Rainfall-runoff modelling of Doddahalla watershed-an application of HEC-HMS and SCN-CN in ungauged agricultural watershed

The scarcity of reliable rainfall-runoff recorded data in Doddahalla watershed is a serious problem for the analysis of the hydrology of watersheds. Sustainable management of the available water in this area is only possible when there was sound information on the rainfall-runoff and other hydrological determinants that influence the water resource. Considering the current problem rainfall-runoff. simulation is carried out using the HEC-HMS hydrological simulation model with integrated use of remote sensing and GIS. Tropical Rainfall Measuring Mission 3 hourly and Indian Meteorological Department daily rainfall datasets are utilised. Cartosat-1 CartoDEM (30 m) was used to delineate the sub-watershed and generate the stream network. Geospatial Hydrologic Modeling Extension (HEC-GeoHMS), along with ArcHydro extension in ArcGIS 9.3 utilised to create the input file for use in HEC-HMS. Indian Remote Sensing Satellite Linear Imaging and Self Scanning sensors (LISS-III, 24 m) and Survey of India (SOI) toposheet are used to prepare the soil and land use map. All the data are georectified and reprojected to Geographic Coordinate System-World Geodetic System 1984 (GCS WGS) Universal Transverse Mercator (UTM) zone 43 North for the easy handling in GIS environment. SCS-CN loss model and SCS unit hydrograph as a transform method was applied to simulate the excess storm water to direct runoff in the watershed. The Muskingum-Cunge model used as channel routing. The model is validated by using field observation data and discharge data from the neighbouring Hoovinahole watershed. The results of simulated and observed stream flow show greater confidence and the reliability of the model. Similar procedure and calibration parameters applied to the ungauged Doddahalla watershed for estimating the rainfallrunoff. The research result gives a general idea regarding the stream flow, peak flow and velocity of the peak flow. The present study concludes that the stimulated result can be useful for the water and land resource planning and management practice in the Doddahalla watershed. The models can be best utilised in ungauged watershed and water scarce region where the monitored data are limited, and runoff estimation is mandatory to sustain the water resources.