| Abstract: | Land use changes are a key factor for altering hydrological response, and understanding
its impacts can help to develop a sustainable and pragmatic strategy in order to preserve a
watershed. The objective of this research is to estimate the impact of land use changes on Bagmati
river discharge and sediment yield at the Khokana gauging station of the Kathmandu valley
outlet. This study analyzes the impact of land use changes from the year 2000 to 2010 using a
semi-distributed hydrological, Soil Water Assessment Tool (SWAT) model. The Load Estimator
(LOADEST) simulates sediment loads on limited available sediment data. Sensitivity analysis is
performed using the ParaSole (Parameter Solution) method within SWAT Calibration and Uncertainty
Procedure (SWAT-CUP), which shows that Linear parameters for calculating the maximum amount of
sediment that can be re-entrained during channel sediment routing is a most sensitive parameter that
affect the hydrological response of the watershed. Monthly discharge and sediment data from 1995 to
2002 are used for calibration and remaining monthly discharge and sediment data from 2003 to 2010
are used for validation. Four statistical parameters including the Coefficient of Determination (R2),
Nash–Sutcliffe Efficiency (NSE), RMSE-observations’ standard deviation ratio (RSR), and Percentage
Bias (PBIAS) are estimated in order to evaluate the model performance. The results show a very
good agreement between monthly measured and simulated discharge data as indicated by R2 = 0.88,
NSE = 0.90, RSR = 0.34, and PBIAS = 0.03. The model shows nearly the same performance also with
sediment data. The land use change data shows about a 6% increase in built-up areas from the years
2000 to 2010, whereas the remaining areas such as Forest, Shrub, Grass, Agriculture, Open Field, and
Rivers/Lakes are decreased. The surface runoff contribution to stream flow and sediment yields are
increased by 27% and 5% respectively. In the contrary, lateral flow contribution to stream flow and
groundwater contribution to stream flow are decreased by 25% and 21%, respectively. |