Augmentation of groundwater recharge and water quality improvement by water harvesting structures in the semi-arid Deccan

The effect of water harvesting structures on groundwater recharge and water quality was evaluated in a watershed situated in a semi-arid region in Andhra Pradesh, India. Two percolation tanks and two check dams with a total storage capacity of 4.209 ha m were selected to assess their effect on groundwater recharge and water quality within the influence zone of the water harvesting structures. Daily rainfall, evaporation and storage depth in structures were measured to quantify percolation. Using rainfall run-off relationship with antecedent precipitation index as a factor, complete water budgeting was carried out. Results show that the threshold value of rainfall for ensuring 1 mm potential recharge is 61 mm. Potential recharge is only 3% of annual rainfall received. Water quality analysis revealed that except pH, all other water quality parameters like electrical conductivity, sodium adsorption ratio, residual sodium carbonate, total hardness, nitrate and fluoride content reached desirable limits in close vicinity (<100 m) to the water harvesting structures. Increased availability of groundwater led to subsequent over-exploitation in below-normal rainfall years and the number of bore wells increased by three times.