Title:

Climate Resilient Stream Crossings: Are We There Yet?

This project, undertaken by seniors in UNH's Civil and Environmental Engineering Department, aimed to assess the climate resilience of Tier 3 culvert stream crossings across New Hampshire. Using the Federal Highway Administration’s HY-8 hydraulic modeling software, stormwater culverts were analyzed to determine their hydraulic performance during a 100-year 24-hour storm event in the year 2100. Input data for the models were gathered using permit applications for culvert replacement projects from 2019-2024, Stream Stats watershed delineation tools, and the New Hampshire Geodata Portal. A sample size of twenty sites were randomly selected to reduce sampling bias. Eight of ten NHDOT-owned culverts, and three of ten municipally-owned culverts, overtopped the roadway and were non-resilient under future flows. Non-resilient culverts under inlet control were modeled with increased spans to determine the feasibility of resilient design. A cost analysis was conducted for these alternative designs showing an average increase of 18% in total project cost between seven sites. This study determined that stream crossings can be assessed for resiliency to future climate conditions, keeping in mind the alternative design limitations of outlet-controlled structures.

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