Water from Small Dams

Chapter 9. Repair and maintenance9.1 Leaking dam reservoirsNewly built earth dams do not usually hold water for as long a period as expected duringthe first couple of years, due to leakages. The reasons and recommendations for curingleakages may be summarised as follows:Leakage problems in reservoirs and recommended solutionsPROBLEM REASON SOLUTIONWater disappearsthrough the floorof a damreservoir.Water seepsthrough anewly-built damwall.The floor wasnot madewater-tight,and holesmade byrodents,rotten treeroots, oldant-hills,forgotten pitsand trial pits,all drainwater into thegroundbelow.The soil inthe dam wallcontains airand waterfilledvoids.The holes must be sealed with clayey soil andcompacted. Stones and boulders must be removedfrom the floor, as water can seep along them intothe ground below. If some boulders are too large toremove, these should be covered with a thick layerof clayey soil to prevent seepage.Should a dam reservoir still leak after the floor hasbeen prepared as described above, the floor shouldbe compacted by either driving a tractor or a herd ofcattle repeatedly over the floor of the reservoir untilthe soil has been compacted firmly.Should the floor of a reservoir still leak aftercompaction, it can be sealed (puddled) with a layerof water-resistant materials, such as clay, powderedant-hills or lime, which are compacted onto thefloor.The voids will be compressed and the seepagesealed by the weight of the soil in the dam wallitself. This process will be faster when the soil ismoist and made flexible by water infiltrating fromthe reservoir, especially when it is full.Water seepsunder the key of adam wallThe key doesnot seal asandy layersituated deepunder the keyThe layer of sand can be sealed by placing avertical and upstream-curved arch membrane madeof thick plastic and/or ferro-cement along either theupstream or the downstream toe of the dam wall.An arched wall, made of plastic sheeting placedagainst ferro-cement and built along a raised stoneapron at the downstream toe, has proved successful.55