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Newsletter and Technical Publications

<Sourcebook of Alternative Technologies for Freshwater Augumentation
in Small Island Developing States>


PART B - ALTERNATIVE TECHNOLOGIES

3. TECHNOLOGIES APPLICABLE TO SMALL HIGH, VOLCANIC ISLANDS

3.1 Freshwater Augmentation Technologies

3.1.4 Spring Capping

Technical Description

Springs are a naturally-occurring source of freshwater on many small islands, and are often exploited using a gravity-fed delivery system. Springs developed for a gravity-fed water supply should be at an elevation above the supply area, and, while an excellent source of water, should be "capped" to prevent contamination. Spring capping typically takes the form of a containment structure, constructed from concrete or masonry, which direct spring flows to an outlet pipe. Spring capping is found in many forms, ranging from relatively simple, uncovered systems to more sophisticated, covered systems designed to exclude leaves, soil and other contaminants such as animal and bird excreta. An example of an enclosed spring capping is shown in Figure 31.

Figure 31

Figure 31. Typical development of a gravity spring. The spring feeds into the rear of the concrete or masonry
chamber, or intake box, which can either be buried as shown or left exposed depending on site conditions. A
delivery pipe fitted with a screen is placed through the front or lower wall of the at a level below the minimum
water level. To relieve pressure due to high flows an overflow pipe is also placed through the chamber at an
higher level (UNESCO, 1991).

Where the spring discharge is below sea level, special difficulties are experienced when attempting to develop the spring for freshwater abstraction. The development of submarine springs is difficult because it requires the use of underwater construction techniques. Also, should the spring be successfully capped or dammed, the freshwater often finds alternate exit via other fissures to the sea. In addition, even relatively small drawdowns from pumping can induce mixing with seawater.

Extent of Use

Springs are used extensively in SIDS for freshwater supply purposes.

Operation and Maintenance

The type of spring capping shown in Figure 31 would generally require minimal intervention for operation and maintenance. Periodically, however, the chamber should be inspected and cleaned.

Level of Involvement

Local people can be trained to develop, cap, and manage springs.

Costs

There are many types of spring caps, ranging from a simple weir structure (open) to more complex constructed (closed) systems. There is also a range of sizes depending on the flow and areal extent of a given spring. Costs are highly variable, but, in general, range from $500 to $5 000 for most applications. These costs do not include pipeline costs which are also highly variable, and depend on location, length, terrain, etc.

Effectiveness of the Technology

Spring capping is an effective method of supplying water. However, care must be taken not to decrease flows through spring development.

Suitability

Spring capping is suitable for use of high islands where perennial springs occur naturally.

Advantages

Springs can provide good quality water at low (operation and maintenance) cost

Disadvantages

Spring development may be detrimental to the rate of discharge of the spring, unless carefully implemented.

Cultural Acceptability

Some cultures are reluctant to use spring water.

Further Development of the Technology

The basic technology is well known. Depending on site-specific conditions, capping design concepts could be improved to provide for better use of local materials, greater protection of water quality, and more efficient delivery of water to users.

Information Sources

AWRC [Australian Water Resources Council] 1989. Guidelines for the Design and Operation of Surface Water Information Networks. Water Management Series No. 18, Australian Water Resources Council, Canberra.

Davies, J. and R. Lambert 1995. Engineering in Emergencies. Intermediate Technology Publications, London.

Gormley, W., D. Goff, and C. Johnson 1984. A Workshop Design for Spring Capping; a Training Guide. Water and Sanitation for Health Project Technical Report No. 28, United Nations Development Programme, New York.

Hall, A.J. 1983. Surface Water Information Network Design for Tropical Islands. In: Proceedings of the Meeting on Water Resources Development in the South Pacific, United Nations Water Resources Series No. 57, 83-95.

Hofkes, E.H. (Ed.) 1983. Small Community Water Supplies, Technology of Small Community Water Supply Systems in Developing Countries, International Reference Centre for Community Water Supply and Sanitation Technical Paper Series No. 18, John Wiley and Sons, New York.

ILO [International Labour Organization] 1989. Spring Protection Works - An ILO Special Works Programme in Western Samoa. In: Interregional Seminar on Water Resources Management Techniques for Small Island Countries. United Nations Department of Technical Cooperation and Development, United Nations Development Programme, Suva.

Jordan, T.D. 1984. A Handbook of Gravity-flow Water Systems. Intermediate Technology Publications, London.

Spangler, C.D. 1980. Low-cost Water Distribution - A Field Manual. Appropriate Technology for Water Supply and Sanitation. The World Bank, Washington.

UNESCO [United Nations Education Scientific and Cultural Organization] 1991. Hydrology and Water Resources of Small Islands, A Practical Guide. Studies and Reports on Hydrology No. 49, UNESCO, Paris. 435 pp.

WHO [World Health Organization] 1976. Typical Designs for Engineering Components in Rural Water Supplies. World Health Organisation South-East Asia Series No. 2, WHO, New Delhi.

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