Executive Summary : | Barrage and bridge constructions significantly impact the morphology and health of large rivers in the Indian subcontinent. These structures create obstacles to the natural flow of water, causing channels to adjust in their physical forms. The effects of these structures on upstream and downstream fluvial environments have been observed in the Indian subcontinent, particularly in mountain terrain. The Darjeeling Himalayan Foothill Zone (DHFZ) has shown large-scale resilience to human-induced activities, with rivers becoming more vulnerable due to significant sediment flux, aggradation-degradation patterns, and dynamic micro fluvial forms. This study aims to investigate the impact of these structures on the hydro-morphological variations of piedmont rivers, affecting their health. Data will be collected from upstream and downstream sections of bridges, using IMD rainfall grid data to interpret the aggradation and degradation behavior over the last 100 years. A multi-scale hydro-morphodynamic model through ArcGIS will be applied to analyze the process of sediment transport, aggradation, and degradation behavior of the channel. HEC-RAS will be used to explain changes in channel morphology and morphometry with the analysis of changing flow patterns. The river bed in this zone has become highly aggraded, reaching a threshold for poor river health and natural flow regime. This results in reduced carrying capacity, floods, and seasonal lifting of deposited boulders and gravels, which have long-term impacts on the river's health. The study will benefit watershed restoration projects, river basin management authorities, Departments of Agriculture, Forestry, and local government bodies in the DHFZ. |