Hard Rock Aquifers of Trivandrum, Kerala, India:A Critical Analysis of its Status and Prospects

Groundwater in the hard rock aquifers of Trivandrum district has been studied to characterize the groundwater potential and prospects. The study area is occupied by four watersheds (Ayirur, Vamanapuram, Karamana and Neyyar) and groundwater is one of the main sources of water for drinking and agricultural purpose. The groundwater scenario has been assessed by using the water table contour maps and groundwater level fluctuation maps based on the data obtained from 93 observation wells. The average water level in the region is 9 to 13 and 8 to 10 mbgl during pre and post monsoon seasons respectively. The deepest water level (20.21 mbgl to 26.67 mbgl) is recorded from places such as Chovvarapotta, Pazhayaucchakkada and Ozhukupara and shallowest water level (0.85 mbgl to 1.61 mbgl) is in places like Irumba, Punnamkarikkakam, Kathipara and Erattachira. Most of the deep dug wells go dry during summer months, though these wells show good water level fluctuation during rainy season. A detailed investigation has revealed that substantial quantity of groundwater is being lost as base flow. This base flow of groundwater makes the rivers and river lets, perennial in the area. The long term trend analysis shows that (ten years data), majority of the wells are showing declining trend (1.99 m/year) and this decline is attributed to the change in land use pattern in the area and less recharge from the rainfall. The rainfall analysis shows that there is not much variation in the rainfall pattern over the last few years. On the basis of mathematical projection the water level trends for the next ten years has been predicted. The analysis shows that the groundwater potential in the hard rock aquifer is depleting hence an immediate recharge measures have to be implemented in this region to arrest the decline trend and the base flow.