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[[Image:Sand dam.JPG|thumb|right|150px|Sand dam construction in Kenya]]
[[Image:Sand dam diagram.JPG|thumb|right|150px|Cross section of a sand dam]]
Regions with highly erratic rainfall often have rivers with temporary seasonal sandy bed streams. They only experience heavy water run-off for short periods of time after rain. During such periods of high flows, large quantities of sand are transported downstream. Some sand can get trapped on the upstream sides of rocks outcroppings along the stream. Such sand traps form natural water storing aquifers. The sand dam technology provides a means to reproduce this water collecting mechanism and to increase the size of existing aquifers.
==Suitable conditions ==
[[Image:Sand dam flood.JPG|thumb|right|150px|Sand dam during flooding]]
Expert input is required to determine the best site for the dam and to make sure the project is adapted to the physical conditions as well as social circumstances of the local community.
====Operation====
[[Image:Sand dam scoop hole.JPG|thumb|right|150px|Women fetching water from a local aquifer through scoop hole]] [[Image:Sand dam scoop hole.JPG|thumb|right|150px|Closed well near a sand dam]]
First an appropriate site needs to be selected, depending on whether it is suitable for a sand dam or not. Then the best section of the riverbed is chosen. Then the dam is designed, depending on the conditions and the water needs of the community, and built. It takes a few rainy seasons to let the aquifer fill up. After that an extraction point is constructed such as a scoop hole or well. Then water can be extracted and used for drinking, agriculture, etc. Meanwhile the local community needs to be trained to manage and maintain the dam.
====Manufacturing====
[[Image:Sand dam trench.JPG|thumb|right|150px|Excavation of a trench for sand dam construction]]
First a trench needs to be dug. Its position is marked out using pegs. Then it is excavated and the soil placed downstream. It can also be dug out into bedrock. It should then be checked for weathering zones and cracks.