Elevation of marsh units in Eastern Shore of Virginia salt marshes

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Frequently anticipated questions:

What does this data set describe?

Title:
Elevation of marsh units in Eastern Shore of Virginia salt marshes
Abstract:
This data release contains coastal wetland synthesis products for the Atlantic-facing Eastern Shore of Virginia (the data release for the Chesapeake Bay-facing portion of the Eastern Shore of Virginia is found here: https://doi.org/10.5066/P997EJYB). Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and tidal range are calculated for smaller units delineated from a digital elevation model, providing the spatial variability of physical factors that influence wetland health. The U.S. Geological Survey has been expanding national assessment of coastal change hazards and forecast products to coastal wetlands 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.
  1. How might this data set be cited?
    Ackerman, Kate V., Defne, Zafer, and Ganju, Neil K., 20230328, Elevation of marsh units in Eastern Shore of Virginia salt marshes: data release DOI:10.5066/P9E6V0QK, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Ackerman, Kate V., Defne, Zafer, and Ganju, Neil K., 2023, Geospatial characterization of salt marshes on the Eastern Shore of Virginia: data release DOI:10.5066/P9E6V0QK, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Ackerman, K.V., Defne, Z., and Ganju, N.K., 2023, Geospatial characterization of salt marshes on the Eastern Shore of Virginia: U.S. Geological Survey data release, https://doi.org/10.5066/P9E6V0QK.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -75.977747
    East_Bounding_Coordinate: -75.474028
    North_Bounding_Coordinate: 37.881830
    South_Bounding_Coordinate: 37.085411
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/63e53993d34efa0476ade042/?name=Elev_ESV_Browse.png&allowOpen=true (PNG)
    Graphic that shows elevation of conceptual marsh units in Eastern Shore of Virginia salt marshes.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2023
    Currentness_Reference:
    publication date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector digital dataset (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 (6358)
    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:
      False_Easting: 0.0
      False_Northing: 0.0
      Longitude_of_Central_Meridian: 0.0
      Standard_Parallel: 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 84.
      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?
    mu_elev_ESV.shp attribute table
    Table containing attribute information associated with the dataset. (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.
    FID_CMU
    Unique whole numbers used to identify each conceptual marsh unit. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:6357
    Units:none
    ATOT_M2
    Total surface area of a marsh unit. (Source: USGS)
    Range of values
    Minimum:123.82663224
    Maximum:1906442.13092
    Units:m^2
    AVEG_M2
    Surface area of the vegetated part of a marsh unit. (Source: USGS)
    Range of values
    Minimum:0.0
    Maximum:1628088.8009
    Units:m^2
    MU_ELEV
    Mean elevation of a marsh unit. If the percent hydro-flattened area is greater than 25 percent (MU_HFAR is greater than 0.25), the marsh unit elevation is set to -9999 indicating insufficient elevation data. (Source: USGS)
    Range of values
    Minimum:-0.89189303
    Maximum:2.13515997
    Units:meters
    VG_ELEV
    Mean elevation of the vegetated area in a marsh unit. If there is no vegetated area in the marsh unit, the value is set to -9999. Also, if the percent hydro-flattened area in the vegetated portion is greater than 25 percent (VG_HFAR is greater than 0.25), the value is set to -9999 indicating insufficient elevation data. (Source: USGS)
    Range of values
    Minimum:-0.390088689988
    Maximum:2.06516431022
    Units:meters
    MU_HFAR
    Percent (in decimal form) of the marsh unit that contains hydro-flattened bathymetric/elevation values. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:1
    Units:none
    VG_HFAR
    Percent (in decimal form) of the vegetated portion of the marsh unit that contains hydro-flattened bathymetric/elevation values. If there is no vegetated area in the marsh unit, the value is set to -9999. (Source: USGS)
    Range of values
    Minimum:0
    Maximum:1
    Units:none
    SKWNSS
    The measure of skewness of the elevation distribution in the vegetated part of a marsh unit. Positive skewness values (i.e., right-skewed distribution) indicate clustering of elevation distribution towards lower elevations. Negative values (left-skewed distribution) indicate clustering towards higher elevations. A value of -9999 indicates no vegetated area within the marsh unit or no elevation value for the vegetated portion. (Source: USGS)
    Range of values
    Minimum:-13.06939983
    Maximum:7.72143984
    Units:none
    LOW3RD
    LOW3RD is the percent of elevation values that fall within the lowest third of the elevation range within the vegetated part of a marsh unit. Value of -9999 indicates no vegetated area within the marsh unit or no elevation value for the vegetated portion. (Source: USGS)
    Range of values
    Minimum:0.00121887
    Maximum:99.76370239
    Units:none
    FLG
    Marsh unit flag indicating anomalous marsh units based on absence of vegetation, elevation, surface area and tidal range extrapolation. FLG values indicate: (-1) no vegetated area in the marsh unit; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than the 0.2 percentile; (-200) greater than 25 percent of the marsh unit elevation is hydro-flattened; (-1000) marsh unit surface area less than 900 m^2; (-10000) mean tidal range of marsh unit is extrapolated; and (0) no flag. Combination of negative values indicates a combination of flags. For example, -1001 indicates no vegetated area and area less than 900 m^2. (Source: USGS)
    Range of values
    Minimum:-11100
    Maximum:0
    Units:none
    Entity_and_Attribute_Overview:
    In this dataset, mean elevation for each conceptual salt marsh unit in the Eastern Shore of Virginia salt marshes has been calculated based primarily on the 1-meter 2015 USGS Lidar DEM source dataset. Decimal values in the attribute table are a result of double precision calculations while significant digits are considered in defining the attribute measurement resolutions. Therefore, the smallest unit increment for area and elevation values is assumed to be 1 meter and 0.01 meter, 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)
    • Kate V. Ackerman
    • Zafer Defne
    • Neil K. Ganju
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    Kate Ackerman
    U.S. Geological Survey
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-548-8700 x2331 (voice)
    508-457-2310 (FAX)
    kackerman@usgs.gov

Why was the data set created?

The purpose of this shapefile is to calculate the mean elevation for each marsh unit and its vegetated component. Analysis of marsh elevation is part of a comprehensive assessment to identify the factors and their weights in determining the vulnerability and resiliency of salt marshes. Elevation distribution in the Eastern Shore of Virginia salt marshes is given in terms of mean elevation of conceptual marsh units, as well as the vegetated portion of the marsh unit. The elevation data is based on the 1-meter 2015 USGS Lidar DEM.

How was the data set created?

  1. From what previous works were the data drawn?
    USGS DEM (source 1 of 2)
    U.S. Geological Survey, 2018, 2015 USGS Lidar DEM: Eastern Shore VA: U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Downloaded 1-meter 2015 USGS Lidar DEM. Projection was NAD 1983 UTM Zone 18N with the North American Vertical Datum of 1988 (NAVD 88). Download date was 04/13/2021.
    Type_of_Source_Media: Digital
    Source_Contribution: Elevation dataset
    CMU_ESV (source 2 of 2)
    Ackerman, K.V., Defne, Z., and Ganju, N.K., 2023, Conceptual marsh units of salt marshes on the Eastern Shore of Virginia: U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution:
    Used conceptual marsh units, generated as part of this data release, to delineate marsh unit boundaries and areas of vegetation.
  2. How were the data generated, processed, and modified?
    Date: 2022 (process 1 of 4)
    This process step and all subsequent process steps were performed by the same person, Kate Ackerman, in ArcGIS Pro (ver. 2.8.8), unless otherwise stated. For simple operations the name of the geoprocessing tool used is given in capital letters; for complex operations, the name of geoprocessing tool used is given in capital letters and 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 (m^2) unless otherwise stated.
    a) Set the data frame coordinate system and projection to NAD 1983 UTM Zone 18N.
    b) Establish marsh unit boundaries. Dissolve the vegetated and unvegetated classes in each marsh unit to have only one class for each marsh unit. DISSOLVE(Input features=[CMU_ESV.shp]; Dissolve field=FID_CMU; Statistics field=ATOT_M2 and FLG with Statistics type= First). PROJECT(Input coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Output coordinate system=NAD 1983 UTM Zone 18N) the feature dataset to obtain dissolved marsh units [mu_diss.shp].
    c) Prepare elevation dataset. Combine all downloaded tiles into one raster, using MOSAIC TO NEW RASTER, and PROJECT RASTER to NAD 1983 UTM Zone 18N.
    d) Create a polygon that covers the area of interest [extent.shp]. CLIP the mosaicked elevation dataset created in step (c) by [extent.shp] to create [elev_mosaic.tif]. Person who carried out this activity:
    Kate Ackerman
    U.S. Geological Survey
    Geologist
    384 Woods Hole Road
    Woods Hole, MA
    US

    508-548-8700 x2331 (voice)
    508-457-2310 (FAX)
    kackerman@usgs.gov
    Data sources used in this process:
    • USGS DEM
    • CMU_ESV
    Data sources produced in this process:
    • elev_mosaic.tif
    • mu_diss.shp
    Date: 2022 (process 2 of 4)
    a) Remove pixels from elevation raster that are hydro-flattened. Use FOCAL STATISTICS(Input raster=[elev_mosaic.tif], Output raster=[FocalStats_3x3_range.tif], Neighborhood settings=3x3 cell, Statistics type=range) and RASTER CALCULATOR to identify (Map algebra expression: Con("%FocalStats_3x3_range.tif%" == 0,-1,1); Output raster=[elev_mosaic_One_NegOne.tif]) and remove (Map algebra expression: SetNull("%elev_mosaic_One_NegOne.tif%", "%elev_mosaic.tif%", "value = -1"); Output raster=[elev_mosaic_noHF.tif]) all hydro-flattened areas from [elev_mosaic.tif] to create [elev_mosaic_noHF.tif].
    b) Calculate the mean elevation for each marsh unit with ZONAL STATISTICS AS TABLE(Feature zone data=[mu_diss.shp], Zone field=FID_CMU; Input value raster=[elev_mosaic_noHF.tif]; Statistics type=Mean; Output table=[mu]; Ignore Nodata=True). JOIN mean elevation from [mu] table to marsh units layer [mu_diss.shp] based on the "FID_CMU" field. Export dataset as a shapefile [mu_elev.shp]. Rename "mu_MEAN" to "MU_ELEV."
    c) Calculate the percent of the marsh unit that has hydro-flattened area. ZONAL STATISTICS AS TABLE (Feature zone data=[mu_elev.shp], Zone field=FID_CMU; Input value raster=[elev_mosaic_One_NegOne.tif]; Statistics type=Mean; Output table=[zs_muelev_HF]; Ignore Nodata=True). ADD FIELD to the output table to calculate hydro-flattened area of each marsh unit (MU_HFAR), CALCULATE FIELD (MU_HFAR= (1-MEAN)/2). JOIN MU_HFAR field to [mu_elev.shp]. If the percent hydro-flattened area is greater than 25 percent, set the marsh unit elevation to -9999.
    d) Calculate the elevation of the vegetated area of the marsh unit. SELECT BY ATTRIBUTES from [CMU_ESV.shp] where "TYP"= 'vegetated', output: [CMU_ESV_VEG.shp]. ZONAL STATISTICS AS TABLE(Feature zone data=[CMU_ESV_VEG.shp], Zone field=FID_CMU; Input value raster=[elev_mosaic_noHF.tif]; Statistics type=Mean; Output table=[vg]; Ignore Nodata=True). Join the mean elevation of the vegetated portion to [mu_elev.shp] and rename the field to "VG_ELEV."
    e) Calculate the percent of the vegetated portion of the marsh unit that has hydro-flattened area. ZONAL STATISTICS AS TABLE (Feature zone data=[CMU_ESV_VEG.shp], Zone field=FID_CMU; Input value raster=[elev_mosaic_One_NegOne.tif]; Statistics type=Mean; Output table=[zs_muelev_HF]; Ignore Nodata=True). ADD FIELD (VG_HFAR) to output table, CALCULATE FIELD (VG_HFAR= (1-MEAN)/2). Join VG_HFAR field to [mu_elev.shp]. If the percent hydro-flattened area is greater than 25 percent, set the vegetated elevation to -9999.
    f) JOIN the vegetated area (AVEG_M2) from [CMU_ESV_VEG.shp] to [mu_elev.shp]. Data sources used in this process:
    • elev_mosaic.tif
    Data sources produced in this process:
    • mu_elev.shp
    Date: 2022 (process 3 of 4)
    a) Run Python script (marsv5.py) in ArcGIS Pro (v.2.8.8) to calculate metrics that quantify the distribution of marsh unit elevation values. Skewness ("SKWNSS") is the measure of asymmetry of the elevation distribution in the vegetated part of a marsh unit. Positive skewness values, i.e. right-skewed distributions, indicate clustering of elevation distributions towards lower elevations. Negative skewness values indicate a left-skewed distribution and clustering towards higher elevations. Lower third ("LOW3RD") is the percent of elevation values that fall within the lowest third of the elevation range within the vegetated part of a marsh unit. SKWNSS and LOW3RD parameters are calculated by applying the formulation of Raposa et al. (2016) to the elevation raster within the vegetated part of each marsh unit. JOIN these values to [mu_elev.shp]. If VG_ELEV= -9999, set SKWNESS and LOW3RD values to -9999. Export to a new shapefile [mu_elev_ESV.shp].
    Reference: Raposa, K. B., Wasson, K., Smith, E., Crooks, J. A., Delgado, P., Fernald, S. H., et al. (2016). Assessing tidal marsh resilience to sea-level rise at broad geographic scales with multi-metric indices. Biological Conservation, 204, 263–275. https://doi.org/10.1016/J.BIOCON.2016.10.015. Data sources used in this process:
    • mu_elev.shp
    Data sources produced in this process:
    • mu_elev_ESV.shp
    Date: 2022 (process 4 of 4)
    a) Add field "FLG" to flag anomalous marsh units based on absence of vegetation, elevation, surface area, and tidal range extrapolation. The flags are calculated in their respective shapefile (i.e., elevation flags are calculated in the elevation shapefile). Set FLG to: (-1) no vegetated area in the marsh unit; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than the 0.2 percentile; (-200) greater than 25 percent of the marsh unit elevation is hydro-flattened; (-1000) marsh unit surface area less than 900 m^2; (-10000) mean tidal range of marsh unit is extrapolated; and (0) no flag. Combination of negative values indicates a combination of flags; for example, -1001 indicates no vegetated area and area less than 900 m^2.
    b) Rearrange field names and change the projection for better performance of web services with online base maps. PROJECT(Output coordinate system=WGS 1984 Web Mercator Auxiliary Sphere) the feature dataset to obtain the final elevation dataset [mu_elev_ESV.shp]. Data sources produced in this process:
    • mu_elev_ESV.shp
  3. What similar or related data should the user be aware of?

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

  1. How well have the observations been checked?
    Marsh units and water and land boundaries inherit their horizontal accuracy from the accuracy of the source data, the conceptual marsh units, and their vertical accuracy from the elevation dataset (1-meter 2015 USGS Lidar DEM).
  2. How accurate are the geographic locations?
    Horizontal accuracy for the polygon boundaries is inherited from the source layer, the conceptual marsh units, and is considered to be +/- 6 meters.
  3. How accurate are the heights or depths?
    Because the elevation values are averaged over delineated polygons, vertical accuracy depends on both the horizontal accuracy of the NWI dataset and the vertical accuracy of the source elevation dataset (1-meter 2015 USGS Lidar DEM). The vertical accuracy is inherited from the source elevation dataset; it is reported to be 0.06 meters. No additional accuracy assessment of the vertical accuracy has been conducted.
  4. Where are the gaps in the data? What is missing?
    The marsh polygons are bound to the borders of the Eastern Shore of Virginia's estuarine intertidal areas that include: 1) emergent wetlands, 2) scrub-shrub areas, 3) rooted vascular aquatic beds, 4) organic unconsolidated shores, and 5) channels of open water that are narrower than 10 meters. Occasionally, marsh units are retained in this dataset even though the imagery displayed extreme change (e.g., partially or completely converted to water) from the NWI wetland delineation (e.g., marsh units 638, 796, 1366). In a few areas, there are no marsh units where there is visible marsh plain (e.g., west of marsh units 4583 and 4566; west of 5878; south of 5910; west of 5855), because the areas are classified in the NWI as estuarine intertidal unconsolidated shore, which is not included in our salt marsh boundaries. In a few locations, there may be areas that that are classified as unvegetated but are in fact very sparsely vegetated. A detailed on-the-ground analysis of a single site may result in a different interpretation of the wetland and marsh unit boundaries than those established through this analysis.
  5. How consistent are the relationships among the observations, including topology?
    Positive elevation indicates above sea level. Marsh units with extremely low elevation (smaller than the 0.2 percentile value), extremely high elevation (larger than the 99.8 percentile value) or areas less than 900 square meters were flagged.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints None
Use_Constraints The mean elevation 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? mu_elev_ESV.zip (ZIP file contains the shapefile mu_elev_ESV.shp and the additional shapefile components), browse graphic (Elev_ESV_Browse.png), and FGDC CSDGM metadata in xml format.
  3. What legal disclaimers am I supposed to read?
    Although these data have been processed successfully on a computer system at 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. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. 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. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Not for navigational use.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 29-Mar-2023
Metadata author:
Kate V. Ackerman
U.S. Geological Survey
Geologist
384 Woods Hole Rd
Woods Hole, MA
US

508-548-8700 x2331 (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:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/SB_data_release/DR_P9E6V0QK/mu_elev_ESV.faq.html>
Generated by mp version 2.9.51 on Wed Mar 29 13:42:27 2023