Abstract
Localized scouring downstream of weirs caused by frequent riverbed dredging often results in river flood disasters, such as the destruction of weirs and the washing away of bed protection works. Downstream bed protection works are usually undertaken to prevent such scouring, but there is a great deal of uncertainty about their effectiveness. The authors therefore decided to conduct a study in which hydraulic experiments were performed to investigate how effective five types of bed protection works, including step-type and slope-type works, would be in reducing scouring. In order to re-create the riverbed scouring conditions that occur downstream of weirs, the authors conducted these experiments using a meandering channel under conditions where alternating bars would be created. The experiments yielded the following conclusions: (1) all five types of bed protection works were found to be effective in reducing riverbed scouring to a certain degree; (2) scouring is expected to be reduced by the use of bed protection works that horizontally alter the direction of the water flow passing over the weir and maintain the water flow spread; and (3) the depth and length of bed protection works are important factors in achieving greater effectiveness, and scouring can be most effectively reduced by using step-type bed protection works.
