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Traditional hand-dug wells

1,568 bytes added, 21:42, 11 April 2012
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These are shallow wells which draw water from a natural aquifer or man-made aquifer, e.g. near sand dam or around ponds, but which are not located inside a riverbed. It can include wells that are far from a river, or wells that receive water from shallow aquifers hydraulically connected to the river. Sometimes the holes dug are very large, allowing people and sometimes animals who are able to walk into the well to where the water is located. ==History Suitable conditions==* Care should be taken to avoid siting wells in perched aquifers (shallow aquifers with limited recharge capacity and social contextwater storage). ====Avoid contamination====Site wells at a sufficient distance away from sources of contamination. For microbiological contamination, the distance from thesource of contamination (e.g. latrine) to the water intake (screen) needs to be sufficient so as to pose a “low” to “very low” risk – this translates into a minimum of 25 days of potential travel of pathogens in the ground. Travel time is influenced by porosity, hydraulic conductivity (permeability) and hydraulic gradient. For medium size sand with an average porosity, the distance equivalent to 25 days is around 30 metres, but this can increase to over 100 metres for coarser sediments. However, the distance from contamination to water intake can reduce significantly where the screen intake is at a sufficient depth – this is due to greater variation of aquifer properties in vertical directions than lateral, meaning that a borehole with handpump could be placed very close to a latrine with low risk. However, screen depth must increase with increased extraction rate.
==Suitable conditions (advantages / disadvantages) ==
{{procontable | pro=
Circumstances which make the construction of large diameter wells necessary:
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