Impact of Land Use Change on Flow and Sediment Yields in the Khokana Outlet of the Bagmati River, Kathmandu, Nepal

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 (R 2 ), 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 R 2 = 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.

Integrated Assessment of Climate Change and Land Use Change Impacts on Hydrology in the Kathmandu Valley Watershed, Central Nepal

“…To better analyze and reduce the uncertainty of the river runoff, a two-year warm-up period was considered. All the calibration of the model parameters was done manually and the base value of the parameters were taken from the previous studies [5,6,15,16,34]. The model performance was evaluated based on widely used statistical parameters such as Nash-Sutcliffe simulation efficiency (NSE), percentage bias (PBIAS), coefficient of determination (R 2 ), and the ratio of root mean square error (RMSE) to standard deviation ratio (RSR).…”

“…The LULC change is becoming a common problem for developing countries that have economies basically dependent on agriculture [6]. Conversion of the LULC type due to urbanization has affected sustainable management of water resources [7].…”

“…The Bagmati river basin's climate varies from alpine in the northern part to sub-tropical in the river bank of the southern part. Basically, river basin precipitation is divided into three seasons, namely pre-monsoon (January-May), monsoon (June-September), and post-monsoon (October-December) for the analysis [6]. An average 10 km horizontal north-south distance creates the 1500 m level difference, so it has a diversified climatic character, topography and runoff pattern within the basin.…”

“…The urban growth rate of the peripheral area of the valley is radically higher than the core urban area, due to lack of open space and unplanned land management [25]. Several studies have covered the population and rapid urban growth scenario of KV (e.g., [6,15,[26][27][28]). Due to rapid population growth and expansion of the urbanized area, a remarkable change in landscape can be observed in KV.…”

The Influence of Rainfall and Land Use/Land Cover Changes on River Discharge Variability in the Mountainous Catchment of the Bagmati River

“…River discharge from the upper catchment during 1992-2017 has decreased by −2.05% per year even though the rate of rainfall decrease is only −0.83%. Despite an increase in urban area, which generally results in higher surface runoff [97,98], the MK test on 1992-2017 estimated that surface runoff for the upper catchment showed a significant decrease of −1.51%. Multiple regression analysis suggested that, compared to the influence of LULC changes, a decrease in rainfall is more influential on river discharge from the upper catchment.…”