Identifying priority watersheds to mitigate flood and drought impacts by novel conjunctive water use management

Abstract

New approaches that are cost effective and sustainable are needed globally to better manage flood and drought impacts. Recharging monsoon floodwaters in upstream areas to boost small-scale groundwater irrigation and to protect flood-affected urbanized areas downstream is proposed as one such approach and has been termed ‘Underground Taming of Floods for Irrigation’ (UTFI). Prospective locations for implementing UTFI are identified using a GIS-based method specifically developed here. There are three main steps to the method: (1) pre-feasibility analysis, (2) spatial data processing, and (3) index determination to rank prospects for establishing UTFI interventions. The methodology was applied to watersheds within the Ganges River Basin in South Asia. Data on the drainage density, flood frequency, flood mortality and distribution, extreme rainfall events, landuse, population density, geology, slope, soil, groundwater level, aquifer transmissivity and economic loss due to floods were used. The ranking and overlay index method adopted in arriving at the final suitability map showed that within the 43 % of the Ganges that is routinely subjected to floods, 68 % of this area had either ‘very high’ or ‘high’ suitability. Most important parameters identified from the sensitivity analysis were flood mortality and distribution, flood frequency and extent, drainage density and groundwater level. Suitability index values were generated for watersheds of different sizes which showed that smaller watersheds (100 km2 or less) provide better results but that up to 1000 km2 was considered acceptable. These results can be useful for prioritizing areas to apply integrated flood and drought management measures. The approach developed here may be directly transferable to other river basins.