A subsurface dam is an impermeable dam built in a surface aquifer or a sand-filled river bed. The method entails that shallow flowing groundwater is collected upstream of the dam and pumped up or lead downstream with gravity pipe. Popular dam materials are concrete, masonry, blockwork, or stone-filled gabions with waterproof layer.
3500 m3 dam in Kenya can cost USD2.40/m3 and in Tanzania USD3.90/m3. In Brazil, a subsurface dam of max. 4m depth and 40m length: material and construction, USD1,400; feasibility study, USD200; technical support, USD275. O&M costs are low.
Implementation can be organized on a local level. A local committee is advantageous for water use control, contamination prevention and maintenance activities. Rationing needed when water availability is limited. The committee can also arrange for financial management.
Suitable where impermeable layer is located at shallow depth and soil (sand) can store good volume of water. Location is important as construction affects people downstream. Water supply might be only seasonal and/or only supplementary to a primary water source.
O&M activities are simple and can be done locally. Typical maintenance includes cleaning of well or pipe and raising crest of dam. Leakages may be difficult to detect, but constructions are usually robust. Larger dam repairs require skilled personnel.
Especially suitable for rural users. Insufficient yield and lack of alternative, improved water source can drive users to unimproved water sources. In such a case, alternative, improved water source is required. Risk of social friction with people living downstream.
No relevant remarks for Subsurface dams.