Insight of Bridge Scour during Extreme Hydrologic Events by Laboratory Model Studies

The occurrence of extreme weather events that lead to flooding are expected to worsen in frequency and intensity. During such extreme events with high water levels, bridges may be subjected to submerged orifice flow and overtopping because they were not designed for such large flows. As a result, bridges over the water course are vulnerable to unexpected excessive scour of the foundations and possible failure. This study presents the results of clear-water local scour and contraction scour experiments using full bridge geometry and river bathymetry and especially their separations from the total scour depth. Three bridge sites were selected for the physical model studies and constructed in a hydraulic laboratory that included upstream and downstream river reaches and bridge structure based on the Froude number similarity between field and laboratory. From observations, the experimental studies elucidated the interaction among the various types of scour, including long-term aggradation or degradation, vertical and/or lateral contraction scour, and local pier and abutment scour. This study proposes a method of separating each scour component from the total scour depth and qualitatively address the effect of vertical contraction to the average contraction scour.