ABOUT THE PROJECT

Coastal environments can significantly buffer people and infrastructure from coastal storms and help mitigate the effects of sea level rise. This study quantified the wave attenuation and flood reduction benefits of salt marshes, and other natural and nature-based features (NNBF) along the shores of Maryland's Chesapeake and Atlantic Coastal bays. 

Hydrodynamic and habitat data collected at target field sites and updated Sea Level Affecting Marsh Model (SLAMM) results were integrated into coupled local and regional hydrodynamic and wave models (ADCIRC + SWAN, XBeach) to demonstrate the wave attenuation benefits of coastal habitats across the Maryland coastline now and into the future. 

Model results were used to:

• Calculate how future land-cover change projections would impact ecosystem services in the region
• Provide relatable, local examples to advance coastal preservation efforts by agencies throughout the state
• Inform the state's management actions to maintain or enhance the ecosystem services of marshes
• Support local outreach and identification of adaptation solutions to enhance coastal ecosystem and community resilience
• Update Maryland's Wetland Adaptation Areas, used by DNR to prioritize areas for conservation
• Inform the blue carbon inventory component of Maryland's greenhouse gas reduction plan
• Improve existing conservation prioritization tools. 

A Management Transition Advisory Group (MTAG) of federal, state and local partners was consulted to ensure study results support the project's management and adaptation planning goals. Collectively, this body of work aimed to incentivize, prioritize, and streamline efforts to conserve coastal landscapes, and thus the people that rely on them, both now and into the future.

Six sea level rise scenarios from Maryland's 2018 report (Sea Level Rise Projections for Maryland) were selected for this study and were used to model future marsh migration. These scenarios incorporate multiple emissions pathways and projection probabilities for application to different audiences. 

Three storms were selected to ensure a broad spectrum of storm intensities for hydrodynamic and wave modeling. Hurricane Isabel, Hurricane Irene and a December 2020 Winter Blizzard were chosen to provide diverse representations of storm characteristics from high to low intensity, respectively.

Focus Areas: Shady Side Peninsula (Anne Arundel County) and Crisfield (Somerset County) were selected as western shore and eastern shore sites for management scenario-modeling to quantify the benefits of various green/gray management strategies.

Sites were selected and fieldwork was completed at Franklin Point State Park, Assateague State Park, Blackwater National Wildlife Refuge and the Chesapeake Bay Environmental Center living shoreline. Local topography, bathymetry, waves, water levels and currents were successfully monitored along nature-based features including marshes with native vegetation, marshes with invasive Phragmites, SAV and one living shoreline.

Project team members introduced the study to local and national audiences at two conferences in fall 2020: 1) Maryland Association of Floodplain and Stormwater Managers Conference; and 2) The National Coastal and Estuarine Virtual Summit. Both talks provided an overview of the project methods and expected outcomes. Project results were presented at the 2022 Restore America's Estuaries conference and the 2023 Patuxent River Conference.

Three peer reviewed papers were published in scientific journals: 

• Cassalho, F. et al. ArcWaT: a model-based cell-by-cell GIS toolbox for estimating wave transformation during storm surge events. Geocarto International 37, 10532–10555 (2022). The ArcWaT GIS toolbox from this study is available on the George Mason University Dataverse.
• Coleman, D. J., Cassalho, F., Miesse, T. W. & Ferreira, C. M. The Role of Invasive Phragmites australis in Wave Attenuation in the Eastern United States. Estuaries and Coasts 46, 404–416 (2023).
• Miesse, T. et al. Numerical modeling of wave attenuation: implications of representing vegetation found in coastal saltmarshes in the Chesapeake Bay. Environ Monit Assess 195, 982 (2023).

Available outreach materials include a project video, storymap, and infographics developed to illustrate the habitat and wave attenuation changes predicted under future sea level rise.

Marsh Modeling: Contractor Warren Pinnacle Consulting, Inc., completed runs of the Sea Level Affecting Marshes Model (SLAMM). Results include a final data layer of current landscape conditions, as well as decadal outputs under six sea level rise scenarios. Results were integrated into Maryland's Wetland Adaptation Areas to help target marsh migration corridors for conservation. 

SAV Modeling: Contractor Warren Pinnacle Consulting, Inc., completed development of the SAV model for Tangier Sound and the Choptank River. Predictions for future SAV presence/absence were modeled under approximately 0.4 meters of sea level rise by 2040 - 2050, 1 meter of sea level rise by 2070 and 2 meters of sea level rise by 2100.

Statewide Hydrodynamic Modeling: George Mason University validated regional coupled models (ADCIRC+SWAN+SLAMM) to investigate wave attenuation benefits of marshes under current and future sea level rise scenarios. results will inform updates to Maryland's Marsh Protection Index to target restoration activities for protective marsh complexes that are vulnerable to sea level rise.

Scenario Modeling: Two modeling studies were collaboratively designed in partnership with local managers, aimed at comparing various adaptation strategies, such as sediment placement and marsh restoration. The model simulations were conducted under different storm and sea level rise scenarios and provided insights to inform decision-making and future studies at each focus area.

Ecosystem Services: Change in ecosystem services associated with land-use change over time was estimated for two of the SLR scenarios. Ecosystem service values were derived from prior DNR work. Under the high SLR scenario ecosystem services were projected to decline by over $500 million of annual benefits associated with carbon sequestration, groundwater supply, wildlife habitat, nutrient processing, flood prevention, and air quality improvement. However, under a lower SLR scenario the decrease was much less, declining by ~$75 million per year. Changes in blue carbon stock under 2 sea level rise scenarios were evaluated as well, and results are available here: Story Map.

Map layers derived from the EESLR project SLAMM model run will be displayed on the Maryland Coastal Atlas Web Map and available for download through Maryland iMap. These include wetland adaptation areas, SLAMM landuse results, and drowned lands at 2050, 2070 and 2100 under the Upper End of the Likely Range, Growing Emissions SLR scenario.

Michelle Canick, mcanick@tnc.org, The Nature Conservancy
Celso Ferreira, cferrei3@gmu.edu, George Mason University
Nicole Carlozo, nicole.carlozo@maryland.gov, Maryland Department of Natural Resources

PROJECT TEAM