Maine Department of Transportation – Bridge Scour Management

Recognizing that climate change will cause changes in precipitation and stream flow, the state of Maine has taken several steps to evaluate the vulnerability of its bridges to scour and implement corrective actions to safeguard those most critical. Among the transportation infrastructure adaptation policies recommended in Maine DOT’s report Climate Change and Transportation in Maine were two scour-related goals: inspecting all bridges at least every two years, and conducting underwater inspections for scour and structural integrity every 60 months. The report also identified the state’s 2009 scour evaluation and its ongoing development of bridge-specific scour Plans of Action (POAs) as contributing to the department’s effort to identify areas of the transportation infrastructure system that are particularly vulnerable to climate change and extreme weather.

Scour, the erosion of the soil around and beneath bridge foundations, is exacerbated by flooding and heavy precipitation, both of which are expected to increase in Maine as a result of climate change. Maine DOT’s 2007 report, Keeping Our Bridges Safe, identified scour as the most common cause of bridge failure and recommended completing and implementing a Scour Plan of Action (POA) for each scour-critical bridge in the state. The report also recommended that Maine DOT prioritize and implement scour countermeasures on critical routes.

In 2008 and 2009, Maine DOT implemented a statewide evaluation of more than 350 potentially scour-susceptible bridges, and rated each bridge “non-scour-critical” or “scour-critical.” Those rated scour-critical would require either flood monitoring plans (short-term POAs), protective countermeasures (long-term POAs), or both. Maine DOT conducted a flood monitoring program for scour-critical bridges, under which onsite flood information is considered in bridge closure decision-making. Such information includes water surface elevations relative to bridge height, potential/predicted scour depths, debris clogging assessments, water diversion conditions, and forecast weather. In the event of a proactive bridge closure, Maine DOT implements pre-planned detour routing and notifies the community.

Maine DOT is improving the efficiency of its scour countermeasure design by combining design and construction contracts for bridges in the same geographic area; this effort can protect multiple bridges at once, extending their service life and removing them from the scour-critical list. Protective counter-measures can preserve scour susceptible bridges at a much lower cost than full bridge replacement. The most common of these techniques is the use of angular stone, or riprap, to provide protective armoring for the bridge’s foundation; proper use of riprap requires consideration of appropriate stone size, the need for a filter layer, and appropriate placement and installation technique in order to maximize the flow area at a bridge crossing and minimize scour.

The 2014 Keeping Our Bridges Safe report indicates that many of the bridges identified as scour-critical have since received countermeasures and are no longer classified as scour-critical. MaineDOT has created and implemented Scour Plans of Action for all scour-critical bridges, and prioritization and implementation of countermeasures on critical routes is ongoing.

 

This Adaptation Clearinghouse entry was prepared with support from the Federal Highway Administration. This entry was last updated on October 22, 2015.

 

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  • Maine Department of Transportation
  • State of Maine

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