RECOVERY OR LONG TERM EFFECTS ON COASTAL GROUNDWATER SYSTEMS?
As time passes, the saltwater that has infiltrated, through the soil surface or from water bodies and wells,
moves through the groundwater in a general downward and lateral direction towards the coast (or maybe
towards a lagoon or inland water body). Eventually, and with a continued influx of rainwater, the saltwater
will be suppressed, mixed, diluted and transported to the open water. These are natural processes that
occur and allow that over the longer term, the aquifer can recover and return fresh.
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The International Groundwater Assessment Centre (IGRAC) made some preliminary estimations of the
time required to naturally rehabilitate the coastal aquifers3. Using a numerical simulation model and applying
some simplifying assumptions of the land-groundwater system it was estimated that it would require a
couple of years to obtain pre-tsunami salt concentrations in the aquifer, under conditions prevailing in the
Maldives, which is an archipelago to the west of Sri Lanka, also impacted by the tsunami. Some of the
uncertainties associated with this simulation are related to:
1. Insufficient knowledge of actual conditions. Some of the factors/parameters that have not been
assessed based on actual conditions and measurements, and may significantly influence the results
are:
• The hydraulic conductivity of the aquifer, which determines the rate at which water moves through
the sediments
• The depth of the aquifers, i.e. if there is an impermeable layer restricting the freshwater lens
• The influence of actual rainfall occurring in the affected areas
• The amounts and patterns of pumping
2. Furthermore, some important processes/phenomena may not have been incorporated sufficiently:
• The infiltration from stagnant water bodies has not been included
• The possible disruption of the freshwater lens due to an underground pressure wave has not been
included
• The possible slow leaching of the saltwater in the aquifer due to low permeable zones, or so-called
double-porosity characteristics
Posted by Aneka Tips
on 17.13. Filed under