The catastrophic collapse of the Interstate 90 crossing of Schoharie Creek near Amsterdam, NY on April 5, 1987 was one of the most severe bridge failures in the United States. Two spans of the bridge fell into the flood waters after a pier, which supported the spans was undermined by scour. Before motorists could be warned, five vehicles plunged into the creek and 10 persons were killed. The National Transportation Safety Board concluded that the bridge footings were vulnerable to scour because of inadequate riprap around the base of the piers and a relatively shallow foundation. The I-90 collapse focused national attention on the vulnerability of bridges to failure from scour and resulted in revisions to design, maintenance, and inspection guidelines.

In 1987, the National Bridge Scour Program was initiated between the Federal Highway Administration (FHWA) and the U.S. Geological Survey (USGS) to provide field data for improved understanding of scour processes and prediction methods. The objectives of the study are to collect scour data to provide quality assurance and technical support, and to provide a national scour data base. The USGS is conducting or has recently completed site assessments for bridge scour in cooperation with State Departments of Transportation in about 35 states. In 1988, the USGS, in cooperation with New York State Department of Transportation (NYSDOT), began a bridge-scour study at 77 sites throughout New York. According to USGS project chief, Gerard Butch, hydrologist, "many scour holes did not backfill after a flood because most streambeds are gravel and cobbles. Water depth, velocity, and bed material are significant factors that affect scour in New York, along with the duration and number of high flows. In 1996, the USGS measured scour holes at the I-90 bridge over Schoharie Creek that ranged from 3 feet - 7 feet deep, well above the new foundation, which was constructed with steel piles set into rock. The scour hole along the west pier was about 70 feet long". Recently, the USGS, evaluated four scour-monitoring instruments for FHWA. "These instruments identified scour that resulted from the January 1996 floods sooner than standard inspection methods, and enabled the USGS to alert NYSDOT to one bridge that was undermined and had exposed pilings", said Butch.

During a flood, USGS personnel collect and monitor hydrologic data that emergency managers use in developing warnings and forecasts on which to base evacuation orders.

Click the following links for other pictures associated with bridge scour monitoring devices: