The Effect of Road Crossing on River Morphology and Riverine Aquatic Life: A Case Study in Kunur River Basin, West Bengal

Abstract

Road crossings play important role in land transport system, but improper designed stream crossing may alter the form and function of stream geomorphology, floodplain ecosystem, habitat and movement of aquatic organisms. The objective of this paper is to explain the local level impact of a road crossing on channel morphology and aquatic lives of the Kunur River, based on geomorphic survey and stream classification. This study shows a comparison between upstream and downstream reaches of Kunur River where the State Highway-14 crossed the river over a bridge. There are changing fluvio-geomorphic indicators like mean and maximum bankfull channel depth, cross-section area, flow velocity, entrenchment ratio, channel bed gradient, water level and depth, braided index (BI), pool-riffle sequence, area and shape of bars, and others taken into consideration. Results are temporally increases of BI and expansions of bars. In the downstream, river channel is deeply incised by massive bed degradation and highly entrenched with high flow velocity and steep channel bed gradient, low entrenchment ratio (<2.2), low width-depth ratio (11.26) and increasing inter pool-riffle distance. Present study reveals that bank failure is a common phenomenon here with deep scours and making unsuitable environment for fish habitat. Alternatively, it has appeared to be greater deposition of fine sediment in the upstream reaches with high braiding index, area of bars. High entrenchment ratio (>2.2) and width-depth ratio (>35) also indicates well developed floodplain ecosystem here.

Key Words: Anthropogenic feature; channel morphology; bed degradation; bank failure; fine sediment