Submitted by: Nawa Raj Pradran
Supervisor:
Dr. Raghu Nath Jha
Abstract
Recently there is a growing consensus in need for integrated water resource management approaches. Integrated water Resource Management can be effectively done within a spatial unit called watershed with the help of an instrument known as modeling. The use of computer has led to increased emphasis on catchment modeling. Evaluation of rainfall-runoff models has become one of the most significant themes in hydrology.
Nepal, with an area of 147,181 sq. km. has more than 6000 rivers stretching from the Great Himalayas with an elevation of more than 8800 m to the southern plain called “Tarai” with an elevation of 100m within a mere 200 km. width. The country has been regarded as one of the richest nations of the world in water resources. While water resources has a vital role to play in shaping the fate of the national economy, it’s successful utilization remains equally challenging from various standpoints. The first challenge stems from the non-availability of hydrological ‘data itself Even the available data has not been used in an optimal way. There are large ungauged catchments awaiting development and management that would benefit from the use of hydro-environmental simulation models to assist with basin planning. The second obstacle is the rugged terrain.
There are several lumped type models such as SCS curve numbers (Soil Conservation Service 1972), IAEC (Feldman, 1981), NAM (Nielsen and Hansen, 1982), Xinanjiang (Zhao et al, 1980), Nash (Nash and Sutcliffe, 1970), SSARR (Rockwood, 1982), etc. Their inability to explicitly handle land-use changes and water use systems modification makes them unsuitable, without extensive modification, for the present requirements. More suitable types of model include distributed models such as SI-IE (Refsgaard and Storm, 1995), HSDI-IM (Herath et al., 1997), but they are data demanding and not yet practical for large ungauged basins. Thus to overcome all the complexities and difficulties stated in above paragraphs, BTOPMC – a physically based distributed hydrological model based on the block wise use of TOPMODEL with Muskingum-Cung flow routing method- was selected to evaluate the applicability in Nepalese catchment. To suit the Nepalese catchment further modification in the model was suggested that lead to the development of BTOPMC version 11. The quality of simulation is classically judged by comparing the simulated flow with observed flow. Model performance was judged by a range of quantitative and Qualitative measures of fit applied to both the calibration and validation periods. The daily stream flow estimation in Sun Kosi river basin was promising. BTOPMC can be successfully used as a tool for integrated water resources investigation in large watershed, mountain physiographic region, of Nepal.
On the other hand Tank Model was used for small and large catchments to analyze the concept of homogeneity. Despite it’s simple logic to understand and operate, it could effectively respond the hydrological and geomorphological phenomenon – that is far from simple- in various scales of catchments.
Tank Model was used in small sub catchments of Jhikhu Khola watershed. The result proved that storage and land use effect played a dominant role in rainfall runoff process of small catchments. From the results of Jhikhu sub catchments, it was found that parameters estimated for one sub catchment did not match the next sub catchment response. But from the results of Sun Kosi catchments-large scale- the estimated parameters for one large-scale sub catchment also proved to give good response for the next large scale sub catchment. It was also concluded that if the basin is large, the effects of random hydrological phenomenon will cancel each other out and the change will be minimal. However, in a small basin these effects of random hydrological and geomorphological phenomenon may cause instability. All these analysis of homogeneity was based on Tank Model response. Thus Tank Model is not a mere black box but has physical meaning.