Estimating groundwater recharge using land use and soil data: A case study in South India

Groundwater recharge is a key factor in water balance studies, especially in semi-arid areas. In India, the Groundwater Evaluation Committee recommends the use of the "water table rise method" to evaluate recharge. However, this method does not account for spatial variation of recharge, which can be very important especially in an agricultural area. We propose a simple methodology that incorporates the one-dimensional agro-hydrological model soil-water-atmosphere-plant (SWAP) in conjunction with data available from government agencies, integrated into a geographical information system, to assess the effect of land use and soil on groundwater budgets at the subwatershed scale. Simulation units (SU), homogeneous with respect to cropping system, irrigation and soil, are defined on the basis of field data. SWAP results indicate that under the conditions of the study area, recharge is more affected by soil type than by land use. However, the groundwater balance is more dependent on the amount of withdrawal than on the recharge rate. The model was tested in Bethamangala subwatershed where groundwater level data are available for a 21-year period. The outputs obtained from the SWAP model are used as boundary conditions for a simple one-dimensional groundwater model. The simulated groundwater heads are consistent with the observed trends, and the estimated recharge rate falls within the same range as the recharge rate estimated with the water table rise method. Results suggest that current agricultural practices, which induce a groundwater recharge of 70 mm/year, could be sustainable. However, scenarios involving an increase in irrigated area reduce simulated recharge