Rivers are the dynamic water resources available on the earth surface. River morphology focuses on water courses' shape and pathways, and how they change over time. In this study, we have focused on the Narayani river using remote sensing techniques to understand the dynamics on river channel shifts . Two different time intervals of 15 years were taken to understand how rivers are changing. We used Landsat 5, Landsat 7, and Landsat8 for rivers images of 1990, 2005, and 2020 respectively. Supervised classification of satellite images was done using ArcGIS Pro 3.0.3, and images are classified into water and non-water bodies. For quantification of river shifting, we adopted two approaches: linear displacement and area change method. In the linear displacement method, we bisected the river with an imaginary straight line along the river length as per latest river flowpath of 2020. Then, we selected the sample points at the fixed distance to measure the width of the river and avoid biases. Finally, we measured river width within those prespecified sample points across the river in each location for all water courses. Thus, river widths are measured in a straight line across the river, averaged them and quantified the change in water course in the span of each 15 years. Secondly, in the area change method, we used image differencing techniques from later to former to see changes in the water course.

Interestingly, the water course of Narayani river increased from 1990 to 2005 but it decreased sharply in 2020. The shifting of rivers was intense in forest areas compared to other land uses. The river width ranges from 80 meters to 302 meters in 2020. Regarding the area, the water course decreased by 2.3 acres and increased by 3.8 acres in 1990-2005. Similarly, the water course decreased by 4.14 acres and increased by 2.25 acres in 2020. Monsoon rain leading to annual flooding is the primary cause for this change in river course. Climate change can be related as a secondary cause for these floods and river shifting because of melting glaciers and increasing water discharge. Apart from this, upland land use change can cause change in water course of Narayani river. This study can be a baseline for researchers to correlate the shifting in river course and its factors; while planners and policy makers can come up with a strategic plan to halt down this process of river change and maintain this natural repository of freshwater intact in the long-run.