water from pounds pans and dams.pdf

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A manual on planning, design,

construction and maintenance

a er rom pon s,pans an ams

TECHNICAL HANDBOOK No. 32


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Technical handbook TH) series

Agroforestry handbook for the montane zone of Uganda

A ex Lwaku a, A ice A. Kau ia an John korio. 2003. TH No. 31. BN 9966-896-55-4

Soil fertility and land productivity

Charles K.K. Gachene and Gathiru Kimaru. 2003. TH No. 30. ISBN 9966-896-66-X

Soi and water conservation manua for Eritrea

Amanuel Negassi, Estifanos Bein, Kie Ghebru and Bo Tengns. 2002. TH No. 29. ISBN 9966-896-65-1

Management of Range ands: Use of natura grazing resources in Southern Province, Zambia

varisto . hi eshe an Aichi Kita yi. 2002. TH No. 28. BN 9966-896-61-9

Edible wild plants of Tanzania

Christopher K. Ruo, Ann Birnie and Bo Tengns. 2002. TH No. 27. ISBN 9966-896-62-7

Tree nursery manua for Eritrea

Chris Palzer. 2002. TH No. 26. ISBN 9966-896-60-0

ULAMP extension approach: a guide for e d extension agents

Anthony Nyakuni, e ion hone an Arne riksson. 2001. TH No. 25. BN 9966-896-57-0

Drip Irrigation: options for smallholder farmers in eastern and southern Africa

Isaya V. Sali. 2001. TH No. 24. ISBN 9966-896-77-5

Water from sand rivers: a manual on site survey, design, construction, and maintenance of seventypes of water structures in riverbeds

Erik Nissen-Petersen. 2000. TH No. 23. I SBN 9966-896-53-8

Rainwater harvesting for natura resources management: a p anning guide for Tanzania

Nuhu Hati u an Henry F. Mahoo (e s. . 2000. TH No. 22. BN 9966-896-52-X

Agroforestry handbook for the banana-coffee zone of Uganda: farmers practices and experiences

I. Oluka-Akileng, J. Francis Esegu, Alice Kaudia and Alex Lwakuba. 2000. TH No. 21. ISBN 9966-896-51-1

Land resources management: a guide for extension workers in Uganda

har es Rusoke, Anthony Nyakuni, an ra Mwe aze, John korio, Frank Akena an athiru Kimaru.2000. TH No. 20. ISBN 9966-896-44-9

Wi d food p ants and mushrooms of Uganda

Anthony B. Katende, Paul Ssegawa, Ann Birnie, Christine Holding and Bo Tengns. 1999. TH No. 19.

ISBN 9966-896-40-6

Banana production in Uganda: an essentia food and cash crop

Aloysius Karugaba and Gathiru Kimaru. 1999. TH No. 18. ISBN 9966-896-39-2

Agroforestry extension manua for eastern Zambia

amue imute, .L. Phiri an Bo Tengns. 1998. TH No. 17. BN 9966-896-36-8

Water harvesting: an illustrative manual for development of microcatchment techniques for cropproduction in dry areas

Mwangi T. Hai. 1998. TH No. 16. I SBN 9966-896-33-3

Integrated soi ferti ity management on sma -sca e farms in Eastern Province of Zambia

Thomas Raussen (ed.). 1997. TH No. 15. ISBN 9966-896-32-5

Agroforestry manual for extension workers in Central and Lusaka provinces, Zambia

osep . an a, enas an a an o engns . . o . . - - -

Facilitators manual for communication skills workshops

Pamela Baxter. 1996. TH No. 13. ISBN 9966-896-25-2

Usefu trees and shrubs in Eritrea: identication, propagation and management for agricutura andpastora communities

Estifanos Bein, B. Habte, A. Jaber, Ann Birnie and Bo Tengns. 1996. TH No. 12. ISBN 9966-896-24-4

Agroforestry extension manua for northern Zambia

Henry hi u ya an Bo Tengns. 1996. TH No. 11. BN 9966-896-23-6

Useful trees and shrubs for Uganda: identication, propagation and management for agricultural andpastoral communities

A.B. Katende, Ann Birnie and Bo Tengns. 1995. TH No. 10. ISBN 9966-896-22-8

The soi s of Ethiopia: annotated bib iography

Berhanu Debele. 1994. TH No. 9. ISBN 9966-896-21-X

Curricu um for training in soi and water conservation in Kenya

tachys N. Muturi an Fa ian . Muya (e s. 1994. TH No. 8. BN 9966-896-20-1

Soil conservation in Arusha Region, Tanzania: manual for extension workers with emphasis on small-scale farmers

Per Assmo and Arne Eriksson. 1994. TH No. 7. ISBN 9966-896-19-8

Usefu trees and shrubs for Tanzania: identication, propagation and management for agricu tura andpastora communities

L.P. Mbuya, H.P. Msanga, C.K. Ruo, Ann Birnie and Bo Tengns. 1994. TH No. 6. ISBN 9966-896-16-3

Agroforestry manua for extension workers in Southern Province, Zambia

Jericho Mu o wa, amue imute an Bo Tengns. 1994. TH No. 4. BN 9966-896-14-7

Useful trees and shrubs for Ethiopia: identication, propagation and management for agricultural andpastoral communities

Azene Bekele-Tessema, Ann Birnie and Bo Tengns. 1993. TH No. 5. ISBN 9966-896-15-5

Guide ines on agroforestry extension p anning in Kenya

Bo Tengns. 1993. TH No. 3. ISBN 9966-896-11-2

Agroforestry manua for extension workers with emphasis on sma -sca e farmers in Eastern Province,

Zambiaamue imute. 1992. TH No. 2. BN 9966-896-07-4

Curriculum for in-service training in agroforestry and related subjects in Kenya

Stachys N. Muturi (ed.). 1992. TH No. 1. ISBN 9966-896-03-1

Technical handbook series, continued...

..continued on inside back cover


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IntroductionChapter 1

The purpose and scope of this book are

presented in this chapter, followed by a

detailed description of the most common

kinds of ponds and dams. Pans used on seasonal

basis by pastoral herders are also described.


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C apter 1 Intro uction

2

1.1 Purpose an scope o t is manua

Bac grounAfrica is considered a water-scarce continent with most of the countriesregularly experiencing extreme water shortage during periodic dryspells. Rapid population growth and ine cient use of resourcesincreases the decit between available water supplies and the needs ofpeople. Many regions in East and Southern Africa are drought proneand the vulnerability of the population to drought is high with morethan 40 per cent of the regions people living in dryland areas.

As resources dwindle and water demand increases, large scalewater supply projects become unviable. There is a need to decentralizewater supply to household and small community level. There is greatpotential to make beer use of water resources by harvesting rainwaterand storing it locally for household and productive purposes.

he need for more ponds and dams

The lack of water is the largest constraint to sustainable livelihoods inmany parts of Africa. Rapid runo during the rainy season frequentlyresults in a high proportion going to waste or even becomingdestructive. Soil erosion, vegetation degradation and decreases insoil fertility are severe problems throughout the region. Harvestingrainwater where and when it falls presents opportunities to address

both water scarcity and soil degradation at a local level. Water canbe harvested and used for many purposes but reliable water storagefacilities are required.

Communities/individuals need help to identify suitable sites forwater harvesting and storage structures, which types are most suit-able, how much water the catchment area gives during the rains, andthe water needs for household, livestock and crops. Local knowledge

is valuable in answering these questions. Local communities must beinvolved and feel ownership from the planning stage all through theconstruction phase, if the project is to endure.

Aim and scope of this book

The purpose of this handbook is to provide a practical guideto extension workers and technicians who assist communitiesand farmers intending to construct a water storage structure foragricultural, livestock watering or domestic purposes. The reader will

nd out how to involve the community in all steps, so they become thetrue owners of the project and ensure the sustainability of the waterstorage structures (Chapter 2). Guidance is provided on planning andfeasibility study including environmental impact and legal aspects


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3

Chapter 3). Various options for water storage are discussed and thedesign and construction of ponds and small earth dams are coveredin detail (Chapter 4). The handbook also deals with the operationsand maintenance once the pond or dam is built (Chapter 5). The lastchapter (Chapter 6) presents several useful tools to use in the planning,design and construction stages.

.2 Types o pon s an pans

onds and pans are naturally occurring or excavated water storagestructures without a constructed wall. They usually store surface run-

o, even though there are examples of constructed ponds storing roofater.

he terms pans and ponds are oen used interchangeably withslightly indistinct meaning. In Kenya both natural and dugout struc-tures are called pans, while in Zambia pans are larger natural watersources and ponds are smaller excavated structures. In general, theterm pan is used to describe structures used by herders, while pondmost oen refers to structures used by farmers. There are also variouslocal terms to add to the confusion.

aturally occurring pans

Natural pans have provided water for wildlife, livestock and humanssince ancient times. They form in depressions in which rainwateraccumulates during the rainy season and they do not have an outowsee Figure 1). Today, most natural water sources are used for watering

livestock during rains and a few months thereaer. Some people stilluse them for domestic water supply even though they are dirty andnot suitable for drinking or washing.

igure 1. atural pan in a pastoral area with livestock and wildlife.


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In some very dry areas such as the Kalahari Desert large natural saltpans are found. These usually hold water only for a few weeks a yearand have been formed by wind action. Smaller natural pans includethe ilanka ya ndovu (elephant dam) common on the eastern Africansavannah, scooped out on at land by elephants, digging for watermany years ago. The animals trample and compact the sediment whenthey enter to drink, making the pans oor watertight.

Many pans suer from high evaporation losses. As they ll withsediment over time and the water becomes shallow, the problem ofevaporation gets worse. Although it may not always be feasible to

build new pans, it is sometimes worth deepening or enlarging existingnatural or articial ones. Herders in particular appreciate the benets

which natural pans can bring even though most are seasonal and can-not store water throughout the year.

Excavated ponds

Excavated ponds come in sizes from the household level of 200 to 500 mup to community level of 10,000 m . They can easily be started witha small capacity and expanded over the years by digging deeper andwider. In areas with impermeable soils and a suitable site the only costof construction is the labour, so a group can dig their own pond with

lile cash expense.

Figure 2. Illustration of a harco pond, note silt traps and spillway.


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onds should be situated at a low point in the catchment area sorainwater runo ows by gravity towards the excavated pond. Thecatchment area can consist of any type of surface such as cropland,grasslands or compounds around homesteads. Hard road surfacesor rock outcrops may also make suitable catchment areas. Rainwaterruno can be diverted from a nearby gully, provided the pond issituated at a lower elevation than the gully. Soil excavated from thepond can be used to make soil bunds for diverting runo water toponds.

In Sudan the name hars describes dugout enlargements of naturaldepressions on the savannah. They range in size from 500 to 10,000 mand provide water for both livestock and domestic purposes. In the

past most hars were dug by hand. Today however, heavy machines,i.e tractors and bulldozers, are commonly used to build them.

In Tanzania dugout ponds are commonly referred to as harcoponds, or alambo in Kiswahili. The harco are common in the drylandsof Tanzania where they are used for watering livestock. In some cases,they are also used through necessity for domestic supply despite thepoor water quality. Farmers build these ponds in stages during dryseasons until they are satised with the capacity. The farmers do notfollow a standard design for their charco ponds and excavate them in

many dierent shapes and sizes (see Figure 2).

orrow pits

Borrow pits (also known as murram pits) are excavated to supply soiland gravel for road construction, but opportunistically used for waterstorage, usually from road runo. As the ownership oen is unclearnobody takes proper responsibility for the borrow pits and they mayeven be sources of conict. If proper regulations were in place to deter-mine how these dugouts could benet both the road construction andthe neighbouring communities, the structures would be more valuablefor a longer time.

When borrow pits are dug in rm soil with lile seepage and havea large catchment area from the road runo, even small rain showers

ill ll them. If they do not normally ll this way, they can fairly eas-ily and at low cost be lled by digging a trench sloping from theroad to divert rainwater runo. This rainwater runo may contain tarand other pollutants, making water from borrow pits unsuitable forhuman consumption.


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6

1.3 Types o ams

Dams are water storage structures on slopes, with walls orembankments on the downhill side. They come in all shapes and sizesfrom the giant Kariba Dam on the Zambezi River to small check dams

built across gullies. In drylands these include various types of earthdams, rock catchment dams, sub-surface dams and sand dams.

This handbook covers the design and construction of small earthdams with storage capacities up to 10,000 m and embankments of upto approximately 3 m in height. It will deal with two types of earthdams only:

Small dams in valleys built with straight embankments, whichis a common and economical type of dam.

Small earth dams on hillsides built with curved embankmentson sloping land, a less common but practical type for individu-al farmers.

Site investigations, design and construction of medium and largedams require experienced engineers and cannot be constructed byeld technicians and farmers. For this reason they are beyond thescope of this handbook.

word of warning: It must be remembered that the construction ofny dam introduces a small risk of failure such as collapse of the damall. Therefore always seek experienced technical advice to minimize

uch risks.

Earth dams in valleys

If a suitable site can be found, constructing a small earth dam at a valleysite is a cost eective way to create a water storage reservoir (see Figure

3). This is because it has a high water storage capacity per cubic metreof soil moved. Nevertheless, the impact of a small earth dam beingwashed away in a ood could be very serious and endanger lives andproperty. This is particularly so for valley dams where a large quantityof water suddenly released would be channelled down the valley. Forthis reason experienced technical help should always be sought for thedesign and construction of any dam which might present a threat todownstream households or communities.

Small earth dams, below 1,000 m can be built manually, usingdraught animals, a farm tractor or a bulldozer. The medium sized,10,000 to 50,000 m , and large earth dams, above 50,000 m , are nearlyalways built using heavy machinery.


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igure 3. llustration of a valley dam. Note sill in spillway, rock toe.

arth dams on hillsides

Small earth dams on hillsides or sloping land are one of the simplestand least costly type of dam to design, construct and maintain. Suitablesites can be found on almost any sloping land that produces rainwaterruno. They may be built small the rst year and enlarged over timesee Figure 4).

ock catchment dams

ock catchment dams store rainwater runo collected from rock out-

crops. In large rock catchments cement and stone guers are used toextend the catchment area to gather runo from several hectares ofrock surface. Rock catchments typically have reservoirs with capacitiesof up to 5,000 m

ub-surface dams and sand damsIn semi-arid areas where dry sandy riverbeds are common, their waterstorage capacity can be improved by building sub-surface or sanddams. These are a kind of weir constructed across the sandy riverbedsto block ood water. Water that inltrates into the sandy riverbed is

trapped in the spaces between the sand particles. This form of waterstorage has the advantage of protecting the water from evaporation as

ell as helping to protect it from contamination.


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Figure 4. llustration of a hillside dam.

The major dierence between sub-surface and sand dams is that sub-surface dams can be built cheaply of soil or stone-masonry to the levelof sand in the riverbed, while a sand dam can be built to a height ofseveral metres above the sand level. Although sand dams shouldproduce more water than sub-surface dams, most of the hundredsconstructed in recent years are not functioning well.


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9

ne of the oldest rock catchment dams built in Kitui, Kenya, in956.

Sand dam with masonry apron in Nyando District, western Kenya.


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Chapter 2 Communityparticipation

All development practitioners should realize by now howimportant community participation is. Many are still struggling

with how to go about it. Chapter 2 provides clear guidelines,

in a logical sequence. It begins with project identication, forming

management structures, and setting SMART objectives. With structures

in place, the text explains the communitys role in feasibility and

planning, design and construction. Throughout, emphasis is given to

the need for capacity building, with a detailed description of the

kinds of training that need to be provided. The roles of government

departments are discussed, as well as the need for monitoring of

progress by the community groups themselves. At the end, there is a

discussion on ways to manage conicts should they arise.


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C apter 2 Community participation

2.1 Intro uction

There are many examples of community water projects that werebuilt and ended up being abandoned or broken down soon aerthe development agency le. Such experience highlights the need toinvolve the community in all stages of a project in order to ensure thatthe community owns the project and willingly takes responsibilityfor it. Community participation is essential to ensure a genuinelysustainable project. Very small pond or dam projects may also be doneat an individual rather than community level. In order to make surethat projects are sustainable, there is need to identify clear steps in theproject implementation process. Turn to page 28 for a useful ow-chart

that shows all steps in sequence.

Such steps include:

roject identication

Community social organization and management structures

easibility, design and planning

Construction

Capacity building

Operation and maintenance

onitoring and evaluation

. roject i enti cation

In the past, the needs of a community were taken for granted. Topdown approaches meant that communities were given whatever

projects the aid agencies or government had funds for. Communitieswere not consulted and their real felt needs were never identied.This resulted in unwanted projects which were neglected and becamewhite elephants.

Pond and dam projects can be identied in many dierent waysbut in all cases the demand for the project should come from thecommunity. Community needs or demands can be identied byassessing their development priorities using techniques such asparticipatory rural appraisal (PRA). Alternatively, there may be a direct

request to a local development agency or government departmentfrom an established community group. Establishing the nature of thegroup or individual requesting assistance should be the rst part of theproject implementation.


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2.3 Community socia organizations an

anagement structuresorming a management structure

In order to implement a successful water project, the community willneed to select a suitable management structure. Possible approachesmight include:

Starting by understanding the existing structures, includingtraditional council of elders.

Raising awareness about the project and the need for a man-

agement structure with the local leadership.Helping the community to develop the roles and responsibili-ties of the proposed commiee.

Within most communities in Africa, there are traditional manage-ment structures for water resources that existed in the past and possi-

bly current management structures for new projects. It is important tounderstand the responsibilities of these structures with regards to us-ing water resources. Analysing these structures can be done for eachtype of management structure using the following checklist to estab-lish the gaps in knowledge and skills:

What do you see and think should be their responsibilities?

Which of the responsibilities mentioned above can they com-fortably take on?

What reasons do you give for their inability to carry out therest of their responsibilities and what possible solutions do yousuggest

Compare roles of the two management structures (traditionaland current) and come up with important roles each can pro-vide that cannot be provided by the other.

he responsibilities that the management structure will have to takeon behalf of the community for the sustainability of the project include:

Coordinating construction and maintenance of the pond/panor dam in the community.

Operation and maintenance of the pond/pan or dam. Havingthe technical know how to carry out repairs with lile or noreliance on external support.

Charging for providing services. Establishing the best revenuecollection method. This includes a cost recovery system for opera-tion and maintenance and managing the funds.


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Supervising sta who work on the water supply system, i.e.operators, fee collectors.

ending meetings and having periodic elections in accept-able format for all community members.

Implementing decisions discussed and taken in meetings.

Equitable distribution of water resources, formulation and en-forcement of by-laws to ensure eective distribution.

Engaging community members on their own terms, minimisingand resolving conict, and identifying and resolving communityproblems.

Having analysed the existing management structures, it is possibleto agree with the community on the most appropriate structure for theplanned project. This is oen a commiee that combines both tradi-tional and modern resource management structures as shown in theexample below.

Formation of management structures for water projectsin Mandera District, Kenya

There is a history of traditional water management in Mandera District

through the council of elders or aba-heriga. Stakeholders at the start of a

new water project debated the strengths and weaknesses of both this and a

modern, elected committee style management structure. The stakeholdersexplored methods of combining modern and traditional systems and the

measures to be taken to ensure representation and accountability, including

how to reduce the inuence of dominant personalities on the process. It was

concluded that:

The inclusion of elders brings considerable advantages to the

management of community water supplies, but may increase conict

within the committee. Comprehensive and enforceable by-laws can play an important role

in ensuring genuine representation by committee members and, by

clearly dening roles and responsibilities, can reduce the inuence of

dominant individuals.

Good record keeping and regular monitoring by support agencies is essentialto check the effectiveness of a committee.

wnership, land tenure and legal issues

Suitable sites for earth dams are normally found in valleys and seasonalwater courses which are oen boundaries between two or morelandowners. In such cases, it is important that the landowners make awrien agreement on sharing the ownership. This agreement should


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include construction cost, usage of water and maintenance of a pondor dam and be nalized before any survey and construction work takesplace. It is also important for the landowners to agree on the locationof an access road to the dam site and on any soil conservation methodsto reduce soil erosion and siltation. Catchment protection can consistof digging trenches, making terraces and planting of grasses or treesin rows along the contours (lines of equal elevation). It also includesthe building of check dams and silt traps in gullies. All land-users ina catchment area should be encouraged to participate in all the soilconservation activities including the maintenance of structures and

egetation cover.Before a pond/pan or dam project can be implemented it is impor-

tant to ensure that the ownership of the site is clear and that access toall users is guaranteed. The box below is an example of the importanceof land ownership.

Gathingi dam, Sweetwaters, Laikipia District, Kenya

uring the initial stages of a project to rehabilitate an old colonial dam

for a community near Sweetwaters game reserve, the implementing

agency surveyed the site and compared the boundary of the proposed damimpoundment area with land settlement maps of the area. During this process,

it became apparent that the actual location of the dam spanned both the

communal land set aside for the dam and private land owned by an individual

in the community. The project could not proceed because the eventual

ownership of the dam and the water resource was not clear and community

access could not be guaranteed.

ollowing intensive facilitation by the development agency the committeeand the land owner agreed to exchange the private land within the dam area

for alternative land nearby. The community arranged for the legal process of

transferring title deeds and establishing the whole dam impoundment area

as public land. This process took three months and only then could the damehabilitation project start.

Initial discussions should be held with the community, or their rep-resentatives, using this checklist:

Who owns the land?

Who has access to the land?

Who owns any existing water source?Who will own this project?

Who will manage it?


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ow will the money collected be used?

Who will maintain the project?

Ideally a community water project must be established on commu-nity owned land. If any part of the water supply passes over privateland, it is necessary to obtain a wayleave which is a legal documentsigned by the land owner that ensures access by the community mem-

bers to the water supply facilities on his/her land.

Compliance with water resource regulations on dam construction

Legal requirements will vary from one country to another. It is alwaysadvisable to ask the authorities before starting any construction workin order to avoid disappointment and legal cases.

Generally, it is understood that farmers may construct ponds ontheir land without asking for permission from anyone, provided theponds are small and do not block water runo to people living down-stream. If in doubt of the legality, the authorities should be asked be-fore starting on the construction work. In the case of earth dams builtin valleys, however, these may interfere with peoples water supplydownstream. Since dams can collapse during exceptionally heavyrainfall due to poor maintenance, incorrect design or poor construc-

tion work, this could endanger people and structures downstream. Forthese reasons, approval for the design and permission for the construc-tion works must be obtained from the authorities.

Lega aspects o community organization

Dierent countries have dierent laws governing associations andcommunity based organizations. The way in which a communitygroup is registered usually dictates how they can operate and howeective they can be at managing a communal resource such as a dam.

Typical legal guidelines for dierent organizations in Kenya are shownin the box below.

Self-help groups registered with Ministry of SocialServices

Can:

Hold meetings without license

Raise funds for the group Open a bank account

Apply for small grants from local donors or NGOs


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Cannot:

Make legal transaction (e.g. legally binding contract)

Seek legal redress against individuals or organizations (e.g. for

misappropriation of funds)

Own land on which to place project assets (e.g. dam, borehole, tanks

etc.)

Own equipment (e.g. generator, pipeline, vehicles etc.)

Associations registered with the Registrar of Societies

Can:

Do all the above plus:

Legal transactions

Own land

Own assets and equipment

Go to court to seek legal redress

n addition if registered as water users association with Ministry of Watercan:

ave status and rights of water undertaker, i.e. right to legally sell water.

It is advisable to check with the relevant government departmentto make sure the community group is properly registered and canhave the legal authority to handle any problems that might arise.

etting project objectivesIt is important for everyone involved in a project to have a commonunderstanding of what they are trying to achieve. Seing clear objec-tives at the start of the project and making sure they are achievable ispart of the preparation for the project. Simple clear objectives should

be dened with the community and bearing in mind the rule that ob-jectives should be SMART, i.e.:

S = Specic= Measurable= Achievable= Realistic= Time bound


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A typical example of an objective for community water projectswhich is not SMART is improved community health. This is not spe-cic, measurable, achievable, realistic or time bound because it is dif-cult to measure improvements in community health and even moredi cult to relate them directly to the construction of a water facilitysuch as a pond or dam. A more reasonable, SMART objective for apond or dam project would be to reduce the time women spend col-lecting water from 2 hours to 30 minutes by the end of the two yearproject. This is very specic about what is being achieved and forwhom, by when and the achievement can be measured.

2.4 easibility, design and planningCommunity involvement in feasibility and design

The important principle for community participation in feasibility, de-sign and planning is to remember who owns the project. Techniciansmust ensure that the community takes part in site selection, survey, en-vironmental impact assessment (EIA) and any other investigations ordiscussions forming part of the feasibility and design. This may meanspending time explaining the design to key members of the commu-

nity and ensure that the project is not disowned at a later stage.The design must also consider community preferences, hygieneand water use practices. Use the following list of questions to gather

basic social data necessary to ensure that the design meets the needsof people.

1. How many people are likely to use the pond or dam? Where arethey? How are they distributed? Are they seled or nomadic?

2. Are there other water and sanitation needs apart from human or domestic?(e.g. irrigation, tree nurseries, livestock) If so, what are the demands?

3. What security factors may interfere with peoples access to the pondor dam?

4. What are the current or likely water and sanitation-related diseases?How can transmission of these diseases be reduced?

5. What are peoples normal household sanitation and hygienepractices, including disposal of childrens faeces?

6. What are the environmental conditions, including drainage, waste

disposal, and location of defecation areas relative to water sources?7. What are the typical water use habits in the community, including

collection practices, preferences for washing selves, clothes andutensils and sources of drinking water?


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Capacity assessment

t this stage it may be useful to carry out a community capacity as-

sessment. The aim of the assessment is to determine what capacity thecommunity has to sustainably manage the pond or dam aer construc-tion. Sustainability aspects that need to be looked at include:

Technical sustainability, referring to balanced demand andsupply of water from the ponds and dams.

Institutional sustainability, referring to the capacity of the institutionswithin the community to plan, manage and operate the system.

Social sustainability, referring to the willingness of the commu-nity to contribute to the project

Economic sustainability, referring to sustainable economic de-velopment and improvement of the welfare of the community.

Financial sustainability, referring to cost recovery.

Environmental sustainability, referring to there being no long-term negative or irreversible eects to the environment owingto the establishment or use of the ponds and dams.

An analysis of the gaps in knowledge and skills required to man-

age the water supply and maintain the structure can assist in the de-sign of a community training component (see Section 2.6). Once the de-sign is complete the detailed planning can take place. There is a need tofacilitate a planning exercise with the community in which communityand implementing agency roles are clearly dened.

Cost sharing

ost development organizations have adopted a cost sharing policytowards their community projects. The reason is that if communities

have to pay for at least part of the project cost, they are more likely toalue the facility and feel a sense of ownership.he willingness and ability to pay a cost contribution varies from

community to community and should be assessed carefully. The actu-al community contribution should be negotiated with the communityand not determined by an external agency. A xed contribution set ata percentage of the cost of the project tends to result in unaordablecontributions in cases where mechanical construction is required. Anin kind contribution in the form of labour and local materials is of-ten easier for poor communities with limited cash. It is important to

monetarize in kind contributions to establish the actual value of thecommunity contribution.

Negotiating the cost of contribution should be done alongside dis-cussions about the design and construction planning of the project. It


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is important to make sure that communities understand the full scaleand cost of the project so that they can appreciate the need for theircontribution. Demanding a certain percentage without explainingwhere the gures come from can lead to communities feeling that theyare being asked for a bribe to get the project started.

Where there is an option of mechanical, animal draught or manualconstruction, it may also be appropriate to give the community thechoice of technology they prefer to contribute to. It is unrealistic to ex-pect communities to provide intensive labour for building a large damor pond without payment.

Pan desilting in Wajir District

Several large pans were desilted following the drought of 19992001

in Wajir. The development agency decided to use Cash for Work to

help drought affected families to recover. Providing cash to families

who contributed labourers for desilting did not undermine the

community sense of responsibility for the pan because the community

fully understood that the cash was being paid as a drought recovery

measure. In these communities, even if the labour had been provided

as a community contribution someone within the community would

have had to pay the workers. No-one is expected to work without

being given something.

For large, complex projects where considerable revenue collection,operation and maintenance will be required it is advisable to carry outan awareness raising exercise with the whole community. This willhelp the community to understand their roles and responsibilities andto feel part of the planning and implementation process. Restricting

community contact to the selected few in the management commieeoen results in conict and confusion at later stages.

. onstruct on

Roles of who should do what should be clear. Typical community rolesduring construction include:

Clearing the site, uprooting trees, removing stones.

Supervising earth works.

roviding labour for minor earth moving (if mechanically dug).

Organizing, supervising and monitoring work (if manually dug).


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Providing local materials for cement works where required(sand, ballast and water).

Providing accommodation and/or food for skilled workers.Fencing and other auxiliary works, i.e. planting grass on em-

bankments, stone pitching the spillway.

he management commiee and possibly other members of thecommunity should be involved in measuring and approving the workcarried out. This ensures that the community is in control of the proj-ect and the commiee can answer any queries that the communitymembers may have about the construction. In addition, where it is notpossible to employ manual labour, the community should decide onthe possibilities of tendering or contracting the work to establishments

ith relevant equipment.

. Capacity ui ing

ationale

istorically, government water departments played a prominentrole in the development and rehabilitation of dams. More recently,

the capacity of the water departments to undertake this work hasdiminished and very lile rehabilitation of community dams takesplace. Under new government water policies, communities have agreater role and responsibility in the management and operationof their water supplies. This responsibility is only meaningful if thecommunities genuinely have the interest and capacity to managetheir water supplies. Typically, the community has a strong interest,

being the principle beneciary of the water supply. However, theoperation and management of a water supply requires awareness,

skills and experience that the communities do not necessarily have,especially if their dam is new or has not been operational for a longtime. The capacity of the community may need strengthening sothey can manage their water supply. A capacity building exercise forcommunity operation and management of water supplies involves thefollowing steps:

Training needs assessment.

Development of an appropriate training programme.

Training of management commiee and other key community

people.

Follow up to monitor progress on operational and managementissues.


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Capacity building should result in the following: that thecommiee selected by the community gains skills on leadership,nancial management and technical operation and management;that the community gains knowledge on water related hygiene andsanitation; and that the community learns how the pond/pan or damwill be operated and learns to demand accountability from theircommiee (community empowerment).

raining needs assessmentThe training needs assessment is a detailed exercise with the commu-nity in which participatory tools are used to:

Discuss the overall project objectives with the community.

Establish existing organizational and management structure.

Establish the capacity of existing management system to han-dle existing water supply system and rehabilitated system.

Discuss expectations and responsibilities involved in commu-nity management of the proposed dam rehabilitation and thesubsequent operation and maintenance.

Identify who should be trained.

Identify external factors that can aect the training and project.

Identify the roles of other stakeholders (e.g. Water Department).

Where a comprehensive capacity assessment was carried out dur-ing the feasibility stage it may not be necessary to undertake a fulltraining needs assessment. However, discussions should be held withcommunity representatives to identify what training they think is nec-essary. The format of the training needs assessment involves discus-sions with the community using PRA tools that help the communityto identify their priorities. This ensures that the opinions of dierent

members of the community (e.g. women, youths, agriculturists, pasto-ralists) are expressed. The community is able to identify their strengthsand weaknesses, with the result that the topics covered in the trainingprogramme can clearly be identied as arising from the community.

The output from the training needs assessment is a report whichprovides details on the key issues that need to be addressed during thecommunity capacity building exercise.

Development of an appropriate training programme

Each community is dierent. It is important to adapt approachesand topics to the needs of each individual community. The generalapproach is to develop a training programme which uses participatorytools (drama, role plays, picture games) to build the capacity of the


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community to operate and manage their water supply.istorically most pans have a traditional, communal ownership

background. This means that capacity building for community man-agement should build on existing systems. The following features arerecommended for pond or dam management training:

Community mobilisation/awareness is a key part.

Training should be on-site and make use of participatory ap-proaches.

Thorough training/capacity building in management at fewsites is preferable to partial training in many sites.

Long-term follow-up process is essential.

Training should involve and encourage women in decision-making.

A typical training programme is divided into modules dealingith dierent topics including:

Community organization and optional management structures.Other issues covered include leadership, gender, equity andconict resolution.

Community self reliance and organizational sustainabilitywhich deals with issues of dependency, organizational records,constitutions and by-laws.

Building nancial sustainability, nancial records (budgeting,book keeping and accounting).

Operation and maintenance which deals with technicalsustainability and includes accessing technical services, spareparts, and routine maintenance activities. This module alsocovers catchment conservation measures and environmental

impacts.

Water, sanitation and hygiene education. Typically, healthbenets from improved water supplies are only obtainedthrough changes in water use habits. The managementcommiee members are generally cast in the role of communityleaders and so have a responsibility to the community to raiseawareness on good environmental health practices at thehousehold, homestead and community level.

Community action plans and community monitoring andevaluation. Indicators are discussed to help the communitymonitor their adherence to their action plans and to monitorany environmental or social impacts.


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An additional module that is useful for dam projects would coversustainable water and land use practises. This module would exploreways of making use of the water facility to enhance the environment(tree nurseries etc.), to create opportunities for coage industries (e.g.sheries) and to encourage micro-irrigation.

Community training approach

Community training takes place in the community area and takes theform of a one to two week exercise in which the dierent training mod-ules are explored with the community members.

Special aention is given to the possibility that individuals withinmanagement commiees may be transitional. It is therefore importantto ensure that the community as a whole is involved in the training.This helps to reduce the likelihood of generating an elite of trainedindividuals. The training has to be appropriate for the community asa whole, hence the limited use of wrien material. Additionally, thetraining may be conducted in the local language.

tafng

Sta ng for the community training component requires a communitytraining specialist and one or two community mobilizers. The training

specialist will be responsible for the content, coordination and reportingof the community training component. The community mobilizers,who speak the local language, will undertake the community trainingand follow-ups.

2.7 Monitoring an eva uationThe community should develop a suitable system for monitoring theirperformance. In addition, the project should involve the communityin evaluation of their works. This is important for management, re-adjustment or introduction of new approaches towards improvingon the existing systems or solving of problems. Tools for monitoringthe performance of the dam or pond and planning operation andmaintenance work are presented in Chapter 6.

2.8 Important considerations in working

wit communitiesGenderTraditional gender roles relating to water in the household areoen divided according to whether the water is for productive or


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reproductive use. For example, domestic water for cooking, drinkingor washing is the womans responsibility. Water for agricultureor livestock is usually the mans responsibility. Women may beresponsible for water collection for kitchen gardens or small livestockraised for the household rather than cash income.

Understanding gender issues within the community where thepond/pan or dam is to be constructed is an important factor in plan-ning a sustainable project. It is useful to analyse womens and mens

ork and their control over resources to establish who is likely to havethe time, interest and authority to take on the management of a pondor dam (see box for questions for gender analysis).

Questions for gender analysis

What role do women have in water issues?

Who controls water sources?

Who is responsible for maintaining water supplies?

W o is responsi e or water use in t e ouse o

t e community manages t e water supp y, s ou women e

involved?

How should they be involved? In the committee or through womens

groups

W at resources o women contro an w at ecision-ma ing power

o they have in the community?*

Do women have time available for community activities?*

What other constraints are there to womens involvement in water

management

W at steps can e ta en to re uce t ese constraints

Who should take these steps?

these issues can be explored using PRA tools such as Gender access and

control to resources and Gender activity schedule.

Women are clearly the ones who benet from improving availabil-ity of water in terms of:

Reduced time spent fetching water

Improved family health

More opportunities for girls to go to school

Potential for market gardening and/or small-scale livestockproduction to increase household income and/or improve nutrition.


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Women therefore have higher interest in improving access towater and are eager to participate in construction. However, in manycases their ability to participate in decision making concerning theplanning, operation and maintenance of the pond or dam is restricted

by traditional practices. There are obvious advantages of includingwomen in the management of water facilities because they are highlymotivated to construct new water supplies and keep them operational.It is therefore important that communities are encouraged to includewomen in the decision making. However, the presence of women in awater commiee is not always su cient to ensure genuine participationin decision making so technicians and extension workers may need tocarry out gender awareness exercises for the whole community to

empower women and encourage them to actively participate.Gender issues should also be taken into account when designing

the pond or dam and thinking about how water for domestic use willbe collected. Womens priorities for water collection facilities may bedierent from mens and they should therefore be consulted. In somecommunities watering livestock is given priority over domestic watercollection. It may be necessary to provide separate abstraction facilitiesfor domestic water to ensure women have access to the water.

Understanding of gender roles in the community is also necessary

when designing follow on projects which make use of pond water,such as market gardens, tree nurseries or brick making. The extent towhich both women and men will benet from these activities needs to

be considered.

Conict mitigation

Conicts over access to water can undermine or even destroy a com-munity water project. All potential conict situations should be thor-oughly explored with the communities involved and conict miti-gation measures agreed and put in place. This may take time andshould involve traditional conict resolution bodies to ensure that anagreement can be reached where more than one tribe or group are in-volved.

Where conicts over land have not been resolved, review ofland acts with consequent reforms should be pursued by the localleadership in conjunction with government o cials. The communityshould be educated on such issues. The box below depicts an exampleof conict mitigation in northern Kenya.


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Conict mitigation in northern Kenya

nreliable and uneven seasonal distribution of rainfall in pastoral

egions o nort eastern Kenya resu ts in great i erences in sur ace

water availability from year to year. Dams and pans in some areas may

ll up while others go dry even in the same district. Such disparities in

ain a an avai a e water orce ivestoc er ers to migrate in searc

f water, sometimes far from traditional grazing grounds and water

oints. In northeastern Kenya, this often means crossing international

orders into Ethiopia or Somalia. This perennial search for water is the

underlying source of conict between pastoral communities. The level of

on ict wi vary, an can e among in ivi ua s, etween c ans, etween

water management committee and the local community, or betweenommunities across national borders.

Causes o con ict

Lack of dened ownership of water sources (pans and dams).

Complex clan relations which are highly heterogeneous within

ommunities, leads to competition between clans for access to

water.

Lack of clear by-laws for water users associations in agropastoral

and pastoral communities

Absence of, or corrupt water management committees.

Disparities in water fees charged by management committees.

n ivi ua s encing o access to pans/ ams.

Upstream water a straction

Mitigation initiatives

ocal communities, especially with support from the relevant authorities or

xternal agencies, have taken initiatives to manage/mitigate conict over

water at different levels. In Kenya (and other countries) the key approach

as een aci itating ia ogue aime at creating mutua un erstan ing

among groups and fostering peaceful coexistence. The following are some

ptions that have been used in Mandera for resolving conict.

Forming water user associations and management committees.

Ensuring suc management structures ave c ear an en orcea e

y-laws.

Capacity building programmes that target both users and

management committees to strengthen their ability to deal with

on ict.

Forming village and cross-border peace committees to facilitate

dialogue and awareness raising.


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F gure 5. Plann ng and des gn ow chart for ponds and dams

Problem identication, identify project objectives

s ma e wa er eman

> Establish scale of project

Does

s te appearfeasible?

lanning

[Manual labour, draught animal traction, or

mec an ze excava on

na ec n ca es gn

> e a e opograp ca survey

> os on o e am wa an sp way

> apac y o e wa er reservo r, e gand length of the dam wall

> esign the foundation

> esign the dam wall

> es gn sp way

> es gn wa er ex rac on

Community

soc o-econom c survey

General feasibility and planning

> Water quality-health considerations?

> What quantity needed vs. available?

> Is it economically feasible?

> What environmental impacts?

Preliminary costing

NO

Is project still

feasible?NO

Site identication and assessment

> Site gradient, along and across valley site (if a dam)

> on pan or am: s wa s ruc ura an ow g

ommun y cos s ar ng

Legal issues, permits

Community mobilization

Community management

s ruc ure,

ra n ng nee s assessmen

Ownership,

ega aspec s, an enure

continues to next page

If a valley dam with wall higher

than 3 metres...NO

Get technical

ass stanceES


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C apter 3 Genera easi i ty an p anning

3.1 Intro uction

To determine whether a pond or dam project is feasible requires look-ing closely at its technical and economic viability as well as the envi-ronmental and social impacts. It is important that these are shown to

be positive. A detailed format for doing a thorough feasibility reportappears in Annex 1.

The most successful projects are those identied and implementedby community groups. This instils a greater sense of ownership by thecommunity who are then more likely to engage in the active mainte-nance of the dam, pond, reservoir and catchment area.

Key questions

These are some of the key questions that you will need to answer at the outset:

What will the water be used for?

Will the water be clean enough for the intended purpose and ifnot, can it be improved?

ow much water is needed?

ow much water will the new source provide?

What will the project cost? What percentage of this can thecommunity aord?

ow much will the facility cost to maintain and operate? Canthe community aord this?

There are ve components to the feasibility assessment. These are:

1. Assessing the quality of the water that will be harvested.

2. Estimating how much water will be needed, to compare withthe capacity of the catchment to supply water.

. Making a preliminary site assessment.

4. Estimating the costs of constructing the pond or dam.

5. Doing an Environmental Impact Assessment. This is requiredby law in most countries.

3.2 Water qua ity an sanitation

The rainwater runo which lls ponds and reservoirs ows overground that is usually contaminated. The ground on catchment areascan have animal droppings, human excreta (especially from youngchildren) and other rubbish on it that will pollute the water. While this


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ater is suitable for livestock, small-scale irrigation and constructionork it is NOT safe for drinking. When planning, be sure to survey

the catchment and identify all possible sources of contamination thatcould jeopardize water quality and users health.

Catchment pollution in northeastern Kenya

orondille is a small settlement in Wajir District. The people rely on a large

pan, located close to the settlement, for their water supply. There are no

draw off structures so women collect water directly from the pan. The

main catchment for the pan is on the other side of the pan, away from the

settlement but population growth and livestock coming to drink at the pan

has meant that a pathway has been formed through town and into the pan.n the rainy season this pathway carries runoff into the pan, collecting all the

waste, including human faeces, from the town and depositing them into the

pan. Even though care has been taken to protect the main catchment, the pan

is still being polluted via an unanticipated catchment.

The community at Korondille are unaware of the health risks caused by theunoff through the town and have made no attempt to correct the problem.

ossible measures to reduce the pollution would be to divert town runoff away

from the pan. Alternatively the temporary settlements in the new catchment

could be moved away from the runoff path and the catchment rehabilitated

to provide better quality runoff.

If the purpose of a pond or a dam is to get clean water for domes-tic needs, then the water should be drawn from an enclosed hand-dug

ell below the dam wall. Drinking untreated water from open watersources is not recommended (unless it has rst been boiled) as it maycause water-borne diseases such as dysentery, diarrhoea or typhoid. If

ater based diseases such as schistosomiasis (bilharzia) carried by wa-ter snails are present in the area, people should be discouraged from

entering the water.

.3 Estimating water demand

o estimate how much water is required and for how long a periodsome simple calculations are required. The demand for water fordomestic purposes, livestock and irrigation can be estimated bylling in the relevant rows in Table 1 below. First, determine from

available rainfall data for your district, or from asking knowledgeablecommunity member, how long the typical dry season lasts or thelength of period when stored water is being used.

o determine the water requirement for any particular householdor community, information on the number of people, livestock and any


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irrigation requirements needs to be gathered. By making a copy andlling in the table below you can calculate the approximate water useof a given village or group of households (to nd an average). At thedistrict level, recent census data is usually available on human andlivestock populations. In Tanzania this data is available even at villagelevel.

In areas where beer quality water sources are available for do-mestic consumption, such as a hand-dug well or rainwater tank, waterfrom a dam or pond will only be required for livestock or irrigation. Besure to ask about such sources when doing the feasibility study.

Estimating water demand

A copy of Table 1 also appears in the feasibility report in Annex 1.

Table 1 Estimating water demand

Item Population Consumption rate(litres/day)

Total

(litres/day)

People x 20

Camels x 15

Cattle x 15

Sheep/goats x 3.5

Donkeys x 15

Irrigation x 20 l/buckets/day

Other + 10%

(seepage+

evaporation loss)

Total (litres/day)

Total (m3/day*)

*divide total litres by1,000.

Livestock water demand

There are standard gures for the dierent types of livestock, as shownin Table 1. It is oen the case that once a large new water supply is built

within a community, people will bring their animals to drink ratherthan go to other sources further away.


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Irrigation water demand

o estimate the water requirement for irrigation, consider the main

factors, such as the irrigation method used (furrow, bucket, drip), thesoil type (sandy, loamy, clay), climate, type of crop and its growingperiod.

See Annex 2 for a table showing typical crop-water requirements ofmajor crops. It is beer to over estimate the quantity of water neededfor irrigation than underestimate.

he capacity of a catchment to supply water

sually the runo from a catchment will be more than su cient to

ll the pond or reservoir. Only in cases where a catchment is verysmall and there is lile sign of runo will further investigations needto be undertaken. Usually, the descriptions from local people whohave watched rainwater runo produce temporary streams or evenoods during torrential downpours in the wet season should providesu cient evidence that there will be su cient water to ll the reservoir.

ore details are provided under site selection below.

.4 Site investigation an se ection

opograp ica survey

otential sites for dams and ponds need to be measured to establishhat volume of water they might be able to store. For very small

reservoir areas (less than 500m you might be able to use a simpletool such as a line-level or circular level (see Tool 1 in Chapter6). For larger dams or pans (above 3 metre dam wall height) it will benecessary to bring a survey team to site and map out the whole area.

ite selection for pondshe best sites for constructing ponds are in places with deep clay, or

silty soils, where surface run-o accumulates during the rainy season.he land surface should be fairly at, ideally with a slope of not more

than 4 per cent (4cm per metre). A natural depression where watercollects during rainy seasons is a suitable site.

he catchment area should be su ciently large to generate ade-quate runo water to ll the pond. Ideally, a pond should be locatednear a gully or a natural waterway, which carries water during and af-

ter rainfall events as this water can easily be diverted. Avoid diggingponds near or downstream from livestock enclosures or mines as theseare likely to suer from organic or chemical pollution.

A suitable site should have deep ne textured soils, preferably clay-ey. Coarse textured sandy soils should be avoided as these are highly


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permeable and water will drain through them easily. Soils with a lowpermeability (e.g. soils with high clay content) should be used for theoor and sides of the pond to avoid seepage losses. If seepage is high,puddling and compacting of the oor may be necessary. Sites with un-derlying strata of sand, gravel, limestone or fractured rock at a shallowdepth may result in high seepage losses and should be avoided (seeSoil analysis on page 38). All other factors permiing, a pond should

be located in such a way that the stored water may be used directlywithout the need for pumping and piping.

ite selection for dams

When undertaking the site investigation the following points need tobe considered.

he seasonal runo from the catchment feeding into the valleyneeds to be su cient to ll any reservoir constructed.

he walls of the earth dam should be situated in a narrow partof the valley. Preferably at a place with a natural depression

just up stream producing some additional storage capacity (seeigure 6).

he dam wall needs to be built in a part of the valley which

provides a water-tight valley oor and sides of either clay oruncracked rock.

he valley oor should not be too steep and sloping as this willreduce the storage volume of the reservoir.

he dam wall should be situated at least 100 m from any bendsin the valley to prevent currents causing erosion when heavyruno occurs.

Suitable clay soils for building the dam wall needs to be avail-

able. Preferably these should come from a borrow pit in thereservoir and from excavating the spillways.

eservoirs should not contain boulders or rock outcrops be-cause they might cause leakage unless covered with clayeysoil.

Natural depressions in the banks of a reservoir should, whenpresent, be used for spillways in order to reduce constructioncosts (see Figure 7).


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oil survey and analysis

The purpose of this exercise is to see whether the local soils are

suitable to use when constructing the dam wall, and to estimate thepermeability of the soil in the impoundment area to understandwhether the site will hold water or lose it all through seepage.

Soils can be classied on the basis of their texture. The nest soilsare clayey and these are impermeable (watertight) and do not allowwater to pass through them. Silty soils are not as ne as clays and morepermeable and unstable. Sandy soils are coarser still and quite perme-able allowing water to pass through them easily. Gravel and soils witha high gravel content are very permeable. Most soils are made up of amixture of clay, silt, sand and gravel.

The rst step is to dig adequate test pits along the dam wall andthroughout the oor of the dam or pond to provide soil samples fortesting (see Tool 2 in Chapter 6).

There are various tests which can be carried out to determine whattype of soil is available at the site. The rst analysis is to establish theseepage rate of the soil (see Tool 4 in Chapter 6). This is a comparativetest so it is helpful to compare the results with a soil with high claycontent (and low permeability) in order to establish the relative perme-ability of the soil samples.

Aer testing the permeability the soil should be tested to determinethe clay content. A simple eld tool for establishing the percent claycontent is described in Tool 3, Chapter 6. It is important to recognizethat some sorts of clay (e.g. black coon soil) must not be used forconstruction because it cracks badly when it dries out.

In order to decide whether the available soil is suitable for storingwater or dam wall construction it is necessary to have a minimum of30 per cent clay content. Simple guidelines for dam construction are asfollows:

he soil with the highest clay content should be used for thekey (cut-o trench), core and diaphragm of the dam wall.

he soil with the next highest clay content should be used forthe upstream side of the dam wall and for a blanket to cover the

hole dam when completed.

he soil with the lowest clay content (the most sandy soil)should be used for building the downstream side of the dam

all.

Estimating spillway sizeThe surplus water of a small earth dam reservoir must be dischargedsafely, otherwise the dam wall will be washed away. Surplus runomust therefore pass over a spillway that is large enough to safely


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Manual labour

Ponds and small earth dams can be constructed manually in several ways:

A community can provide manual labour during a dry seasonfor construction of their pond or dam. The value of their labourmay be regarded as cash input by a donor organization willingto contribute a similar amount for payment of technicians toassist the community.

A farmer can hire people to build his pond or dam for a xedprice, usually between Ksh 100 and Ksh 150 (US$ 1.25 to $2) forevery cubic metre of soil excavated and transported in wheel-

barrows to the dam wall. An able bodied person can excavate

and transport up to three m of soil in a day.A simple way to distribute the work is to divide up the areato be excavated. Each cubic metre of soil to be removed can bemarked as a plot (see photo section) and given to a person oncontract basis. Plots can be pegged out in dierent shapes, allhaving a volume of 1 cubic metre.

Draught animal powerOx scoops have been used for construction of ponds and earth dams

in Machakos and Kitui districts of Kenya since the 1950s, and morerecently in Garissa. A man with two trained oxen, a plough and an oxscoop can excavate and transport up to 30 m of soil in a day, or tentimes as much as could be moved manually.

In areas where few households are able or willing to provide man-ual labour, it might be viable to use ploughs, scoops or carts pulled byoxen, donkeys or camels. The cost of the scoops, ploughs and carts can

be covered by the need to purchase fewer hand tools and by the lowercost per cubic metre of soil.

Mechanised excavation

Mechanised excavation using soil moving equipment can be usedin places where farm tractors are used instead of animal draught. Insome cases, particularly for the construction of larger reservoirs whereseveral hundred cubic metres of soil needs to be excavated, it might

be economically the most viable option (see Table 2). Even if it may beslightly cheaper to hire a tractor, this needs to be balanced against theemployment opportunities and degree of ownership that will resultfrom hiring local manual labour. Such decisions should be made withthe community and will also depend on the local economic conditionsat the time. For example, compare the cost of hiring a farm tractor orcommunity members willingness to provide free or subsidised la-

bour. The most expensive option is to hire a bulldozer for earth mov-


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ing. In addition to the cost of about Ksh 5,000 per hour, a mobilisationfee of several hundred thousand shillings has to be paid plus daily al-lowances for two or three drivers and their supervisor. In all, the totalcost may be about Ksh 60,000 per working day.

stimating costs

he table below gives an example of the theoretical costs of excavatingthree dierent types of water storage reservoirs of volumes rangingfrom 500m to 5,000m using dierent methods of excavation: manualby hand using shovels and wheelbarrows); oxen (as draught powerto pull ox scoops, ploughs and carts); tractor with plough, scoop andtrailer and bulldozer. The same table can be used for estimating thesecosts, rst by nding out actual local rates for each option, then llingin the quantity of soil to be excavated.

Table 2 Worksheet for estimating cost of excavating

ype ofeservoir

Constructionethod*

Reservoirvolume(m

Watero soilatio

Excavatedsoil (m )

Coster

(m

Total cost(Ksh)

Cost perm ofwaterstorage(Ksh)

example: Tractor 500 1:1 500 x 150 = 75,000 150

ond anual* :1 x ___

ractor* :1 x ___

xen* :1 x ___

example Tractor 500 1.5:1 33 x 150 = 49,950 100

illside

dam

anual 1.5:1 x ___

ractor 1.5:1 x ___

xen 1.5:1 x ___

example Tractor 5,000 :1 1,670 x 150 = 250,500 50

ulldozer :1 x ___

anual :1 x ___

ractor :1 x ___

xen :1 x ___

This relates to whether excavation is done manually with shovels and wheel barrows,using draught animals with ox scoops, ploughs and carts or by hiring a bulldozer.


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Estimating the benets

The main cost for a dam or pond is paid at the time of construction

but the benets can be calculated over the life of the reservoir or atleast 10 years, assuming it will eventually ll with silt and need to berehabilitated. Economic benets will include the value of labour andtime saved fetching water and watering livestock. Benets may also re-sult from improvements in the condition of livestock and small stock,cash from sale of irrigated farm produce and value of food grown for thehousehold.

It is helpful to estimate the cash value of the benets - especially ifa community is currently spending scarce cash on buying water. Thefeasibility study should consider additional income, time and labour

saved resulting from any project and comparing these with the cost(see Table 3).

Table 3 Estimated annual value of benets from a 1,000 m3

water reservoir

Examples of annual income and savings Value (Ksh)

Labour saved on fetching water (Ksh 5,000 x 3 months) 5,000

Labour saved on watering livestock (Ksh 5,000 x 3 months) 5,000

Income from sale of tomatoes and kale from one quarter

irrigated acre

2,000

Savings from household consumption of tomatoes and

kale

500

Total income from a 1,000 m3 water reservoir after a rainy

season

42,500

Establish the most cost-effective options

If suitable sites exist the construction of valley dams is less expensiveper cubic metre of stored water than the construction of excavated tanksand ponds. This is because less material needs to be moved for eachcubic metre of storage capacity created. The most expensive option (as-suming the labour is being paid) is the manual excavation of tanks andponds because only one cubic metre of water storage capacity is cre-ated for each cubic metre of soil excavated.

The cheapest construction method is to use oxen if available. Thecost can be as low as Ksh 20 per cubic metre of storage capacity createdin the case of valley dams. This type of dam is, however, the mostdi cult for a community, farmer and/or water technician to construct.

Where feasible another option is a small hillside dam constructed


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ny environmental impact assessment should include a risk as-sessment to consider the likely eects of a worst case event, such asan earth dam wall being washed away in a major ood. An alternativelocation for the dam should be found if households or downstreamselements might be put at serious risk by a washout.

Checklist of impacts of earth dams, pans and ponds

Positive impacts Negative impacts

. rrigating elds and tree nurseries

for generating income and re-

planting forests.

2. Watering livestock near villages

aves time and reduces erosion

caused by cattle tracks.

3. Providing domestic water from

a hand-dug well generates

income and can lead to health

improvements.

4. aising ducks, geese and sh

farming for food and income.

5. Making bricks and construction

works for income generation.

. educing water-borne diseases by

providing improved water supply

for domestic use.

7. Saving peoples time by reduced

walking distances to fetch water.

8. educed impact of oods by storinginitial oodwaters, controlling

erosion.

9. aising the water table down-

tream of ponds and dams, higher

water levels in hand-dug wells.

0. Increasing the value of land near

an earth dam, because of all the

above benets.

1. Improving incomes using thewater, through the money-making

activities described above.

. Loss of some land taken up by the

pond or reservoir and its spillway(s).

2. Risk of increased cases of malaria

(can be reduced by introducing

Tilapia nilotica to eat mosquito

larvae).

3. Risk of increased cases of bilharzia

(schistisomiasis), cholera, dysentery

and typhoid.

[Note: disease risk can be reduced by

fencing reservoir and drawing water

from hand-dug wells or draw-off

pipes and if people do not bath and

wash clothes in the reservoirs].

. Increased soil erosion along roads

due to people and animals coming

for water at the dam or pond.

5. Risk of dam wall collapse if poorly

designed or constructed incorrectly,

releasing a violent ash-ood

damaging everything in its path.

. Siltation of dam reservoirs shortens

the lifetime of dams unless proper

soil conservation is implemented in

the catchment areas.

7. Risk of people and animals drowning

if they try to bath or swim across a

dam reservoir.

8. Impact on downstream users who

may be deprived of water or subjectto pollution or increased sediment

load due to upstream usage.


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Once the feasibility study has shown which type of water

storage structure is viable, this chapter explains:

How to calculate the exact volume of the water

reservoir, the height and length of the wall for dams

and embankments for ponds.

How to design the foundation, dam wall or

embankment and spillway.

How to prepare the bill of quantities, calculate theexact costs and develop the construction plan.

How to peg to the site and what is involved in the

construction.

Chapter 4 Design andconstruction


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6

C apter 4 Design an construction

4.1 Intro uction

For small ponds and earth dams on sloping land of sizes not exceeding1,000 m , these calculations are fairly easy and are done using simple

methods. For larger structures, always seek technical assistance for the

calculations, as small mistakes in the design phase can make the whole

project fail and not hold water.

In particular, earth dams in valleys involve advanced constructionmethods that require experienced technical assistance to design the

structures and supervise the construction. This is because valley dams

are situated in seasonal water courses which ood during heavy rains.

Spillways must be designed to discharge surplus water safely. Thedam wall must be strong enough to withstand several metres of waterpressure from ash-oods.

4.2 Design and construction of smallearth dams in valleys

This section will lead the reader through the steps of designing and

constructing a valley dam. Earth dams in valleys should always bedesigned, calculated and supervised by an experienced person, andalways seek advice or a second opinion from skilled engineers if there

are any hesitations. This is because failure of a valley dam may have

disastrous consequences.

Design

Through the feasibility study we already have good information aboutthe site. We have a fair idea how the dam will look and what costs

are involved. Now we need to precisely position the dam wall and

spillway, design the dam in detail and make exact cost calculations,

to allow us to hire contractors and/or go ahead with the constructionwork.

Now we need to make a detailed topographical survey and on the

map precisely locate the dam wall and the spillway, to enable us to

exactly calculate its storage capacity and the height and length of the

wall. Thereaer we will design the foundation, the wall and the spill-

way. This will give the basis for preparing the bill of quantity (the vol-ume of soil to be moved) and planning for and calculating the costs of

the construction phase.


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8


ndicate the position for the dam wall and the spillway on the map.

Bench Mark

Horizontal centreline

Rocks

istance

oint0 1.5

1

5.2

2

8.0

3

11.7

4

14.0

5

17.0

6

20.7

7

22.0

8

27.6

9

41.6

10

1.

2

1.

7

4.

0

5.

1

5.

5

4.

8

4.

5

1.

81.1

Figure 9. Prole of the dam site.

Capacity of the water reservoir, height and length of the dam wall

The approximate capacity of the reservoir taken from the feasibilitystudy, should guide the estimation of the height and length of the damwall. This calculation will have to be repeated a couple of times untilthe height of the dam wall is nally established. First nd and markout the contour line that you believe corresponds to the approximatewater capacity. On the same topographical map, the shape of the water

reservoir is marked, which gives the maximum width, maximumdepth and the throw-back, that is the full length of the reservoir whenit is full of water, (see Figure 10). See Chapter 6, Tool 6 for two methodsof calculating the reservoir volume.


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not be too wide for that will increase the volume and cost of earthworks. The minimum width of a crest should be 3 to 4 metres, for let-ting vehicles pass over the dam wall. On very small dams (less than1,000 m two metres is enough.

The type of earth dam wall to construct depends on the availabilityof dierent types of soils. At this stage, the soil analysis from the feasi-

bility study may have to be complemented with further tests to makesure enough of the needed types are available. Three common types ofearth dam wall are as follows:

Homogeneous dam wall. If the soil samples of a dam site have the

same type of stable soil with 20 to 30 per cent clay (especially clayeygravel, clayey sands) or alternatively inorganic clay, a dam wall is builtof the same type of soil throughout. This is called a homogeneous damwall, i.e. all made of the same material (see Figure 14a). It is the easi-est type of dam wall to construct. Normally, homogeneous dam wallsshould only be built on smaller dams, at the most up to a height of 6metres. Where higher dam walls are required the design should bechanged to a zoned dam wall as described below.

Zoned dam wall. This is the most common type of dam wall. Itconsists of a key and a core of clayey soil whose sides are supportedwith graded gravels and sands or sandy soil (see Figure 14b). It is suit-able where clayey soils are available only in limited supply. It is also amore stable and economical design than a homogenous dam wall be-cause it is built with steeper slopes, thereby reducing the cost of earth

Table 4 Example: Calculating the outline of the base for a dam wall

Point Depth fromcentre tothe ground(m)

Gradient ofupstreambatter3:1

pstreamength ofbase fromkey (m)

Depth fromcentreline to theground(m)

Gradient ofdownstreambutter 2.5 :1

Downstreamength of basefrom key (m)

1.2 X 3 3.6 1.2 X 2.5 3.0

2 1.7 X 3 .1 1.7 X 2.5 4.25

3 4.0 X 3 2.0 4.0 X 2.5 0.00

4 5.1 X 3 5.3 5.1 X 2.5 2.75

5 5.5 X 3 6.5 5.5 X 2.5 3.75

4.8 X 3 4.4 4.8 X 2.5 2.00

7 4.5 X 3 3.5 4.5 X 2.5 1.25

8 1.8 X 3 .94 1.8 X 2.5 4.50

1.1 X 3 ,4 1.1 X 2.5 2.75


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esign drawings

rawings useful to prepare for the construction are:

plan of the dam wall and spillway.

cross section of the dam wall.

prole of the dam site (longitudinal drawing of the dam wallincluding key and crest).

An example of a plan of an earth dam with homogenous wall isshown in Figure 15. The plan compiles all data on the catchment, dam

all, core trench, spillway, reservoir and water abstraction method.

A spillway being lined with stone.


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Figure 15. Complete plan and data for an earth dam

Bench mark

Freeboard Water levelCentre line

Convex crest

Allowance for settlement

Clay key

Rock

Concrete

collars Downstream batter

Upstream batter

Crest Centre line

Pipe


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complete design drawings, design reports, and must be signed by aqualied engineer.

Make sure all documentation for the dam project is archived safelyfor any future extensions, repairs or other alterations.

Construction

Before construction work begins check that the following criteria havebeen met and relevant procedures followed:

. suitable site for the dam has been identied and its feasibilityinvestigated in terms of the issues highlighted in Chapter 3.

2. wrien agreement on the ownership of the dam site, an ac-

cess road, usage of water from the dam and conservation of

water from pounds pans and dams.pdf

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