Development of Pilot Extreme Flood Vulnerability Assessment Protocols Under Present and Future Climatic Conditions for Roadway Stream Crossing Structures within the Deerfield River Watershed, Massachusetts

Field work

The fragmentation of river and stream habitats by roads is a primary barrier for aquatic species and may inhibit the ability of fish and wildlife to move throughout their habitats and adapt to climatic changes. These barriers also limit the ability of water to flow freely during extreme storms and heavy precipitation events, often resulting in intense flooding and washed out roads. Given the prevalence of road-stream crossings, such as culverts or bridges, across our landscape, transportation agencies and partners must consider how to minimize negative impacts. A thoughtfully-designed and well-placed road-stream crossing upgrade or replacement can both increase the resiliency of roads to extreme weather events and increase habitat connectivity for fish and wildlife.

Multiple factors should be considered when making decisions about replacing or upgrading aging transportation infrastructure. With this in mind, we are working on a cross-sectoral climate adaptation project led by the MA Department of Transportation and the University of Massachusetts-Amherst in the Deerfield River Watershed in Massachusetts.

A primary objective of the project is to create comparable scoring systems that address the vulnerabilities of ecological infrastructure (river and stream networks) and transportation infrastructure (road networks). Our project team is using existing methods to evaluate the habitat fragmentation impacts of road-stream crossings and developing methods to assess vulnerability of road-stream crossings to extreme flooding under present and future climate conditions.

We are developing a ranking system and decision-support matrix that includes aquatic connectivity, risk of failure (hydrologic and hydraulic conditions[1], structural condition, and geomorphic response[2]), aquatic stream continuity and fragmentation[3], and potential for disruption of local emergency services. Our project includes integration of the vulnerability factors into a decision support tool that complements, supports, and augments present MassDOT system planning, project development, and bridge/culvert inspection processes.

Beyond providing a vulnerability assessment specific to the Deerfield River watershed, our aim is to identify the strengths, weaknesses and sensitivities of the various methodologies utilized to analyze each objective. Based on this information, the project team will provide recommendations for a transportation vulnerability assessment framework that could systematically and cost-effectively be applied to the rest of the Commonwealth.

[1] Hydrologic conditions refers to estimates of what flow and stream power will be under future climate scenarios.

[2] Geomorphic response refers to the river’s reaction to outside stressors, which include changes in hydrologic, hydraulic, and sediment load conditions. Examples of river response include changes in horizontal and vertical channel dimensions (e.g., scour, aggradation, meander development, widening) plus slope and substrate size). This assessment will not be linked directly to changes in precipitation, but will be predicted to change along similar trends as precipitation and stream power estimates increase.

[3]   Aquatic stream continuity and fragmentation affect aquatic and wildlife organism passage along the river system, and maintaining and/or increasing connectivity is thus an important factor contributing to the adaptive capacity of these organisms. Because of the coupled nature of the transportation and river systems, the resilience to change of the transportation network, and thus the adaptive capacity of the coupled transportation-river system, is in part dependent on aquatic stream continuity.