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==Technical specificationConstruction, operations and maintenance==Hand-dug wells have a tendency to have very little water or even dry up in the dry season. This is largely to do with the factthat the intake area is not deep enough inside the dry season water table. Shallow aquifers tend to reflect recharge more sharply than deeper aquifers, resulting in water table fluctuations of several metres between seasons – these fluctuations need to be accounted for in the construction method. Several techniques can ensure that wells are sunk deep enough:* Construct wells using a telescopic system, where an a permanent lining is created above the water table, together with a smaller diameter telescopic lining that enters the water table. The advantage of this system is that the smaller lining can be deepened at a later date without affecting the permanent lining and slab, e.g. in case the well was not sunk deep enough the first time. Another advantage is that the shaft has less chance to go out of vertical alignment during caissoning (where a shaft is sunk by digging). * Use an effective method of de-watering during caissoning within the water table. Many hand-dug wells are dug without using a de-watering pump – consequently, the limit of penetration into the water table is about only 1 metre. Providing a de-watering pump will allow the shaft to be sunk deeper into the water table, but note:# Type of pump depends on the height from ground level to water table – for a suction pump, the limit will be 6-7 metres, after which a submersible pump and generator needs to be considered. The type of pump should allow a certain amount of solid particles to be pumped.# Attention needs to be given to safety considerations when using a motorized pump with someone digging in the well – engines should be located downwind so fumes do not enter the well, a 100 – 150mm vent pipe can be temporarily tied to the crossbeam to ventilate the well (in similar way to a VIP latrine), submersible pumps should be fitted with circuit breakers in case of electrical shortcuts to avoid electrocution, digger should be wearing construction harness attached to rope, and rescue & recovery action should be in place and practised regularly. * Where using a de-watering pump results in subsidence around the well (in the case of flowing sands), another idea is to use a bailer instead of a pump. A bailer is normally used in percussion drilling, and consists of a heavy hollow metal tube with a valve on the bottom. When the bailer is dropped, sediment enters which does not come out when the bailer is removed. This method takes longer, but can be performed at ground level without a de-watering pump – since the water is not being pumped, flowing sand has less incentive to enter and the well shaft can sink slowly.* Aim to dig wells during the latter half of the dry season when water table will be at their lowest.
====Operation====Where deepening the well further is not possible due to water/sand ingress, jetting in the bottom of the well can provide a means of faster recharge into the well from deeper in the aquifer, meaning the well dries up less quickly. In this case a larger diameter screen (can be wrapped with geotextile) is jetted into the well base with the end protruding above the bottom of the well, after which it is plugged using a small bag of gravel.
====Maintenance====Where wells still dry up in the dry season, recharge techniques could be used upstream of the well.
====Manufacturing ====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.
==Cost==Simplify construction methods while getting a more robust end product in a safer fashion. Using lining & telescopic lining has the advantage that heavy lifting equipment for pre-cast rings is obsolete while procedures are inherently safer. Lining is made using one-skin moulds that hold concrete against the dug wall of the hole, while the telescopic shaft can be made from curved blocks built onto a foundation cutting ring – the blocks can be extended as and when necessary.
==Country experiencesCosts==
==ManualsField experiences== ==Reference manuals, videos, and links==* An excellent guide to a relatively safe method of digging hand dug wells can be found at:
[http://www.consallen.com/welldigging/ Consallen]
==Movies== ==External links==* An excellent but slightly outdated summary of hund dug wells by Koegel is made available by the UN FAO at [http://www.fao.org/docrep/X5567E/x5567e06.htm#5.%large%diameter%wells Large Diameter Wells]
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* An excellent guide by the highly experienced British Drilling Company can be found at [http://www.consallen.com/welldigging/ Consallen]
==ReferencesAcknowledgements==* CARE Nederland, ''Desk Study Resilient WASH systems in drought prone areas.'' October 2010.