Decreasing Downstream Channel Capacity of a Low-Lying Ephemeral River of Bengal Basin, Eastern India

This paper discusses various aspects of channel morphology on an ephemeral Dwarkeswar River from the western part of the Bengal Basin. Geologically, it extends from the Proterozoic Granite Gneiss Complex to recent Holocene alluvium, creating three typical geomorphic regions, e.g. dissected plateau, plateau-fringe and alluvial plain. Sixty cross sections from the source to the mouth of the river were surveyed, and the bankfull channel parameters were measured. Consequently, sediment samples were collected and Manning’s roughness coefficient were determined to estimate velocity, discharge and stream power. The exponents of hydraulic geometry (width, depth and velocity) vary significantly with respect to physiographic divisions of the study area. Width, width–depth ratio and channel capacity enlarge up to the plateau-fringe area. Thereafter, reduction of channel capacity, width and W / D ratio has been observed in the alluvial plain area by 81.3%, 87.3% and 91.3%, respectively, which is associated with lowering of sea level, high topographic sinuosity index, extremely elongated basin, very low slope, wide flood plain area and cohesive bank materials. So, channel capacity reduces in the downstream direction and floods became an unavoidable part of this region.