Small islands water resources development-a holistic approach

Transcription

1 Small islands water resources development-a holistic approach by Nicos X. TSIOURTIS Senior Water Engineer Water Development Department Nicosia Cyprus Abstract: Small islands have fragile ecosystems with very limited water and other resources and great care of the environment is required for support of the inhabitants. The nature of small islands with very small catchments area for rainfall, the small and limited surface storage capacity, the limited groundwater storage capacity combined with the fact that aquifers are surrounded by saltwater, the fact that that high porosity aquifers allow mixing of fresh water with sea water and the fact that wastewater may be discharged to the aquifer, make the management of the limited water resources very complicated. With the available water resources not being enough and getting less due to pollution by the human action and with demand growing due to population growth, due to improvement of the standard of living and the introduction of other activities needing water for a socioeconomic development, the need for the protection of the existing water resources is becoming a top priority, where additional water resources must be developed. The small islands water problem may be tackled by the introduction of the holistic approach, which provides an integrated water resources management. The solution would be the protection and development of the freshwater resources, the introduction of water demand management, the treatment and re-use of the domestic effluents and if still the fresh water resources are not enough to cover the demands for a sustainable development from the socioeconomic and environmental aspects then desalination of sea or brackish water or barging or transportation of fresh water would be introduced. All domestic effluents must be treated and re-used for irrigation and the production of desalinated water to be made by the installation of wind power generators either for co-production of electricity and water or by stand-alone systems supported by generators or the local grid. The choice of the technology of unconventional water production has to be based on a techoeconomic study and environmental study. Keywords: Small islands, water scarcity, integrated water resources, Re-use, desalination, cogeneration of water and electricity, stand-alone desalination systems. 1. Definitions, classification 1.1 Definition of small and very small islands. From a hydrological perspective, a small island can be considered to be one on which water resources are very scarce. Water development measures on small islands are special and usually they are not those normally considered as standard on continents or larger islands. The 1 definition adopted by UNESCO in 1991 defines as small islands those having an area equal or less than 2000 square kilometers and the width does not exceed 10 kilometers. The definition also introduces the concept of a very small islands which includes islands whose surface area does not exceed 100 square kilometers or the width is not greater than 3 kilometer and where the water scarcity is even more acute and surface water resources are normally absent. On small

2 or very small islands groundwater is normally the only naturally occurring water resource, where surface water is very scarce and difficult to catch if any. From 64 islands in Greece 37 have an area less than 100 square kilometers, 8 no between 100 and 200 Km2, 12 no between 200 and 500 Km2, 3 no between 500 and 1000 Km2, 2 no between 1000 and 2000 Km2 and 2 no above 2000 Km2. In other words 37 can be classified as very small islands, 25 no as small islands and the rest two as large islands. 1.2 Special characteristics of small islands The major influences on the small islands hydrological characteristics are the climate the physiography, the geology, the hydrogeology, the soils, the vegetation cover, the location, the shape and the human intervention. The climate influences the availability of freshwater. The rainfall quantity and its variation with respect to time and space and the evapotranspiration play an important role on the availability of the freshwater resources. The temporal variation is usually high in small islands where the spatial variation is a function of the islands physiography. The physiography plays an important role on the classification of small islands high or low. High islands are those that can influence the precipitation patterns and with some runoff and low islands are those without any effect on the precipitation pattern and no significant surface runoff. High islands have steep topography with flashy surface water resources, since they are volcanic islands, with low permeability bedrocks. These islands have small perennial streams at high elevations and the surface water may form an important component of the water balance. Low islands have a flat topography with a minimum of surface runoff and the groundwater is a major component of the water balance. Low islands are also affected by their height above sea level, which determines the risk of overtopping. The geology and hydrogeology influences the availability, the type and the distribution of the water resources. Groundwater is abundant in islands with soils and rocks of moderate to high permeability, where surface water resources occur on islands with soils and rock with low permeability. Very high permeability causes the mixing of freshwater and seawater resulting to brackish groundwater. UNESCO has classified the small islands according to their geology into Volcanic islands, limestone islands, coral atolls, bedrock islands, unconsolidated or sand islands and islands of mixed geology. Volcanic islands are of the andesitic sub-type (islands on the continental sides of deep trenches) with groundwater yields generally low and the basaltic or oceanic, which rises from the ocean floor in the middle of the tectonic plates with high groundwater potentials. Volcanic islands are of the High type islands. Limestone islands are generally karstic and weathered due to fluctuating sea levels and alternate periods of submergence and exposure. Permeabilities are relatively very high and freshwater lenses are generally no more than 10 cm to 20 cm thick, with caves and cavities found along the shoreline and within the interior of the islands. Limestone Islands are of the low type islands. Coral Atolls islands are found in the Pacific and the Indian oceans and typically they consist of a chain of low coral islands surrounding a shallow lagoon, consisting of a layer of recent sediments on top of an older limestone. The upper sediments are of primary importance since freshwater lenses are found in this layer due to its moderate permeability. Bedrock islands are formed by igneous or metamorphic 2

3 rocks such as granite, diorite and schist, found mainly on the continental shelves or adjacent to large islands. Unconsolidated islands are consisting of sand, silt or mad and are found in the deltas of major rivers, where mixed geology islands are those islands with a mixture of volcanic and limestone rocks. Soil types play an important role in the hydrological cycle. Sandy soils found in limestone and coral islands with high permeability do not allow the creation of surface runoff, where clay soils found in volcanic islands have a lower permeability allow the creation of surface runoff. Soil water retention capacity is an important factor in the evapotranspiration and recharge. The retention capacity is a function of the texture of the soil and the thickness of the soil. Recharge is enhanced by coarse grain soils (sand) and fine grain soils reduce the recharge. Vegetation in small islands, generally adapted to the local climatic conditions, consists of a variety of trees, bushes and grasses, and normally does not require irrigation. The type and density of the vegetation affects the hydrological cycle, water interception and transpiration reduce recharge, slow surface runoff and reduce erosion on High Islands thus increasing infiltration of water into ground. Generally the benefits of vegetation outweigh the negative effects on the water resources. The Location of the islands with respect to the continent or other large islands classifies the island to those that can be supplied with water, by pipelines or sea transport and those that have to be supplied only from their own sources or by desalination. 1.3 Special Problems of the islands Small islands are usually densely populated with high water demand and high potential for pollution of the water resources. High water demand causes over-abstraction and depletion of the aquifers and increased development (housing) has led to the contamination of the underlying or nearby aquifers. Small islands are vulnerable to aquifer depletion, groundwater contamination by human and animal activities, and suffer from water scarcity. Another hazard is the use of agrochemicals (herbicides and insecticides) and the fuel storage facilities. Generally small islands require special measures for their water development and protection and additional water must be imported from outside sources for safeguarding the sustainable development and preserving the present level of standard of living. 2. Water Management and development in small islands 2.1 General Small island s freshwater resources are very limited, scarce and fragile. With growing demand (due to population growth and other development), on water quantity and quality there is a need to maximize the use of the existing freshwater resources before unconventional options are considered. Therefore the planning and management of small islands water resources and water developments are limited to the issue of maximizing and augmenting freshwater resources as follows. 2.2 Freshwater resources development Freshwater includes all naturally available water, surface, groundwater and wastewater. i) Freshwater resources assessment. The first step in water resources management is the assessment of the available water resources both 3

4 groundwater and surface. The assessment should be made through a water survey using sound hydrological and hydrogeological methods. ii) Water demand assessment. Water demand assessment and projections should be made taking into consideration present population and future population growth, present and future tourist development and present and future activities in irrigation, in industry and other activities for a sustainable development and demand for the conservation of the environment. iii) Water development and use. Water development includes all structural and operational measures for freshwater development and utilization including surface water structures (dams, offstream ponds), borehole drilling, controlled groundwater pumping, efficient water conveyance and distribution systems, infiltration galleries, water treatment plants, wastewater collection and treatment plants, and reuse schemes. iv) Water demand management. Since water is scarce and very limited, its use should be done efficiently and effectively. Distribution systems should be very efficient, water losses should be minimized, and water consumption should be measured and billed to the consumers, at its total cost. The consumers must be encouraged to use water saving equipment, encouraged to save water and discouraged to use it wastefully. The principle the beneficiary and the polluter pays must be applied and public awareness must be promoted. v) Treated wastewater re-use. This method of water conservation must be used in cases and domestic effluents must be treated and re-used for irrigation or for other purposes productively. Dualpurpose systems may be used for effective and efficient use of the potable water and for the treated effluents, one distribution system for potable water and a second distribution system for the treated effluents. Disposal of treated or even untreated wastewater to the sea or to the aquifers must be avoided, after all it is banned by the European Directives, for environmental, water conservation reasons and for eliminating the risk of pollution of the groundwater aquifers. vi) Water pricing and public awareness. Water must be costed taking into consideration the capital investment costs, the operation and maintenance costs, the energy costs, the environmental costs and the resource depletion costs. Water pricing and tarification must be such as to discourage wasteful use and encourage efficient and effective use. It is recommended that water pricing should be such for full cost recovery, which will encourage water saving. Public water awareness must be created by education of the consumers, by water saving campaigns and by adopting the right pricing system both for freshwater and treated wastewater use and for wastewater disposal. If the price is right the consumers will save water and will also reduce waste disposal. vii) Environmental Considerations. Water conservation and water development measures should not overlook the environmental needs and requirements. Environmental needs must be satisfied to the fullest possible way by providing water for wetlands, for natural vegetation, for the wildlife and for any other important reason related to the environment. For example aquifer pumping should be limited to the safe yield of the aquifer and continuous monitoring of the pumping must be carried out. viii) Setting up an Entity. Water management shall be efficient and 4

5 effective if an entity is given the administrative, legal power, technical, economic and other means to carry out this task. The entity must have legal and executive power on the management and development of water resources for the whole water cycle including freshwater, wastewater and desalinated or imported water. ix) Level of involvement. Water resources development should be a participatory process involving all water stakeholders, consumers, engineers, water managers and politicians. The community should be the owner of the scheme and should participate at all stages of project implementation and the selected technology should be the least complex technology within the capability of the community to install and maintain. x) Integrated water resources. Finally but not the least water resources management shall be carried out in an integrated manner, regarding water demand, water resources availability and water development technologies, economic and social development, energy, human resources availability and other sources availability and utilization. Water and energy are interchangeable commodities and saving of one leads to the saving of the other and vice versa. 2.3 Non-conventional water resources Where water resources available are not adequate or where all available water resources have been utilized to the maximum and efficiently and still they are not enough, non-conventional technologies may be introduced. Such non-conventional technologies are water barging (by ship or barge), water transportation pipelines and desalination of seawater or brackish water. i) Water Barging. This involves the transportation of freshwater from one location where there is water for export to another, by sea, using barge or sea-going vessel. The ship or barge should have adequate volume capacity and the distance should be such that transportation is low cost and effective. The method requires qualified and skilled personnel for loading and unloading the water, on land storage capacity for storing the water and loading and unloading facilities. Barging is a relatively expensive method since it requires expensive loading and unloading facilities, and storage facilities on both ends. Cost varies from $1.5 to $5.0 depending on the distance. The technology is not dependable since it depends on sea conditions, but acceptability is not high in those cases where the water comes from a different country and creates dependability to a foreign country. This technology has been used in emergency conditions in the Mediterranean islands of Majorca, and in the occupied part of Cyprus and in Morocco. The technology was under consideration by Cyprus and Israel but desalination has been chosen instead because of higher cost, unreliability depending on sea conditions and the creation of the dependability to a foreign country. ii) Transportation. Submarine pipelines are used to convey water to small islands from nearby continents or other islands with excess water. The investigation, design and construction of such pipelines requires specialized engineering practice and involves high capital cost and periodic inspection to ensure its integrity especially after storms. Submarine pipelines must be anchored to the seabed by special anchor blocks and installation requires a specialized Contractor. Due to the high costs involved and to the limit of depth that a pipeline can be installed, the method is limited to islands not far away from the water continents with excess water. The method is suitable for islands 5

6 close to the continents, it allows the transport of water from excess water areas but reliance on water from offisland or from a foreign country may cause concern. iii) Seawater or brackish water desalination. Desalination is the process of separation of water form salt to produce water free of salts. This technology of water augmentation on small islands is offered because seawater or brackish water is abundant. Desalination can be carried out by thermal or membrane process. The thermal process is the distillation and includes the Multi-Stage Flash (MSF) method, the Multi Effect Distillation (MED) method and the Vapor Compression Distillation (VC) These methods are usually combined with thermal power stations for reducing the energy consumption. About 55% of desalination plants in operation worldwide use the thermal method for water desalination. The membrane process includes the Reverse Osmosis and Electro dialysis. Reverse Osmosis use pressure to desalinate water and represents around 40% of the total installed capacity worldwide. The energy for desalination may be in the form of fossil oil or renewable forms of energy such as solar, wind, geothermal, ocean energy etc. The renewable solar energy may be in the form of solar using the humidification, the solar distillation, and desalination with photovoltaic cells. All processes require skills and know-how for carrying out the operations. The capital investment varies from $1000- $2500 per cubic, meter where specific energy requirements are high varying from 2.5 to 10 KWh per cubic meter. The advantage of reverse osmosis is that the specific energy for desalination is a function of the salinity of the water, with brackish water having lower specific energy requirements. Energy for the desalination process may be obtained from the electrical grid, produced at the side or use wind or power energy depending on the specific case. Small islands situated in windy areas may utilize the wind energy or the solar energy, but both require larger surface areas for their installation. For small units a solar humidification, or distillation (both thermal processes) or photovoltaic cells may be used to capture solar energy but usually they require well trained and skilled labor to operate and maintain. 3. Small islands holistic approach to water resources management. 3.1 General Holistic approach means integration of all water resources (conjunctive use of surface, groundwater, treated wastewater and desalinated or imported water) of all water development technologies, of all water demand sectors (domestic, irrigation and industrial sectors), use water efficiently and effectively at any stage of the water cycle, combined with various forms of energy and taking into consideration economic and social development and environmental needs. This approach is most suitable to small islands or to isolated areas, where the area is small, the population density is high and the legal and administration frameworks are not complicated and the structures are light. 3.2 Proposed approach for small islands for freshwater development. The proposed technology for a holistic approach should include the following. Evaluation of total freshwater, surface and groundwater Evaluation and projection of demands by sector of the economy and for the environment for a sustainable economic and social development. 6

7 Select technology for freshwater development and effective and efficient use. Implement water demand methods for minimizing water losses and avoiding wasteful use by utilizing the modern technology for water distribution, water use and by implementing full cost recovery charges. Provide sewage collection and wastewater treatment plants and wastewater distribution systems for use of treated domestic effluents. Dual water supply systems, one for potable water and the other for the reuse may be implemented. 3.3 Non Conventional water Barging of water depends on distance of transfer and the facilities available at the source and the point of delivery, which determine the cost as well as the acceptance of dependency on the supply from another country. Desalination of brackish or seawater is another method for increasing water resources. This requires a lot of energy, high-level technology and skilled personnel for the erection, operation and maintenance of the plant. Small islands found in the open seas are blessed with relatively strong winds and sunshine, which can be used as energy for desalination in addition to local power produced by using fuel or energy from the national electric grid. Following are a few proposals for combination of wind power with electric power from the grid or locally produced energy using diesel engines for a dependable seawater or brackish water desalination. i) Stand Alone Wind Generator Systems. This uses wind energy produced at the site by wind generators and electric power from the grid or locally produced energy by diesel generators. During high velocity wind 7 periods the wind generator provides enough energy for the desalination plant and when the energy produced is not enough energy is taken from the local grid or produced at the site by diesel generators. This system requires standby electric or diesel-produced energy, which is not always feasible. ii) Water and Energy co-generation system. This system uses wind generators for electrical energy production, both for desalination and for electricity production. During high wind periods electricity produced is used for both desalination and electricity supply and when wind is low velocity the total power produced is used for desalination only. iii) Production of steady quantity of water and use power the grid as a balancing reservoir. If the national grid has enough energy capacity to give and or accept energy the system is tuned to produce a fixed amount of water and excess energy produced by wind generators is diverted to the electric grid and when energy produced by the wind generators is not enough for desalination then the grid supplies the deficit. iv) Wind generators for water production. This system is used only for the production of water and water produced during high wind periods is stored in surface reservoirs for use during high water demand periods. Under these conditions the water may need further treatment before us for domestic purposes. There may be other combinations with the objective of cost reduction. The selection of the best system must be made after a detailed study of the options available concerning the availability of electric power from the local grid, the wind velocity pattern, the water demand pattern, the use of water, the costs

8 involved, the financial and economic capabilities of the community and the capability of the community to maintain and operate such a system. References Review-Sourcebook of Alternative Technologies for Freshwater Augmentation in Small Island Development States. Antony, S.S 1992 Electromagnetic methods for mapping freshwater lenses on Micronesian atoll islands, Journal of Hydrology Vol.137(1-4)pp Ayers, J.F., 1990 Shallow seismic refraction used to map the hydrography of Nukuoro Atoll, Micronesia. Journal of Hydrology Vol. 113: Ayers, J.F, Vacher, HL. Hydrogeology of an atoll island: a conceptual model from detailed study of a Micronesian example. Ground Water 24/2; Pages Herman,M.E.,Buddemeier, R.W., Wheatcraft, S.W., A layered aquifer model of atoll island hydrology: validation of a computer simulation. Journal of Hydrology Vol.84, 83-4) pages Jacobson G. and Hill P.J., Hydrogeology of a raised coral atoll-niue Island, South Pacific Ocean. BMR Journal of Australian Geology & Geophysics 5: Lloyd, JW, Miles, JC, Chessman, GR, Bugg,SF, A ground water resources stuffy of a Pacific Ocean atoll- Tarawa, Gilbert Islands. Water resources Bull Issue 16/14; pages Oberdorfer, J.A., Hogan, P.J., Buddemeier, R.W., Atoll island hydrogeology: flow and freshwater occurrence in a tidally dominated system. Journal of Hydroplogy Vol. 120 (1-4), pp Υδατικοί Πόροι Ι. Τεχνική Υδρολογία. Εκδότης Γ. Τσακιρης Αθήνα Multicriteria decision analysis in Water resources Management. Edited by: Janos J. Bogardi, Hans-Peter Nachtnebel UNESO 1994 Ayers, J.F. Edited by Nicos TSIOURTIS Water resources management under drought or water shortage conditions. Balkema European conference on Desalination and the Environment water shortage. Proceedings I Volume 138, European Desalination Society European conference on Desalination and the Environment water shortage. Proceedings II Volume 139, European Desalination Society Guidelines for water resources development co-operation Towards sustainable water resources management.by European Commission Sptember 1994 HYDROTOP 2001 Colloque scientific et technique Avril 2001 Marseille- France. Water for the 21 st Century Vision to Action. Mediterranean vision on water, population and the environment by Jean Margat and Domitille Valle, Blue Plan World Water Vision Making water everybody s business William j. Cosgrov and Frank Rijsberman, World Water Council Nicos X. Tsiourtis, Framework for action Mediterranean Islands December The ABCs of Desalting by O.K. Buros. Published by the International Desalination Association. Second Edition Eheatcraft, S.W.; Buddemeier, R.W., Atoll island hydrology. Grund Water (3) pp