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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 rock outcroppings along the stream. The sand traps form natural water storing aquifers. Sand dam technology provides a means to reproduce this water collecting mechanism and to increase the size of existing aquifers.

==Suitable conditions ==

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. Having a lead artisan per catchment area to decide on siting seems to help success rates. Physically, the site must be suitable for construction of a dam, provide safe drinking water, and be able to use sand sedimentation to increase water availability. Firstly it must be decided if the river is appropriate, secondly the best section of riverbed must be chosen, and then the optimum location for extraction.

==Construction, operations and maintenance==

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. Round bars are placed vertically along the trench to reinforce it. Then a foundation is laid consisting of 2 layers of cement with barbed wire in between. Once this has set, the trench is filled with masonry of mortar and hardcore. The wing walls and final dam wall can then be constructed. Finally any exposed parts of the construction are plastered.

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

* Timing is important: dams should be built during the dry season, but don’t build dams too close to the rains in order to avoid the trench filling up with water or the dam being washed away.

* 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 (cheapest and easiest) and brickwork require skilled labour for construction, but are stronger and have a longer lifespan.

After the dam is built, an outlet for water extraction must be constructed for drinking, agriculture, etc.. Hand dug scoop holes are the simplest possibility, however the water can easily be contaminated. Covered wells, with hand or rope pumps protect the water much better. It is also possible to construct an outlet pipe with a tap. In certain designs for sand dams, a pipe is shown that takes water by gravity through the dam wall. These are said to not work well due to either a blocked intake, a broken tap on outlet side and the possibility of weakening the dam wall. <br>

====Maintenance====