Local Scour at Bridge Abutments

Laboratory data for local scour depth at bridge abutments are presented. These include sufficient data to demonstrate the effects on scour depth of abutment length, flow depth, and abutment shape and alignment. In addition, some data for the effects of sediment characteristics, flow intensity, and approach channel geometry are given. The data are rationalized in terms of the ratio of abutment length to flow depth, L/y. Two limiting cases are identified. For large and small values of L/y, the abutments are termed long and short, respectively, and it is shown that the maximum scour depths measured in the laboratory for these cases are 2L and 10 y. Most actual cases of abutment scour lie between the limiting cases, and it is demonstrated that, in such situations, scour depth is proportional to the square root of the product L/y. These relationships are formulated in a simple design method, which is used on some illustrative examples. Limitations to the design method are discussed.