The impact on groundwater resources of the tsunami is likely to be most severe in low lying limestone islands where populations rely on water from wells, trenches and boreholes dug into fragile freshwater lenses (see BBC News article). Damage may be caused by inundation of wells and by the flooding of land leading to direct infiltration into the rocks. In the worst cases the damage may be bad enough to render the groundwater un-useable for many years until infiltrating rainfall has re-established the freshwater lens.
Most of the other areas affected by the tsumani are characterized by low groundwater storage and high rainfall, and in the medium term natural flushing out of salinity might be quite quick (a few years), particularly with the heavy monsoon rains.
In the affected areas it is highly likely that open dug wells will have been filled with seawater. Although these might be of a large diameter, as the water table in coastal or low-lying areas will be close to the ground surface, the total volume of seawater going into the aquifers may not be large. The degree to which the saline water spreads out is dependent on the permeability of the rocks. Water in these wells may be undrinkable for some time, but it may be possible to flush them out by pumping. Eventually this water will be replaced by freshwater flowing naturally from inland towards the coast and rain falling locally.
The wells are also likely to be polluted by bacteria and viruses in water inflowing directly from the surface. Pollution getting into the ground via wells is likely to be local to the area of the wells. Digging new wells away from polluted wells might provide a solution. In the low permeability areas, although individual wells many have been affected, it may be possible to obtain fresh water not far away.
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Pollution of groundwater from broken sewers, flooded septic systems, ruptured fuel filling station tanks etc. is highly likely in urban areas. Mass burials could also be a source of groundwater pollution, if the burials sites are located in or above aquifers. Some wells may also be blocked by debris and sand suspended in the tsunami water.
Agricultural soils inundated by seawater could be severely affected by salinity. Some coastal crops will have been destroyed and in the short term it will be difficult to cultivate the land covered in sand and other debris. In areas where groundwater is used for irrigation, the groundwater quality may recover before the soil quality.
(this text was produced by the British Geological Survey in response to a request from the BBC World Service Radio)
Resources for helping to deal with water supply problems related to the tsunami can be obtained from the Water, Engineering and Development Centre and the World Health Organisation. |
