Scour at selected bridge sites in Alabama, 1991-94

Scour data were collected at 15 sites on streams in Alabama during high flow conditions. The recurrence intervals of the streamflows ranged from less than 2 to 10 years. Scour depths measured near bridge piers ranged from 0.3 to 5.8 feet. The Colorado State University (CSU) local scour equation recommended in the Federal Highway Administration Hydraulic Engineering Circular No. 18 was used to estimate scour depths at the study sites. Estimated scour depths based on the CSU equation ranged from 2.5 to 12.7 feet with residuals (measured scour depth minus estimated scour depth) ranging from -8.1 to -1.4 feet. A comparison of the residuals with the estimated scour depths indicated that the CSU equation overestimated the measured scour depths throughout the range of measured data by an average of 434 percent.