Simulation of Kathmandu Valley River Basin Hydrologic Process Using Coupled Ground and Surface Water Model

Achieving water security is challenging for Kathmandu Valley, Nepal. Conjunctive use of ground and surface water is inevitable for the sustainable use of water within the valley. The focus of this study is to develop a robust groundwater model that can be used for better understanding surface and ground water interaction. For this purpose, a three-dimensional transient model is constructed using the U.S. Geological Survey (USGS) integrated model GSFLOW. This study tries to provide some insights on groundwater extraction volume especially that of Deep Aquifer system. A pumping sensitive analysis of groundwater system in Kathmandu valley shows that the area near Dharmasthali, Dhapasi, Maharajganj Sankhu and Gokarna has a decline of 0.02 to 0.12 m in head with per unit rise in pumping (m3/s) whereas the area near Balaju, Samakhusi and Shywambu showed more decline of upto 0.12 m to 0.23 m. The proposed extraction rate map prepared through this analysis also indicates that the northern part of the ground water basin has more volume of water available per unit decline in head per year and the value of the extraction rate is decreasing as we move from northern part of groundwater basin to the southern part. Finally, a Village Development Committee (VDC) wise extraction rate map is prepared using the proposed extraction rate map which showed that Sangla, Baluwa and Danchi VDC have higher value of proposed extraction rate where, Danchi VDC is showing highest extraction rate of upto 6,273,967 m3/yr.