Storm Surge Scour at Coastal Bridges: Documenting the Effects of Hurricanes Bonnie and Floyd in North Carolina

Scour at bridges; over coastal waterways is caused by unsteady flows due to diurnal and semi-diurnal astronomical tides, storm surges (hurricanes, extratropical cyclones, and tsunamis), and combined riverine and tidal flows. Continuous rising: and failing, astronomical tides influence long-term trends of aggradation or degradation and produce some local scour around bridge piers and abutments. However, large amounts of contraction scour and severe local scour may be caused by storm surge that can exceed 23 ft (7 m) on the open coast. Storm surge can greatly increase water surface elevations and currents at coastal bridges, although durations of the increases are comparatively short, usually lasting no longer than several hours. Therefore, reliable estimates of water-level changes and currents under storm conditions are needed to account for roadway overtopping, hydrodynamic loads, and scour when planning and designing coastal bridges.