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Riverbed hand-dug wells

No change in size, 00:14, 12 April 2012

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# That there is less chance that the well shaft and pipework will be washed away in a flood event. Sand becomes mobile to a certain depth which differs for different rivers but has been recorded to be normally between 0.66 and 2 metres in seasonal riverbeds.

* The well shaft can also be made so that it protrudes from the riverbed sand level. A slab is made to cover the top ring and a manhole access cover is installed for dry season access. In such a case:

* *The well shaft needs to be protected – a hydrodynamic well head should be constructed to minimize damage from floodwater and the debris it contains. This well head has a shape of an upturned boat which deflects water and debris in the floodwater. The manhole cover opens in the upstream direction so that it closes when the floods arrive.

** Such a construction is probably best suited to riverbeds of low porosity and permeability where sediments have some stability and little is transported in floodwater, otherwise damage to the well could easily take place.

The use of porous concrete in part of the section of the well shaft which is underwater can help increase flow velocity into the well. Porous concrete is made using a of 1 : 1 : 4 (cement : sand : aggregate) and can be used for curved blocks or also for a central portion of any pre-cast concrete ring. Also perforated pointed steel pipes can be driven horizontally into the aquifer using a jack – this can also increase flow velocity into the well.

Winona

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