| Sinking Method |
A sinking method is a specific way of
sinking a well. Wells may be dug by hand, drilled
with hand tools, or drilled with motorized equipment. Many methods
and techniques are used. The particular choice depends on the
available materials and equipment, the expected ground conditions at the
well site, and your familiarity with a specific sinking technique.
Motorized drilling techniques are summarized in the section
on Drilled Wells, but are not described in detail because
of the high level of technical expertise necessary in the use of the equipment.
The following are general
descriptions of hand-dug and hand-drilled sinking methods. For more details,
see the manual sections on Hand-Duq Wells and Drilled Wells.
1. Hand-dug wells are sunk
by digging a hole as deep as is necessary to
reach water. Once the water bearing layer is reached, it
should be penetrated as far as possible. This process is
always basically the same, with only minor variations because of
the particular tools and equipment available and the variety of
ground conditions (see Fig. 1-3).
Advantages
This procedure is a very flexible one. It can be easily
adapted with a minimum of equipment to a variety of soil conditions,
as long as cement is available.
Because the resulting well is wide-mouthed, it is easily adaptable to
simple water-lifting techniques, if pumps are not available or appropriate.
It provides a reservoir which is useful
for accumulating water from ground formations which yield water slowly.
FIG. 1-3. DIGGING A WELL
Disadvantages
A hand-dug well takes longer to construct than a drilled well.
It is usually more expensive than a hand-drilled well.
It cannot easily be made into a permanent water source without the use of cement.
Hand-digging cannot easily penetrate hard ground and rock.
It may be difficult to penetrate deeply enough into the aquifer so that the well will not dry up in the dry season.
2. Drilled wells are sunk by using a special tool, called a bit, which acts to loosen whatever soil or rock is at the bottom of the hole. It is connected to a shaft or line which extends to the ground surface and above. The part of the shaft or line extending above the ground can then be moved to operate the bit (see Fig. 1-4).
FIG. 1-4. DRILLING A WELL
Advantages
It is fast.
Where cement is not available, wells can be sunk with locally made drilling equipment and lined with local materials.
While not easy, it is possible to penetrate hard ground and rock formations that would be very difficult to dig through.
Drilling usually requires fewer people than hand-digging.
It is especially suitable for use in loose sand with a shallow water table.
Disadvantages
There are a number of different hand-drilling techniques that are suitable for a wide range of ground conditions. However, each requires special equipment.
Pumps almost always have to be used because buckets are too large to be lowered into the well.
Limited depth can be reached with hand-powered drilling equipment.
Suitability of Well Construction Methods to Different Geological Conditions