Application of remote sensing and GIS to understand the spatio-temporal shifting of Bagmati River of Nepal

Abstract

Geomorphology, hydrological conditions and human activities, alter river morphology and shift channels, causing environmental and socio-economic impacts. River shifting in Nepal is well-documented for large rivers like the Koshi and Karnali, while smaller rivers like the Bagmati have received less attention. This study employs geospatial tools and techniques to understand the morphological changes, quantify the spatio-temporal shifting, and erosion and deposition of the Bagmati River channel in Nepal over a 30-year period (1988–2018). The morphological changes were measured in terms of sinuosity index, river width and water area. The entire river maintained a generally sinuous character throughout the study period. The total average width of the river decreased by more than four times from 1287.17 m to 300.01 m from 1988 to 2018, and the water area also decreased by 6.59 km² over the same period, reflecting a transition of the river into a narrower channel over the decades. Overall, the Bagmati River channel slightly shifted eastward in the upstream and downstream sections while significantly shifting westward in the midstream section with an annual rate of 9.94 m, 4.83 m and 41.5 m respectively. The annual rate of bank erosion was found to be one-fourth of the deposition (0.72 km² per year), with the higher erosion and deposition in the east bank and midstream section of the river. This study highlighted the morphological changes, spatio-temporal channel shifting, and erosion and deposition of the Bagmati River located in the floodplain of Tarai region of Nepal.