Sand dams and other miracles

Tuesday, May 3rd, 2011

In some areas of Kenya – like where I live in Coast Province, finding clean water is almost impossible. With little rain and salty groundwater, people travel for miles with jerry cans to find fresh springs or river beds where they can dig for water.

For us, the question is often not “Do we want to help?”, but rather “Can we work out a way to help?”. And by implication, do we have the partners who can work in such challenging conditions? As you may be aware from earlier posts, part of my work this year is about partner development. I’m currently on the hunt for organisations that The Water Project can partner with in the future. This is a tricky assignment for me, and three months in to my year here, I’m realising that it is a slow process. It’s important we take the time to hear the inside story and make sure we do due diligence. We need to make sure we are giving our donors genuine value for money, as well as serving communities in the best and most sustainable manner possible.

To date, the partners we have are ‘well’ focused (excuse the pun!), in that they base their implementations on boreholes or hand dug wells, but as I’ve mentioned, this approach is not always appropriate. As such, another focus of this year is to try and diversify the approaches we fund. Each development situation, each community, is different and  it’s vital that we (and our partners) are able to think creatively when tackling WASH issues.

On Thursday I’m visiting a group who could well fit the bill. They’re active in a number of places in Kenya, and have a track record of designing and implementing sand dam projects. So, before I visit, I wanted to read up a little and try and understand their approach. What is a sand dam, and how can a dam filled with sand provide water? With the help of Wikipedia, let me try and explain what I’ve found.

In Kenya we have two rainy seasons and two dry seasons. In the wet, the rains come hard and fast, and flash flooding is common. The question is, how can communities harness the potential of the rains, to provide water throughout the year – especially during the long hot dry season between November and March? Is there a way that we can slow the flow of water to the sea, and store it for use throughout the year?

The first step in making a sand dam is to identify a river or stream (in the middle or upper sections) which has significant seasonal flow, and to find a section of the water course that has exposed the bed rock or at least the dense sub soils. Step two is to mobilise the community, and get their help as they collect sand, rocks and cement, as well as digging into the river banks to stop erosion around the sides of the well in the future. With these things in place, the construction of the dam can take place. During construction, a pipe is laid through the dam to allow for the future supply to be accessed.

Typically the concrete dam will be between 2 and 4 meters high, and allow for continued river flow through a sluice.  Next, with all the construction complete, is the wait for the rains. As rivers swell and the flow increases, so the dam is back filled with all the sand and silt that the upper sections of rivers typically carry down stream. In one or two seasons, the dam will become completely filled with sand, and the river will flow normally over the concrete dam. The sand dam is now ready for use.

The key to understanding the beauty of a sand dam, is to understand that there are gaps between the sand particles. As the river flows, these gaps (or pore spaces) become filled with water. In a typical dam, between 25 and 40% of the volume of the dam is made up of water. It is this water that is able to provide for the community.Not only that, but because the water has been filtered through the sand before it enters the pipe, it is typically suitable to drink right out of the tap! Pretty neat huh?

We think so, and are keen to explore ways of funding groups who know about this technology, and have proven experience of putting it to use.

I’ll let you know how it goes on Thursday, and keep you updated as we explore future opportunities. Good technology – simple and effective – the question now is whether we can find groups know what they’re doing, and who are suitable to partner with.

Thanks for reading – more soon!

(Sorry about the lack of images – if you’re interested why not do a quick Google search for “sand dam” and see what you can find?!)

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