Water from Small Dams

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ForewordThis handbook on water from small dams by Danida in Kenya has been produced at atime when Kenya through the newly restructured Ministry of Water and Irrigation hasestablished Regional Water Services Boards whose mandate now includes that ofdesigning and constructing small dams for rural water supply. Indeed small earthdams as water sources are needed most in arid and semi arid lands where fresh watersupply is a priority for vulnerable pastoralist communities. Besides the provision ofwater for domestic needs, small earth dams otherwise also referred to as water pansare good water sources for livestock.Water from Small Dams is a handbook that is expected to serve as a guide fortechnicians and water users who are contemplating to design and construct small earthdams. It emphasizes the need for feasibility studies during the planning stage and alsodelves into other considerations before construction. Options for water supply areprovided by some descriptions of various types of dams such as charco dams, hillsidedams and valley dams. The issues of concern in planning for small earth dams such asdesign, construction and maintenance, bill of quantities and constraints/limitationshave been discussed as well.This handbook provides insights into site investigations, designs, cost estimates, legalaspects and construction and maintenance of small dams. This information is requiredby local technicians for planning and constructing small dams. Conditions ofownership and other water related legal issues and the significance of environmentalimpact assessments are discussed in the handbook. Photo illustrations and diagramsmake the information more comprehensive and easily understood by any reader.It is with the understanding of the information contained herein that wise decisionscan be reached when choosing the right type and size of small dams for given localenvironmental conditions. Finally, this handbook does underscore the importance ofwater sanitation through catchment and reservoir protection. This would ensure thatthere is quality and quantity in constructed small earth dams.Julius KiptarusDirector of Livestock DevelopmentMinistry of Livestock and Fisheries Developmentviii
TECHNICAL VOCABULARYASAL = Arid and Semi-Arid LandsASALCON = ASAL Consultants Ltd.Batter = Gradient of a dam wallBench mark (BM) = A fixed point for taken measurementsBerm = Area between a reservoir borrow pit and dam wallBase = Foundation for a dam wallBorrow pit = An excavation from where soil is takenBill of Quantities (BQ)= List of materials and labour, with costingCatchment = Area draining rainwater run-off to a common pointCentre line = An imaginary line through the centre of a crest atthe upper level of the freeboardContour line = Horizontal line connecting points of equal altitudeCrawler = BulldozerCrest = Top of dam wallDanida = Danish International Development AssistanceDiaphragm = Blanket of soil on upstream side of embankmentDownstream batter = Downstream slope of a dam wallDownstream toe = Downstream edge of a dam wallDraw-off pipe = Pipe draining water by gravityEmbankment = Dam wallEvaporation = Water lost as vapour from a water surfaceEU = European UnionFreeboard = Safety height of dam wall from maximum water levelGradient = SlopeHafir (Arabic term) = A type of earth dam for livestock and peopleInselberg = A massive bare rock outcrop common in the tropicsImpervious = Not letting water throughKey (Cut-off trench) = Trench of clayey soil to prevent seepageLive fencing = Fence of vegetation, preferably thornyMurram = A clayey soil packed with stones found under lateritesoilSeepage = Water seeping through soilSediment = Soil deposited in reservoirSettlement = Soil compacting and shrinking in height due to weightSIDA = Swedish International Development AssistanceSill = Low concrete wall across spillwaySiltation = Dam reservoirs being filled with siltSiphon = Pipe lifting water over a high point to a lower levelSODIS = SOlar DISinfection (of water)Spillway = Overflow channel discharging excess floodwaterStorage ratio = Volume of water in relation to volume of soilTurbid = Muddy, unclear water carrying sedimentThrow-back = Length of a reservoir full of waterTopographical = Relating to the shape and height of the landUNDP = United Nations Development ProgrammeUpstream batter = Upstream slope of a dam wallUpstream toe = Upstream edge of a dam wallValley dam = Dam constructed in a valley with a straight embankmentWashout = Section of a dam wall washed out by waterix
Page 1 and 2: Water from Small DamsA handbook for
Page 3 and 4: ContentsAcknowledgement ………
Page 5: AcknowledgmentsMuch gratitude is du
Page 9 and 10: Chapter 1.Introduction to small dam
Page 11 and 12: Borrow pits, also called murram pit
Page 13 and 14: Rock catchment dams can either bebu
Page 15 and 16: Chapter 2.Considerations before con
Page 17: It is difficult to estimate the wat
Page 21 and 22: If the answers to the questions lis
Page 23 and 24: 3.3 OwnershipValley dams are normal
Page 25 and 26: Chapter 4.Charco damsFarmers and ca
Page 27 and 28: Since there are no documented guide
Page 29 and 30: 4.4 ConstructionThe construction si
Page 31 and 32: Simple equipment for measuring leve
Page 33 and 34: Another very positive feature of hi
Page 35 and 36: For manual excavation, divide the a
Page 37 and 38: A hillside dam built by a tractorpl
Page 39 and 40: The rainwater runoff from the catch
Page 41 and 42: 6.4 Measurements to be taken of a d
Page 43 and 44: The sketch shows that a freeboard 1
Page 45: Homogeneous dam walls can be built
Page 48 and 49: 6.8 Bill of Quantities (BQ) and cos
Page 50 and 51: The table below shows all the tools
Page 52 and 53: 6.9 An example of a complete design
Page 54 and 55: It is a good idea to have an experi
Page 56 and 57:
Water drawn directly from a dam res
Page 58 and 59:
Usually, soil for building the side
Page 60 and 61:
The usual types of pit latrines wit
Page 62 and 63:
Silt traps made of vegetation plant
Page 64 and 65:
9.2 Washed-out dam wallsThere are s
Page 66:
ReferencesBrown, L.N. 1965. Small e
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Water from Small Dams

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