Polygons for marsh migration under 2 feet of sea-level rise in Chesapeake Bay (ver. 2.0, May 2026)

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Frequently anticipated questions:

What does this data set describe?

Title:
Polygons for marsh migration under 2 feet of sea-level rise in Chesapeake Bay (ver. 2.0, May 2026)
Abstract:
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 2 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 0.5 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
  1. How might this data set be cited?
    Defne, Zafer, Ackerman, Kate V., Andrews, Brian D., and Ganju, Neil K., 20260526, Polygons for marsh migration under 2 feet of sea-level rise in Chesapeake Bay (ver. 2.0, May 2026): data release DOI:10.5066/P18BWN2U, U.S. Geological Survey, Reston, Virginia.

    Online Links:

    Other_Citation_Details:
    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.
    This is part of the following larger work.

    Defne, Zafer, Ackerman, Kate V., Andrews, Brian D., and Ganju, Neil K., 2025, Chesapeake Bay marsh migration potential under sea-level rise (ver. 2.0, May 2026): data release DOI:10.5066/P18BWN2U, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    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.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -77.3747
    East_Bounding_Coordinate: -75.5934
    North_Bounding_Coordinate: 39.5898
    South_Bounding_Coordinate: 36.3744
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/677d87ded34e009b43365947?name=marsh_mig_poly_CB_2ft.png&allowOpen=true (PNG)
    Marsh migration polygons under 2-feet of SLR in Chesapeake Bay overlaying Esri basemap.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2025
    Currentness_Reference:
    publication date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: Vector Digital Data Set (Polygon)
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • G-polygon (46457)
    2. What coordinate system is used to represent geographic features?
      The map projection used is WGS 1984 Web Mercator Auxiliary Sphere (ESRI Full Name: WGS_1984_Web_Mercator_Auxiliary_Sphere).
      Projection parameters:
      Standard_Parallel: 0.0
      Longitude_of_Central_Meridian: 0.0
      False_Easting: 0.0
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.6096
      Ordinates (y-coordinates) are specified to the nearest 0.6096
      Planar coordinates are specified in meters
      The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    marsh_mig_poly_CB_2ft.shp Attribute Table
    Table containing attribute information associated with the data set. (Source: USGS)
    FID
    Internal feature number. (Source: ESRI) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: ESRI) Coordinates defining the features.
    ASQM
    Area of migration polygon in square meters. (Source: USGS)
    Range of values
    Minimum:1.89445095522e-05
    Maximum:21530264.4354
    Units:square meter
    Entity_and_Attribute_Overview:
    In this dataset, marsh migration area under 2 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.
    Entity_and_Attribute_Detail_Citation: USGS

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Zafer Defne
    • Kate V. Ackerman
    • Brian D. Andrews
    • Neil K. Ganju
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    U.S. Geological Survey
    Attn: Zafer Defne
    Oceanographer
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2254 (voice)
    508-457-2310 (FAX)
    zdefne@usgs.gov

Why was the data set created?

This shapefile presents the migration space for marsh units in Chesapeake Bay.

How was the data set created?

  1. From what previous works were the data drawn?
    md_marshmigration_2016.zip (source 1 of 7)
    Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Office for Coastal Management (OCM), 201907, NOAA Office for Coastal Management Marsh Migration: NOAA's Ocean Service, Office for Coastal Management (OCM), Charleston, SC.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution: Marsh migration inland boundary under sea-level rise
    va_marshmigration_2016.zip (source 2 of 7)
    Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Office for Coastal Management (OCM), 201907, NOAA Office for Coastal Management Marsh Migration: NOAA's Ocean Service, Office for Coastal Management (OCM), Charleston, SC.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution: Marsh migration inland boundary under sea-level rise
    nc_marshmigration_2016.zip (source 3 of 7)
    Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Office for Coastal Management (OCM), 201907, NOAA Office for Coastal Management Marsh Migration: NOAA's Ocean Service, Office for Coastal Management (OCM), Charleston, SC.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution: Marsh migration inland boundary under sea-level rise
    SLR data (source 4 of 7)
    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: NOAA Technical Report NOS 01, National Oceanic and Atmospheric Administration, Silver Spring, MD.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution: Sea-level rise projections for 2100 for selected scenarios
    mu_UVVR_CB.shp (source 5 of 7)
    Ackerman, Kate, Defne, Zafer, and Ganju, Neil Kamal, 2022, Geospatial characterization of salt marshes in Chesapeake Bay: data release DOI:10.5066/P997EJYB, U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution: Marsh unit outlines
    NHDPlusCatchment (source 6 of 7)
    U.S. Geological Survey, 20220324, National Hydrography Dataset (NHD): U.S. Geological Survey, Reston, Virginia.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution: NHD Plus Catchment polygons
    NWI (source 7 of 7)
    U.S. Fish and Wildlife Service, 20191001, National Wetland Inventory: U.S. Fish and Wildlife Service, Madison, WI.

    Online Links:

    Other_Citation_Details:
    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.
    Type_of_Source_Media: Digital
    Source_Contribution: Wetland classification
  2. How were the data generated, processed, and modified?
    Date: 2024 (process 1 of 3)
    This process step and subsequent process steps were performed by the same person, Zafer Defne, in ArcGIS Pro (ver.3.3.2) 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 four scenarios: 0.5, 1.0, 1.5, 2.0 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]. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Zafer Defne
    Oceanographer
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2254 (voice)
    508-457-2310 (FAX)
    zdefne@usgs.gov
    Data sources used in this process:
    • md_marshmigration_2016.zip
    • va_marshmigration_2016.zip
    • nc_marshmigration_2016.zip
    Data sources produced in this process:
    • mm_MD_VA_NC_merge_UTM18_2011.shp
    Date: 2024 (process 2 of 3)
    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.shp]. Data sources used in this process:
    • mm_MD_VA_NC_merge_UTM18_2011.shp
    • mu_UVVR_CB.shp
    • NHDPlusCatchment
    Data sources produced in this process:
    • marsh_mig_poly_CB.shp
    Date: 2026 (process 3 of 3)
    This is the revision step for Version 2.0. Download the original dataset [marsh_mig_poly_CB.shp]. Add the previously missing documentation of processing step of erasing open water using National Wetlands Inventory's E1 attribute. Although performed, this step was omitted from the metadata in version 1 of this dataset. Update the Abstract and Lineage components to reflect this change. Export data and metadata after appending "_2ft" to all names to differentiate between different cases. Data sources used in this process:
    • marsh_mig_poly_CB.shp
    Data sources produced in this process:
    • marsh_mig_poly_CB_2ft.shp
  3. What similar or related data should the user be aware of?
    Ackerman, Kate V., Defne, Zafer, and Ganju, Neil K., 2022, Geospatial characterization of salt marshes in Chesapeake Bay: data release DOI:10.5066/P997EJYB, U.S. Geological Survey, Reston, VA.

    Online Links:

    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: NOAA Technical Report NOS 01, National Oceanic and Atmospheric Administration, Silver Spring, MD.

    Online Links:

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    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.
  2. How accurate are the geographic locations?
    Horizontal accuracy is inherited from the source datasets; the marsh units, and the boundaries of marsh migration inherit from the NOAA migration raster datasets.
  3. How accurate are the heights or depths?
    Dataset has no vertical values.
  4. Where are the gaps in the data? What is missing?
    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. 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.
  5. How consistent are the relationships among the observations, including topology?
    Migration potential is zero for a marsh unit that is not connected to any migration area.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints No access constraints. Please see Distribution Information for details.
Use_Constraints 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.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey - ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? The dataset contains polygon marsh units with migration data (marsh_mig_poly_CB_2ft.shp and other shapefile components) browse graphic, and the FGDC CSDGM metadata in .xml format.
  3. What legal disclaimers am I supposed to read?
    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.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 26-May-2026
Metadata author:
U.S. Geological Survey
Attn: Zafer Defne
Oceanographer
384 Woods Hole Road
Woods Hole, MA

508-548-8700 x2254 (voice)
508-457-2310 (FAX)
whsc_data_contact@usgs.gov
Contact_Instructions:
The metadata contact email address is a generic address in the event the person is no longer with USGS.
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/SB_data_release/DR_P18BWN2U/marsh_mig_poly_CB_2ft.faq.html>
Generated by mp version 2.9.51 on Tue May 26 17:00:01 2026