An Application of the Distributed Hydrological Model (BTOPMC) in the Sunkoshi River Basin

Abstract

The BTOPMC refers to “Blockwise use of TOPMODEL with Muskingum-Cunge routing”. This model was developed at University of Yamanashi, Japan. It implements the concepts of TOPMODEL with Muskingum-Cunge method for flow routing. The model performs distributed calculations of flows, but it is conceptually semi-distributed in terms of parameterizations. In Nepal, most of the river basins are data poor or ungauged so it may be the better option to use a runoff simulating tool that uses a global public domain datasets. Therefore, to calibrate and validate the model in the Sunkoshi river basin using local available hydrometeorological data and global public domain dataset was the main objective of the study. The Sunkoshi river basin lies in the central northern part of the Nepal and is one of the river basins with good hydrology with a suitable topography for planning any type of hydropower projects. The total basin area of the Sunkoshi river basin at Pachhuwarghat gauging station is 4920 sq. km. It mainly covers two districts of Nepal (Sindhupalchok and Kavrepalanchok) and about 27 % of the total basin area lies in Tibet, China. The elevations in the basin under study range from 602 m, at gauging station in Pachhuwarghat, to 7786 m at high Himalaya. Owing to large differences in the elevations of the topography the basin is characterized by diversified climatic patterns. The study area receives an annual rainfall of 2300 mm. The study covers eight years period from 1994 to 2001. The period of 1991 to 1997 was used for calibrating the model and the period of 1998 to 2001 was used for validating the same. The local available hydro meteorological data (discharge, rainfall, and temperature) were collected from DHM whereas other various global datasets were collected from different public domains. The model requires feed various kinds of data into its own standard format. To prepare data into the standard format, different tools like Arc view/Arc Info, MS Excel, Google Earth, Win BTOPMC preprocessor tool and other different tools provided by COE-UY were used. The processed data were finally fed into the model and results were analyzed to meet the objectives of the study. The model was calibrated and validated using the options “calculate using land cover and soil data” and “calibrate” for Srmax computation. The Nash Sutcliffe efficiency of 81.41 % and 82.87 % were obtained from using the former option for Srmax computation and the Nash Sutcliffe efficiency of 81.67 % and 82.01 % from the latter option. The annual potential evapotranspiration from the Shuttleworth-Wallace model were estimated as 833 mm in 1994, 856 mm in 1995, 811 mm in 1996, 876 mm in 1997, 815 mm in 1998, 841 mm in 1999, 759 mm in 2000, and 806 mm in 2001. Finally, it was concluded that the BTOPMC is an applicable and reliable model for carrying out research in large river basins such as Sunkoshi River basin.