A review of scour conditions and scour-estimation difficulties for bridge abutments

This paper is a review of the scour conditions, and scour-estimation difficulties, associated with scour at abutments of bridges over rivers and streams. A recent survey of abutment-scour problems in the U.S., Korea, and abroad, shows that several scour conditions can occur, and that existing relationships for scour estimation, besides being inaccurate do not match the scour conditions. Moreover abutment scour is found to be primarily a concern for bridges over smaller rivers and streams than for larger rivers, because inadequate design and monitoring attention has been give to abutment scour at the many small bridges. This paper also discusses the difficulties confronting accurate estimation of abutment-scour depth. The difficulties, which include similitude aspects of laboratory experiments on scour at bridge abutments, complicate the development of reliable scour-estimation relationships. In a practical sense, the difficulties imply that design relationshipsfor scour-depth estimation inevitably have to be of approximate accuracy given the great variability of channel conditions at most abutments.