Induced shear stress measurement in overtopped floodwalls

The scour generated by water overtopping floodwalls results in tilting and sometimes failure of floodwalls. The water free fall induces shear stress, which is difficult to measure, at the levee surface and if it exceeds the critical shear stress, scouring initiates. It is perceived that once a pool of water is generated at the levee crest due to scour, the induced stresses on soil surface at the pool bottom will decrease. The scour progress is stopped once the induced shear stresses at the pool bottom are less than critical shear stress; however, due to the low values of critical shear stress, the scour most likely continues for a long time. A methodology was developed in this study to measure the induced shear stresses. Based on the tests conducted in this study, the generated pool will decrease the induced shear stress until constant erosion rate is achieved. This shear stress is defined as ‘equilibrium’ shear stress herein.