Evaluation of Selected Instruments for Monitoring Scour at Bridges in New Yorkby Gerard K. Butch,
Document Type: Proceeding Paper
Part of: North American Water and Environment Congress & Destructive Water
Reliable methods to monitor scour at bridges are needed to ensure public safety and minimize the cost to repair or replace vulnerable bridges. The U.S. Geological Survey, in cooperation with the New York State Department of Transportation, is evaluating four instruments for the Federal Highway Administration.s Demonstration Project 97, Scour Monitoring and Instrumentation. The instruments include (1) a magnetic sliding collar developed in the National Cooperative Highway Research Program (NCHRP), (2) an NCHRP sonar system, (3) a commercial sonar and satellite telemetry (SST) system, and (4) a commercial multichannel sonar and telephone telemetry (MSTT) system. The instruments were installed between August 1994 and February 1995 and were not damaged by ice or debris during the first year of operation. The reliability of the equipment requires further evaluation because the 1995 peak discharges were less than 50 percent of the mean-annual peak discharges at the study sites. Minor errors in the sliding-collar measurements resulted from accumulation of excess sensor cable at bends in the pipe. The errors between median sonar depths and field-measured depths ranged from 0.2 to 0.4 feet. Sonar data were adversely affected whenever a transducer was exposed to air, ice, or debris, or located less than the minimum distance fmm the streambed (1–2 feet). The MSTT system measured 0.4 feet of scour that developed during a 12-hour period beginning about 6 hours before the 1995 peak discharge.
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