Subsurface Hydrogeochemical Processes in Lower Bhavani River Basin, Tamil Nadu, India

Abstract

Bhavani River is one of the important tributaries of Cauvery River, and originates in the Silent Valley range of Kerala State, India. The Lower Bhavani River Basin lies between 11 15' N and 11 45' N latitudes and 77 00' E and 77 40' E longitudes with an area of 2,475 km2. Variation of groundwater quality in an area is a function of physical and chemical parameters that are greatly influenced by geological formations, recharge-discharge mechanisms of groundwater and anthropogenic activities. The correlation of groundwater chemistry with hydrologic and geologic environments gives valuable information to understand the effect of these processes and to properly manage aquifer systems. A detailed study has been carried out to understand the subsurface hydrogeochemical processes that are responsible for the quality variation of groundwater. Residence time of groundwater was also considered to be an important parameter to study groundwater evolution. The NETPATH computer code was used to model the major subsurface processes contributing to the evolution of groundwater chemistry. The occurrence of such chemical processes as silicate weathering, carbonate dissolution, ion exchange and dilution due to rain were verified by performing inverse mass balance modeling using the same code. The net geochemical mass balance reactions between initial and final water were identified and quantified based on the flow in selected well pairs. The model output shows that dilution, ion exchange and illite precipitation are the dominant processes that control the chemistry of the groundwater along the flow paths. Calcite and NaCl dissolution are also involved to a certain extent. Reverse ion exchange process is also observed in two models.