Newsletter and Technical Publications
<Sourcebook of Alternative Technologies for
in Small Island Developing States>
PART B - ALTERNATIVE TECHNOLOGIES
3. TECHNOLOGIES APPLICABLE TO SMALL HIGH, VOLCANIC ISLANDS
3.1 Freshwater Augmentation Technologies
Groundwater is the most common source of freshwater on small islands. It
is used extensively on small, low-lying islands for most uses, including
potable uses. It is also used on small, high islands, particularly those
where surface water catchments do not exist or are too small or too
difficult to develop. Dug wells and infiltration galleries, which are the
preferred technologies on small, low-lying islands were described in
Section 2 of Part B. This section covers technologies like boreholes and
other types of deeper-water wells.
The same basic considerations that apply to dug wells also apply to
boreholes. Boreholes are generally appropriate for use when the distance
from the land surface to the water table is too great or geological
conditions too difficult for alternatives such as dug wells or
infiltration galleries to be satisfactorily used. As previously noted, a
thorough hydrogeological investigation should be conducted prior to
locating and selecting a groundwater abstraction system. A list of the
different groundwater assessment technologies can be found in Section 1 of
There are a number of well construction techniques including driving,
jetting or drilling (boring). Drilling is the most common. No single water
well construction technique is applicable for all conditions. The most
appropriate technique will depend on hydrogeological, environmental,
social, cultural, and economic conditions at the site of the proposed
well. Detailed information on these techniques, particularly different
methods of drilling, well construction, and development can be found in
other specialised literature.
In general, every well consists of two main elements, the casing and the
intake (Figure 28). The casing serves as a housing for the pumping
equipment, and as a vertical conduit for the water flowing upward from the
aquifer to the pump intake. The part of the borehole length serving as a
conduit may be left uncased when the well is constructed in consolidated
rock. This intake portion of the well, when constructed in unconsolidated
and semi-consolidated aquifers, is generally screened to prevent sediment
from entering the borehole with the water and to serve as a structural
retainer supporting the loose material on the sides of the hole. After the
completion of each well, its performance must be assessed normally by
conducting a pumping test which provides information about yield and
drawdown of the well. Pump selection has been described previously in
Section 2 of Part B. Detailed information and specifications of the
different types of pumps are obtainable from pump manufacturers and
Extent of Use
This technology is extensively used on the high islands of Fiji, French
Polynesia, American and Western Samoa, Vanuatu, Solomon Islands, Hawaii,
Seychelles, Mauritius, Jamaica, Montserrat, Aruba, and Barbados.
Operation and Maintenance
The operation and maintenance of water wells or boreholes mainly
concerns the pump unit and associated equipment. Relevant information
relating to the operation and necessary maintenance of specific pumps is
provided by pump manufacturers and suppliers. In addition, the well,
itself, should be checked periodically to ensure that the flow of water
into the well through its screens is not impeded.
Figure 28. Schematic diagram of a typical well (Davis and
Level of Involvement
Professional engineers or hydrogeologists are required for
investigations, initial well design, drilling supervision, well
development and testing, and pump selection. Experienced drilling teams
are also required. Some small islands have their own drilling teams, while
most have contract drilling teams that can be used as necessary.
Construction costs include the costs of drilling and pump installation.
Operational costs include the costs of energy required for pumping and the
cost of maintaining the equipment. In Western Samoa, typical groundwater
development costs in 1995 were as follows:
* Construction of 50 m depth borehole for submersible pump unit
(drilling and case only) $430/m3
* Construction of 25 m depth borehole for handpump (drilling and case
* Operation cost to supply pumped groundwater (diesel driven) $0.19/m3
Effectiveness of the Technology
Assuming the wells have been correctly sited, this is a very efficient
technology. Wells are a very reliable sources of freshwater, even during
extended dry periods. Furthermore, in the case of deep wells, the risk of
contamination of the water is lower than in shallow wells.
This technology is suitable for use on islands where there are adequate
volumes of groundwater available. Groundwater abstraction should be
considered as an appropriate water supply option whenever possible.
Groundwater abstraction using this technology provides a reliable
quantity of freshwater at a reliable quality when abstracted at a rate
equal to or less than the sustainable yield of the aquifer.
Development of borehole wells requires skilled drillers and trained
operators, and sometimes incurs high construction costs. Deep wells have
high operating and maintenance costs compared with shallow wells. Because
of the specialised nature of the submersible pumps used with this
technology, spare parts may not always be accessible. Overpumping of wells
can lead to seawater intrusion into the aquifer, particularly in
Land ownership issues may preclude the drilling of wells in otherwise
Further Development of the Technology
The technology is already well developed. However, minor improvements in
drilling technologies, and in the materials and equipment, used in
constructing deep wells and for pumping are continually being made.
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