DEVELOPMENT OF FLOOD FORECASTING MODELS FOR THE BAGMATI BASIN IN NEPAL

摘要

Flow estimation at a point in a river is vital for a number of hydrologic applications including flood forecasts. This paper presents the results of a basin scale rainfall-runoff and hydraulic m odeling in Bagm ati river basin in Nepal. The hydrologic model HEC-HMS incombination with Geospatial Hydrologic Modeling Extension-HEC-GeoHMS, was used to convert the precipitation excess to overland flow and channe 1 runoff. Model was run with rain gauge data alone, Tropical Rainfall Measuring Mission (TRMM) data alone and both rain gauge and TRMM data. The simulation was done for a period off our months (June-September) covering the whole rainy season of year 2004. The predicted hydrogra ph was calibrated against observed one and the model param eters were manually optim ised for good sim ulation. The predicted peak discharge, using rain gauge data, was close to the observed value and the smaller discharges followed the observed trend. The model framework developed in the study considered the spatial variation in the runoff response of the watershed through the use of Curve Numbers based on soil type and land use and the spatial distribution of the rainfall in the watershed. The peak flow of the derived hydrograph was used as an input in hydraulic model (HEC-RAS) for producing flood maps showing inundation area extent and flood depths, thus directly linking the model to operational flood forecast. A schematic for flood early warning system has been proposed.