Characterizing cross-sectional morphology and channel inefficiency of lower Bhagirathi River, India, in post-Farakka bar
- PDF / 6,906,916 Bytes
- 34 Pages / 439.37 x 666.142 pts Page_size
- 44 Downloads / 177 Views
Characterizing cross‑sectional morphology and channel inefficiency of lower Bhagirathi River, India, in post‑Farakka barrage condition Aznarul Islam1 · Sanat Kumar Guchhait2 Received: 21 June 2019 / Accepted: 2 July 2020 © Springer Nature B.V. 2020
Abstract The present research based on 39 cross sections, historical maps, satellite images, and intensive field investigations intends to portray the changes in the cross-sectional morphology and channel efficiency of the lower Bhagirathi River (Katwa to Nabadwip) after the Farakka barrage was constructed over the Ganga River in 1975. The study reveals that majority of the cross sections have undergone significant changes in terms of higher width/depth ratio (1972:71.4 and 1984:85.1), higher channel form index (1972:28.06, 1984:33.44), and higher areal asymmetry (1972:0.244, 1984:0.287). Thus, discriminant analysis based on the principal component analysis Z-score of the derived indices shows a reversal of the quadrant reflecting a definite change in cross-sectional morphology in the post-Farakka barrage condition. Though the Reynolds number and specific stream power increased due to the increase in the lean period (January to May) discharges by the controlled hydrology, channel efficiency has decreased which is reflected through the higher Chezy roughness factor (1972:0.095 and 1984: 6.802) and increasing braiding index (1994:0.103, 2019:0.294). This is due to the emergence of the transport-limited condition triggered by the inadequate discharge compared to the huge sediment load contributed by Bhagirathi bank erosion and the Ajay–Mayurakshi system. Moreover, the role of erosion permitting sand and silt facies triggering higher channel oscillation along the left bank and presence of plug bar deposits coupled with the suspected attraction of subsurface fault are also noted on the relative stability and channel orientation of the middle part of the study reach. Keywords Channel form ratio · Channel asymmetry · Channel efficiency · SL index · Farakka barrage · Ajay–Mayurakshi system
* Aznarul Islam [email protected] 1
Department of Geography, Aliah University, 17 Gorachand Road, Kolkata 700 014, India
2
Department of Geography, The University of Burdwan, Barddhaman 713 104, India
13
Vol.:(0123456789)
Natural Hazards
1 Introduction Cross-sectional morphology signifying adjustment to river hydraulics changes more frequently than the longitudinal profile. Any phenomenal change in discharge or sediment budget induces noticeable changes in cross-sectional behaviour. For example, an increase in discharge leads to change in both channel width and depth with a variable intensity depending on local hydro-geomorphic processes and human interventions (Leopold and Maddock 1953). Similarly, the substrate at the bed and bank material determines the nature of the cross section like narrow and shallow (Schumm 1977). Artificial control of river regime by the construction of dams and barrages profusely alters channel morphology by regulating timing and volume of dis
Data Loading...
