Abstract

The conceptual and physically based models can be categorized as lumped, semi-distributed and distributed. Lumped model treats the catchment area as one or more homogeneous land segments where the inputs are averaged. Distributed model explicitly represents the spatial variability by dividing the catchment into grids and modeling each grid cell individually. Semi distributed model is a conceptual model that bridge the gap between lumped and distributed models. It utilizes conceptual relationships for hydrological processes that are applied to several relatively homogeneous sub-areas of the catchment area. The main objective of this research paper is to assess the effect of channel geometry of basin at the outlet of basin in semi-distributed rainfall-runoff modeling and to determine performance of the different channel sections that will produce the best results for that basin. From study on the Gandaki river basin, the efficient section for routing depends upon the purposes of the simulating rainfall runoff process. Trapezoidal section is more efficient than other sections for determination of flood forecasting and both trapezoidal and triangular section is efficient for simulating to determine the total annual runoff volume.