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Abstract:
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The problem in arid and semi-arid regions of developing countries with irregular rainfall is storing water during a rainy season in order to preserve it for the dry one. An interesting and useful technique to solve the problem is to store water in sub-surface flow dams. Two types of sub-surface flow dams are defined, namely sub-surface dams and sand-storage dams. The former is constructed below ground level and it arrests the flow in a natural aquifer, whereas the latter is raised above ground level and it impounds water in sediments accumulated bythe dam itself. Climatic conditions of low rainfall, high evaporation, topography and hydrogeology are the main facotrs which influence planning and construction of sub-surface flow dams. It is necessary to make good investigations of new dam sites as regards these factors, for the success of the dam. Topograpnical and geological maps are appropriate instruments for regional investigations. The best instrument for finding actual sub-surface flow damsites is air photo interpretation combined with map studies and field reconnassance. It is important to incorporate data from studies carried outpreviously. Bedrock foundation, water storage capacity, water discharge recharge, specific yield and dimensioning of the dam are important factors to be considered when designing sub-surfacefloe dam schemes. The most common types of sub-surface dams are clay, stonemasonry and concrete walls. Sand-storage dams are usually constructed by concrete and stonemasonry. Water is extracted mostly by hand pumps from large diameterwells, or when topography permits, by gravity. Operation and maintenance requirements of sub-surface flow damschmes are less than that of bore holes and conventional open storage dams, provided water is supplied by hand-pumps or by gravity. /Kir09 |