Why Worry about Existing Bridges Recently Designated as Scour Critical?

This paper will describe the approach that many state DOTs have taken to develop proactive statewide scour programs to assess, prioritize and protect all types of over-water bridges. FHWA compliance requires that a plan of action be implemented if a bridge is coded/rated scour critical. When this occurs, bridge owners are often required to implement a short term flood monitoring program until protective more permanent scour stabilization alternatives can be designed and installed. Scour awareness has increased over the past 25 years and FHWA design standards for new bridges have been updated and revised; however, predicting future scour at existing bridges remains challenging and requires engineering judgment. Bridges owners do remain skeptical of the need to install effective countermeasures when their 75 year old bridge shows no observed signs of scour and the bridge has withstood multiple flood events. Scour is the number 1 cause of bridge failures in the United States and experience is needed to recognize a truly vulnerable bridge and protect it from damage.