A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering. School of Civil Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1998

Banganga Irrigation System, Nepal is experiencing water deficit in rainy seasons due to the frequent level rising of river and not taking the water having elevation more than 110.50 m above mean sea level. Actually the project personnel are not aware of the level of river water up to which can be taken profitably. This study is aimed to find out whether some elevated water in the river can be taken profitably or not. In this study Ackers-White and Engelund-Hansen Formulae are used to find sediment concentration in different elevated discharges. Sediment quantity is estimated by multiplying discharge quantity taken into the system and sediment concentration. Hence the total cost for sediment removal is the product of total sediment quantity and unit cost of sediment removal. Crop evapotranspiration, effective rainfall, river discharge, net irrigation required, net irrigation applied, ETa and yield reduction factor are calculated to find the actual yield. When the actual yield for each additional water is obtained, the net benefit is calculated for 60%, 80% and 95% probability of exceedance of rainfall and river discharge. The results show that for 60% probability of exceedance it is not profitable to take any additional water whereas in case of 80% and 95% probability of exceedance the most profitable additional water are about 12,435,120 m 3 and 19,200,000 m 3 respectively. If more water is taken in case of 95% probability of exceedance the net benefits start to decline. Hence, it can be said that except for nearly average year "it is profitable to take some additional water of elevation higher than 110.50 m above mean sea level in the average dry year and severe dry year".