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close this bookSourcebook of Alternative Technologies for Freshwater Augmentation in Small Island Developing States (UNEP-IETC, 1998, 230 p.)
close this folderPart A - Introduction
View the document1. Background
View the document2. Purpose of the source book
View the document3. Structure of the source book
View the document4. How to use the source book
Open this folder and view contents5. Methodology for the identification and classification of small islands
View the document6. Results of the discussions at the workshop on augmenting freshwater resouces
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3. Structure of the source book

The Source Book is in three major parts:

- Part A provides an introduction to freshwater augmentation: what it is and why it is necessary. Part A also outlines the purpose of the Source Book; reviews the methodology used in this Source Book for the classification of "small islands"; and, presents an overview of how to use the Source Book.

- Part B briefly describes a series of alternative technologies available and used in Small Island Developing States (SIDS), and presents a consistent and comparable set of data about the technologies which can be used to compare their relative advantages for maximizing water-use efficiency and augmenting existing water supplies in small island states. The objective of these technology profiles is to provide a reasonably comprehensive inventory, summarised in Table 1, that water resources professionals can use when planning water development projects on SIDS.

- Part C comprises case studies that highlight specific technologies that have been adopted in the region, and summarizes the experiences gained from their implementation.

For the purpose of this Source Book, the technologies applicable to Small Island Developing States, discussed in Part B, are divided into four subsections:

- The first subsection reviews those technologies that are generally applicable to small islands regardless of their geological and topographical configuration. These include technologies such as alternative (dry) sanitation, water quality improvement, irrigation systems, and water conservation and groundwater assessment technologies.

- The second subsection reviews those technologies applicable to very small, low coral islands. These include technologies such as rainwater harvesting and groundwater abstraction techniques such as dug wells and infiltration galleries, as these islands are not likely to have surface water resources and moderate to low availability of groundwater resources.

- The third subsection reviews those technologies applicable to small, high volcanic islands which are likely to have greater options for water resources development. These include technologies for the development of rainwater, surface water and groundwater resources.

- The fourth subsection covers islands where specific problems or circumstances make it necessary to pursue alternative (and not so commonly used) technologies. These include technologies such as desalination, dual water distribution systems, importation, and wastewater reuse.

TABLE 1. Summary of Freshwater Augmentation Technologies Applicable to Small Island Developing States.

TECHNOLOGY

EXTENT OF USE

SUITABILITY

ADVANTAGES

DISADVANTAGES

REMARKS

RAINWATER HARVESTING

Most SIDS

Suitable for very small islands without other options Suitable for islands where rainfall is evenly distributed throughout the year

Provides an additional source of water at the point of use Owner operated and managed Provides supplemental water source Water quality may be better than groundwater

Rainfall dependent Water can be contaminated within the catchment area Drought management may be required

On small coral islands, rainwater harvesting is often used to supplement groundwater sources

RAPID SAND FILTRATION

Mauritius, Seychelles

Suitable for larger urban water supply systems

Improved water quality Smaller land requirement than slow sand filtration

High capital cost Pretreatment required Trained operators required


SLOW SAND FILTRATION

Urban and rural water supply systems in Seychelles, Western Samoa, Cook Islands, and French Polynesia

Suitable for urban and rural water supply systems using surface water resources

Low construction cost Low operation and maintenance costs Energy source not required Improved water quality Unskilled labour can be used in operation and maintenance of units

Requires large land area Sensitive to certain toxins and high concentrations of colloids


DISINFECTION

Widely used throughout SIDS

Suitable for most water supply systems

Reduced occurrence of disease vectors Generally, easy to apply

Testing for residual chlorine concentrations is recommended Sodium hypochlorite is not always readily available Special care and handling of chlorine and chlorine compounds is required


ALTERNATIVE (DRY) SANITATION

Limited use in Kiribati and Federated States of Micronesia

Suitable for use on small, low islands where water is scarce and groundwater is sensitive to contamination

Conserved water Protects groundwater quality Produces compost for gardening use

Toilet bins are located above-ground Potential health hazard if not properly operated Can attract insects if not properly maintained Expensive

Should be used in conjunction with groundwater development projects on small coral islands Case Study included in Part C

WATER CONSERVATION

Widely used in SIDS

Suitable for all public water supply systems

Reduced water consumption Improved water quality Increased revenue Improved knowledge of system operations

Added cost Unpopular with consumers Meters require maintenance

Water conservation programmes should be integrated into all public water supply system operations

GROUNDWATER ASSESSMENT

Most SIDS

Suitable for assessing community water supply requirements Essential for small coral islands with limited groundwater resources

Contributes to sustainable use of groundwater Provides information necessary to optimally site wells and/or infiltration galleries

High cost of investigations, especially if drilling is required

See also Annex 4, Part D

IRRIGATION SYSTEMS

Limited to a few SIDS

Suitable for use on islands with adequate and sustainable water resources

Increased crop production

Increased water consumption Potential to contribute to water quality degradation


DUG WELLS

Most SIDS

Especially suitable for use on small, low islands

Simple to construct and use Provides water during dry periods Provides supplemental water resource

Potential water quality problems due to surface and subsurface contamination


INFILTRATION GALLERIES

Marshall Islands, Kiribati, Cook Islands, Cocos (Keeling) Islands, and Barbados

Most suitable for use in community water supply systems on small, coral sand islands

Improved water quality (lower salinity) without decreased yield Drilling may not be required Little maintenance required

Initial construction costs may be higher than those of dug or drilled wells Greater land area required


HAND PUMPS

Most SIDS

Suitable for use in abstracting water from shallow wells

No operational cost Low maintenance cost Minimal risk of overpumping aquifer Protects well from surface pollution Maintenance can be performed by users

Spare parts are required


SOLAR PUMPS

Islands in the Straits of Torres (Australia/New Guinea), Federated States of Micronesia, French Polynesia, and Kiribati

Suitable for use on islands where adequate solar energy is available, and where sufficient clear space exists for erection of solar panels

No on-going fuel costs Little maintenance required Quiet, pollution-free operation

High initial cost If used with back-up battery systems, problems may occur with battery maintenance in tropical conditions

See Case Study, Part C

HYDRAULIC RAM PUMPS

Limited to a few SIDS: Solomon Islands and Vanuatu

Suitable only for use on high islands with perennial, steeply sloping water courses

Low operating cost Minimal environmental impact Little maintenance required May be manufactured locally Automatic, continuous operation

Use limited to small-scale operations in hilly areas with suitable surface water resources Pumps a small proportion of the available water to higher elevations High capital costs Specialised design skills are required


BOREHOLES

Extensively used on high islands

Suitable for use on islands with adequate groundwater resources

Produces water of reliable quality and quantity

Requires skilled drill operators and technicians May have high construction costs May have high operating and maintenance costs Spare parts are required


RUNOFF COLLECTION USING IN-STREAM STRUCTURES

Used on most small islands with surface water resources

Suitable for use on islands with perennial streams

Diversion is less expensive than pumping Limited operating and maintenance requirements Can be operated by unskilled labourers

May be an unreliable source of supply May need pretreatment if used for potable purposes Moderate to high risk of contamination exists


RUNOFF COLLECTION USING SURFACE STRUCTURES

Used on larger islands: Guam, Malaysia, Indonesia, China, Cook Islands, and Hawaii

Suitable for use on large islands where topography, geology and economic factors permit

Provides medium to large volume storage Limited operating and maintenance costs and requirements

Can have environmental and public health consequences Water quality may be variable throughout the year Constructions costs are high Risk of failure exists


SPRING CAPPING

Extensively used in SIDS

Suitable for use on high islands where natural springs occur Suitable for use in all climates

Provides good quality water Low operating and maintenance costs

Could negatively impact spring discharge


IMPORTATION

Rarely used; Fiji and Bahamas Frequently used in emergencies

Suitable for use in emergencies or where economic demands can sustain this option (e.g., resort islands)

Provides freshwater

Incurs an high cost of transportation May be affected by sea conditions and availability of suitable vessels/barges Requires loading/offloading facilities and distribution systems


SUBMARINE PIPELINES

Rare; Seychelles, Western Samoa, Hong Kong, China, Malaysia

Suitable for use on small islands located close to continents or large islands with surplus water

Gravity-fed systems have low operating costs Effects distribution of water from water-rich areas to water-poor areas

High construction costs Subject to damage from storms, tidal flows, or shipping


DISTILLATION

Netherlands Antilles, Guernsey, Canary Islands, US Virgin Islands, Singapore, Antigua, and Cayman Islands

Suitable for use in all climates Most suitable for use in dual purpose facilities (e.g., water supply and power generation)

Provides good water quality More tolerant of poor quality feedwater than most desalination processes

High capital cost High production (operation and maintenance) cost Large capacity plants are unwieldy to transport and install


ELECTRODIALYSIS

Gran Canary, Bermuda, and some Chinese and Japanese islands

Best suited for use with feedwater having a total dissolved solids content of less than 4 000 mg/1

Provides an high rate of recovery of product water Energy efficient Requires little chemical pretreatment of feedwaters

Clogging may occur if the feedwater has an high bacterial content Not economic for seawater desalination


REVERSE OSMOSIS

Malta, Gran Canary, Bermuda, and Cape Verde

Suitable for use in desalinating brackish and sea waters in all climates

Simple design Removes ionic and non-ionic particulates Can be combined with energy recovery processes

Membranes are sensitive to feedwater quality Skilled operators are required Process requires spare parts availability and chemical pretreatment

See Case Study, Part C

SOLAR DESALINATION

Limited

Not suitable for use on most islands due to cost

Low energy costs

High capital costs Requires large land area for solar energy generation

Further development to make this technology more cost effective is required

WASTEWATER REUSE

Cape Verde, US Virgin Islands, Fiji, Canary Islands, Bermuda, and Barbados

Suitable for use on islands that have wastewater collection and treatment systems, where there is a need for large volumes of low quality water

Conserves potable water resources Provides large volumes of water suitable for use in irrigation, etc.

Potential public health risk Consumer resistance Variable quality of product water if system is not operated efficiently

See Case Study, Part C

DUAL DISTRIBUTION SYSTEMS

US Virgin Islands, St. Lucia, Bahamas, Kiribati, and Marshall Islands

Suitable for use where non-potable water resources are available

Conserves potable water resources Suitable for distributing seawater/wastewater for fire fighting, irrigation, etc.

High capital cost due to the need for two parallel distribution systems High operation and maintenance costs Risk of cross-contamination and/or groundwater contamination Potential public health risk among children and elderly



Figure 1. Possible applications of water supply technologies for small high islands.


Figure 2. Possible applications of water supply technologies for small low-lying islands.

It should be noted that there are no fundamentally new technologies available to resolve the difficulties imposed on SIDS by their limited water resources. For very small, coral islands, either rainwater or groundwater is available. Most SIDS cannot afford desalination as an option, and importation of water by barge or submarine pipeline, similarly, is not often feasible. Small volcanic islands often have surface water as a third option, together with rainwater and groundwater. However, desalination and importation, likewise, are rarely used and only where there is no other feasible alternative and consumers can afford to pay for it. For these reasons, emphasis is placed on conserving and protecting the quality of the existing water resources. Pollution of groundwater and surface water resources is increasing due to untreated human waste discharges from individual households, hotels and industries, and urgent steps need to be taken to halt or minimise pollution of these water resources. Similarly, the water that is supplied to consumers is often wasted, and/or lost through delivery system leaks and illegal connections, and improved management of water resources and supply systems is needed. Often water is supplied without charge, even though costs are incurred in providing and maintaining the supply service. The technologies described in Part B address many of these issues.