Changes

Regions with highly erratic rainfall often have rivers with temporary seasonal sandy bed streams. They only experience heavy water run-off for short periods of time after rain. During such periods of high flows, large quantities of sand are transported downstream. Some sand can get trapped on the upstream sides of rocks outcroppings along the stream. Such sand traps form natural water storing aquifers. The sand dam technology provides a mean means to reproduce this water collecting mechanismand to increase the size of existing aquifers.  Water in natural collection sites is usually clean for drinking but quite finite and quickly gets depleted. Sand dams are an artificial improvement of sand beds where more water can be recharged and stored for water use. A dam of concrete, clay soil or stone masonry is constructed across the channel at specific sites to trap and hold back the sand during flooding; this creates an additional sub surface water bank to be harvested during the dry season.

Water in natural collection sites is usually clean for drinking but quite finite With an accurate and quickly gets depleted. Sand dams are an artificial improvement appropriate location choice the total amount of water available in the sand beds where more water dams can be recharged and stored for water use. A concrete wall is constructed across the channel at specific sites to trap and hold back the sand during flooding; this creates an additional sub surface water bank for harvestingover 6000m³.

 In Kenya, it has been used with good outcome in the Kitui, Machakos and Samburu districts. Other countries with similar dry environments such as the U.S.A, Thailand, Ethiopia and Namibia also have used it in numerous and divers diverse forms. Sand dam projects here have not only improved water availability, but benefited the community socially and economically. Locals are trained to participate in construction of the dam, maintenance, financial management, and also in natural resource management.

 Expert input is required to determine the best sitefor the dam and to make sure the project is adapted to the physical conditions as well as social circumstances of the local community. Problems primarily relate to aspects  Physically, the site must be suitable for construction of a dam locations , provide safe drinking water, and constructionbe able to use sand sedimentation to increase water availability. Accurate estimation Firstly it must be decided if the river is appropriate, secondly the best section of riverbed must be chosen, and then the optimum location for extraction.  Generally, the dam requires a sandy riverbed in a hilly area. Preferably the groundwater reserves riverbed consists of coarse sands layed on impermeable bedrock. The river should be seasonal but must have a base flow. Whether this is difficultthe case can be determined by the type of vegetation growing around the river. The river shouldn’t be too wide (max. Risk of erosion 25m) and contamination during the rainy seasonshould have two high riverbanks. With an accurate  These conditions and appropriate location choice also others related to, for example; climate, presence of boulders, or gradient of the total amount riverbed must be analyzed in detail to determine suitability of water available in the sand dams site. Also, though it can be over 6000m³artificially improved, the water quality must be good enough for drinking (not too saline, contaminated, etc.)

Regular checks If done timely, the maintenance required is not costly. Small malfunctions in the dam however can lead to destruction of the entire dam. Therefore, the dam should be regularly checked for cracks and repairs are required damage. Particularly after floods, and extreme temperature changes cracks are likely. These need to be repaired as soon as possible by a trained mason.  Further the outlet and upstream riverbed should be cleaned regularly to make sure the dam does not get blocked. Silt, rocks, dead animals, etc. should be removed regularly. This can also help prevent contamination of the water. The quality of the water in the well should be checked once in a while by an expert. 

First a trench needs to be dug. Its position is marked out using pegs. Then it is excavated and the soil placed downstream. It can also be dug out into bedrock. It should then be checked for weathering zones and cracks.  Then the dam is constructed. The method depends on the type of dam and the type of ground. The construction of sand dams in cascades improves total storage and efficiency and minimises minimizes seepage losses. Dams made of concrete, stone-masonry and brickwork require skilled labour for construction, but are stronger and have a longer lifespan.

* [http://www.thewaterchannel.tv/index.php?option=com_hwdvideoshare&task=viewvideo&Itemid=53&video_id=63 Kitui Sand Dams - CPWC]