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[FAQ] Sand Dams
What is a sand dam?
A sand dam is a reinforced concrete wall built across a seasonal river bed. Sand that has been captured behind the wall holds water long after the rainy season has ended. Unlike other river sediment such as silt and clay, sand can hold large amounts of moisture ( up to 40% of the volume behind the dam is water). This means that a single dam can hold an incredible 2 to 10 million litres!
After refilling every rainy season, each dam provides a clean water supply for up to 1,200 people and animals in addition to irrigation for trees and vegetables. Furthermore, the effect of improving water availability in a 20km radius means that a sand dam may indirectly benefit up to 100,000 people. Water is drawn from beneath the sand either through a filtering pipe, or by simply collecting it from holes dug in the riverbed.
Why sand? What is the advantage over a surface dam?
Sand dams offer a number of advantages over surface dams in a semi-arid climate:
How are sand dams constructed?
Experience tells us that the successful construction of sand dams depends on two key factors: correct design and community ownership.
Excellent Development only builds dams where communities want them - demonstrated by their willingness to collect all the water, sand and stones required for construction. This amounts to 50% of the total cost. The communities build them too, so because they own the dams, they take great pride in the benefits they bring. Terracing the land around the dams improves their effectiveness and very little maintenance is required.
After the best site is chosen, the craftsmen employed by Excellent Development construct a timber frame as the basis for the dam. The frame is filled with stones collected by the community group members, along with cement to set the structure and barbed wire for reinforcement. The cement is mixed on the ground using shovels, and passed along a line of people to reach the dam. This goes on until the dam is full with cement. Community groups from different areas often come to help their neighbours build dams. This is part of the Kamba tribe's tradition of Mwethya where people work together to achieve great things. When the Kola community self help group built an extension to their dam in 2004, an amazing nine community groups came from as far as 30km away to help out!
How did MCC become involved in the construction of sand dams?
Sand dam technology draws on the innovation of local farmer, Joshua Mukusia, who began experimenting with rainwater harvesting about 30 years ago. MCC became involved with Mukusia several years ago... Today the spread of the technology in Kenya (over 500 dams have been built so far) is led by MCC's local partner Utooni Development Organization (Excellent Development). Africa is scattered with washed away dams, but partners of MCC, led by Joshua Mukusya have built over 450 dams, none of which has washed away.
Where are sand dams located?
MCC supported sand dam projects have been largely focused in Kenya, but working with local partners, MCC has also sought to transfer the technology across the region to semi-arid regions in Tanzania and Mozambique. Not just any dry riverbed can be turned into a sand dam. The areas suitable for sand dams are chosen based on a specific set of factors:
What do sand dams have to do with food security?
In Kenya, smallholder farmers are benefiting from increased livelihood diversification through the expansion of agricultural productivity in the vicinity of mature sand dams. Cultivation prior to the construction of sand dams was normally restricted to the wet-season. As a result of greater water availability the diversity and intensity of agricultural activity has increased substantially. Some farmers have chosen to diversify crop production including the growing of plants such as spinach, onions,kales, tomatoes, coriander, arrow roots, maize, and fruit trees.
What do sand dams have to do with climate change?
Climate change will continue to affect hydrological systems across Africa. In particular, the Intergovernmental Panel on Climate Change projects that climate
What do sand dams have to do with gender?
Women are central players in this social organization and in the actual building of dams. The sand dam results in significant labour savings for women who are able to spend more time on income-generating activities such as growing and selling vegetables. In addition, those who rely on dairy-producing livestock, particularly women, benefit from the increased seeding of grass alongside stream beds and on terraces.
“So when you grow too old to work, will you pass the land on to your children? Already I am giving the land to my children because I have to train them on how to [farm] for themselves. And when we grow old, we will have some of the things that can keep us in old age, like trees we have planted with Excellent and sand dam water that we will be able to sell. We will not depend completely on our children. There are some families where people do not know what they will eat, they don’t have money, they don’t have assets to sell. They will be a burden to their children. That’s what needs to be taught to communities, they have to think of old age, not [just] present age.”