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< prev - next > Disaster response mitigation and rebuilding Emergency relief KnO 100648_Water Supply during emergencies (Printable PDF)
Water Access in Emergencies
Practical Action
Wells & Boreholes
In any scenario with groundwater, it is likely that the majority of it will exist in the water table
below the surface. If there are no springs, or they are not able to meet supply, wells and boreholes
must be dug to reach the water.
The locating of a well can be difficult if the geology of the sub-terrain is unknown. Expertise can
be sort from a hydrogeologist if available, but often it requires luck and several attempts to find
an area of water table with sufficient yield. Refer to WEDC’s guide on Emergency Water Sources
for detailed information and checklists on the siting of groundwater sources.
Typical Features
The picture below demonstrates the main features of a well:
Aquifer water is drawn down to
the pump level, below the static
water level
Figure 11: Schematic diagram of a typical well
Source: Davis, J. and Lambert, R. (2002)
The well will typically have a screen extending down its length into the water-drawing area, to
reduce sedimentary intake to the pump. The hole will have an impermeable casing at the upper
end, to prevent contamination, often made of bricks or concrete rings. The well will be sealed at
the top to prevent dirty water or pollution entering. These features may differ depending on the
geological conditions and the height of the water table.
Options for well construction
There are several methods for constructing a well, ranging from hand-digging to drilling with
industrial machinery. The most practical method depends on a range of factors, including ground
condition, supply requirements, yield, geology, manpower and machinery available.
In general, hand dug or drilled wells can be constructed quickly, requiring only manpower and
simple tools. However, the depth to which they can be dug is limited to approximately 30m in
normal conditions (Davis, J. and Lambert, R. (2002)). Additionally, hand-powered machinery is
either slow or unable to dig through difficult ground.
Machine drilling can be much quicker, and is capable of drilling boreholes through harder ground
to much deeper levels. The requirement to import specialist machinery to achieve this results in
an increased cost. Drilling methods are traditionally divided into ‘percussion’ (repeated beating of
ground by drill-piece) and ‘rotary’ (conventional rotation of cutting tool) drilling, although a
combination of both can be used. Refer to Engineering in Emergencies for information of several
methods of drilling and well lining, and their corresponding advantages and disadvantages.