Streambed-scour was assessed at 1,338 federal-aid bridges in southwestern Indiana during 1991. The assessments were conducted as part of a 7-year study by the U.S. Geological Survey in cooperation with the Indiana Department of Transportation (INDOT) that will evaluate 5,600 bridge sites throughout the State. Measurements and observations of remnant scour made during low-flow discharges were used to record site conditions. These remnant-scour data were used to develop an observed streambed-scour index that provides a screening mechanism for ranking existing streambed scour. The observed- streambed-scour ranking values range from 10 (no observed scour) to 0 (pier[s] with pile[s] exposed). This index is based on the relative integrity of the substructure of each bridge with respect to observed scour. This observed-streambed-scour index was developed by use of qualitative criteria established with cooperative input from Indiana Department of Transportation and is intended as a screening tool to rank existing scour conditions. Numerous other factors that have not been included in this indexing scheme need to be considered when evaluations of overall bridge integrity are made.
