facilities of Pekua Rubber Dam through forming
different management bodies composed of the stakeholders.
Coordination between the parent department with local organizations, who are directly
or indirectly related with the project benefits and their use, is another important aspect
to achieve long term sustainability of a project benefits through its good management
and maintenance. This was found absence in case of BWDB in Pekua Rubber Dam
project. There was lack of coordination between BWDB and Water User Group,
Agriculture Extension Officer, Fishery Officers, NGOs, etc., who were responsible for
local irrigation management, agriculture, fisheries, environmental management, etc.
From the above discussion it is clear that there was absence of formal participation of
the stakeholders in management of the project. Also there was lack of coordination
between BWDB and other local organizations. As a result, the local office of BWDB
failed to develop required responsibility and skills of the local people in managing the
rubber dam project well. So, there is a need to different local level management
committee(s) for running the Pekua Rubber Dam Project as like as the Bakkhali &
Idgha Rubber Dam Projects of LGED where the stakeholders have formed different
implementation committees for managing the project and its benefits (Raquib, 1999)
and build up coordination with different organizations.
6.4 Impact of the Pekua Rubber Dam Project
Performance evaluation of the Pekua Rubber Dam project was also done based on its
impact on socio-economic status of the local people, agriculture and environment.
Socio-economic impact was analyzed through some indicators, namely annual income,
range of annual income increase, poverty alleviation and employment. The impact on
agriculture was evaluated on the basis of increase of agricultural production. The
environmental impact was evaluated by measuring the dam’s impact on draught,
ground water table, water logging and fisheries. Data were collected through
administering a questionnaire on a group of 50 respondents, who were beneficiaries of
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the rubber dam project. The questionnaires were administered through field visit of the
researcher with the help of BWDB officials and local people. Besides, data were also
collected from some other sources like NGO and GO officials working in the research
locality through open discussion. The findings are presented in the following
paragraphs under three major headings, namely impact on socio-economic status
(6.4.1), impact on agriculture (6.4.2) and impact on environment (6.4.3).
6.4.1 Impact on Socio-economic Status
Impact of the dam on socio-economic status was assessed based on annual income
increase of the stakeholders and the range of increase as well as considering the
changes in their poverty and employment levels.
Annual Income Increase
The impact of Pekua Rubber Dam in terms of annual income increase of the
stakeholders is presented in the following table.
Table 6.1: Impact on Annual Income
Income increased Income did not increase
41
(82%)
09
(18%)
Quite majority of the respondents (82%) opined that their yearly income increased after
implementation of the Pekua Rubber Dam Project. Less than one fifth reported no
increase in their income level. Respondents (41), who answered positively, were again
asked if their income increased then to what extent it had increased. The data collected
in this regard are presented in Table 6.2.
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Table -6.2 Amount of Annual Income Increase due to Construction of
Pekua Rubber Dam Project
Amount of annual income increase
(In Taka)
No. of stakeholders Percentage
01 – 10,000 02 05
10,001 – 20,000 06 15
20,001 – 30,000 12 29
30,001 – 40,000 13 32
40,001 – 50,000 08 19
Total 41 100
The data in the above table show varied levels of income increase of the beneficiaries.
Majority of the respondents (32%) mentioned that their yearly income increased
between Tk. 30,001 - 40,000. Almost similar percentage (29%) of the respondents
reported an increase of Tk.20,001 - 30,000. A good number of the respondents (19%)
reported the highest level of increase in their yearly income. Combining these three
groups, it is seen that absolute majority (29%+32%+19%=80%) of the respondents had
significant increase in their income level. Only 20% reported of yearly income less than
Tk. 20,000. Thus, the data in Tables 6.1 and 6.2 clearly indicates significant
improvement in economic status of the Pekua Rubber Dam stakeholders due to
construction of the project.
Impact on Poverty Alleviation
The findings on impact on poverty alleviation are presented in Table 6.3 of next page.
Out of the 50 Respondents, 56% agreed that due to the rubber dam project poverty level
of the locality decreased significantly while 24% mentioned that it remained the same.
The discussion made with the stakeholders revealed that due to irrigation facilities
created under the rubber dam project significant amount of non-cultivable land has
Table 6.3: Poverty alleviation
Poverty decreased
Poverty remained same
38
(76%)
12
(24%)
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transformed into cultivable land due to regular irrigation facilities. Consequently, the
amount of agricultural land of the stakeholders has increased, which resulted in
increased total agricultural production of the area. Because of improvement in soil
condition more plants and vegetables are growing there. Moreover, due to the improved
water facilities fish production has increased than before. All these are helping to
improve the poverty level of the people. So, their economic condition has improved.
Impact on Employment
To assess the impact of socio-economic condition due to the construction of the rubber
dam project the respondents were asked whether their employment increased or
decreased as a result of the construction of the rubber dam, findings of that are
presented in Table 6.4.
Table 6.4: Impact on Employment due to Rubber Dam Project
Employment opportunity increased Employment opportunity did not increase
36
(72%)
14
(28%)
According to the data in Table 6.4, out of the 50 respondents, 36 (72%) opined
positively i.e. employment opportunity increased and 28% opined negatively. From the
open discussion the overall scenarios stands that due to the rubber dam project
employment rate increased through increased agriculture land and production, fish
production, business, etc.
The stakeholders further mentioned that development of the above mentioned aspects
(income, poverty and employment opportunity) helped to enhance socio-economic
condition by reducing poverty, creating more employment opportunity and increasing
income level. All these are helping their family in terms of schooling opportunity of
their children, better food, better clothing, better housing facilities, etc. In other words,
the rubber dam project is helping to establish a better quality of socio-economic life for
the stakeholders of the Pekua Rubber Dam project.
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6.4.2 Impact on Agriculture
To assess the impact of the rubber dam on local agriculture, the respondents were asked
whether their agricultural production increased as a result of the construction of the
rubber dam, if increased then to what extent it increased and how was the amount of
increase of different agricultural products. Findings of these inquiries are presented in
Tables 6.5, 6.6 and 6.7.
According to the data in Table 6.5, 94% of the respondents opined in favor of increased
agricultural productions. Only 6% said that their agricultural production did not
increase.
Table 6.5: Impact of Agricultural Production
Production increased Production did not increase
47
(94%)
3
(6%)
The responses regarding the investigation - “if increase, how much” the responses are
presented in the following table.
Table 6.6: Amount of annual increase in agricultural production
Amount of annual agricultural
production increased
(In mound per acre)
No. of Stakeholders Percentage
5- 10 25 50
10- 15 15 30
15-20 10 20
The data reveal that for 50% of the respondents the amount of increase was 5 to 10
mound per acre. For a significant portion (30%) the production raised for 10 to 15
mounds per acre, while it was 15 to 20 mounds for 20 percent of the respondents. The
findings mentioned above clearly indicate a very positive impact of the rubber dam on
the agricultural production of the catchments areas of the rubber dam. It is very much
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obvious from general idea and proved in research that the higher the facility of
irrigation the higher the agricultural production is. So, people always employ various
ways and means to irrigate their crop land as much as possible and if they are unable to
provide it they suffer from huge loss in terms of quantity of production. The rubber
dam has made the life of the local farmer easy in terms of irrigation facilities and
everybody is getting this facilities and being benefited from the rubber dam.
Table 6.7: Amount of annual crop production before and after implementation of
the rubber dam project
Types of crops Amount production after rubber dam project (Mound per acre)
Amount of production before rubber dam project (Mound per acre)
Paddy 60 45
Vegetable 16 3
Salt 320 420
Pan 12 6
From Table 6.7 it is seen that before implementation of the rubber dam project, the
amount of production of paddy, vegetable and pan were lesser and after implementation
of the rubber dam the crop production increased significantly. But the result of salt
production was reverse. As agriculture land increased due to the rubber dam project,
the land for salt production naturally decreased. So, after the rubber dam project salt
production decreased.
6.4.3 Impact of Environment
For assessing the impact of the rubber dam on environment, its impact on draught,
ground water table, water logging and fish production were considered. Data in these
regards were collected through open discussion with relevant people, findings of which
are presented in the following paragraphs.
6.4.3.1 Impact on Draught
As reported by the respondents, a mild draught used to prevail in the locality during dry
season before construction of the rubber dam project. This has now been removed and
the weather has become soothing. The reason for this, as mentioned by them, is that due
80
to the rubber dam sweet water retains in the upstream of the dam and is distributed over
the land by means of gravity or LLP. As a result green crops grow in the area and no
draught can occur in dry period.
6.4.3.2 Impact on Ground Water Table
The local people informed that the level of ground water table was low before the
construction of the rubber dam project, but the level has become high than before the
project implementation. It is also seen from the soil boring test that higher water table
remains there than the post project condition. Before the project, the non cultivable
plants and vegetation like bamboo, jack fruit, mango trees and other trees in both
upstream and downstream of the project turned into yellow due to lack of optimum soil
moisture content during dry period. After the rubber dam project, the plants and
vegetation remain green due to supply of optimum soil moisture content during dry
period. This is due to the rise of ground water table as result of constant water retention
in the upstream of the rubber dam project. It is also noticed that after the project,
varieties of plants like Mehagani, Rain tree, Jack trees are being cultivated. The
adjoining area of the project has become saline free due to prevention of saline
intrusion in to the project area by building rubber dam project in dry period. Uncultured
plants and vegetation are getting soil moisture properly due to rise of water table in the
project area and have become green. These findings reveal that there is positive impact
on environment with respect of ground water table due to the construction of the Pekua
Rubber Dam. It definitely indicates a positive impact of the dam on environment
6.4.3.3 Impact on Water Logging
Before the construction of Pekua Rubber Dam, there was no scope to change the height
of the earthen dam, constructed by local people, which created more water logging in
the adjacent area of the earthen dam. After construction of Rubber Dam, the dam height
can be raised or lowered according to necessity. As a result no water logging is
occurred due to the Rubber Dam Project.
6.4.3.4 Impact on Fisheries
Data in Table 6.8 reveal a positive impact of the project on fish production. More than
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Table 6.8: Impact on Fish production
Fish production increased Fish production did not increase
35
(70%)
15
(30%)
two-thirds (70%) of the respondents opined in favor of increased fish production and
30% opposed it. Through open discussion with beneficiaries of the project it is learned
that after the project there is an increase of about 15% in fisheries and especially prawn,
putty has marked production. Culture fisheries like Rui, Katla, Telapia have also
increased as reported by local people.
Increase of fisheries is due to constant sweet water retention in dry season in the
catchments area of the upstream of the rubber dam project. In the pre-project condition
deep water pool could not be maintained due to failure of earthen dam. In that case fish
production was not good as like as post project period. So, there has positive impact on
environment with consideration of fish production due to the rubber dam project.
In brief, the overall findings from the analysis of design, maintenance and management
aspects as well as the impact on socio-economy, agriculture and environment indicate
that the Pekua Rubber Dam Project has many positive and few unfavorable
performances. For example:
• The design parameters and the design principles set for the dam were ok
• Minor operation and maintenance problems, like repair of rubber bags and pump
machines, removal of silt over the deflated rubber dam bag, removal of silt over U/S
& D/S stilling basin, cleaning work for clogging of foot valve
• Maintenance of the machineries of the dam is possible to do locally and institutionally
• Absence of any user committee/body for implementing and maintaining the project is
a threat to its proper management
• Stakeholders lack formal participation in the management of rubber dam.
• Lack of institutionalized management system
• Boat communication is hampered during the irrigation time
• Silt deposition at different level and parts of the rubber dam is a common phenomena
• The Alternative foot bridge is helpful for easy communication
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• The dam has positive socio-economic impact in terms of yearly income, reducing
poverty and increasing employment opportunity
• Agricultural production has increased due to increase of agricultural land and
irrigation facilities
• Local environment has improved through curtailing drought, elimination water
logging, and increasing ground water table and fish production.
Chapter 7
Conclusion and Recommendations
7.1 Conclusion
Based on the performance evaluation of the Pekua Rubber Dam the following
conclusions have been drawn.
1 The length, height, shape, site selection, foundation design, floor length, depth
of cut-off wall, fitting-fixing of rubber sheet, fixation level of overflow pipe,
etc. of the dam were ok in terms of the design parameters consideration.
2 The rubber dam was working well since its implementation and during the last
five and a half years of operation (since June-2004).
3 The dam had minor maintenance problems, like repair of pump machines,
removal of clogging of foot valve and removal of silt from the dam body, U/S
stilling basin & D/S stilling basin, which easily can be solved with local level
expertise and service providers.
4 The rubber dam suffered from any safety devise for automatically inflating and
deflating the dam body in case of emergency.
5 The rubber dam had both positive and negative impact on local communication
system. The foot bridge, constructed over the upstream of stilling basin to save
the dam from trespassing of the public, has improved the local communication
process. But the dam is interrupting boat communication between the two sides
of the dam during the irrigation period i.e. dam activation time.
6 Implementation of the dam helped to increase annual income of the
stakeholders, alleviating poverty and creating more employment opportunity.
All these helped to increase the socio-economic status of the local people.
84
7 The dam had positive impact on local agriculture through increasing cultivable
land and various agricultural productions.
8 The dam helped to improve the environment of the locality by removing mild
draught and water logging from the project area and increasing the ground water
table which has good impact on all kind of green vegetation, plantation,
agriculture, flora and fauna as well as in declining salinity.
9 The stakeholders of the dam had lack of formal participation in maintenance
and management of the rubber dam. As a result, some management problems
were created among the users, like distribution of water through the channels,
differences of opinion in maintaining water level, irresponsibility in maintaining
the channels and gates, etc.
10 There found a lack of coordination among the local level institutions, like
BWDB, Agriculture Extension Group and other local Water User Groups
responsible for local level irrigation management, agriculture, fisheries,
environmentalist etc.
11 The institutional aspect of BWDB was supportive for operation of the dam. But
the dam no full time operator to pump the machine. The master role basis pump
operator can create problem in operating the dam.
12 The present study shows that rubber dam had some specific strengths in terms
of implementation time, cost incurred and simplicity of construction. The time
required for implementation of the rubber dam was relatively shorter than
construction a regulator or barrage; the construction cost was relatively low and
construction of the rubber dam was comparatively simple.
13 In fine it could be concluded that the Pekua Rubber Dams Project was
technically attractive, economically viable and less costly, socially acceptable,
environmentally sustainable and agriculturally helpful to increase various
production. Thus it is helping to lift local economy and alleviating poverty. The
little problems as identified in this study were not big issues and could be easily
85
solved with local technology and initiatives. Therefore, the rubber dam
technology could be quite appropriate for irrigation in the hilly regions as well
as in other areas of Bangladesh.
7.2 Recommendations Based on the findings and the above mentioned conclusions the following
recommendations have been proposed.
1. In order to enhance the overall performance of the Pekua Rubber Dam, its
maintenance and management process should be strengthened. For this the
following measures should be taken by BWDB:
Appoint full time pump operator(s) to run the pump machine of
the dam.
Form different kinds of local bodies/committees with
participation of the stakeholders for efficient management of the
dam.
Establish coordination between BWDB local office and different
local relevant organizations, who are directly or indirectly related
with the dam benefits, through forming coordination committee.
2. As the Pekua Rubber Dam showed good performance in terms of the aspects
assessed in this study, BWDB should take more such projects replicating the
ideas gathered from it. In doing so the following should be considered.
• A safety devise should be introduced for automatically inflating and
deflating the dam body in case of emergency.
• A modified design of inlet and outlet pipe should be developed so that
the mouths of the pipes can not be blocked with silt deposition.
• A submergible pump should be introduced for curtailment of the huge
costing of pump house.
3. Recommendations for Future Study
The following study could be undertaken in the future:
86
3. A water filled rubber Dam takes 8~10 hrs for filling the rubber dam body
according to its pump capacity and embedded pipe line and its regulating
devices. But an air filled Rubber Dam’s inflation time is shorter than water
filled bag. Pekua Rubber Dam was a water filled rubber dam project. Another
project may be taken by BWDB as pilot project to investigate to compare the
performance of two types of rubber dam.
4. A study should be undertaken to compare the performance of a rubber dam with
that of a conventional water retention structure based on primary data.
5. The environmental impact of the dam was assessed in terms different aspects
like weather, water logging, plantation etc. However, as a rubber product its
impact on chemical effect is very important. Therefore, a chemical assessment
of the rubber dam body under water and above water should be done to look at
its impact on environment.
87
REFERENCES
BWDB, 2003 Some still picture of rubber dams constructed by BWDB. BWDB & EPC, 1995. The Feasibility Study of Matamuhuri Irrigation Project under BWDB. CHANSON, H. 1996. "Some Hydraulic Aspects during Overflow above Inflatable Flexible Membrane Dam." Report CH47/96, Dept. of Civil Engineering, University of Queensland, Australia. CHANSON, H. 1998. "Hydraulics of Rubber Dam Overflow : a Simple Design Approach." Proc. 13th Australasian Fluid Mech. Conf., Melbourne, Australia, 13-18 December, M.C. THOMPSON & K. HOURIGAN Ed., Vol. 1, pp. 255-258. Design catalogue, BWDB, 2003 Design catalog of Pekua Rubber Dam under Matamhuri Irrigation Project, prepared by Bangladesh Water Development Board (BWDB). Design Report, 2003. Design report of Pekua Rubber Dam, Prepared by Design Office of BWDB. Fahmida, K, Dept. of WRE, BUET, Dhaka; Develop a research proposal on evaluation of Rubber Dam Technology as an alternative to Traditional Dam Projects for sustainable development Geosynthetica.net. Inflatable Rubber Dam; International Water Power and dam construction; WWW/ Geosynthetica.net Hossain, A. 1992. Diagnostic Study of Failures of Hydraulic Structure in Bangladesh Case studies of failure in Chittagong district, M. Engg. Thesis Department of Water Resource Engineering, BUET, Dhaka IWHR, 1994. Rubber Dam – a new type of flexible hydraulic structure , a paper prepared by Institute of Water Conservancy & Hydroelectric Power Research & Beijing Keyu Water Engineering Technology, China. IMED, 2007. The Impact Evaluation of Matamhuri Irrigation Project 1st Phase of BWDB (Pilot Project) LGED, 1994. Study Report on Feasibility of Rubber Dam in Bangladesh. Institute of Water Conservancy & Hydroelectric Power Research (IWHR), People Republic of China and Technical Design Unit, Institutional Support Project (ISP), Rural Employment Sector Programme -11 (RESP-11), Local Government Engineering Department, Dhaka, Bangladesh.
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MPO, 1991. National Water Plan Project Phase-II, Ministry of Water Resource, Dhaka. Michael R. Markus, Curtis A. Thompson, and Matt Ulukaya (From Water & Waste Digest) 1995. Aquifer Recharge Enhanced with Rubber Dam Installations published by Water Engineering and Management, January, 1995. Nahar, J, 2004. Preliminary Study on Design of Rubber Dam in Bangladesh with special reference to the use of locally available materials. Undergraduate Thesis, Department of Water Resource Engineering, BUET, Dhaka. OGIHARA, K., and MARAMATSU, T. 1985. "Rubber dam: Causes of Oscillation of Rubber Dams and Countermeasures." Proc. 21st IAHR Congress, Melbourne, Australia, QHEPIL, 1999 Qingdao Huahai Environmental Protection Industry Co. Ltd. China. The Rubber Dam and the Technical Standard of Rubber Dam. Raquib, M.A. 1999. Performance evaluation of Rubber Dam Projects in Bangladesh. M. Engg. Thesis, Department of Water Resource Engineering, BUET, Dhaka. Saleh, M., Fazal, A. and Modol, M. S. 2000. Performance Evaluation of rubber dam projects in irrigation development. A publication under Institute of flood control and drainage research, BUET, Dhaka. SEIL, 1985. Sumitomo Electric Industries Ltd, Japan. Technical description of SUMIGATE Inflatable Rubber Ram. Soil investigation report, 2002. Soil investigation report of Pekua Rubber Dam site, prepared by Ground Water Division-1, BWDB Terzaghi and Peck, 1948. The allowable bearing pressure based on tolerable settlement. Wikipedia –the free encyclopedia. Inflatable Rubber Dam, http:// en.wikipedia.org/wiki/inflatable_Rubber_Dam Yantai C.S.I. Rubber Co. Ltd, http://www csirubber.com Zhang X. Q., Tam, P. W. M., and Zheng, W. 2002. Construction, Operation, and Maintenance of Rubber Dams. Canadian Journal of Civil Engineering, 29(3):409-420.
Design & Features
Strong Body Secure Anchor Simple & Reliable
An inflatable bladder made of heavy-duty, nylon-reinforced rubber, with EPDM cover to withstand ozone and ultraviolet light. Thickness of bladder ranges from 9.5 to 25mm, depending upon the dam height. The minimum safety factor for the bladder is 8.0.
The bladder is anchored to the foundation using a simple clamping system composed of anchor bolts and steel clamping plates. This simple design produces an extremely dependable air-tight seal. The system can be installed quickly but firmly with standard tools. The minimum design safety factor for the anchor system is 3.0.
A low pressure system, usually between 0.05kgf/cm2 to 0.6kgf/cm2
depending on dam height. Air is supplied using air blowers. No overhead structure or hydraulic system are required. Inflation & deflation of rubber dams is highly reliable and little maintenance is required.
Flat On Foundation Longer Span Flexible Control
The FIN structure allows the fabric to Lay-Flat when deflated. This prevents damage from debris or ice. The lay flat characteristic eliminates the bulge at the end of the deflated body, which is prone to serious vibration & abrasion. It also permits passage of debris.
The Bridgestone Rubber Dam permits very long spans, thus reducing the need for intermediate piers necessary in steel gate installations. The long span of the rubber dams also maximizes discharge as there are few piers obstructing the water flow.
Inflation & deflation can be manual or automatically controlled. The automatic control system can monitor the upstream water level and adjust the air pressure in the dam to maintain a prescribed water level in the upstream pool.
Oscillation Reduction Variable Side Slope Low Maintenance
When inflated, the FIN structure works as a deflector to create aeration below the fin. This effectively reduces the phenomenon of oscillation up to a 50% overflow when compared to FIN-LESS bladders.
Rubber Dams can be installed in rivers with any side slope angle, eliminating the necessity of modification to river bank, unlike steel gates which can only be installed on vertical side slopes.
Other than normal maintenance of control equipment, blowers and actuators, rubber dams are virtually maintenance free. This is a big advantage over steel gates, where removal of rust, painting and changing of hydraulic oil are required.
Copyright © 2002 Bridgestone Corporation. All Rights Reserved.
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