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Sand dams are a simple, low cost and low maintenance, replicable rainwater harvesting technology. They provide a clean, local water supply for domestic and farming use and are suited to semi-arid areas of the world. ==The Operation == A sand dam is a reinforced concrete wall (or a similarly robust and impermeable weir) built 1–5 metres high across a seasonal sand river. When it rains the dam captures soil laden water behind it – the sand in the water sinks to the bottom, whilst the silt remains suspended in the water. Research on Kenyan dams shows that only 1 to 3% of rainwater is retained behind any individual dam, the remainder continues its natural flow towards the ocean.〔Hut et al 2008〕 Eventually the dams fill with sand - sometimes after only one rainfall or over 1 – 3 seasons. 25 to 40% of the volume of the sand held is actually water. A mature sand dam can store millions of litres of water – refilling after each rainfall providing a year round supply of clean water to over 1,000 people. File:sand dam illustration 2.jpg File:sand dam illustration 3.jpg File:Find a rock base.jpg File:Build a concrete wall.jpg File:Rain fills it.jpg File:Sand sinks.jpg 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sand dam」の詳細全文を読む スポンサード リンク
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