The effect of parallel wall on reduction of bridge abutment scour in compound channels

Scour can be the main factor of bridges failure, collapsing, and as a result excessive repair costs and decreasing the access to the paths. Bridge failures due to scour at bridge abutments reveal importance of scour prediction and countermeasure. Most of the bridges abutments are located in floodplains. This study aims to investigate the effect of parallel wall construction on vertical wall abutment scour in compound channels. Experiments were carried out in different parallel wall lengths under clear water condition. The results show that with increasing the parallel wall length, the scour depth at the upstream corner of the abutment (critical point of scour) is decreased and in some cases at the upstream corner of the abutment the deposition was observed. Parallel wall can keep the maximum scour depth away from the upstream corner of the abutment and transfer it with a lower depth to the parallel wall nose. For constant flow depth and with increasing the parallel wall length, percentage reduction in scour depth at the upstream corner of the abutment increased, with a decreasing rate. Also, for constant flow depth and with different lengths of the parallel walls, same approximate scour depth results were seen at parallel wall noses. With increasing the flow depth, scour depth at the parallel wall nose increased. Using a parallel wall with length of half of the abutment length, depend on flow depth, 51 to 64 percentage reduction in scour depth at the upstream corner of the abutment was observed.