Rate of shoreline change of marsh units in north shore Long Island salt marsh complex, New York

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Frequently anticipated questions:

What does this data set describe?

Title:
Rate of shoreline change of marsh units in north shore Long Island salt marsh complex, New York
Abstract:
This data release contains coastal wetland synthesis products for the geographic region of north shore Long Island, New York. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, mean tidal range, and shoreline change rate are calculated for smaller units delineated from a Digital Elevation Model, providing the spatial variability of physical factors that influence wetland health. Through scientific efforts initiated with the Hurricane Sandy Science Plan, 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.
This dataset displays shoreline change rates for north shore Long Island. Shoreline change rates are based on analysis of digital vector shorelines acquired from historical topographic sheets provided by National Oceanic and Atmospheric Administration (NOAA). Analysis was performed using the Digital Shoreline Analysis System (DSAS), an extension for ArcMap, created by the U.S. Geological Survey. Linear Regression Rates (LRR) and End Point Rates (EPR) of shoreline change were averaged along the shoreline of each salt marsh unit to generate this dataset. LRR rates were used in areas where three or more historical shorelines were available while EPR was used in areas where two were available. Positive and negative values indicate accretion and erosion respectively.
  1. How might this data set be cited?
    Welk, Robert, Defne, Zafer, and Ganju, Neil K., 20200602, Rate of shoreline change of marsh units in north shore Long Island salt marsh complex, New York: data release DOI:10.5066/P9UNOMM8, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Welk, Robert, Defne, Zafer, and Ganju, Neil, 2020, Coastal wetlands of north shore Long Island, New York: data release DOI:10.5066/P9UNOMM8, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Suggested citation: Welk, R., Defne, Z., and Ganju, N.K., 2020, Coastal wetlands of north shore Long Island, New York: U.S. Geological Survey data release, https://doi.org/10.5066/P9UNOMM8.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -73.7523079
    East_Bounding_Coordinate: -72.7695214
    North_Bounding_Coordinate: 40.9750166
    South_Bounding_Coordinate: 40.7771079
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/5e85f188e4b01d50927ef70d?name=ShCR_NSLI_browse.png (PNG)
    Graphic that shows the shoreline change rate overlaying Esri Map.
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2020
    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 (1385)
    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 Meter
      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?
    mu_shoreline_NSLI
    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 number that represents the identification number for each conceptual marsh unit. (Source: USGS)
    Range of values
    Minimum:37
    Maximum:1778
    MEAN_LRR
    Mean shoreline change rate based on a linear regression method. A -9999 value may indicate that the marsh unit does not have a shoreline (SHORE_LEN=-9999), or no transect is available for calculation (TRANS_PER_L=-9999). (Source: USGS)
    Range of values
    Minimum:-1.66
    Maximum:2.50
    Units:meters/year
    MEAN_EPR
    Mean shoreline change rate based on an end-point method. A -9999 value may indicate that the marsh unit does not have a shoreline (SHORE_LEN=-9999), or no transect is available for calculation (TRANS_PER_E=-9999). (Source: USGS)
    Range of values
    Minimum:-1.48
    Maximum:0.58
    Units:meters/year
    TRANS_PER_L
    Average shoreline length,in meters per LRR transect. Calculated by dividing SHORE_LEN by number of LRR transects. A value of -9999 indicates no LRR transect is available or the marsh unit has SHORE_LEN=-9999. (Source: USGS)
    Range of values
    Minimum:0.066152
    Maximum:325.309125
    Units:meters
    TRANS_PER_E
    Average shoreline length, meters represented per EPR transect. Calculated by dividing SHORE_LEN by number of EPR transects. A value of -9999 indicates no EPR transect is available or the marsh unit has SHORE_LEN=-9999. (Source: USGS)
    Range of values
    Minimum:0.212455
    Maximum:1111.783957
    Units:meters
    SHORE_LEN
    Shoreline length of marsh unit in meters. A value of -9999 indicates that the marsh unit does not have a shoreline or that the value is not available. (Source: USGS)
    Range of values
    Minimum:0.006401
    Maximum:3330.42018
    Units:meters
    FLG
    Marsh unit flag indicating anomalous marsh units based on elevation, surface area, and absence of vegetation. 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 0.2 percentile; (-200) greater than 25% of marsh unit has hydroflattened area (and has -9999 as its elevation value); (-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 indicate combination of flags. For example, -1001 indicates no vegetated area and area less than 900 m^2. (Source: USGS)
    Range of values
    Minimum:-11201
    Maximum:0
    Units:None
    Entity_and_Attribute_Overview:
    In this dataset, shoreline change rates are averaged over each conceptual marsh unit in north shore Long Island. Negative and positive values indicate erosion and accretion, respectively. 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 shoreline change rate values can be assumed to be a practical value such as 0.01 meters/year.
    Entity_and_Attribute_Detail_Citation: U.S. Geological Survey

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • Robert Welk
    • Zafer Defne
    • 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: Robert Welk
    Hydrologic Technician
    2045 Route 112
    Coram, NY

    631-736-0783 x141 (voice)
    rwelk@usgs.gov

Why was the data set created?

Analysis of shoreline change rates is part of a comprehensive assessment to identify the factors and their weights in determining the vulnerability and resiliency of salt marshes. This polygon dataset facilitates quantifying these rate changes in the north shore Long Island salt marsh complex by summarizing the rate change results over the previously determined conceptual salt marsh unit polygons.

How was the data set created?

  1. From what previous works were the data drawn?
    LRR_transects (source 1 of 3)
    Welk, Robert, 2019, Rate of shoreline change statistics for New York State coastal wetlands: data release DOI:10.5066/P9JVMLFT, U.S. Geological Survey, Reston, Virginia.

    Online Links:

    Type_of_Source_Media: Online
    Source_Contribution:
    Used the LRR and EPR transects to calculate the shoreline change rates at each marsh unit. Download date was 2019/08/01.
    CMU_NSLI (source 2 of 3)
    U.S. Geological Survey, 2020, Coastal wetlands of north shore Long Island, New York: U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution: Used conceptual marsh units to delineate marsh unit boundaries.
    NWI (source 3 of 3)
    U.S. Fish and Wildlife Service, 2017, National Wetland Inventory New York Wetlands: U.S. Fish and Wildlife Service, Madison, WI.

    Online Links:

    Type_of_Source_Media: Digital
    Source_Contribution:
    Downloaded wetlands data for the state of New York in shapefile format from the NWI download page. Projection was NAD 1983 Albers. Download date was 2019/08/01.
  2. How were the data generated, processed, and modified?
    Date: 2020 (process 1 of 4)
    This process step and all subsequent process steps were performed by the same person, Robert Welk, in ArcMap (ver. 10.7.1) using tools from ArcToolbox, 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 (m^2) unless otherwise stated.
    Shoreline change rates for the north shore Long Island salt marsh complex are based on "Rate of shoreline change statistics for New York State coastal wetlands" by Welk (2019. Person who carried out this activity:
    U.S. Geological Survey
    Attn: Robert Welk
    Hydrologic Technician
    2045 NY 112
    Coram, NY

    631-736-0783 x141 (voice)
    rwelk@usgs.gov
    Date: 2020 (process 2 of 4)
    Calculate shoreline length for each marsh unit. a) From NWI, SELECT BY ATTRIBUTES(WETLAND_TY = 'Estuarine and Marine Deepwater') to obtain coastal water polygon features. EXPORT to obtain [NWI_deepwater.shp].
    b) DISSOLVE (Input Features = [NWI_deepwater.shp]) to obtain Output Feature Class = [NWI_deepwater_dissolve.shp].
    c) BUFFER (Input features=[NWI_deepwater_dissolve.shp]; Linear unit= -5 meters; Dissolve type=All) to obtain [NWI_deepwater_buffern5m.shp].
    d) Create a bounding box polygon [bounding_box.shp].
    e) ERASE(Input Features=[bounding_box.shp]; Erase Features=[NWI_deepwater_buffern5m.shp]; Output Feature Class=[land_polygon.shp]).
    f) ELIMINATE POLYGON PART(Input Features=[land_polygon.shp]; Output Feature Class=[land_polygon_elim.shp]; Condition='Percent'; Percentage=99; Eliminate contained parts only).
    g) Revert back to open water polygon by ERASE(Input Features=[bounding_box.shp]; Erase Features=[land_polygon_elim.shp]; Output Feature Class=[open_water_polygon.shp]) and BUFFER(Linear unit= 5 meters) to obtain [open_water_buff5m.shp].
    h) DISSOLVE(Input Features = [CMU_NSLI.shp]; Dissolve Field=FID_CMU) to obtain [CMU_dissolve.shp] and convert to line feature by POLYGON TO LINE to get [CMU_line.shp]
    i) Obtain marsh unit shorelines by INTERSECT(Input Features = [CMU_line.shp] and [open_water_buff5m.shp]; XY Tolerance=1.0 meters; Output Type=LINE) to obtain [mu_shorelines.shp] Data sources used in this process:
    • CMU_NSLI.shp
    • NWI
    Data sources produced in this process:
    • mu_shorelines.shp
    Date: 2020 (process 3 of 4)
    Calculate the transect coverage and mean LRR and EPR shoreline change in each marsh unit. Transect coverage is the average shoreline length represented by the transects in a marsh unit.
    a) EXPORT dissolved marsh unit layer [CMU_dissolve.shp] to obtain [mu_ShRC.shp]
    b) SPATIAL JOIN(Target features=[mu_ShRC.shp]; Join features=[LRR_transects.shp]; Output features=[mu_LRR_trans_join.shp];Join_one_to_many; Match option=INTERSECT) to assign LRR values to the intersecting marsh units. Repeat step for EPR transects to obtain [mu_EPR_trans_join.shp].
    c) Calculate the mean LRR for each marsh unit with SUMMARY STATISTICS(Input table=[mu_LRR_trans_Join.shp]; Output_table=[s_LRR]; Statistics Fields=LRR; Statistics type=MEAN; Case field='TARGET_FID'). Repeat step for EPR transects to obtain [s_EPR].
    d) Join statistics fields to the marsh unit layer using JOIN FIELD(Input Table=mu_ShRC.shp; Input Join Field=FID_CMU; Join Table=s_LRR; Output Join Field=FID_CMU; Join Fields=MEAN_LRR, FREQUENCY). Repeat step for EPR.
    e) ADD the TRANS_PER_L field and calculate it as the total shoreline length divided by FREQUENCY. Assign a value of -9999 if the number of transects is equal to zero. Repeat step for EPR transects by adding the TRANS_PER_E field and making the same calculation.
    f) Edit the attribute table to choose fields to keep and to format the field names. Export the dataset as final output [mu_LRR_NSLI.shp] Data sources used in this process:
    • CMU_dissolve.shp
    • LRR_transects.shp
    • EPR_transects.shp
    Data sources produced in this process:
    • mu_shoreline_NSLI.shp
    Date: 06-Aug-2020 (process 4 of 4)
    Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
  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?
    Water-land boundaries and marsh unit boundaries inherit their accuracy from the source data, the conceptual salt marsh units. Shoreline change rate is calculated by averaging the values from the source layer (shoreline change transects are drawn every ~50 meters along a baseline) for each marsh unit. Shoreline change rates in the source data are influenced by the availability and accuracy of historical shoreline data.
  2. How accurate are the geographic locations?
    Horizontal accuracy for the polygon boundaries is inherited from the source layer, the conceptual marsh units and considered to be +/- 6 meters.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    The results are specific to the conceptual marsh unit polygons as defined within the boundaries of the north shore Long Island 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. All of the marsh units are assigned a value. Some marsh units may have a MEAN_LRR or MEAN_EPR rate, but no SHORE_LEN value available while others have a calculated SHORE_LEN but no available MEAN_LRR or MEAN_EPR.
  5. How consistent are the relationships among the observations, including topology?
    Mean Linear Regression Rate (MEAN_LRR) is calculated by averaging the LRR transects that cross the shoreline of a marsh unit. Likewise, Mean End-point Rate (MEAN_EPR) is calculated by averaging the EPR transects that cross the shoreline of a marsh unit. If a marsh unit has a shoreline, but no transect is available to assign a shoreline change rate, the mean LRR and/or mean EPR is set to -9999.

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 shoreline change rates in this dataset are 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_shoreline_NSLI.shp (and files associated with a shapefile), browse graphic (shoreline.png), and CSDGM metadata in XML format.
  3. What legal disclaimers am I supposed to read?
    Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm 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: 06-Aug-2020
Metadata author:
U.S. Geological Survey, Northeast Region
Attn: Robert J Welk
Hydrologic Technician
2045 Route 112
Coram, NY
US

631-736-0783 x141 (voice)
rwelk@usgs.gov
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_P9UNOMM8/mu_shoreline_NSLI.faq.html>
Generated by mp version 2.9.50 on Tue Sep 21 18:19:47 2021