Assessing the bridge construction effect on river shifting characteristics through geo-spatial lens: A case study on Dharla River, Bangladesh.

The key objective of the bridge structure on a river is to confirm and assist the continual communication. On the other hand, it also has a harmful effect on the hydrological and morphological behavior of the neighboring zone as of the river width contraction. The present study assessed the Bridge construction effect on river shifting characteristics for Dharla River. For doing so, this study followed two steps. First, Landsat imageries for both pre-bridge structure period (1988, 1993 and 1998) and post-bridge structure period (2003, 2008, 2013 and 2017), has been processed and used to determine the thalweg line. Then, geo-spatial environment has been used to assess the thalweg line shifting characteristics and channel width variations. The results revealed a frequent shifting of thalweg line towards both the east and west direction at the upstream side of this Bridge and also the dominating eastwards shifting at the downstream side of the Bridge. After constructing the Dharla Bridge on Dharla River (i.e. post-bridge structure period) the movement of the channel has been changed at a significant level. Particularly, it has been found that the east side shifting is higher than the west side. Thus, the existing of Dharla Bridge has an abundant effect on the shifting characteristics of thalweg line. The study concluded that the shifting of the thalweg lines of Dharla River undergoes a drastic change of study period and the River can be treated as a very dynamic one. The results of this study might supportive for the sustainable and future development of the rivers and adjacent flood plain in Bangladesh.