Rapid-Estimation Method for Assessing Scour at Highway Bridges Based on Limited Site Data

Potential-scour assessments and estimates of scour depth using different techniques at selected bridge sites in Missouri

“…The Level 1 assessments identified 1,327 bridges as scoursusceptible. As a way to reach the second goal of the study and to meet time-frame requirements established by the FHWA, a rapid estimation method (hereinafter referred to as "Level 1+") developed by the USGS in Montana (Holnbeck and Parrett, 1997) was used to evaluate bridges deemed scour-susceptible by the Level 1 assessment to identify bridges that might be scour critical. In 2002, 104 bridges were identified that had not been assessed for scour-susceptibility; these bridges received a Level 1+ assessment without a Level 1 assessment.…”

“…Upon completion of the Level 1 work, detailed hydraulic assessments (Level 2's) had been completed at 35 bridges that the Level 1 assessment indicated were most susceptible to scour, as well as 2 overflow bridges that the Level 1 assessment indicated were not susceptible to scour, but were in proximity to 1 of the 35 bridges. A rapid estimation method (Level 1+) developed by Holnbeck and Parrett (1997) was utilized to further evaluate the remaining 1,292 bridges deemed scour-susceptible based on the Level 1 assessment, and approximate scour depths were calculated. Sites that had scour depths greater than defined values were then assessed with a detailed hydraulic assessment (Level 2) using the guidelines set forth in Hydraulic Engineering Davis, 1995, 2001).…”

“…Scour is the removal of the channel bed and bank material by flowing water, and is the leading cause of bridge failures in the United States (Richardson and Davis, 2001). Total scour is divided into three primary components: general scour, which refers to long-term geomorphicological processes that cause degradation (lowering), aggradation (filling), or lateral shifting of the natural channel; contraction scour, which refers to the erosion of material that occurs when the cross-sectional flow area of the stream is reduced or contracted; and local scour, which refers to the localized erosion of material caused by flow vortex action that forms near bridge piers and abutments others, 1991, 1993;Davis, 1995, 2001;Holnbeck and Parrett, 1997). Although scour processes continually are at work, the processes are accelerated during high-flow conditions, and the potential for scour-related problems at a bridge tend to increase during such events.…”

Calculation of scour depth at the Parks Highway Bridge on the Tanana River at Nenana, Alaska, using one- and two-dimensional hydraulic models

“…Bridge scour is erosion of the streambed resulting from local flow accelerations caused by bridge piers, abutments, and, during extreme flows, the bridge structure and deck. According to Holnbeck and Parrett (1997), "the most common cause of bridge failure has historically been the scour or erosion of foundation material away from piers and abutments during large floods. "…”

“…To address scour concerns, the Federal Highway Administration (FHWA) established a national bridge-scour program in 1991. The purposes of this program are to evaluate existing bridges for scour potential and to conduct research in scour-related areas (Holnbeck and Parrett, 1997). In 1994, the U.S. Geological Survey (USGS), in cooperation with the Alaska Department of Transportation and Public Facilities (ADOT&PF) and the FHWA, began a cooperative study to analyze scour potential at bridges in Alaska.…”