DNREC Releases Updated Marsh Migration Model

Additional Information from DNREC:

Originating from the DNREC Wetland Monitoring and Assessment Program (WMAP) and the DNREC Coastal Programs, the marsh migration modeling study is built from numerous mapping layers which, when combined, were scored on a rating from 12 (highly suitable) down to 0 (unsuitable) as locations where tidal wetlands might move to in the state. Study results highlight areas identified as highly suitable landing spots for marsh migration.

Ground where the tidal wetlands have migrated from is eventually flooded and becomes open water. Knowing where these wetlands could migrate to is critical for land use managers and property owners and helps DNREC environmental scientists and biologists with their work ensuring that wetlands have a future along Delaware’s coasts.

During 2023, the two DNREC programs set out to update DNREC’s 2017 Marsh Migration Model by conducting a suitability analysis on land in Delaware that may have the potential for future marsh migration under different sea level rise scenarios. The elevation-based GIS (Geographic Information System) model combined many layers of geospatial data, the different SLR scenarios, and an area’s distance to the nearest tidal wetland.

Delaware’s 2-foot, 4-foot and 7-foot sea level rise scenarios were used in the suitability analysis. Under a 4-foot sea level rise scenario, the model estimated that 21,449 acres of land in Delaware were highly suitable for marsh migration, with suitable areas also enumerated for each county. Sussex County led with 9,418 highly suitable acres; Kent County was also a good landing spot with 8,482 highly suitable acres, and New Castle County was found to have 3,549 highly suitable acres, according to the modeling study results.

Other notable results from the analysis found that:

• Non-tidal wetlands and agriculture lands make up 70% of highly suitable areas.
• Most of the highly suitable land for marsh migration is privately owned.
• Areas that received lower suitability scores may still have the potential to convert to tidal wetlands.

DNREC’s data was used to create a technical analysis and a user-friendly outreach flyer for widespread distribution. The technical analysis summarizes not only the study results, but details the methods used in compiling it and underscores changes from the 2017 Marsh Migration Model. The outreach flyer condenses general information on marsh migration, summarizes the Delaware mapping study, and helps the public to better understand anticipated habitat changes and potential management options. The 4-foot sea level rise scenario output layer has been made available on FirstMap Delaware, the State’s online platform that provides access to Delaware’s publicly-available geospatial data.

Based on the results of the mapping study, DNREC analyzed the intersection of suitable areas with ownership and land use. The study also provided case studies in Delaware to show how the model can be used as a screening tool for professionals and landowners for better land management decisions and resiliency planning for a spectrum of stakeholders and groups.

The study’s usefulness extended to

• Facilitating marsh migration within management plans for publicly owned lands.
• Putting a priority on areas for conservation.
• Identifying locations where barriers to migration may exist due to disconnections in hydrology.
• Consideration of non-tidal wetlands as migration pathways, and
• Promoting future stakeholder engagement.

For more information, the DNREC Wetland Monitoring and Assessment Program in the Division of Watershed Stewardship and DNREC Coastal Programs in the Division of Climate, Coastal and Energy offer a variety of reports, research, and education about wetland and coastal topics. The Delaware Marsh Migration Suitability Analysis and accompanying materials are found at de.gov/marshmigration.