Research needs in geomorphology pertaining to bridge scour

The failure of bridges across rivers is a well known problem facing the transportation engineer. It is typically associated with bed or bank scour, and may not be directly due to inadequate structural design. Research to date on bridge scour has tended to focus on processes in the immediate vicinity of bridge piers or abutments. These processes are, however, influenced in a fundamental way by larger geomorphic processes, which reflect both natural and human-induced change. For example, meandering rivers tend to shift, inexorably leading to a deterioration in angle of approach. Lowered base level on a stream due to, e.g., river training works can lead to upstream-migrating degradation on tributaries. The degradation itself can endanger bridge piers; the channel widening commonly associated with it can endanger abutments and approaches. This paper summarizes that part of a study conducted for the National Cooperative Highway Research Board (NCHRP 24-8) that pertains to research needs in geomorphology as they affect bridge scour problems.