Time evolution of scour and deduction of the required minimum test duration for a clear-water scour test at a bridge pier

In reality, peak flood flows may last for only a few hours or days in the field. For such short duration floods, the peak flow duration may be insufficient for achieving an equilibrium scour depth. In such instances, the actual scour depth may only be a small percentage of the equilibrium scour depth, which could take weeks to fully develop if at all such an equilibrium position is achievable. As part of model studies, many researchers have attempted to describe the behavioural pattern of scour at a cylinder pier with respect to the variation of scour depth with time. As regards this, numerous experimental and numerical studies have also been carried out by researchers in an attempt to quantify the equilibrium depth of scour in various types of soil material. Few researchers has also worked to assess the occurrence of an equilibrium scour condition, if achieved, or of the implications of not achieving such a condition in respect of interpreting the results obtained from a physical hydraulic model study related to pier-scour experiments. In addition, many equilibrium scour depth prediction equations as well as some definitions of equilibrium scour depth can be found in the literature. However, this study gives an approach for determining the minimum test duration required for the estimation of the equilibrium scour depth. Also, evaluated using new data-set is the use of the average values of the constants in the Franzetti et al. (1992) equation, [7].