Rip Van Winkle Bridge Scour Susceptibility Study

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. Ten people perished. Scour, it was concluded, was the cause of the collapse. Scour is defined as “the erosion or removal of streambed or bank material from bridge foundations due to flowing water”. It is the most common cause of highway bridge failures in the United States. Consequently, the FHWA has mandated that every bridge over water should be assessed as to its vulnerability to scour to determine what prudent measures are needed for that bridge.  The New York State Bridge Authority, tasked with safely and efficiently managing, maintaining and operating six major Hudson River crossings - handling over 58 million vehicles annually - acted upon the FHWA directive. They selected Modjeski and Masters (M&M) to investigate the possibility of scour at their Rip Van Winkle Bridge.

 

M&M has inspected the Rip Van Winkle Bridge for decades. We are intimately familiar with its design and condition of its major structural components. Our scour vulnerability study commenced with the collection of existing field and design data. We then calculated the maximum scour depth using FHWA guidelines. This data helped us determine the stability of the bridge for incremental scour depths between the as-built ground elevation and the maximum-calculated scour depth and gave us the information we needed: the critical scour depth. The results of the study, along with our recommendations, were integrated into a comprehensive report that was delivered to the NYSBA.