Surface and groundwater dynamics of rainwater harvesting in Rajasthan, India: A GIS and tracer approach

As the largest and driest state in India, Rajasthan is faced with a daunting task of meeting many different water demands every year. In light of this water scarcity, rainwater harvesting (RWH) has been widely promoted in Rajasthan as a means to increase surface water supplies, as well as to recharge local groundwater. In the midst of widespread adoption, a knowledge gap exists in the understanding of the hydrologic impacts. In order to close this gap, a rainwater harvesting study was carried out from May-July 2006 in the Wakal River Basin, Rajasthan, India. Within this study, geographic information system (GIS) and tracer tools were utilized to investigate the surface water and groundwater dynamics of rainwater harvesting. Results of this study provide evidence that most of the RWH structures in the study will fill up annually, even under the most conservative scenarios. Furthermore, the hydraulic gradient provides evidence that groundwater flows from the RWH structures toward downstream wells. Finally, the use of delta18O and Cl- as geochemical tracers of water provides evidence of harvested rainwater in these nearby wells.