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Water Portal / Rainwater Harvesting / Surface water / Catchment and storage dams

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[[Image:dam icon.png|right]]

[[Image:Catchment dam.jpg|thumb|right|350px| Turkana men and women build a dam on the river Lokitaung in northern Kenya. Photo by AFP/Simon Maina.]]

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Water can be made available by damming a natural rainwater catchment area, such as a valley, and storing the water in the reservoir formed by the dam, or diverting it to another reservoir. Important parameters in the planning of dams are: the annual rainfall and evaporation pattern; the present use and runoff coefficient of the catchment area (e.g. bare rock catchments have high runoff coefficients, around 0.9); water demand; and the geology and geography of the catchment area and building site.

The water stored behind a dam should normally be treated before entering a distribution system.

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==Suitable Conditions==

Site reservoirs where the base will be impermeable (e.g. unfissured rock or clay) in order to save costs and prevent having to find a form of lining. Alternatively cracks and fissures could be sealed up with mortar or concrete. Rock catchment dams work well mostly in hilly or mountainous regions where other water sources are scarce. These types of dams should be bare and free of vegetation/soil. When siting for rock catchment dams make sure to maximize the natural topography – to get the best volume, make dams on the lower side of existing rock pools.

Winona

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