Bridge Abutment Scour in Compound Channels

Experiments are reported that quantify the effect of channel geometry on local scour at abutments for bridges crossing compound river channels. The data apply to the case of the abutment extending into the main channel. The channel geometry effects are represented by a multiplying factor. This factor, K _G, has the effect of reducing the scour depth from that in the “corresponding” rectangular channel, which is defined as the channel that has the same overall width as the compound channel and the same depth as the main channel of the compound section. Up to threefold reductions in scour depth, from that in the corresponding rectangular channel, were observed. It is shown that K _G, as determined by a simple expression involving the cross-section geometry and roughness of the main and flood channels, is consistent with the experimental data. An expression for the equivalent length of abutment in a compound channel is proposed also.