UPDATE: BRIDGE SCOUR

Nearly 500 bridges have failed because of hydraulic conditions—primarily scour—since 1950, but the collapse of the Route 90 bridge over Schoharie Creek in April 1987 focused national attention on the issue. Procedures developed by the Federal Highway Administration call for a team approach, which includes qualified hydraulic, structural and geotechnical engineers, each with several years of experience. Procedures used to counter scour include installation of riprap, guide banks, steel sheetpiles and underpinning. However, FHWA has left the ways and means of coping with scour to each of the state departments of transportation. New York State DOT, for one, with its aggressive approach to scour, summoned an independent task force. New York's strategy may be adopted or modified by other states, such as Colorado, and the techniques for scour evaluation in general will evolve as more states establish programs to comply with FHWA requirements.