Just a Drop’s work in Kenya focuses on Makueni County, a semi-arid area which is vulnerable to climate variations and drought which can often lead to severe water shortages and famine. Working with our local partner, Africa Sand Dam Foundation, we are constructing sand dams and rock catchments to ensure that communities have a lasting supply of clean water.
So what is a sand dam?
Sand dams are not only a low cost and low maintenance means of providing water for a community, but are also an effective part of climate adaptation and mitigation. They can provide a year-round source of water, and therefore help to overcome the water shortages that seasonal fluctuations in rainfall and drought can cause. One sand dam can store up to 20 million litres of water and supply water to up to 1,000 people!
Areas with irregular rainfall tend to have rivers with temporary seasonal sandy bed streams. During periods of heavy rain and subsequent high flows in these rivers, large amounts of sediment are transported downstream and end up trapped against rock outcroppings, where they form natural aquifers. Sand dams, then, are a means of reproducing this water collecting method. They usually consist of a reinforced concrete or stone masonry wall constructed across a sandy riverbed. Over one to three rainy seasons (though sometimes it may only take one), the dam fills with sand that has been trapped as it washes downstream. However, over a third of the volume trapped behind the dam is actually water that is between the sand grains which can then be extracted. This type of dam is also advantageous in that the water is less likely to become contaminated or evaporate away, meaning it is a safe and reliable source.
For constructing the dam, a trench must be dug and reinforced with vertical bars. The foundation can then be laid, made of two cement layers with barbed wire in between. Once the foundation sets, the trench is filled with masonry or mortar, and the final dam wall is built. After construction is completed, a means of water extraction must be made. The simplest ways of extracting the water are by scooping a hole in the sand from which the water will naturally emerge, or by burying a pipe in the sand and through the dam wall to a tank, tap or hand pump. Sand dams can then last around 30 to 50 years with almost no maintenance, and so are a very sustainable form of water supply.
The completion of a sand dam construction project means that many of the communities we work with no longer have to walk for miles to fetch their water. This seemingly simple change means the world of difference – not needing to walk long distances to collect water means women and children have more time for education and employment; the cleaner water supply means less risk of disease and loss of life; and there is higher food security due to the reliable water source for farmers.
Written by Helen Turner.