Abstract
There have been many bridges constructed over alluvial rivers in monsoon regions. However, the characteristics of local scour around bridge piers in such rivers have not been well analyzed. The past researches are all based on the assumption that flow is steady, sediment transport is under a certain equilibrium condition, and that the flood continues only during limited time. On the other hand, actual hydraulic conditions in the rivers are different; flow / sediment transport conditions are unsteady and high water levels continue for several months during wet season, which repeats every year. In this paper, authors clarified the change of the river bed topography around the bridge over Meghna River in Bangladesh, a typical of the rivers, using actual survey data between 1984 and 2007 for 23 years. The result shows that the local scouring progressed for 16 years after its construction in 1991. The values of scoured depth are larger than those estimated with the methods proposed by past papers. The facts founds research are practically important and will contribute to planning and maintenance of bridges over identical rivers.
