A modified index for assessment of potential scour at bridges over waterways

The modified potential-scour index described in this report is based on a potential-scour index used by the U.S. Geological Survey Maryland District (Maryland index), and a prototype index developed by the U.S. Geological Survey Tennessee District (Tennessee index). The modifications were made to (1) improve the technical content of theMaryland index, and (2) provide a more extensive set of index variables for assessment of potential scour at bridges. The report demonstrates and describes problems that were encountered when using the Maryland index in a study of county- maintained bridges in Maryland from 1993 to 1995.The modifications made to specific index variables and ranking values in the Maryland index are presented and discussed. A comparison of potential-scour ratings from the modified potential- scour index, as applied to two bridges, is presented.This comparison indicates that the modified potential-scour index produces potential-scour ratings that most consistently reflect scour conditions observed at these bridges.