Quantifying the impacts of rainwater harvesting in a case study catchment: The Arvari River, Rajasthan, India

Abstract

Rainwater harvesting (RWH) is the collection and storage of runoff for the primary purpose of groundwater recharge in arid and semi-arid regions of India. In India, investment in RWH for groundwater recharge is increasing. However, despite this very little is known on the catchment hydrological impacts of RWH. Although RWH is a small-scale operation, when implemented across a catchment, the impact on groundwater and river flow could be significant. However, there is currently no study that has comprehensively quantified this impact. This paper therefore proposes a method to explore the effects of RWH in a case study catchment of the 500 km2 ungauged Arvari River Basin in Rajasthan, India, where 366 RWH structures have been built since 1985. Difficulties associated with working in semi-arid regions, such as this catchment, include the high spatial and temporal variability of climate, particularly rainfall, and landscape conditions and data scarcity. Detailed field studies of local scale effects of RWH and recharge under a number of structures were studied during the monsoon of2007 in the catchment. Discharge over anicuts on the river was also monitored and subsequent water level rise in wells. These results will be extended to the catchment scale using a conceptual catchment water balance model that captures the main hydrological processes. Water moves through the catchment in a series of linked storages for each land use, where the upper and lower catchments are separate domains. The groundwater system consists of an unconfined alluvial aquifer over a confined hard rock aquifer. This will allow different scenarios of land use and levels of RWH to be explored to quantify the hydrological impact on the catchment.