CONTINUOUS HYDROLOGICAL MODELING USING HEC-HMS CONCEPTUAL MODEL

Abstract

For efléctive planning and sustainable management of natural resources like land and water, for a catchment area, proper assessment of resources is required. The assessment of water resources can be effectively achieved with the help of appropriate well calibrated hydrologic model. The Hydrologic Engineering Center Hydrologic Modeling System, l-IEC-lIMS has gain a lot of popularity in the recent past decades because of its wide range of capabilities to simulate rainfall -runoff modeling. The present study has been undertaken to evaluate surface runoff generation and to test - the performance of the HEC-HMS model in Vamsadhara River basin in India. The Vamsadhara river basin is situated between the well-known Mahanadi and Godavari river basins of south India. The total catchrnent area of Vamsadhara river basin, upstream to the last gaging station (Kashinagar) is 9721km2. In this study the 1-lEC-Geol-IMS 10.1 software was integrated with ArcG1S 10.1 and has been used to prepare basic basin model, meteorologic model and control specification. The developed basin model and meteorologic model have been used by the HEC-HMS model to simulate runoff at the outlet of the basin. SRTM DEM with a resolution of 90m has been used for this study. Land use/Land cover map of the area on a scale of 1:50,000 have been obtained from National Remote Sensing Centre (NRSC), ISRO. The soil map of the study area has been obtained from the National l3ureau of Soil Science & Land Use Planning (NBSS&LUP) which is classified into different categories on the basis on USDA taxonomy. Rainfall data has been acquired as gridded rainfall value from the Indian Meteorological E)epartment (IMI)) and discharge data collected from Central Water Commission (CWC) and through website of India-WRIS has been used. The entire watershed has been divided into 15 subbasins with 7 reaches interlinking between the sub basins and outlet point at the gauge site Kashinagar to facilitate model calibration. Soil Moisture accounting (SMA) method recently added in the HEC-LIMS software enables the software for continuous simulation including both dry and wet periods involving series of event rainfall. SMA algorithm adopted in this study is the backbone of the study which simulates runoff from the year 1984 to 1989 as calibration of the model and from the year 1990 to 1993 for verilication of the model. III All the required data sets has been prepared using the sofiwares ArcGlS, Matlab, SPAW, VBA and in the IIEC-GeoHMS itself Sensitivity analysis has been performed on the 13 parameters of the SMA algorithm adopted in this study. The sensitivity of model parameters has been assessed based on percentage changed in the simulated volume by varying the model parameters from -50% to +50% in step of 10% keeping other 12 parameters constant. It reveals that the soil storage is the most sensitive parameter followed by soil percolation, maximum infiltration, impervious area and tension storage. Other remaining parameters have been found to be less sensitive with GW2 percolation rate to be the least sensitive. The HEC-1-IMS model has been calibrated using data for 6-year period (1984-1989), and predicted stream flows have been validated using data for 4-year period (1990-1993) on daily basis. Statistical and visual evaluation has been carried out to determine the perfbrmancc of the llEC-HMS model in the Vamsadhara River basin. For the calibration period, the performance of the model ranges from good to excellent model with coefficient of determination, R2 0.71, Nash-Sutclilfe Efficiency, EFF=0.701, percentage error in volume, PEV2.64%, percentage error in peak, PE11 0.21%, root mean square error, RMSE49.4 cumecs and index of agreement. d0.94. Similarly, for validation period, the model performance ranges from good excellent model with R2 0.78, EFF=0.762, PEV12.33%, PEP = -15.2%, RMSE = 74.4 cumecs and d= 0.93. Overall, the model performance has been satisfactory and finally is concluded that lIECHMS model is applicable to the Vamsadhara River basin for hydrologic modeling.