groundwater training course sopac, april 2005 · pdf filegroundwater development methods. dug...

Groundwater Training CourseGroundwater Training Course

SOPAC, April 2005SOPAC, April 2005

Groundwater Development MethodsGroundwater Development Methods


• Dug wells• Boreholes• Infiltration Galleries

• Tunnels• Spring cappings

(Note: springs are groundwater outflows but are generally developed at the surface)

Groundwater Development (Pumping) Groundwater Development (Pumping) (on small coral islands and coastal zones of high islands)(on small coral islands and coastal zones of high islands)

•Dug wells

•Boreholes

•Infiltration galleries


Dug wells:• Relatively easy to construct in sand

• Harder in limestone and volcanic rock (some up to 50m deep)

• Generally used for small demands (e.g. domestic and other small users)

Dug wellsDug wells

Open wellOpen well

Sealed well with Sealed well with hand pump and hand pump and small tanksmall tank


Boreholes:• For larger aquifers

• Where water depth is large (greater than about 4-5 m)

• Caution is required with pumping rates in freshwater lenses

Boreholes Boreholes -- productionproduction

ExamplesExamples


Infiltration Galleries:• Useful where water table is shallow (less than

about 4m deep)

• Good control on seawater intrusion

• Preferred method on small coral islands or coastal zone of medium size islands where large quantities of water are needed

Infiltration galleries for pumping fresh Infiltration galleries for pumping fresh groundwatergroundwater

BonrikiBonriki island, Tarawa atoll, Kiribatiisland, Tarawa atoll, Kiribati

17 galleries each 300m long in this area

Infiltration galleries layoutInfiltration galleries layoutBonrikiBonriki, Tarawa, Tarawa

Infiltration galleries Infiltration galleries –– typical cross sectiontypical cross section

Infiltration galleries Infiltration galleries –– plan view of one plan view of one example fromexample from BonrikiBonriki

BonrikiBonriki galleries photosgalleries photos

Infiltration galleriesInfiltration galleries

Ideal locations: central areas of small coral islands

Groundwater pumping strategy for Home Island, Cocos (Keeling) Islands

• Coral atoll in Indian Ocean (territory of Australia)• Groundwater supplied to 500 people on Home Is

Groundwater pumping strategy for Home Island

Fresh groundwater occurs in the form of a freshwater lens (approx 5-10m deep in centre)


Typical infiltration gallery details


Sustainable yield (safe pumping rate) of the freshwater lens:

– 150 kilolitres per day (kL/day)

– Groundwater is regularly monitored

Layout of Galleries and Boreholes (Main Lens)

Groundwater pumping strategy for Home IslandRegular monitoring of groundwater salinity and rainfall:• Daily: Rainfall and volumes of water pumped from each gallery• Monthly: Groundwater salinity data from 9 galleries every month

(7 in main lens and 2 in northern lens)• Quarterly: Groundwater salinity v depth data from 18 boreholes

Daily-read raingauge Borehole monitoring

Typical slotting pattern for gallery pipesTypical slotting pattern for gallery pipes


Tunnels:

• Special example of galleries where they are excavated well below ground level

• More expensive than boreholes but much larger yields

• Could have application in some situations (e.g. horizontal drilling from base of quarries on limestone island

TunnelsTunnels

Tunnel in limestone rock with vertical access, Barbados

Tunnel in volcanic rock with incline access, Hawaii

groundwater training course sopac, april 2005 · pdf filegroundwater development methods. dug...

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