|Sourcebook of Alternative Technologies for Freshwater Augmentation in Small Island Developing States (UNEP-IETC, 1998, 230 p.)|
|Part A - Introduction|
With growing demands on water resources (both quantity and quality), and increasing costs of water and sanitation systems especially in small island countries, there is a need not only to maximise the use of existing systems but also to develop new sources of freshwater supply. Development of all freshwater resources must be done in a way which ensures the sustainability of the resource for both present and future generations. There are numerous techniques, modem and traditional, for improving the use, and augmenting the supply, of water resources which are currently in use throughout the world. These include direct techniques such as rainwater harvesting, groundwater abstraction, desalination, and reuse of wastewater as well as indirect techniques such as demand management and leak reduction. In many Small Island Developing States (SIDS), application of these technologies has been limited by lack of information on the available approaches and their performance.
Chapter 34 of the Earth Summit's Agenda 21 (the Programme of Action arising from the United Nations Conference on Environment and Development held in Rio de Janeiro, Brasil, in 1992) addresses the need to transfer environmentally-sound technologies and improve cooperation and building capacity within developing countries. Improved access to information on environmentally sound technologies has been identified as a key factor in transferring technologies to developing countries. Further, Chapter 18 of Agenda 21 deals with the utilisation of appropriate technologies in water supply and sanitation. The Barbados Plan of Action (United Nations Global Conference on Sustainable Development of Small Island Developing States, 1994) emphasises improved access to environmentally-sound and energy-efficient technologies and information on freshwater augmentation. The primary objective of improving access to technical information is to enable developing countries to make informed choices that will lead to the adoption of technologies appropriate to their situations.
The United Nations Environment Programme (UNEP), as part of its Mission, undertakes the identification and dissemination of information on sustainable utilisation of, and improved access to, water resources. Pursuant to this charge, UNEP, through its Water Branch and International Environmental Technology Centre (IETC), recognised the need to provide water resource managers in developing countries and countries with economies in transition, with information on alternative technologies for augmenting freshwater resources in order to promote informed decision-making on technology choices in the field of water resources management. UNEP, therefore, commissioned surveys of freshwater augmentation technologies in Eastern and Central Europe, Latin America and the Caribbean, Africa, Asia and Small Island Developing States. This volume reports on the findings of the surveys conducted in Small Island Developing States.
Small islands have special physical, demographic and economic features. Their limited surface areas, shortages of natural resources (e.g., arable land, freshwater, extractable minerals and conventional energy sources), geological and orogenic complexities, isolation and widespread territories, and potential exposures to natural disasters (e.g., typhoons, hurricanes, cyclones, earthquakes, volcanic eruptions and tsunamis) contribute to the sometimes serious nature of their hydrological and water resources problems. Increasing demographic pressures and economic fragility add to the natural problems of many small island states. Thus, small islands are unique and fragile land units. The impact of the sea is more pronounced on these fragile units than on the continental land masses and on large islands. For example, small islands can be damaged and even overtopped by storm-generated waves. As a consequence, the predicted sea-level rise, due to the global warming and the greenhouse effect, is of real concern to many small island countries, particularly the very low-lying coral atolls and cays. In addition, their proximity to the sea also gives rise to corrosive atmospheric conditions, which cause equipment and materials to rapidly deteriorate (UNESCO, 1991).
Problems of water availability arise from difficult climatic conditions which include capricious rainfalls, and from geological conditions which range from extremely permeable rock (of volcanic origin or karstic limestone) to highly impermeable rock without significant storage potential, and from topographic features not suited to the development of surface water resources. In extreme cases, there may be no permanently available freshwater resources at hand as heavy seas can deposit seawater on the land surface that contaminates the freshwater aquifers that might have existed. Permanent rivers and springs rarely occur and only where rainfall is relatively high and well-distributed throughout the year, and where favourable topographic and geological conditions exist. In most cases, natural base flows of greater than a few decilitres per second cannot be guaranteed. On most islands, river basins (catchments) are often present in large numbers but they are small in size and have limited regulation capability, although a few "high islands" have topographical, geological and hydrological conditions suited to the construction of significant water storages.
The turnover time of groundwater systems on most small islands tends to be short, generally ranging from a few years at most to shorter than a year in many cases. Thus, freshwater lenses and perched aquifers may be depleted during the dry seasons to a point where they become extremely limited or nonexistent even under natural (no pumping) conditions. The additional stresses of pumping from such lenses can easily induce saltwater intrusion if care is not taken in the design and operation of extraction facilities. On some high limestone islands, the rocks are too permeable to enable a freshwater lens to form and there may be no fresh groundwater or surface water. Seawater intrusion is a serious water quality problem for small and very small islands, especially where over-exploitation occurs due to increasing populations, tourism, and industrial and agricultural development. In these cases, the natural water balance can be dramatically and adversely altered. The tourism industry, a major economic activity on many small islands, demands large volumes of water of high physical, chemical and bacteriological quality. Frequently, tourist accommodations have such a high rate of water consumption that they can severely stress or exceed the water resources of an island. Then, the development of non-conventional water resources, such as desalinated seawater or brackish groundwater or the importation of water using tankers and barges, may be required to satisfy the demand for freshwater.
Inorganic and organic contamination of drinking water wells and rivers is another frequent phenomenon on many small islands. Water pollution, caused by the uncontrolled use of fertilisers, herbicides and pesticides, is prevalent on some islands. In addition, domestic wastewaters (grey water), as well as other more aggressive wastewaters from beer factories, distilleries, agro-industries, and other industries, may be dumped directly into the available streams and rivers, causing them to become polluted and biologically dead. Such phenomena may be found in the lower reaches and estuaries of a few rivers and streams on small Caribbean islands. Groundwater in shallow aquifers in porous rocks or sandy rock formations may also be very sensitive to contamination from land use activities. Wastewater disposal systems, particularly on very small islands, may be as important as the water supply distribution system for protecting the public health. Serious conflicts between groundwater source-protection measures and wastewater treatment methods commonly occur.
Islands in humid tropical regions are often exposed to frequent torrential rains. When heavy rainfall is combined with local factors, such as steep topographies, short river channels, deforestation and easily erodible soils, it can cause siltation of water storages with consequent capacity reduction and adverse effects on water quality (high turbidity). On some islands, silt may have to be removed from reservoirs at the end of every wet season. High turbidities may result in water supplies becoming non-potable or severely impaired. Where water treatment plants are used, high turbidities may severely impair the performance of the treatment plants.
Despite their small areas, many small islands are very heavily populated. High populations and high birth rates place great stresses on the limited, naturally-occurring water resources. Population densities of over 10 000 persons/km2 occur on some islands. An extreme example is Male, in the Republic of Maldives, where the population density on the 1.3 km2 island exceeds 48 000 persons/km2. High population densities not only create high demands for water but also increase the risk of pollution since the population is often living above the groundwater used for potable and other purposes. Likewise, the accession to independence or internal self-governance has generated great expectations among the population of improved living conditions, which also increased water demand proportionate with the drive toward economic self-sufficiency. Economic imperatives often result in competition for limited water resources between urban and rural communities, with tourism (one of the major sources of income on tropical islands) competing with small agro-industries (producing sugar, oils, and copra) and irrigated agriculture.
Hydrological studies, based on concepts and criteria appropriate for large islands and continents but inappropriate for small island states, are frequently carried out in small islands. Small islands require either island-specific or regional studies to properly identify their water resources and to implement effective development and management programmes. However, the lack of skilled, local personnel often forces small island states to seek external assistance, including both specialists and specialised equipment, to carry out water resources assessment surveys, which are difficult and expensive to conduct, and which perpetuate the use of potentially inappropriate paradigms. On some mountainous small islands, despite their limited territories and apparently short distances between mapped features, the lack of access roads or tracks often demands the use of ingenious combinations of modes of transportation (including, for example, boats, aeroplanes, helicopters, motorcycles, bicycles, horses or other animals, and, often, feet) to carry out hydrological studies. This often increases the cost of obtaining basic water resources assessment data and may require the installation of sophisticated remote measuring equipment. Further, where transportation between the numerous and often isolated islands within island groups is also limited, the difficulties in acquiring hydrometric data compound the problems of making water resources assessments in these regions.
While water resources on some small islands have been developed in an efficient and economic fashion, water development projects on most small islands have not achieved their goals because the technologies, designs, and materials were either not suitable for their environment or the cultural habits of the population, or not properly operated and maintained due to excessive costs and lack of trained staff.