Road-stream crossing an in-stream intervention to alter channel morphology of headwater streams: case study

Abstract

ABSTRACTBasin-scale hydrological response on the geomorphology of lowland headwater streams is often neglected during the in-stream engineering works in rural India. Standard protocols to construct road-stream crossing (RSC) reveals that crossing structures at headwater streams of the Kunur River Basin in eastern India are inadequate to maintain longitudinal continuity in channel hydraulics as well as morphology. The role of crossing type (pipe, box, and small bridge) and catchment land cover are also considered for site-wise variation in channel deformation. The detailed geomorphic survey with 10 cross-sections (5 in the upstream and 5 in the downstream of crossing structure) and 1 longitudinal profile from each of the 10 sample sites were used to run one-dimensional flow modelling in Hydrologic Engineering Center’s River Analysis System, statistical analysis of channel morphometry, manning and rational methods for discharge estimation, and hydroengineering equations. Result shows that in comparison with the extreme upstream (50 m upward from RSC), a significant increase in channel width (30%), depth (17%), and cross-section area (54%) has been observed at the immediate upstream and downstream of RSC. Longitudinal profiles of channel bed, water surface, and energy gradient are also showing the development of knick points, deep scours, and supercritical conditions below the crossing structure. The morphological deformation is more prominent at pipe culvert followed by box and bridges, whereas forested catchment has reduced the effect with less runoff than agricultural. Structural enhancement and regular monitoring might be effective in reducing the problems and constructional cost at RSCs.