Abstract
This study is conducted to evaluate the ongoing geoenvironmental impacts of Brahmaputra-Jamuna (BJ) River around the Jamuna Bridge (JB) site which was modified prior to the construction of Jamuna Bridge in 1996. Remote sensing and GIS techniques are adopted to evaluate the temporal and spatial geohazards. This study shows that the intensity of channel shifting has been increased due to regulation of river width at Sira-jganj–Bhuiyapur section from 11 km to 4.8 km. Planform analysis shows that the major channel has been stressed to migrate (315 m/year) eastwards. The phenomena of channel changes are predicted to be the con-sequences of interaction of water flow, sedimentation and channel corridor. The erosion and deposition have complicated variations over time and space due to the abrupt changes of flow and sedimentation around the regulated section. Due to width reduction, the bridge site in the braided system acts as sluice gate which can not accommodate the entire flow to release downstream properly. The helical flow developed with the inter-action of guide bund creates local scours and helps to shift the river bank eastward.
Highlights
Fluvial channels usually maintain specific physical characteristics, flow regimes and capacity for sediment transportation controlled by the hydrodynamics environment of existing river basins
Fluvial hazards involve both flooding and river bank erosion, only the river bank erosion aspects can be considered as geomorphic hazards [2]
For identification of the river planform changes due to structural development, a comparative analysis of channel changes (Figure 3) around Jamuna Bridge (JB) site has been conducted by GIS techniques over a period of 9 years (1992–2001)
Summary
Fluvial channels usually maintain specific physical characteristics, flow regimes and capacity for sediment transportation controlled by the hydrodynamics environment of existing river basins Any alterations in these systems perhaps change the response of some of those phenomena. The hydraulic structures developed across the flow path create a strong perturbation of fluvial dynamics, changing the natural cycle of the river and interfering in the transportation and deposition processes, together with a reduction of biodiversity by destroying the natural habitat of many species [1] and turn into hazard. Fluvial hazards involve both flooding and river bank erosion, only the river bank erosion aspects can be considered as geomorphic hazards [2]. The river flow was partly restricted at different points in upstream by construction of hydraulic
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