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


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United Nations Environment Programme
Division of Technology, Industry and Economics

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PART B - ALTERNATIVE TECHNOLOGIES

4. TECHNOLOGIES APPLICABLE TO SMALL ISLANDS WITH SPECIFIC PROBLEMS OR CIRCUMSTANCES

4.1 Freshwater Augmentation Technologies

4.1.2 Submarine Pipelines

Technical Description

Submarine pipelines are pipes installed underwater and used to import water to small islands from nearby continents or larger islands with available water. Conveyance of water may be by gravity flow or by pumping.

Extent of Use

Because of the high cost and maintenance difficulties, this technology is only used to supply those islands close to continents or larger islands. Examples include the Seychelles, where five small islands are supplied through submarine pipelines of up to 5 km in length; Manono, Western Samoa, which was supplied with water through a submarine pipeline until the pipeline was damaged during a storm; Fiji, where several small islands with tourism resorts are supplied through submarine pipelines; Hong Kong Island, where 50% of the potable water requirement is supplied by gravity flow from China through twin
1 000 mm diameter, 1.3 km long steel submarine pipelines with a combined design capacity of 180 000 m³/d, and 25% of the requirement is piped from nearby Lantau Island (Lamma and Ma Wan islands, Hong Kong, also receive water by submarine pipeline); Penang, Malaysia, which receives some of its water supply from the Malaysian peninsula via twin 3.5 km long, 900 mm diameter submarine pipelines; and, Xiamen Island, China, which receives about 50% of its water from surface water storages in the adjacent Fujian Province of mainland China via a 50 km pipeline and 2.3 km submarine crossing (UNESCO, 1991).

Operation and Maintenance

This technology has no special operational requirements. However, periodic inspection of submarine pipelines is recommended, especially after storms, to ensure the integrity of the pipelines. Specially-designed anchor blocks are needed to ensure that the pipeline is not damaged by tidal flows and storms. In the Solomon Islands, fish have been known to attack underwater pipelines.

Level of Involvement

The investigation, design, and construction of submarine pipelines require highly-specialized engineering inputs, and use of this technology should be based upon favourable feasibility studies that have given consideration to the pipeline route, water depth, sea floor conditions, and oceanic currents.

Costs

Submarine pipelines are economically feasible only on a small percentage of islands located close to (not more than a few kilometres from) other land masses with surplus water resources. Submarine pipelines are expensive due to their high costs for engineering and construction (UNESCO, 1991).

Effectiveness of the Technology

Submarine pipelines may be very effective under favourable conditions. Investigations and feasibility studies are necessary to determine the costs and risks involved.

Suitability

This technology is only suitable for small islands close to continents or larger islands with a surplus of water, and when others alternatives are severely limited.

Advantages

This technology incurs minimal operational costs if operated with a gravity-fed supply. It also permits diversion of water from water-rich areas to water-poor areas.

Disadvantages

This technology incurs very high engineering and construction costs, and is susceptible to damage due to heavy seas and tidal flows.

Cultural Acceptability

Reliance on water from off-island, particularly if those sources are in a different country, may be a cause of concern.

Further Development of the Technology

Further research into improved pipe materials and installation techniques might be a consideration.

Information Sources

Lee, Yow Ching 1989. Development of Water Supply in Penang Island, Malaysia. In: Proceedings of the Seminar on Water Management in Small Island States, Commonwealth Engineers Council, London. pp. 38-43.

Little, M.J. 1986. New Pipelines on Land and Across Victoria Harbour, Hong Kong. Journal of the Institution of Water Engineers and Scientists, 40(3):271-287.

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.

Zhang, Zongwang and Liang Zhixin 1988. Study of Water Supply to Xiamen Island. In: Proceedings of the Southeast Asia and the Pacific Regional Workshop on Hydrology and Water Balance of Small Islands, UNESCO-ROSTSEA, Nanjing, China. pp. 134-140.

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