Water from Small Dams

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5.3 ConstructionPegging out the outline of a hillside dam is done by hammering a peg into the run-offline of the rainwater. Preferably, the peg should be placed in a depression in the run-offline, because that will provide free storage capacity.A plan and a photo of a hillside dam that is placed correctly across a run-off line ofrainwater. The two ends of the dam wall must be horizontal to function as spillways. Ahorizontal line can be found by either a transparent hosepipe filled with water or acircular transparent hosepipe filled halfway with water. Please, see Chapter 8 for details.Excavation workThe excavation and soil works for a small earth dam on a hillside site can be donemanually, with oxen, a plough mounted on a farm tractor, or a crawler. The constructionwork involves excavating soil <strong>from</strong> the central pit and placing it in a semi-circular linealong the downstream side of the excavation as shown below.The curved heap of soil will become the dam wall, while the excavated pit will be thewater reservoir. The size of the dam wall and its reservoir depends on the capacity forremoving soil <strong>from</strong> the reservoir and placing it on the dam wall. The gradient (slope) ofthe sides of the dam wall should be 2:1, which is 2m of width for every 1m of height.26
For manual excavation, divide the area to be excavated into “plots”, each plot beingexactly 1 cubic metre as shown above. Each plot is numbered and given to an “owner”.Plots are being marked out with wooden pegs.Excavation work is halfway completedAn ox-scoop with two men and oxen can excavate and move more soil than 12 men.27
Page 1 and 2: Water from Small DamsA handbook for
Page 3 and 4: ContentsAcknowledgement ………
Page 5 and 6: AcknowledgmentsMuch gratitude is du
Page 7 and 8: TECHNICAL VOCABULARYASAL = Arid and
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: Another very positive feature of hi
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

Water from Small Dams

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