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MANAGED AQUIFER RECHARGE

Managed aquifer recharge, or MAR, refers to the intentional recharge of water to aquifers for subsequent human use or environmental benefit. It is a potential adaptation option for Pacific Island Countries such as atoll islands who depend upon groundwater as their primary water supply source. MAR is used to supplement natural groundwater storage and increase resilience of water supplies. The approach can also have the benefit of mitigating floods as high flows are captured and fed into aquifers.Image removed.

In atoll islands, ground water occurs in shallow aquifers called ‘freshwater lens’. This freshwater pocket floats on sea water because of its higher buoyancy. These freshwater lenses are recharged naturally by rainfall and this natural recharge could be supplemented by MAR through the techniques outlined below.

 



Methods of managed aquifer recharge include:
•    Modifying the landscape to hold surface water in place to allow for infiltration to groundwater. This can include check dams, retarding basins or wetlands. 
•    Building infrastructure such as direct injection wells to place rainfall directly into aquifers or freshwater lenses.  This is a more infrastructure and energy intensive approach.
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  • Provides an alternative reliable water source in areas of increasing variability in surface water availability.
  • Access to a reliable water source can have positive impact in lives and livelihood of people.
  • The infiltration process can improve water quality, thus reducing the need for costly treatment.
  • Aquifers tend to be less affected by extreme events such as cyclones and storm surges (compared to surface water).
  • Overextraction of groundwater can lead to saltwater intrusion and land subsidence.
  • Knowledge of aquifer areas and recharge volumes is limited in many Pacific Island Countries.
  • Pacific Island Counties have highly porous soils which makes aquifers vulnerable to pollution.
Indicative cost

Managed Aquifer recharge can be low (e.g. recharging through similar retention ponds) to high (e.g. drilling of artificial recharge well) cost depending on the method adopted. Whilst providing cost estimates is difficult given the broad range of influencing factors across the Pacific, the below table outlines the key components that should be considered when estimating a managed aquifer recharge project budget for a specific location.

Components

Unit
(A)

Number of units (B)

Unit Cost
(C)

Budget
(B x C)

Establishment Cost

        
  • Planning and design including community outreach

e.g. $/hour

      
  • Land (if not already held)

e.g. km2

      
  • Site preparation (e.g. clear bush, tree protection, topsoil preparation)

e.g  $/hour

      
  • Materials (e.g. materials for injection well)

e.g. number 

      
  • Labour

e.g. hours

      
  • Reporting to donor (if required)

e.g. hours

      

Ongoing Cost

        
  • Maintenance Cost (materials and labour)

e.g. number and hours

      
  • Reporting and Monitoring

e.g. hours

      

To alleviate water stress, countries augment surface water supplies with different sources such as groundwater, wastewater, desalination and imported water. Groundwater sources supported by aquifer recharge can be compared to other sources such as wastewater, desalination and imported water supplies:

-  Groundwater recharge is an inexpensive technology compared to other centralised water supply options such as desalination or wastewater treatment.

-  Groundwater as an alternative water source can be more reliable and resilient than the other options as the water is stored in naturally occurring aquifers which are less impacted by hazards such as storm surges and cyclones.

On-ground impacts that the EbA option addresses
Decreasing water availability
Poor water quality

Case study

Groundwater for resilience

Yaro Village, Fiji

Whilst there are limited examples of Managed Aquifer Recharge being undertaken in the Pacific, there are numerous examples of the use of groundwater sources to improve access to water supplies.

For example, after the devastation caused by cyclone Yasa, Fiji’s Mineral Resources Department and the Pacific Community (SPC) partnered to locate groundwater in the Yaro Village, a remote part of Fiji’s northern division. With no access to a reliable water source Yaro village had been rationing water twice a week from the village tanks to conserve water for the community. Two sites were selected using geophysics analysis and site visits, and a ground water extraction system was installed. The system pumps safe drinking water straight into the community for the first time and each household now has access to a tap outside their home.

The case study can also be accessed through https://www.youtube.com/watch?v=-IVGNtDMjjU

Reference: Groundwater of Resilience, More than 5million Pacific people don’t have access to basic drinking water: this needs to change | The Pacific Community (spc.int)