Executive Summary : | Lakshadweep is an archipelago of atolls and submerged atolls situated 200-440 km off the southwest coast of India. The Lakshadweep islands lie on a north-south oriented submarine ridge known as the Lakshadweep-Chagos Ridge. These islands comprise mainly atoll types of coral islands, consisting of coral reefs, coralline limestone and carbonate/coral sands formed by wind and wave action. The Lakshadweep islands have a small surface area of some 32 km², whereas the calm lagoon area is about 4200 km², and is rich in marine wealth. In total, there are 27 islands, 6 submerged sand banks, and 3 coral reefs, representing a combination of emerged and submerged atolls. Ten islands in the Lakshadweep archipelago are inhabited (Agatti, Amini, Andrott, Bitra, Chetlat, Kadmat, Kalpeni, Kavaratti, Kiltan and Minicoy). The most significant threat to inhabitants of Lakshadweep islands is the limited quantity of freshwater for drinking, cooking and other purposes; a critical challenge for the residents of atoll islands globally. Most of the freshwater requirements of the Lakshadweep islands’ population have been met from groundwater sources, which are obtained mainly from open wells and ponds, as there are no streams or rivers on the islands. Fresh groundwater is separated from the underlying seawater by a transition zone, wherein the salinity of groundwater gradually increases downwards. In most of the islands, the thickness of the transition zone is equal to or more than that of the thin freshwater lens. As a consequence, freshwater extraction from the aquifer may induce upward movement of saline water such that wells are contaminated by brackish and saltwater. In many cases, over-extraction of groundwater has led to the salinization of the primary water supply wells for island communities. Groundwater contamination from human activities in populated areas compounds the issues of freshwater availability on Lakshadweep islands. While previous studies have considered the water quality and hydrogeology of Lakshadweep islands, a systematic evaluation of the current and future conditions of groundwater has not been undertaken, in particular considering the seasonal volume changes in the freshwater lens and the quantity of groundwater discharged to the sea. The proposed study has the following objectives: (i) To understand the hydrogeology and 3-D aquifer geometry of the island aquifers of Lakshadweep archipelago, including freshwater extent (lens geometry), and the nature (quality and rates) of discharge to adjoining marine water bodies (ii) To characterize the freshwater-saltwater distribution in four island aquifer systems using geophysical techniques (Electrical Resistivity Tomography). The seasonal changes in the freshwater lens geometry and groundwater quality in the islands will be studied applying resistivity imaging techniques. |