A sand dam in semi-arid eastern Kenya.
Note: Thanks to Harold Miller, a loyal Reports from Kenya reader, for introducing me to sand dams many, many years ago.
As I sit on my computer here in Lumakanda, I read about robots that flip hamburgers for McDonalds, self-driving cars, and so many other amazing technological developments. Therefore it is refreshing to learn about a simple, ancient technique that benefits people with essential year-around water – sand dams.
In a semi-arid area it may pour during the rainy season and much of the water flows away in small streams. Then during the dry season, which can last for six or more months, as the streams dry up there is no water. Women and sometimes children then have to spend hours and hours per day searching and fetching water. If people build a normal dam, the water will collect behind the dam, but evaporation in the hot climate will soon empty the reservoir. If the dam is silted up with sand, the water then doesn’t evaporate and lasts throughout the dry season. Moreover the water is kept safe from contamination, for example, by livestock defecating in the water.
There is an organization based in England called Excellent Development which promotes the building of sand dams. Since 2002 this organization has built 1120 dams in nine countries, benefitting 1,077,763 people. Their goal is to build 1 million sand dams to provide water to 500 million people by 2040. Here is a quote from their webpage:
Water behind a sand dam raises the water table in the surrounding area which improves the soil, creating better conditions for crops and grazing. More trees can be planted which ensures that more water infiltrates the ground and less soil is washed away – creating a virtuous cycle of soil and water conservation.
This is a diagram of how the dam works as the soil and water flow over the dam but the sand sinks. There needs to be solid bedrock under the stream so that the water does not percolate into the earth. Therefore it is not possible to build a sand dam everywhere. On the other hand since most of the water flows over the dam, one stream can have a number of sand dams on it. Also, since most of the water goes over the spillway in the dam, it does not cut much into the amount of water for the people downstream from the dam.
It takes two to seven years for a dam to be completely filled up with sand. A dam can hold up to 40,000,000 liters (10,000,000 gallons) of water.
The water can then be accessed by digging a hole or putting in a pump to draw the water next to the dam.
Another advantage to sand dams which are always quite modest in size is that it can easily be constructed with locally available materials and well within the capabilities of any African mason. Frequently the effected community itself will assist in building the dam. As you can see from the picture above, women can help with the construction. Unlike the massive dams that governments like to built, the sand dams cost a modest amount. The average cost is about $7500 and can last fifty or more years.
Another advantage to the sand dams, as can be seen in this picture, is that there is water for irrigation of crops during the dry season. Notice in this picture there are two sand dams one right after the other on this stream.
The Kamba counties of Machakos, Makueni, and Kitui east of Nairobi are building about 130 sand dams per year.
Countries in Africa and the Middle East that have sand dams (dark green) or the potential for sand dams (light green).
Sand dams therefore are an ancient low-tech, cheap, easily installed in the right places with bedrock, to provide people in arid and semi-arid climates to be blessed with year around water. Which is more important – building a sand dam or a robot to flip hamburgers?
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