Distribution of major ions in ground water, river water and estimation of ground water recharge in Mulki river basin, South-West Coast of India

This study focuses on the seasonal variations in ground water, river water chemistry and estimation of ground water budgeting using chloride mass balance method around Mulki River basin. Chloride ion is used as a tracer due to its conservative nature, thus making it easier for estimation of ground water budgeting as well as to assess the sources in river and ground water of Mulki River basin. The seasonal variability of major ions, Na/Cl ratio in ground water and river water revealed that, the dissolution of Ca-bearing silicate rocks and atmospheric inputs are the major sources vis-à-vis anthropogenic sources. The annual ground water recharge estimation reveals that the mean ground water recharge (272mm/year) is lower than the mean river water discharge (58 m³/s) and annual rainfall (3763 mm). This decrease in the ground water recharge may be due to the impact of evapotranspiration (1466 mm/year), high discharge in to the river due to steep slope and the presence of granitic terrain that possess less porosity and are of impermeable nature. This method is found to be suitable for ground water budgeting in places where there are less number of rain gauge stations on river basins in India. This baseline study would be very helpful for ground water modelling and water resource management. This work could be the first report on the seasonal variability of major ions, their source determination using chloride ion as a tracer in ground water, river water and also water budgeting using chloride mass balance technique in Mulki River basin Southwest coast of India.