APPLICATION OF HEC-HMS MODEL FOR RAINWATER HARVESTING

Abstract

In order to augment the depleting groundwater resources, it is essential that the surplus monsoon runoff that flows into the sea is conserved and recharged into the aquifers. Rainwater harvesting using check dams is one of the best suited conservation methods for small watersheds. Check dam enables the harvested water to store and, subsequently, recharge the aquifer. Hence, there is a need to quantify the harvested rainwater at the outlets of the small watershed and to estimate the peak flood to facilitate the design of check dams. In this study an attempt has been made to investigate the hydrological aspects of rainwater harvesting by check dams and subsequent recharging of the aquifer. The kinematic wave method available in the HEC-HMS hydrologic modelling package, developed by U.S. Army Crops of Engineers (USACE), is used for assessing the surface yield. For assessing the rate of recharge into of the impounded water into the aquifer, analysis is done using the Green and Ampt infiltration equation and assuming the channel profile behind the check dam follows Kozney profile. This analysis is applied to study the recharge rate of the aquifer by the surface water impoundment created by the check dam in the small watersheds. The time of concentration of the harvested rainwater in the watershed is estimated based on the step-wise regression relationship developed using the watershed area, channel length, roughness coefficient, channel slope, overland slope, and effective rainfall intensity. Six different regression relationships linking the time of concentration with the watershed and rainfall characteristics were studied based on 80 sets of runoff generation events made using the HEC-HMS model on the basis of kinematic wave runoff generation analysis. Using. 42 sets of independent rainfall-runoff events generated on hypothetical "V" shaped watersheds, the best regression relationship was identified and it is expressed as: iv