Mean tidal range of marsh units in Eastern Shore of Virginia salt marshes

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Frequently anticipated questions:

What does this data set describe?

Title:
Mean tidal range 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, Mean tidal range 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/63e53ab5d34efa0476ade04a/?name=MN_ESV_Browse.png&allowOpen=true (PNG)
    Graphic that shows mean tidal range 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_MN_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
    MN
    Mean tidal range in meters averaged over a marsh unit. A no data value of -9999 is assigned to marsh units that are greater than 25m from a VDatum data point. (Source: USGS)
    Range of values
    Minimum:0.0
    Maximum:1.361678
    Units:m
    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
    Entity_and_Attribute_Overview:
    In this dataset, tidal range for each conceptual salt marsh unit in Eastern Shore of Virginia salt marshes has been calculated based on a 0.0005 arc degrees interpolated VDatum 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 tidal range 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 mean tidal range in each marsh unit. Analysis of mean tidal range is part of a comprehensive assessment to identify the factors and their weights in determining the vulnerability and resiliency of salt marshes. Biomass production is positively correlated with mean tidal range in salt marshes along the Atlantic coast of the United States. Recent studies support the idea that enhanced stability of the marshes can be attributed to increased vegetative growth due to increased tidal range. This dataset displays the spatial variation of mean tidal range (i.e., mean range of tides, MN) of marsh units in Eastern Shore of Virginia salt marsh complexes. Mean tidal range, MN, was based on the calculated difference in height between mean high water (MHW) and mean low water (MLW) using the VDatum (v.4.5.1) database (http://vdatum.noaa.gov/).

How was the data set created?

  1. From what previous works were the data drawn?
    CMU_ESV (source 1 of 1)
    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 6)
    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=GCS NAD 1983) the feature dataset to obtain dissolved marsh units [mu_diss.shp]. 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:
    • CMU_ESV
    Data sources produced in this process:
    • mu_diss.shp
    Date: 2022 (process 2 of 6)
    Generate a point cloud of coordinates indicating calculation locations for the mean range of tides (MN).
    a) CREATE CONSTANT RASTER with 50 m spacing (Constant value= 0; Output cell size: 50) that surpasses the marsh unit boundaries by 300m.
    b) RASTER TO POINT to generate an array of points [pts.shp]. PROJECT [pts.shp] to GCSNAD 1983. Calculate latitude and longitude of each point [pts.shp]. Export the shapefile to a text file (TABLE TO TABLE (output table= [Tidal_Points.txt]). This text file includes latitude, longitude and height (set to zero). Data sources produced in this process:
    • Tidal_Points.txt
    Date: 2022 (process 3 of 6)
    Calculate Mean Range of Tides (MN) using the VDatum (v.4.5.1) database covering this region. Mean range of tides (MN) = mean high water level (MHW)- mean low water level (MLW) in the VDatum database. Interpolate MN to the point dataset.
    a) Input point cloud file [Tidal_Points.txt] to VDatum. Set the REGION (Chesapeake/Delaware Bay), HORIZONTAL INFORMATION (Reference Frame (IGS14-use ITRF2014), Coordinate System (Geographic)) to be the same for the source and target. Set the VERTICAL INFORMATION (Source Reference Frame: MHW (meters); Target Reference Frame: MLW (meters)). Choose ASCII FILE CONVERSION (exclude NODATA points) and save output [MN.txt]. The resulting text file includes latitude, longitude and MN. Data sources used in this process:
    • Tidal_Points.txt
    Data sources produced in this process:
    • MN.txt
    Date: 2022 (process 4 of 6)
    Create a raster surface dataset from the feature points.
    a) Convert points from [MN.txt] to a shapefile using MAKE XY EVENT LAYER (Z field= Value; Spatial Reference: GCS_NAD_1983; Layer Name: MN_lyr) and COPY FEATURES [MN.shp].
    b) Create a raster surface with inverse distance weighting. IDW (Input point features: [MN.shp]; Output Cell Size=0.0001 degree; Power=2; Search Radius=Variable; Number of Points=12; Input barrier polyline features – if necessary) to obtain [MN_raster_idw.tif]. After running this tool, it may be apparent that input barrier polyline feature(s) need to be created to separate areas of unrelated tidal range data (e.g., where values from one body of water cross land to another body of water); in those cases, this tool was re-run with the input barrier polyline features specified. Data sources used in this process:
    • MN.txt
    Data sources produced in this process:
    • MN_raster_idw.tif
    Date: 2022 (process 5 of 6)
    Clip the raster to marsh boundaries. A buffer zone is created around the marsh boundaries to facilitate alternative interpolation and clipping options in future studies.
    a) Create 300 m buffer around the marsh units polygons [mu_diss.shp] to create a clipping mask [mu_buff300m.shp]. BUFFER(Side type= Full; Method =Geodesic; Dissolve type= All).
    b) CLIP the raster [MN_raster_idw.tif] with the clipping mask. EXTRACT BY MASK (Mask=[mu_diss.shp]) to obtain [MN_IDW_MU.tif]. Data sources used in this process:
    • mu_diss.shp
    • MN_raster_idw.tif
    Data sources produced in this process:
    • MN_IDW_MU.tif
    Date: 2022 (process 6 of 6)
    Calculate mean tidal range value for each marsh unit and flag the marsh units that have tidal range values that are extrapolated.
    a) ZONAL STATISTICS AS TABLE(Feature Zone Data=[mu_diss.shp]; zone field=FID_CMU; Value Raster=[MN_IDW_MU.tif]; Output Table=[mn]; Statistics type=MEAN).
    b) JOIN FIELD(Input table=[mu_diss.shp]; Input join field=FID_CMU; Join Table=[mn]; Output join field=FID_CMU; Join Field= MEAN). Export dataset as a shapefile [mu_MN_ESV.shp] and change “MEAN” to “MN.”
    c) Identify marsh units that are greater than 25 m from the VDatum data. SELECT BY LOCATION (Input feature= [mu_diss.shp]; Relationship=within_a_distance; Selecting Features: [MN.shp]; Search distance= 25m; Selection type= New_Selection; Invert Spatial Relationship). Assign the marsh units with a distance greater than 25 m from VDatum data a tidal range value of -9999 and a “flag” of -10000.
    d) 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.
    e) 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 mean tidal range dataset [mu_MN_ESV.shp]. Data sources used in this process:
    • MN_IDW_MU.tif
    Data sources produced in this process:
    • mu_MN_ESV.shp
  3. What similar or related data should the user be aware of?
    NOAA, 20221116, VDatum (v.4.5.1): NOAA, 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 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 datasets (1-meter 2015 USGS Lidar DEM). Mean tidal range is calculated from the VDatum database, then interpolated on a raster surface and averaged at each marsh unit. If a marsh unit does not overlap with any raster cell center, it is assigned the value of the raster cell with the largest overlap.
  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. The point cloud used for calculating tidal range with VDatum had a 0.0005 arc degree (~50-meter) resolution that was interpolated over a 0.0001 arc degree raster prior to clipping and calculating the mean value for each marsh unit.
  3. How accurate are the heights or depths?
    The maximum cumulative uncertainty for the Virginia/Maryland/Delaware/New Jersey-Mid-Atlantic Bight shelf operational VDatum region is 0.068 meters. See VDatum's "estimation of vertical uncertainties" for more information (https://vdatum.noaa.gov/docs/est_uncertainties.html).
  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?
    Polygons do not overlap and mean tidal range is positive. During processing of conceptual marsh units, small polygons (less than 9 m^2) were assumed to be marginal and were assigned the classification from the surrounding majority value.

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 tidal range 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_MN_ESV.zip (ZIP file contains the shapefile mu_MN_ESV.shp and the additional shapefile components), a browse graphic (MN_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_MN_ESV.faq.html>
Generated by mp version 2.9.51 on Wed Mar 29 13:42:27 2023