Estimating aquifer recharge in fractured hard rock: analysis of the methodological challenges and application to obtain a water balance (Jaisamand Lake Basin, India) [Estimation de la recharge des aquifères de roche de socle fracturé: analyse des enjeux méthodologiques et application pour obtenir un bilan en eau (bassin du lac Jaisamand, Inde)] [Estimativa de recarga em aquífero fraturado: análise dos desafios metodológicos e aplicação para obtenção de um balanço hídrico (Bacia do Lago Jaisamand, Índia)] [Estimación de la recarga de acuíferos en roca dura fracturada: análisis de los desafíos y las aplicaciones metodológicas para obtener un balance de agua (Cuenca del lago Jaisamand, India)]

Groundwater recharge is an important metric for sustainable water management, particularly in semi-arid regions. Hard-rock aquifers underlie two-thirds of India and appropriate techniques for estimating groundwater recharge are needed, but the accuracy of such values is highly uncertain. The chloride mass balance (CMB) method was employed to estimate annual groundwater recharge rates in a monsoon-dependent area of Jaisamand Lake basin in Rajasthan, which contains the Gangeshwar watershed. A monitoring program was established within the watershed during summer 2009, with local participation for the collection of rainfall and groundwater samples. Groundwater recharge was estimated spatially over a 3-year period with pre-monsoon and post-monsoon datasets. Recharge rates estimated using the CMB method were then compared to those estimated using the water-table fluctuation (WTF) method. Specific yield was 0.63 % and assumed to be homogenous across the watershed. The average recharge rate derived from the WTF method (31 mm/year) was higher than that derived from the CMB method (24.3 mm/year). CMB recharge rates were also applied to obtain a water balance for the watershed. CMB recharge rates were used to estimate annual groundwater replenishment and were compared with estimates of groundwater withdrawal using Landsat imagery. Over the 2009–2011 study period, groundwater demand was about seven times greater than the estimated groundwater renewal of 5.6 million cubic meters. This analysis highlights the challenges associated with estimating groundwater recharge in fractured hard-rock aquifers, and how renewable groundwater-resource estimates can be used as a metric to promote sustainable water use. © 2015, Springer-Verlag Berlin Heidelberg.