Zafer Defne Kate V. Ackerman Brian D. Andrews Neil K. Ganju 20260526 1.0 Vector Digital Data Set (Polygon) data release DOI:10.5066/P18BWN2U Reston, Virginia U.S. Geological Survey Suggested citation: Defne, Z., Ackerman, K.V., Andrews, B.D., and Ganju, N.K., 2025, Chesapeake Bay marsh migration potential under sea-level rise (ver. 2.0, May 2026): U.S. Geological Survey data release, https://doi.org/10.5066/P18BWN2U. https://doi.org/10.5066/P18BWN2U https://www.sciencebase.gov/catalog/item/69cfc08db66b01c06b645a97 Zafer Defne Kate V. Ackerman Brian D. Andrews Neil K. Ganju 2025 2.0 vector digital data data release DOI:10.5066/P18BWN2U Reston, VA U.S. Geological Survey Suggested citation: Defne, Z., Ackerman, K.V., Andrews, B.D., and Ganju, N.K., 2025, Chesapeake Bay marsh migration potential under sea-level rise (ver. 2.0, May 2026): U.S. Geological Survey data release, https://doi.org/10.5066/P18BWN2U. https://doi.org/10.5066/P18BWN2U https://www.sciencebase.gov/catalog/item/671a7d8ed34efed5620f910c Marsh migration potential in the Chesapeake Bay (CB) salt marshes is calculated in terms of available migration area for each marsh unit defined by Ackerman and others (2022). The space available for landward migration is based on the NOAA marsh migration predictions under 4 feet of local sea-level rise (SLR). The migration space is further divided by National Hydrography Dataset (NHD) Plus catchments before assigning related catchment polygons to each marsh unit. The migration rates are then calculated using present day estimates at the prescribed rate of SLR, which correspond to the 1.0 meter increase in Global Mean Sea Level (GMSL) scenarios by 2100 from Sweet and others (2022). Through scientific efforts, the U.S. Geological Survey has been expanding national assessment of coastal change hazards and forecast products to coastal wetlands, including the Chesapeake Bay salt marshes, with the intent of providing Federal, State, and local managers with tools to estimate the vulnerability and ecosystem service potential of these wetlands. For this purpose, the response and resilience of coastal wetlands to physical factors need to be assessed in terms of the ensuing change to their vulnerability and ecosystem services. Marsh migration is one of the natural responses to SLR. References: Ackerman, K.V., Defne, Z., and Ganju, N.K., 2022, Geospatial characterization of salt marshes in Chesapeake Bay: U.S. Geological Survey data release, https://doi.org/10.5066/P997EJYB. Sweet, W.V., Hamlington, B.D., Kopp, R.E., Weaver, C.P., Barnard, P.L., Bekaert, D., Brooks, W., Craghan, M., Dusek, G., Frederikse, T., Garner, G., Genz, A.S., Krasting, J.P., Larour, E., Marcy, D., Marra, J.J., Obeysekera, J., Osler, M., Pendleton, M., Roman, D., Schmied, L., Veatch, W., White, K.D., and Zuzak, C., 2022, Global and regional sea level rise scenarios for the United States—Updated mean projections and extreme water level probabilities along U.S. coastlines: National Oceanic and Atmospheric Administration, NOAA Technical Report NOS 01, 111 pp., https://oceanservice.noaa.gov/hazards/sealevelrise/noaa-nos-techrpt01-global-regional-SLR-scenarios-US.pdf This shapefile presents the migration space for marsh units in Chesapeake Bay. 2025 publication date Complete None -77.3747 -75.5934 39.5898 36.3744 ISO 19115 Topic Category oceans inlandWaters environment elevation USGS Thesaurus geospatial datasets wetland ecosystems wetland functions coastal ecosystems coastal processes sea-level change sediment transport estuarine processes vegetation None salt marsh marsh health lifespan estuary Long-Term Ecological Research LTER CommonGeographicAreas Atlantic United States Maryland Virginia Chesapeake No access constraints. Please see Distribution Information for details. These data are marked with a Creative Commons CC0 1.0 Universal License. These data are in the public domain and do not have any use constraints. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. The migration potential for each marsh unit is defined for scientific research purposes and should not be used as a sole source of reference for any regulations and policy making. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the source of this information. U.S. Geological Survey Zafer Defne Oceanographer mailing and physical address

384 Woods Hole Road

Woods Hole MA 02543 508-548-8700 x2254 508-457-2310 zdefne@usgs.gov https://www.sciencebase.gov/catalog/file/get/69cfc08db66b01c06b645a97?name=marsh_mig_poly_CB_4ft.png Marsh migration polygons under 4-feet of SLR in Chesapeake Bay overlaying Esri basemap. PNG Environment as of Metadata Creation: Microsoft Windows 10 Version 0.1 (Build 19042); Esri ArcGIS Pro 3.4.3 Kate V. Ackerman Zafer Defne Neil K. Ganju 2022 1.0 vector digital data data release DOI:10.5066/P997EJYB Reston, VA U.S. Geological Survey https://doi.org/10.5066/p997ejyb Sweet, W.V. Hamlington, B.D. Kopp, R.E. Weaver, C.P. Barnard, P.L. Bekaert, D. Brooks, W. Craghan, M. Dusek, G. Frederikse, T. Garner, G. Genz, A.S. Krasting, J.P. Larour, E. Marcy, D. Marra, J.J. Obeysekera, J. Osler, M. Pendleton, M. Roman, D. Schmied, L. Veatch, W. White, K.D. Zuzak, C. 2022 NOAA Technical Report NOS 01 Silver Spring, MD National Oceanic and Atmospheric Administration https://oceanservice.noaa.gov/hazards/sealevelrise/Sea_Level_Rise_Datasets_2022.zip https://oceanservice.noaa.gov/hazards/sealevelrise/noaa-nos-techrpt01-global-regional-SLR-scenarios-US.pdf Marsh units, water and land boundaries inherit their accuracy from accuracy of the source data, Chesapeake Bay marsh units. Landward migration boundaries inherit accuracy from the source data; USGS National Hydrography Dataset (NHD) Plus Catchment and NOAA Office for Coastal Management Marsh Migration raster datasets. These boundaries are used in calculation of area available for migration. The results are specific to the marsh polygons definition within the boundaries of the Chesapeake Bay salt marsh complex. A detailed on-the-ground analysis of a single site may result in a different interpretation of the wetland and marsh unit boundaries. Migration potential is zero for a marsh unit that is not connected to any migration area. Because multiple layers are overlaid during the analysis, the migration polygons occasionally contain very small polygons that remain attached to larger ones. To preserve connectivity, no minimum-area threshold was applied to remove these features. In rare cases, this resulted in the presence of sliver polygons. Horizontal accuracy is inherited from the source datasets; the marsh units, and the boundaries of marsh migration inherit from the NOAA migration raster datasets. Dataset has no vertical values. Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Office for Coastal Management (OCM) 201907 raster digital data Charleston, SC NOAA's Ocean Service, Office for Coastal Management (OCM) Download date was 01/23/24. https://coast.noaa.gov/slr https://coast.noaa.gov/digitalcoast/data/slr-wetland.html Digital 2016 ground condition md_marshmigration_2016.zip Marsh migration inland boundary under sea-level rise Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Office for Coastal Management (OCM) 201907 raster digital data Charleston, SC NOAA's Ocean Service, Office for Coastal Management (OCM) Download date was 01/23/2024. https://coast.noaa.gov/slr https://coast.noaa.gov/digitalcoast/data/slr-wetland.html Digital 2016 ground condition va_marshmigration_2016.zip Marsh migration inland boundary under sea-level rise Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Office for Coastal Management (OCM) 201907 raster digital data Charleston, SC NOAA's Ocean Service, Office for Coastal Management (OCM) Download date was 01/27/2026. https://coast.noaa.gov/slr https://coast.noaa.gov/digitalcoast/data/slr-wetland.html Digital 2016 ground condition nc_marshmigration_2016.zip Marsh migration inland boundary under sea-level rise Sweet, W.V. Hamlington, B.D. Kopp, R.E. Weaver, C.P. Barnard, P.L. Bekaert, D. Brooks, W. Craghan, M. Dusek, G. Frederikse, T. Garner, G. Genz, A.S. Krasting, J.P. Larour, E. Marcy, D. Marra, J.J. Obeysekera, J. Osler, M. Pendleton, M. Roman, D. Schmied, L. Veatch, W. White, K.D. Zuzak, C. 2022 NOAA Technical Report NOS 01 Silver Spring, MD National Oceanic and Atmospheric Administration https://oceanservice.noaa.gov/hazards/sealevelrise/Sea_Level_Rise_Datasets_2022.zip https://oceanservice.noaa.gov/hazards/sealevelrise/noaa-nos-techrpt01-global-regional-SLR-scenarios-US.pdf Digital 2022 ground condition SLR data Sea-level rise projections for 2100 for selected scenarios Kate Ackerman Zafer Defne Neil Kamal Ganju 2022 vector digital data data release DOI:10.5066/P997EJYB Reston, VA U.S. Geological Survey https://doi.org/10.5066/p997ejyb https://www.sciencebase.gov/catalog/item/630f9ba4d34e36012efa0924 Digital 2022 publication date mu_UVVR_CB.shp Marsh unit outlines U.S. Geological Survey 20220324 vector digital data Reston, Virginia U.S. Geological Survey Download date was 01/27/2026. https://www.usgs.gov/core-science-systems/ngp/national-hydrography Digital 20220324 publication date NHDPlusCatchment NHD Plus Catchment polygons U.S. Fish and Wildlife Service 20191001 vector digital dataset (polygon) Madison, WI U.S. Fish and Wildlife Service Downloaded wetlands data for Virginia, Maryland and North Carolina in shapefile format from the NWI download page. Projection was NAD 1983 Albers. Download date was 01/02/2020. https://www.fws.gov/wetlands/data/Data-Download.html Digital 2019 publication date NWI Wetland classification This process step and subsequent process steps were performed by the same person, Kate Ackerman, in ArcGIS Pro (ver.3.4.3) unless otherwise stated. For complex operations, names of specific tools used are given in CAPITAL letters (any critical parameters used are given in parentheses, separated by a semicolon, immediately after the tool name). The input and output file names are provided in [square brackets] when necessary. Units for length and area calculations are meters (m) and square meters (m2) unless otherwise stated. This processing step defines the extent of migration area. a) Download the NOAA Sea level rise wetland impacts and migration datasets for the Chesapeake Bay domain [md_marshmigration_2016.zip, va_marshmigration_2016.zip, nc_marshmigration_2016.zip]. These datasets present the potential distribution of each wetland type based on their elevation and frequency of inundation under different SLR rates. Use scenarios: 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0 feet of SLR as input. b) From each scenario select classes of Palustrine Emergent Wetland (15), Brackish/Transition Wetland (17), Estuarine Wetland (18) by EXTRACT_BY_ATTRIBUTES(VALUE = 15 Or VALUE = 17 Or VALUE = 18). c) Mosaic all four rasters from previous step into to a new raster for Maryland (MD) while setting the coordinate system to NAD1983 (2011) UTM Zone 18N. MOSAIC_TO_NEW_RASTER(Pixel Type="1bit"; Spatial Reference=NAD_1983_2011_UTM_Zone_18N; Mosaic Operator="Maximum"). Export only the values greater than 1 as a new raster and convert to polygon. RASTER_TO_POLYGON(Field = "VALUE"). Repeat the same steps for Virginia (VA) and North Carolina (NC) domains. And merge the results into a single feature dataset [mm_MD_VA_NC_merge_UTM18_2011.shp]. md_marshmigration_2016.zip va_marshmigration_2016.zip nc_marshmigration_2016.zip 2026 mm_MD_VA_NC_merge_UTM18_2011.shp U.S. Geological Survey Kate Ackerman Geologist mailing and physical address

384 Woods Hole Road

Woods Hole MA 02543 508-548-8700 x2331 508-457-2310 kackerman@usgs.gov This processing step delineates the migration area based on the USGS National Hydrography Dataset Plus High Resolution (NHD Plus HR) catchments map. First, the catchments intersecting the marsh units are selected as immediate catchments. Then, if the inland boundary of the migration layer spans across multiple catchments, those catchments are merged to the immediate catchments by proximity. Catchments areas beyond the inland boundary of migration layer are clipped to the boundary. The resulting product is the marsh migration polygons which is the migration zone delineated with catchments. a) Download Chesapeake Bay marsh units dataset [mu_UVVR_CB.shp] and NHD Plus HR catchments datasets for the domain. [mu_UVVR_CB.shp]; NHDPlusCatchment feature datasets [NHDPlusCatchment_0206.shp], [NHDPlusCatchment_0207.shp], [NHDPlusCatchment_0208.shp] and [NHDPlusCatchment_0301.shp]. b) Project all source feature datasets to the same coordinate system with the previous processing step, NAD1983 (2011) UTM Zone 18N. Resulting projected data sets are: Marsh units [mu_UVVR_CB_UTM18_2011.shp]; NHDPlusCatchment feature datasets [NHDPlusCatchment_0206_UTM18_2011.shp], [NHDPlusCatchment_0207_UTM18_2011.shp], [NHDPlusCatchment_0208_UTM18_2011.shp] and [NHDPlusCatchment_0301_UTM18_2011.shp] c) Merge all catchment feature datasets to create the total catchment area [HDPlusCatchment_merge_0206_0207_0208_0301.shp]. d) Select parts of migration area that intersect with marsh units. SELECT_LAYER_BY_LOCATION(Input features=mm_MD_VA_NC_merge_UTM18_2011.shp; Selecting features=mu_UVVR_CB_UTM18_2011.shp; Relationship=Intersect; Search distance =1 meter). Export features as [mmp_by_mu.shp]. e) SELECT_LAYER_BY_LOCATION(Input features=HDPlusCatchment_merge_0206_0207_0208_0301.shp; Selecting features= mmp_by_mu.shp, Relationship=Intersect). Export features as [cathments_selected.shp]. f) Intersect the two feature datasets to identify the immediate catchment polygons. PAIRWISE_INTERSECT(Input features=catchments_selected.shp, mmp_by_mu.shp). Export features as [mmp_iniside_cat.shp]. g) Remove the immediate catchments from the overall marsh migration area so that the catchments in the migration area but beyond the immediate ones can be processed. PAIRWISE_ERASE(Input features=mm_MD_VA_NC_merge_UTM18_2011.shp; Erase features=mmp_inside_cat.shp; Output=mm_outside_cat.shp). MULTIPART_TO_SINGLEPART(Input features=mm_outside_cat.shp; Output features=mm_outside_cat_single.shp) and SELECT_LAYER_BY_LOCATION(Input features=mm_outside_cat_single.shp; Selecting features=mu_UVVR_CB_UTM18_2011.shp; Relationship=Intersect; Search distance =1 meter). Export features as [mmp_outside_cat.shp]. h) Union the immediate catchments with the remote catchments to create a union set of catchments. UNION(Input features=mmp_iniside_cat.shp, mmp_outside_cat.shp; Gaps allowed=Yes, Output features=mmp_all.shp). i) Prepare the open water mask. Download NWI layers for VA, MD and NC, then project to the same coordinate system with the rest of the input data and merge. SELECT("ATTRIBUTE" LIKE 'E1%') and export as [E1_CB.shp]. j) Prepare and split the union of catchments to immediate catchments and remote catchments so that the remote catchments can be merged by proximity. Specifically, to prepare, ERASE the open water mask and marsh units from the union of catchments and MULTIPART_TO_SINGLEPART to obtain [mmp_all_single.shp]. Create two feature datasets from this dataset: For immediate catchments SELECT_LAYER_BY_LOCATION(Input features=mmp_all_single.shp; Selecting features=mu_UVVR_CB_UTM18_2011.shp; Relationship=Intersect; Search distance=0.001 meter) and export as [input_mmu.shp]. For remote catchments SELECT_LAYER_BY_LOCATION(Input features=mmp_all_single.shp; Selecting features=mu_UVVR_CB_UTM18_2011.shp; Relationship=Intersect; Search distance=0.001 meter, Invert Spatial Relationship=Yes) and export as [near_mmu.shp]. k) Run the HYDUNITLOOP tool to merge catchments. At each iteration step, the script uses NEAR tool to find remote catchments from the [input_mmu.shp] within 1 meter of an immediate catchment [near_mmu.shp] and merges them to it using UNION and DISSOLVE tools. The catchments merged with an immediate catchment are removed from the remote catchments dataset. The script iterates until there is no change in the number of remote and immediate units. The remaining catchments are those that are more than 1 meter away from any immediate ones and they are discarded. The resulting final dataset is [final_mmu.shp]. HYDUNITLOOP(Input features=input_mmu.shp; Near features=near_mmu.shp; Output features=final_mmu.shp]. l) Because of the resolution difference between the datasets, processing sometimes creates sliver polygons around the edges. To clean up the final output, remove detached marsh migration polygons with area smaller than a threshold value. Specifically, first PAIRWISE_DISSOLVE(Input features=final_mmu.shp; Output feature class=final_mmu_diss.shp) and CALCULATE_GEOMETRY_ATTRIBUTES(Input features=final_mmu_diss.shp; Geometry attributes field=ASQM; Property=Area (geodesic); Area unit=Square meters; Coordinate system=NAD_1983_2011_Contiguous_USA_Albers). Then, select polygons with areas greater than 300 square meter to export [fmmu_gt_300.shp] and use them to select from [final_mmu.shp] dataset by SELECT_BY_LOCATION(Input feature=final_mmu.shp; Relationship=Within; Selecting features=fmmu_gt_300.shp; Search distance=0 meters). Finally, export the selected features as [marsh_migration_polygons.shp]. m) Keep only the field ASQM and project to Web Mercator projection to obtain [marsh_mig_poly_CB_4ft.shp]. mm_MD_VA_NC_merge_UTM18_2011.shp mu_UVVR_CB.shp NHDPlusCatchment 2026 marsh_mig_poly_CB_4ft.shp Vector G-polygon 46457 WGS 1984 Web Mercator Auxiliary Sphere (ESRI Full Name: WGS_1984_Web_Mercator_Auxiliary_Sphere) 0.0 0.0 0.0 0.0 coordinate pair 0.6096 0.6096 meters D_WGS_1984 WGS_1984 6378137.0 298.257223563 marsh_mig_poly_CB_4ft.shp Attribute Table Table containing attribute information associated with the data set. USGS FID Internal feature number. ESRI Sequential unique whole numbers that are automatically generated. Shape Feature geometry. ESRI Coordinates defining the features. ASQM Area of migration polygon in square meters. USGS 1.89180231468E-05 39467956.1129 square meter In this dataset, marsh migration area under 4 feet of SLR are computed for each conceptual salt marsh unit in Chesapeake Bay. Decimal values in the attribute table are a result of double precision and they should not be taken as significant digits. Significant digits for are and migration rate are assumed to be 1 square meter and 1 square meter per year, respectively. USGS U.S. Geological Survey - ScienceBase mailing and physical address

Denver Federal Center, Building 810, Mail Stop 302

Denver CO 80225 1-888-275-8747 sciencebase@usgs.gov The dataset contains polygon marsh units with migration data (marsh_mig_poly_CB_4ft.shp and other shapefile components) browse graphic, and the FGDC CSDGM metadata in .xml format. Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Shapefile ArcGIS Pro 3.4.3 This zipped file contains a polygon shapefile and its components, metadata in xml format and a browse image. 67 https://www.sciencebase.gov/catalog/file/get/69cfc08db66b01c06b645a97 https://www.sciencebase.gov/catalog/item/69cfc08db66b01c06b645a97 https://doi.org/10.5066/P18BWN2U The first link in network resources is to download data directly. The second link points to a landing page with metadata and data where files can be downloaded individually. The third link is to the main landing page of the data release. None. No fees are applicable for obtaining the data set. 20260526 U.S. Geological Survey Zafer Defne Oceanographer mailing and physical address

384 Woods Hole Road

Woods Hole MA 02543 508-548-8700 x2254 508-457-2310 whsc_data_contact@usgs.gov The metadata contact email address is a generic address in the event the person is no longer with USGS. FGDC Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998