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[[Image:SubsurfaceDamSite.JPG|thumb|right|400px|Subsurface dam being built out of soil across a sandy riverbed in Kitui, Kenya, 2007. They are working in the dry season; note the riverbank is much higher than they are working.]]
==Suitable conditions==
* Siting requirements are similar to the [[sand dam]].<br>
* Subsurface dams should be built where sand volume is already sufficient to store water.<br>
- the possible dam construction sites may be too far from the water users<br>
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==Resilience to changes in the environment==
====Drought====
'''Effects of drought''':
'''Underlying causes of effects''': Less recharge of aquifer due to less rainfall; Increasing population & water demand; Size of aquifers – e.g. limited sand volume; Too much silt accumulates behind dam; Wells not sunk deep enough into water table; Incorrect siting causes leaking dams.
'''To increase resiliency of WASH system''': Competent siting & construction; Build sand dam in stages to reduce silt; Soil & water conservation techniques in upper part of catchment; Dig abstraction wells/pipes deeper.
==Construction, operations and maintenance==
'''General advice on cement''': A common cause of cracks in structures and linings (e.g. in tanks, dams, waterways, wells) is errors in mixing and applying the cement. First of all, it is important that only pure ingredients are used: clean water, clean sand, clean rocks. The materials have to be mixed very thoroughly. Secondly, the amount of water during mixing needs to minimal: the concrete or cement needs to be just workable, on the dry side even, and not fluid. Thirdly, it is essential that during curing the cement or concrete is kept moist at all times, for at least a week. Structures should be covered with plastic, large leaves or other materials during the curing period, and kept wet regularly.
'''Specific advice''':
[[Image:SubsurfaceDam.jpg|thumb|right|300px|Mechanics of a subsurface dam.]]
