Prediction of scour depth and dune morphology around circular bridge piers in seepage affected alluvial channels

Prediction of scour depth is one of the most significant problems in designing of bridges. Due to complexity of scour phenomenon, available empirical equations do not always offer accurate scour depth prediction. In this work, experiments were conducted on non-uniform sands using two piers of different diameter with and without seepage conditions. It has been found that, the scour depth at upstream of piers is decreased with application of downward seepage. The observed scour depths are compared with scour depth predicted by various prediction methods and it has been observed that the available equations are not suitable for seepage conditions. The present work thus introduces a new empirical equation for prediction of scour depth at piers with inclusion of seepage. The features of migrating dune like bedforms at downstream of piers due to deposition of scoured bed material are also explored. Height of deposition is found to be increased with downward seepage. The empirical equation describing morphology of dunes behind piers is also developed by incorporating downward seepage parameter.