Semi-Analytical Model for Estimation of Unsteady Seepage from a Large Water Body Influenced by Variable Flows

The paper presents semi-analytical mathematical model to estimate unsteady groundwater recharge resulting from variable depth of water in a large water body, influenced by time variant inflows and outflows. The model has been derived by integrating Hantush’s (1967) analytical expression for water table rise due to recharge from a rectangular spreading basin into the water balance equation of the water body. The model has been applied to a test study site in Raipur (India) for assessing viability of Managed Aquifer Recharge (MAR) from a lake located on an area dominated by the massive limestone formation. The components of the water balance equation have been carried out by the comprehensive analysis of the hydrological and hydrogeological aspects of the lake. The hydrological components include analysis of rainfall-runoff, evaporation rate, lake water quality and the hydrogeological components include aquifer characterization, parameters estimate, ambient groundwater level and quality. The time variant depth of water resulting from the interaction of water balance components, computed using the model, has been compared with the measured data and found a satisfactory match, as revealed from RMSE analysis. Compared to the inflows and lake storages, the recharge rates from the lake found very less, which ranged between 3.75 and 4.82 mm/day for depth of water ranged between 2.5 and 3.36 m. The lake water quality indicated contamination by bacteriological parameters (viz. Fecal coliform and Total coliform), turbidity and COD, exceeding the permissible limit of drinking water standards (IS-10500:2012). The aquifer formations below the lakebed and around possess thick limestone formation - a limiting factor for MAR-ASTR proposition, and hence no engineered hydrogeological intervention has been found viable to enhance the recharge rate.