Two coastal aquifers in India respectively in Oman and management options

Category Hydrogeology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Jacks, Gunnar۱; Unnikrishnan Warrier, C۲; Shammas, Mahaad۳
Holding Date 29 September 2008

Coastal areas in S Asia are heavily populated and the groundwater resources are subject to stress. Two examples of aquifers which are over-pumped and the management options to solve the situation are described here.
The Kerala coast is built up of Holocene, Pleistocene and Tertiary sediments which contain 3-4 aquifers sandwiched upon each other. In the deeper aquifers there is a sequence from the south to the north of Ca-HCO3, Na-HCO3 to brackish groundwater. The presence of the Na-HCO3 indicate flushing of a formerly saline groundwater with freshwater. According to 14C dating this flushing took place more than 20 000 years before present when the sea level was about 120 m below the present level. In one section the pressure level of the groundwater is up to 5 m below the sea level, raising worries for sea water intrusion. There is probably no immediate danger as the saltwater-freshwater interface may be offshore, something that is seen in other large coastal aquifers in S and SE Asia. However on the long run additional water sources must be taken into account. One option is the shallow groundwater in Holocene-Pleistocene sediments. This groundwater is sensitive to pollution and to salinisation from brackish water in estuaries like Vembanad lake. More information is needed regarding the sensitivity of the surface near aquifers. A positive move is that ecological sanitation has been introduced and accepted which may diminish substantially the risk for pollution.
The other example is from the Salalah Plain in southern Oman. The aquifers here are substantially smaller and sea water intrusion is already observed. The main recharge comes from the mountains behind the Plain and the main mechanism is fog condensation on a mountain forest during the monsoon period. In view of the immediate danger a number of measures have already been taken. Treated sewage water is infiltrated along the coast and the large camel population on the mountain slopes has been decimated as they by their browsing are threatening the forest. Reforestation is also taken up. A dam in the mountain is constructed which in rather rare occasions arrests flood water. In spite of the measures the groundwater budget is still negative. A major portion of the water is used for irrigation of vegetable cultivation and for fodder production for milk farms. While the irrigation of vegetables can be optimized by introduction of drip irrigation the fodder production may not be sustainable.