Major Factors Affecting the Performance of Bridges During Floods

About the report:

The models used to predict the depth of scour that might occur in a river when a bridge is constructed across it were based on laboratory data. Within the decade of the 1980s, the Federal Highway Administration encouraged the states to collect field data on flooding and its effect on bridges. These data were used to verify the models for those conditions and geographic areas for which the data were applicable. High water during floods is the test of such models. Thus, after the severe flood in November 1985, as much information as possible was collected and compiled about the flood waters, the geology of the site, the configuration of the river and its flood plain, the bridge, and the damage done by the flood at four sites. Some of the data were used to calculate hydraulic parameters, and depths of scour; and the sediments collected were processed to determine their engineering properties. At least a year after the calculations were made, the Federal Highway Administration issued a technical advisory (1) on scour at bridges which contained recommendations that would have changed the results had they been available when those calculations were made. It was recognized that the information collected in Virginia was limited in scope relative to the tremendous variability in characteristics and conditions that exist for rivers throughout the United States. Thus, in order to cooperate in a regional to national effort, this information was transmitted to the Hydraulics Section of the Federal Highway Administration where it was used to verify and modify the predictive models.

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