"A sand dam is a reinforced concrete wall built in a seasonal riverbed that captures and stores water beneath the sand. Seasonal rains fill the dam, which contains silt and sand. Water is then stored within the sand , making up 25-40% of total volume. Evaporation is minimised because the water is stored below the sand, which also protects it from parasite carriers such as mosquitoes and snails. The water is extracted by pipe filtration or shallow wells with pumps." "Sand dams raise the water table around the dam, allowing trees to grow naturally, and there is enough water for croops to be properly irrigated. Sand dams allow 97-99% of water to flow over the dam to communities further down stream. One sand dam can store between 2 million and 20 million litres of water."
Lorna Howarth, "An Ancient Idea for a Sustainable Future", Resurgence and Ecologist Jan/Feb 2013 (No link available) [verified 4/17/14]