Decreasing Downstream Channel Capacity of a Low-Lying Ephemeral River of Bengal Basin, Eastern India
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RESEARCH ARTICLE
Decreasing Downstream Channel Capacity of a Low-Lying Ephemeral River of Bengal Basin, Eastern India Sadhan Malik1 • Subodh Chandra Pal1 Received: 6 March 2020 / Accepted: 3 August 2020 Ó Indian Society of Remote Sensing 2020
Abstract 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. Keywords Dwarkeswar River Channel degradation Sea level change Elongation ratio Topographic sinuosity index
Introduction Downstream variation of channel morphology is one of the significant aspects of flood control, hydrograph construction, floodplain development, reservoir construction and construction of a number of engineering works, which can have an impact on the local people’s economy (Chin et al. 2002). Systematic variations in channel morphology, such as channel width (w), mean flow depth (d), mean flow velocity (v) and discharge (Q), have been termed as ‘hydraulic geometry’ by Leopold and Maddock (1953). The channel morphology and channel flood plains are the results of diverse sedimentological character, climatic condition, flow properties, tectonics and topographic settings and character of flood plain vegetation (Kemp 2010). & Subodh Chandra Pal [email protected] Sadhan Malik [email protected] 1
Department of Geography, The University of Burdwan, Burdwan, West Bengal, India
Investigations on the different aspect of downstream variations in hydraulic parameters have been investigated by several scholars (Knighton 1999; Leopold and Maddock 1953; Leopold et al. 1964; Park 1977; Pitlick and Cress 2002; Schumm 1960). Most of them showed that the bankfull channel capacity, width, depth and discharge increases downstream (Knighton 2014; Schumm 1960) and can also be found in ephemeral rivers, although with different rates (Kale and Gupta 2001; Leopold and Miller 1956a, b; Park 1977; Wolman an
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