Changes

====Building the sand dam (and wing wall)====

* The method depends on the type of dam and the type of ground. The construction of sand dams in cascades improves total storage and efficiency and minimizes seepage losses. Dams made of concrete, stone-masonry and brickwork require skilled labour for construction, but are stronger and have a longer lifespan.

* Key into banks (sub-surface dams) or construct wing walls to avoid erosion around edges of the sand dam. Where wing walls are built, a good technique is to start from the wing walls and work inwards to the centre, since community enthusiasm lags by the time wing walls are constructed (if not built first), yet they are essential to proper functioning. Length of the wing wall varies according to bank characteristic: loose riverbanks, 7 metres; hard soils, 5 metres; hard & impermeable soils or rocks, wing wall is not needed. Planting napier grass along upstream riverbanks controls erosion and fixes the course of the river in a flood.