The Challenge
Massachusetts is planning for a rise in relative mean sea level of up to 2.5 feet by 2050 and 4.3 feet by 2070 (compared to 2008 mean sea level) if global emissions are not significantly reduced (ResilientMass Plan 2023). As the sea level has continued to increase, there has been a corresponding increase in minor (or disruptive) coastal flooding associated with higher-than-normal monthly tides. Flooding impacts associated with these tides are becoming more noticeable and often result in the flooding of roads and parking lots with bimonthly spring tides. Greater flood levels (spatial and temporal) associated with more episodic, major, or event-based natural disturbances, such as hurricanes, nor’easters, and seismic waves, will impact built infrastructure directly, often with devastating effects. In addition to contributing to high-tide flooding, sea level rise will also exacerbate storm-related flooding due to the higher tidal elevation. Other impacts associated with more severe coastal flooding include beach erosion; loss or submergence of wetlands and other coastal ecosystems; saltwater intrusion into drinking water and wastewater infrastructure; high water tables; loss of coastal recreation areas, beaches, protective sand dunes, parks, and open space; and loss of coastal structures (sea walls, piers, bulkheads, and bridges) and buildings (ResilientMass Plan 2023).
The challenge for regulatory agencies is to determine how best to protect, manage, and regulate coastal areas that are under threat from mean sea level rise. The Federal Emergency Management Agency (FEMA) maps are the current standard for regulatory protection of floodplains; however, FEMA only considers current flood elevations and do not consider rising sea levels in their current maps. To best protect the Commonwealth, an analysis of the Massachusetts Coast Flood Risk Model (MC-FRM) planning tool (current version as of April 2021) was performed to determine the feasibility of adopting the current planning tool as regulatory for coastal areas.
Project Scope
To better understand the implications of converting a planning tool like the MC-FRM into a regulatory tool, a comparison with FEMA Flood Insurance Rate Maps (FIRMs) was conducted for various metrics. Some metrics were assessed to better understand the function of the tool as regulatory, while other metrics focused on the differences to landowners, cities, and towns when and if the MC-FRM could be adopted. These metrics included overall comparability, the jurisdictional extent, and effects on cost and implementation.
Metrics
Success for the project was determined by the ability for MassDEP, and EEA and CEI, to adequately assess the feasibility of the MC-FRM for regulatory adoption. Expertise for this assessment depended on a technical skillset of map development and cost calculations, but also a large emphasis on the implications of regulatory implementation.
Results
The MC-FRM and FEMA models have significant differences including regulatory suitability, modeling methodology, flood zone definitions, the coastal inland boundary, and overall usability. Four examples, located in different locations along the Massachusetts coastline, were developed to show comparison specifics. Overall results concluded that while the MC-FRM is a valuable planning tool for cities, towns, property owners, and planners, it is not currently appropriate for use as a regulatory tool and was not intended to replace FEMA FIRMs.
Best Practices and Lessons Learned
Best practices here included ensuring input from both technical and regulatory experts with knowledge of the MC-FRM model, FEMA flood maps and MassDEP regulations.
Project Alignment with ResilientMass Plan Priority Actions
This project aligns with Action Topic 4 “Improve coastal wetland mapping, resilience planning, and restoration efforts” of the 2023 ResilientMass Plan urgent priority impact: Coastal Wetland Degradation, particularly to action 4f: Develop updated wetlands restoration guidance and regulations to improve climate resilience. This project contributes to this framework by examining the data used to predict the flood levels and rates on Land Subject to Coastal Storm Flowage. With better prediction models, we can prepare the Commonwealth by regulating buildings and infrastructure to better meet a changing climate.
Further Action
The MC-FRM is a valuable tool that can be used by countless entities for planning purposes to understand the potential area that would be inundated in scenario years with sea level rise; however, it has limitations and was not developed to be used as a regulatory tool. The MC-FRM development team plans to improve the model in future years but the commitment for those changes and improvements to align with a regulatory tool is unclear. Ultimately, optimizing the tool for planning purposes may conflict with optimizing the tool for regulatory purposes in the short term with funding and resource limitations. Regardless, the MC-FRM team has developed an invaluable resource in better understanding sea level rise and predicting the coastal flood inundation extents that may occur in future coastal storms.
For regulatory protection of future conditions, MassDEP will continue to be engaged in the development and/or revision of various tools and explore various other regulatory strategies to best protect the coastal floodplain.