An energy conservation model for the temporal evolution of local scour depth at bridge piers during floods

Local scour at piers is one of the primary causes of bridge failures. The prediction method for the temporal evolution of local scour depth at bridge piers during floods was investigated based on the law of conservation of energy. The energy transfer process between water flow and sediment during the local scour process at bridge piers was theoretically analyzed based on the current understanding of the mechanism of local scour. The results show that there is a dynamic equilibrium relation between the energy loss of water flow and the energy gain of eroded sediment during the local scour process. This relation is applied to establish a mathematical model for predicting the temporal evolution of scour depth. This model has only one parameter, which is the energy transfer efficiency between the water flow and the eroded sediment. The energy transfer coefficient is mainly determined by the flow intensity under clear-water scour conditions, and an empirical formula for calculating it is obtained. The proposed model was evaluated using measured data of local scour depth under both well-controlled flows and natural floods. The results show that the model is able to provide satisfactory predictions and its performance can be further improved by including more sophisticated methods for determining the critical velocity for incipient scour. Meanwhile, the performance of the model is insensitive to the possible uncertainties introduced when determining the energy transfer coefficient. The research results indicate that it is feasible to establish a theoretical prediction model for accurately forecasting the local scour depth at bridge piers.