Indiscriminate sand mining, unscientific construction and over-extraction of water have led to the depletion and environmental degradation of the Sasthamkotta freshwater lake, impacting on the biodiversity and groundwater availability in the region.
A study conducted by the National Centre for Earth Science Studies (NCESS) and the Cochin University of Science and Technology (Cusat) has found that instream and floodplain sand-mining over the last three to four decades had severely damaged the underground aquifers feeding the lake, affecting groundwater replenishment.
Spread over an area of 3.75 sq km, the Sasthamkotta lake is the major drinking water source for about 7,00,000 people in Kollam city and seven adjacent panchayats.
The report says the unscientific construction of an embankment on the southern side had isolated the lake system, cutting off the flood pulse of monsoon waters from the Kallada river which also acted as a biological corridor for aquatic animals to feed and breed.
The study, which analysed borehole cores retrieved from the floodplain areas of the Kallada river, revealed highly varied climate and sea level conditions that existed during the evolution of the lake, the largest freshwater body in Kerala and a Ramsar site since 2002.
According to the report of the study, which appeared in the latest issue of the Geosciences journal, the sand layers embedded within the alluvial sediments of the late Quarternary age (1.8 million years ago) acted as a major aquifer contributing a substantial proportion of freshwater to the lake system.
The authors, S. Vishnu Mohan, Sheikha E. John, Rajimol T.R., Maya K and D. Padmalal from the NCESS and Prof. Sajan K from the Cusat, point out that rampant removal of sand from aquifers using high-power pumps had affected the water balance of the lake.
Over-extraction of water is pointed out as another factor responsible for the depletion of the Sasthamkotta lake during the summer months.
Sand-mining
The report has called for immediate steps to regulate sand mining from the Kallada river as well as the floodplains of the lake. It also recommends an integrated effort to nourish the water potential of the region through scientific interventions both in the river and lake catchments.
Underground aquifers damaged by sand mining
Seasonal inflow from river affected by embankment
