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Natural or artificial ground catchment and Lined sub-surface tanks

858 bytes added, 23:39, 5 April 2012

→‎Construction, operations and maintenance

* The main advantage of polypropylene is that it comes in large sheets larger than 50’ x 100’. If you are building an extremely large pond, polypropylene may be a viable option.

* A limitation of EPDM is its size they typically arrive in sheets ranging from 5’ x 10’ to a 50’ x 100’ roll.

 

====Roof construction====

Sub-surface tanks are usually small enough that it is viable to have a roof to limit evaporation (and improve water quality if possible, which means less algae build-up). Shading can reduce evaporation by around 30%. Placing local bush or grass materials on a frame of wires doesn’t seem to work well because they get blown off, and also still let light in, which creates algae growth. Corrugated iron roof on wooden frame works well but is expensive (about $20 per m2 in Somaliland). In addition, if the tank is not fenced, animals walking on the roof can damage it. The challenge is to make a roof that is cost-effective for small-scale farmers – one idea is to investigate income-generating roofs since that can help pay for the structure (e.g. passion fruit). Excavated water cellars by their nature have small area roofs.

==Costs==

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