EFFICIENT WATER-SUPPLY DEVELOPMENT AND EFFICIENT WATER-SUPPLY DEVELOPMENT AND MANAGEMENT FOR SMALL, ARID, OCEANIC ISLANDS MANAGEMENT FOR SMALL, ARID, OCEANIC ISLANDS

BASED ON WATER USEBASED ON WATER USE

EFFICIENT WATER-SUPPLY DEVELOPMENT AND EFFICIENT WATER-SUPPLY DEVELOPMENT AND MANAGEMENT FOR SMALL, ARID, OCEANIC ISLANDS MANAGEMENT FOR SMALL, ARID, OCEANIC ISLANDS

BASED ON WATER USEBASED ON WATER USE

Espen Ronneberg,

UNDESA

Allen L. Zack,

Hydrologic Consultant for UNDESA

towards the sustainable development of water and the reduction of waste

Many SIDS have inadequate freshwater supplies, yet Many SIDS have inadequate freshwater supplies, yet lack the financial and technical resources to implement lack the financial and technical resources to implement seawater desalination for all of their population.seawater desalination for all of their population.

Non-potable water uses have been sought for brackish Non-potable water uses have been sought for brackish and gray wastewater to moderate the demand for and gray wastewater to moderate the demand for potable water.potable water.

The sustainable development of water and the The sustainable development of water and the reduction of wastewater in SIDS can be improved reduction of wastewater in SIDS can be improved by matching appropriate water-quality requisites to by matching appropriate water-quality requisites to the various water-use sectors in order to the various water-use sectors in order to accommodate both potable and non-potable water accommodate both potable and non-potable water supplies.supplies.

There can be no single strategy for appropriate water-There can be no single strategy for appropriate water-quality partitioning based on use.quality partitioning based on use.

The amount of saltwater (chloride concentration) – or The amount of saltwater (chloride concentration) – or other contaminants – present in the water supply would other contaminants – present in the water supply would dictate which non-potable use of the water can be dictate which non-potable use of the water can be considered.considered.

Existing and evolving technologies can be Existing and evolving technologies can be considered to provide adequate, affordable, and considered to provide adequate, affordable, and sustainable water for all sectors with minimal sustainable water for all sectors with minimal environmental disturbance.environmental disturbance.

Water-quality requisites for Water-quality requisites for intended useintended use

Drinking water less than 250 mg/L chloride

Industrial uses vary widely

Agriculture can accept higher salinity, but depends on crop tolerance and rainfall

Golf-course irrigation graywater, up to 500 mg/L chloride, treated sewerage effluent

Toilet flushing saltwater, in dual water-distribution lines

Wastewater discharge to the environment is Wastewater discharge to the environment is reduced by optimizing freshwater reduced by optimizing freshwater

production and matching water quality to production and matching water quality to other water usesother water uses

Islands of the Caribbean Region

The availability of freshwater resources depends upon the geomorphologic history of the islands and rainfall

accumulation

Greatest availability: large

islands, sufficiently elevated to

have orographic effects and

exhibiting extensive coastal

accumulation of sediment

Lowest availability: small, low-lying islands having less than 50 centimeters of yearly rainfall, without coastal embayments

Middle Caicos, TCI

St. Lucia

0

0.5

1

1.5

2

2.5

3

3.5

4

-2 0 2 4 6

LOG OF AREA, IN SQUARE KILOMETERS

LOG

OF

ELE

VA

TIO

N,

I N M

ET

ER

S Volcanic core, perenialstreamflow, extensivecoastal aquifers

Volcanic core, intermittantstreamflow, limited groundwater in embayments

Volcanic rocks pluslimestone; limited groundwater in carbonates

Limestone and/or corallinerock (freshwater lensdevelopment)

Information not available

Influence of island size and elevation on the occurrence of groundwater resources, rainfall, and potential for saltwater contamination

more rainfall

less rainfallless rainfal

Fresh groundwater lenses subject to vertical saltwater intrusion (upconing) during well pumping.

Case study ICase study ICase study ICase study I

Small, arid, limestone/coralline Small, arid, limestone/coralline platforms or atolls extending a few platforms or atolls extending a few meters above sealevel, exhibiting meters above sealevel, exhibiting subterranean drainagesubterranean drainage

Freshwater lens typical of small, low-lying carbonate islands showing disruption of the freshwater/saltwater interface by pumping wells

Minimal, unsustainable freshwater recovery using trench-and-skimming, radial Minimal, unsustainable freshwater recovery using trench-and-skimming, radial wells, gentle/intermittent abstractionwells, gentle/intermittent abstraction

•Only hydraulic formula for stabilizing the interface

•Greater quantities of fresh groundwater continuously

•Scavenger-well effluent must be discharged to the sea or deep wells – or used for some non-potable water use

SCAVENGER-WELL COUPLESSCAVENGER-WELL COUPLES

Hydraulic maintenance of the freshwater lens by operating Hydraulic maintenance of the freshwater lens by operating the scavenger wellthe scavenger well

Pre-pumping conditions

Production well withdrawing a mix of freshwater and saltwater

Scavenger well withdrawing saltwater

Production well withdrawing freshwater

PROVIDENCIALES, TURKS AND CAICOS ISLANDS

The Bight, freshwater lens

0.0 0.5 1.0 1.5Time (decimal days from begining of pumping)

2000

4000

6000

8000

10000

Sp

eci

fic C

on

du

cta

nce

Improvement in freshwater abstraction by pumping the scavenger well

scavenger well as production well is pumped

production well as scavenger well is pumped

scavenger well pumping alone

production well pumping alone

detectability limit (500 mg/L cl)

USEPA limit (250 mg/L cl)

Time (decimal days from beginning of pumping)

COZUMEL, QUINTANA ROO MEXICO

Cozumel wellfield

Simultaneous pumping of production and scavenger wells Simultaneous pumping of production and scavenger wells for pozo 4, eje 6+200for pozo 4, eje 6+200

Majuro Atoll, Republic of the Marshall Islands

Iroij well, chloride (1)

0

125

250

375

500

625

750

0 50 100 150 200 250

Time in minutes

Chl

orid

e (m

g/L)

Cl-scav

Cl-prod

saltwaterfreshwater

Delap, chloride

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250

500

750

1000

1250

0 20 40 60 80 100 120

Time in minutes

Chl

orid

e (m

g/L) Cl-scav

Cl-prod

saltwater

freshwater

• Efficient utilization of scavenger-well effluent:– flushing toilets– washing vehicles– filling swimming pools

• Efficient utilization of scavenger-well effluent:– flushing toilets– washing vehicles– filling swimming pools

• Final wastewater discharge:– the sea– deep wells, screened far below the

freshwater/saltwater interface

• Final wastewater discharge:– the sea– deep wells, screened far below the

freshwater/saltwater interface

Intermittent streamflow recharges the wedge of fresh groundwater residing in coastal sediment. During droughts, saltwater migrates inland horizontally from the sea, displacing abstracted or naturally discharged freshwater.

Case study IICase study II Case study IICase study II

Elevated islands of relatively small Elevated islands of relatively small size, having high rainfall, size, having high rainfall, intermittent surface drainage and intermittent surface drainage and sedimentary coastal embaymentssedimentary coastal embayments

Tortola, BVI

Fresh groundwater withdrawals from coastal Fresh groundwater withdrawals from coastal embayment aquifers can initiate the horizontal migration embayment aquifers can initiate the horizontal migration

of saltwater toward pumping centers. of saltwater toward pumping centers.

Retention structures placed at appropriate downstream Retention structures placed at appropriate downstream locations in ephemeral drainages enhance groundwater locations in ephemeral drainages enhance groundwater recharge by retaining rainfall runoff for greater periods recharge by retaining rainfall runoff for greater periods

of time.of time.

Although retention structures have been used Although retention structures have been used throughout history to increase groundwater storage, no throughout history to increase groundwater storage, no

engineering studies have been conducted to relate engineering studies have been conducted to relate storage to aquifer diffusivity, rainfall, basin storage to aquifer diffusivity, rainfall, basin

evapotranspiration, and surface-water head.evapotranspiration, and surface-water head.

However, wastewater issues are somewhat However, wastewater issues are somewhat more problematic in islands having retention more problematic in islands having retention structures because there are fewer options for structures because there are fewer options for environmentally compatible discharge.environmentally compatible discharge.

WastewaterWastewater will be of higher will be of higher quality in the elevated quality in the elevated islands having coastal islands having coastal retention structures because retention structures because of its origin; it can often be of its origin; it can often be considered for agricultural or considered for agricultural or golf-course irrigation.golf-course irrigation.

Annual rainfall accumulation for Caribbean islands with the longest period of record

Desalination:

Catchments:

•Rooftop

•Roadway

•Runway

Islands without freshwater resourcesIslands without freshwater resources

•Flash distillization

•Efficient reverse osmosis(Clark pump)

International forum of hydrologic scientists in International forum of hydrologic scientists in cooperation with AOSIScooperation with AOSIS

Demonstrating, documenting, and publicizing new Demonstrating, documenting, and publicizing new technologiestechnologies

Small Island Developing States Information Small Island Developing States Information Network (SIDSNet)Network (SIDSNet)

Application of new technologies to improve Application of new technologies to improve freshwater development and reduce wastewaterfreshwater development and reduce wastewater

Application of new technologies to improve Application of new technologies to improve freshwater development and reduce wastewaterfreshwater development and reduce wastewater

Support provided by:Support provided by:

U.N. Development Program

University of the West Indies Center for Environment and Development

U.N. Department of Economic and Social Affairs

U.S. National Weather Service, National Oceanic and Atmospheric Administration

Programa de Modernización del manejo del

agua (Mexico),

U.N. World Meteorological Organization