The link between downstream river planform changes and upstream changes or processes in high energy mountain rivers

The river morphologies and the associated landscape experience considerable changes in response to landslides and floods. The young and tectonically active Himalayan region is more prone to such natural hazards. The impacts of climate change and anthropogenic activities have further increased the frequency and intensity of such natural disasters in this already active region. These disasters cause vast losses of life, property, infrastructure and disturb the ecological balance. This study explores the geomorphological changes occurring in the downstream river reaches of the Alaknanda River using the Google Earth Engine (GEE) cloud-based computing tool. We extract the active river channel width using Landsat multispectral images. The initial results show considerable changes in width over the years (1990-2021) and the changes start from the knickpoint continuing towards downstream. The changes in the river’s bank line indicate the bank erosion and relocation of sediments along the river, likely supplied by erosion processes at upstream reaches. Here, we try to identify the critical point where the deposition process first starts to highlight the most vulnerable zone geomorphologically. We further check whether there has been an increase in sediment deposition in recent years due to likely increased erosion related to deforestation on higher reaches of the Alakananda catchment. We try to achieve this goal by correlating the river landform changes and land cover changes along riparian areas of the river temporally. Our overall objective is to develop a framework to correlate changes or processes in upstream reaches to depositions or erosions along the downstream sections of a high-energy river.

 

Keywords: Landscape evolution, natural hazards, erosion, deposition, River-line