Hydro-morphological effects of bridge-crossings on large braided/anabranched sand-bed rivers

In large rivers, most bridge crossings locally reduce the transverse floodplain width. This leads to adverse hydro-morphological effects, such as river bed and bank erosion, as well as increased upstream flood levels. In this study, we used a 2D morphodynamic model developed in Delft 3D to investigate the hydro-morphological impact of bridge span. The tool was applied to the Talibwala Bridge across the Chenab River in Pakistan. Our findings indicate that not only the length but also the location of the bridge span across the floodplain and bridge orientation influence the river hydro-morphodynamics. Smaller bridge spans exert more pronounced impacts, particularly during high flood events. We highlight that bridge span enlargement can serve as an effective intervention to reduce the adverse effects of existing bridges. These results emphasize the importance of considering the morphological river response during the design phase of bridges and of using morphodynamic instead of hydrodynamic models for flood level assessments.