United States Department of Transportation
i
Two Northeastern DOTs Consider Green Infrastructure Techniques for Coastal Highway Resilience: A Joint Study with Divergent Outcomes
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2018-08-01
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[PDF-12.82 MB]
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Abstract:The Maine and New Hampshire Departments of Transportation studied the potential for green infrastructure techniques to protect Route 209 in Phippsburg, ME and Route 1B in Portsmouth, NH from coastal flooding. Maine results show it is possible to extend the time before a conventional gray infrastructure solution (sheet pile wall or riprap) becomes necessary to protect Route 209, ranging from an expected 19 years in the no-action scenario to 83 years in the most aggressive gray infrastructure scenario. On ecological grounds, results suggest the most favorable alternative would be seaweed management and staked snow fencing to hold sand in place, plus a coir log or root wad crib structure at the toe of the front dune of the beach adjacent to Route 209, plus plantings above and below the current erosional scarp and sand behind the coir log wall or root wad crib structure. In New Hampshire, results show that intermediate-low levels of sea level rise may cause the existing causeway to be inundated only once in 2060 and twice in 2065. However, if sea level rise follows an intermediate-high trajectory, the causeway may be inundated 188 times in 2060 and 338 times in 2065. The team evaluated ecological benefits of elevating Route 1B (such as enhancing biodiversity, carbon sequestration, and transitional habitat through the addition of fringing salt marsh), along with alternatives of restoring habitat in the vicinity.
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