SIMULATION OF RAINFALL RUNOFF PROCESS USING HEC-HMS MODEL FOR KANKAI BASIN, NEPAL

Abstract

Hydrological simulation work with computerized models is becoming an essential tool for understanding human influences on river flow and designing sustainable water management approaches. The HEC-HMS model developed by US Army Corps of Engineer is a reliable model which could be used for different types of hydrological simulation works in different regions of the world. This model has been used to simulate the rainfall-runoff process in Kankai Basin, Nepal. In the model Clark unit hydrograph method of rainfall-runoff transformation, deficit constant loss method, constant monthly base flow method, Muskingum method of flow routing, constant monthly evapotranspiration etc. have been selected. The daily rainfall-runoff data of the year 2005-2007 has been used for calibration purpose. The model has been calibrated by adjusting the different parameters (infiltration rate, time of concentration, Muskingum constants etc.) that directly affects the runoff such as and observing the output of the model (resulting hydrograph) till it best matches with the observed hydrograph at the outlet. The evaluation has been done in terms of various efficiencies such as Nash-Sutcliffe efficiency, percent error in peak estimate and percent error in volume estimate, coefficient of determination. During the calibration period the model performance was found satisfactory and the efficiencies were within the acceptable limits. The model is then validated for the period 2008-2010 with the observed daily rainfall and discharge data. During this period, the performances of the model in terms of various efficiencies were also found satisfactory. The study is limited to rainfall-runoff simulation works of kankai basin, Nepal using HEC-HMS Model. There is variation in quantity as well as timing of runoff prediction as seen in output. The performance of rainfall runoff model largely depends upon how the various factors affecting the runoff are considered in the modeling and also on the availability of hydro-meteorological as well as other data. Thus the further works should incorporate the event based simulation work with shorter time step data, use of remote sensing and satellite data and the modeling of the basin in grid level so that rainfall-runoff process can be represented more accurately in quantity with reference to time. And such models can be used for water resources planning, development and management within the basin as well as in other basin lying in the same region.