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Subsurface harvesting systems

1,335 bytes added, 19:10, 7 April 2012
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The use of sub-surface dams in naturally occurring alluvium creates groundwater storage upstream of the dam, raising the water table and preventing evaporation losses.A subsurface dam is constructed across a valley is a seasonally dry, sandy riverbed, by digging a trench down to the bedrock or other impervious layer. The dam, which is placed in the trench, may consist of a wall or screen and covered with excavated material until it is completely concealed. The refill material must be properly compacted. ==Suitable conditions==* Seasonal rivers in semi-arid regions with permeable sediments and an impervious layer at a shallow depth (maximum 3 to 4m deep).* River valleys with gradients of between 1 and 2% usually enable the highest storage.* Ideal where groundwater flow converges from a large catchment into a narrow passage.  {{procontable | pro=- Subsurface dams are not likely to deteriorate, with little danger of breaching <br>- Construction has long lifespan and require minimal maintenance <br>| con= - Leakage is often difficult to detect <br>- Downwater flow will be impacted to communities downstream}} ==Construction, operations and maintenance== ==Costs==* Materials costs and construction: US$1,400* Feasibility study: US$200* Technical support: US$275* Operation and maintenance: low ==Field experiences==A subsurface reservoir in Pernambuco, Brazil has an average depth of 4m, is 50m wide, and 500m long, storing about 4,000m3 of water.  ==Acknowledgements=
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