The African Sand Dam Foundation (ASDF) and TCF have been partnering since 2012 to build Sand Dams in Makueni, Machakos and Kitui Counties in Kenya. A total of 30 sand dams have so far been constructed through the projects.
Pastoralists and farmers have collected water from seasonal sandy riverbeds since time immemorial, by digging or scooping into the sand. The reason is that if a natural barrier prevents the water from draining downstream, it is stored in the sand behind the barrier and below 50 cm water stored in the voids between the sand corn does not evaporate. Depending on the coarseness of the sand particles, up to 35-40% of the volume behind the dam can be water.
The natural barriers can be rock bars or undulations in the bedrock forming a natural dike. A sub-surface dam or a sand dam built on top of the dike enhances the natural barrier and increases the storage capacity. The water can then be extracted with a shallow well behind the dam wall.
The site survey and design of the dam is critical for the dams to last through seasonal flash floods and for the reservoir to fill with coarse sand as opposed to silt.
A recent analysis of the sand dams constructed found substantial financial benefits derived from the sand dam in addition to gains for the individual farmers and the communities around the dams in terms of quality of life. Attendance rate for children in school has doubled. Sicknesses has reduced and hygiene increased because of the clean water at close proximity to the homestead. Malnutrition is no longer an issue as every household is able to water a kitchen garden throughout the year. The ability to produce a high yield from irrigated farms with the option to sell excess has increased the families’ expendable income. Livestock is able to be kept and sold at a higher price. Families have more time to invest in their future and less stress about basic living amenities.
From an ecological perspective the sand dams are also very valuable as they recharge aquifers and rejuvenate the riverine ecology enabling increased vegetative cover and bio-diversity along the river.