a Dug
Wells
http://en.wikipedia.org/wiki/Water_well
www.karmayog.org (17.10.2013)
Hand-dug wells are
excavations with diameters large enough to accommodate one or more persons with
shovels digging down to below the water table. They can be lined with laid stones or brick; extending this lining upwards above the ground surface
to form a wall around the well serves to reduce both contamination and injuries
by falling into the well.
Hand dug wells provide a
cheap and low-tech solution to accessing groundwater in rural locations in
developing countries, and may be built with a high degree of community
participation, or by local entrepreneurs who specialize in hand-dug wells. They
have been successfully excavated to 60 meters. Hand dug wells are inexpensive
and low tech (compared to drilling) as they use mostly hand labour for
construction. They have low operational and maintenance costs, in part because
water can be extracted by hand bailing, without a pump. The water is often
coming from an aquifer or groundwater, and can be easily deepened, which may be
necessary if the ground water level drops, by telescoping the lining further
down into the aquifer. The yield of existing hand dug wells may be improved by
deepening or introducing vertical tunnels or perforated pipes.
Drawbacks to hand-dug
wells are numerous. It can be impractical to hand dig wells in areas where hard
rock is present, and they can be time-consuming to dig and line even in
favourable areas. Because they exploit shallow aquifers, the well may be
susceptible to yield fluctuations and possible contamination from surface
water, including sewage. Hand dug well construction generally requires the use
of a well trained construction team, and the capital investment for equipment
such as concrete ring moulds, heavy lifting equipment, well shaft formwork, motorized
de-watering pumps, and fuel can be large for people in developing countries.
Construction of hand dug wells can be dangerous due to collapse of the well
bore, falling objects and asphyxiation, including from dewatering pump exhaust
fumes.