Guidelines for predicting and minimising sedimentation in small dams

Lawrence, P. (2004) Guidelines for predicting and minimising sedimentation in small dams. Project Report. HR Wallingford Ltd.

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Abstract

Many of the small dams constructed in semi-arid regions of Africa rapidly fill with sediments, sometimes after only a few years. When dams silt up the rural communities that rely on them for cattle watering or small-scale irrigation are deprived of the water and food security that dams provide, and their livelihoods are seriously affected. Predicting soil erosion, sediment yields and dam sedimentation rates can be a complex task, requiring specialist expertise, and is generally poorly covered in small dam design manuals. This results in many small dams being constructed with little or no consideration of the impact of future siltation of a dam's life or on water yields. These guidelines were prepared to enable dams where siltation rates will be unacceptably large to be identified at the planning or design stage of small dam projects. Where siltation rates are expected to be large measures have to be taken to reduce sedimentation. Approximate methods for estimating the impact of remedial measures, such as catchment conservation or engineering interventions, on dam lives and water yields are also described. The methods were selected, or in some cases specifically developed, for use in typical small dam design studies. In such studies there is usually neither the site specific data nor the time and resources needed to carry out the more detailed studies that precede the construction of larger and more expensive dams.

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