South suffers sodium chloride deposits
 

by Afreeha Jawad

Following Tsunami's onslaught in December 2006 Southern Sri Lanka is into heavy deposits of Sodium Chloride. As a result, electrical conductivity in drinking water has gone upto 8,000 micro siemens per centimetre exceeding even WHO's accepted levels of 1,000 micro siemens per centimetre.

Aggravating the problem into a near beyond redemption state is the ad hoc and haphazard digging of wells and ponds where the collapsing earth along with water salinity causes twin damage. Should the status quo continue, the intended social cost certainly will be irreversible.

"The sea water rushed inland with such force covering a distance of about 2-3 kilometres. However, depending on the land formation, elevation and vegetation the salinity varies in degrees from place to place", said Dr. Ranjana U. K. Piyadasa, Hydro-geologist, Colombo University when the Sunday Observer met him recently.

The sea water density being higher than fresh water, greater complication sets in when the rivers were intruded with sea water that heightened salinity levels. In between the rivers and the coastal belt the situation remains unrectified.

Nature helps fight the present crisis even though temporarily. For instance high rainfall mitigates underground water salinity. The rain that lashes on highland which water reaches the ground keeps a constant flow enabling the cleansing of ground water salinity yet during the dry season this process is halted impacting negatively into its re-emergence.

However the coastal belt's flat land and river based areas continue to record high salinity levels.

Listening to Dr. Ranjana Piyadasa this is certainly not a hopeless situation provided professional assistance of scientists is sought. Some organizations tried to clean the wells following the tsunami damaging the interface between fresh and saline groundwater.

The interface believably nature's finest asset- a sort of protective cover, in the process upcones resulting in sea water intruding fresh water.

Thus the natural cleansing process of salinity through rain is hindered in coastal and hilly areas.

Artificial groundwater re-charge like wells and ponds says Dr. Ranjana Piyadasa is the best way out to reduce salinity in flat land, yet calls for cleansing professional help. The rain water filled ponds and wells help in salinity which method is popular even in European countries and India - not necessarily following a tsunami.

Dr. Ranjana Piyadasa is the team head of a group comprising the Colombo, Ruhuna and Kelaniya Universities studying hydrological conditions and groundwater quality distribution in tsunami affected south.

Studies pertaining to groundwater quality and water table behaviour at Weligama Bay where ninety affected shallow dug wells situated on an 8 kilometre coastal strip reveal high levels of saline.

"The underground pressure wave which developed due to the tsunami may have disturbed the fresh water - salt water equilibrium resulting in the mixing of fresh ground water with saline water. Under natural conditions and equilibrium exists between sea water and fresh water depending on the geological and hydro-geological condition.

Due to the high density of sea water, it tends to force its way underneath the fresh water.

However as the piezometric head of the fresh water is higher than sea water, the fresh water continually discharges to the sea. Fresh water discharges are opposite to the inland seawater movement whereby an equilibrium exists.

Sea water that moves inland causes salt water intrusion. Once the groundwater equilibrium is established, the water level will stabilise and fluctuates only annually with seasonal changes and natural hazards," he said.

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