ABSTRACT
The 6.2 km long Padma River Bridge currently under construction in Bangladesh, is probably the largest fluvial bridge crossing in the world. The bridge has been designed for a river discharge of 148,000 m3/s and corresponding flood level at El. 7.7 m. Natural scoured depths in excess of 50 m have been observed at the site. Since the Padma River south bank consists of highly erodible loose alluvial deposits, the project includes a 11.3 km long river training work along the south bank to prevent the river from damaging the access road to the bridge and outflanking its south abutment. A curved guide bund (bank) extending 3 km upstream of the south abutment aligns the river flow and protects the abutment by forcing the scour hole to develop up the upstream head of the guide bund, instead of the bridge abutment. Physical model studies have shown that minimum bed levels at the head of the guide bund can reach down to elevation of −60 m.
Erosion in a simplified version of the south bank protection was studied numerically using three depth-averaged flow and sediment transport models: River2D-MOR, Telemac2D-Sisyphe and Delft2D-MOR. The numerical models were able to predict the shape, location and depth of the equilibrium scour holes along the south guide bund, in good agreement with previous observations made in physical models. This paper summarizes and discusses the scour depth predictions by the three numerical models.
