Long-term shoreline change rates for the Virginia coastal region, calculated with and without the proxy-datum bias using the Digital Shoreline Analysis System version 5.1

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Frequently anticipated questions:

What does this data set describe?

Title:
Long-term shoreline change rates for the Virginia coastal region, calculated with and without the proxy-datum bias using the Digital Shoreline Analysis System version 5.1
Abstract:
The U.S. Geological Survey (USGS) has compiled national shoreline data for more than 20 years to document coastal change and serve the needs of research, management, and the public. Maintaining a record of historical shoreline positions is an effective method to monitor national shoreline evolution over time, enabling scientists to identify areas most susceptible to erosion or accretion. These data can help coastal managers and planners understand which areas of the coast are vulnerable to change.
This data release includes a compilation of previously published historical shoreline positions for Virginia spanning 148 years (1849-1997), and two new mean high water (MHW) shorelines extracted from lidar data collected in 2010 and 2017. These data provide a standardized shoreline database for the state. This release includes both long-term (up to 168 years) and short term (~20 years) rates. Files associated with the long-term and short-term rates are appended with "LT" and "ST", respectively. A proxy-datum bias reference line that accounts for the positional difference in a proxy shoreline (e.g. High Water Line (HWL) shoreline) and a datum shoreline (e.g. MHW shoreline) is also included in this release.
Supplemental_Information:
Rate calculations were computed within a GIS using the Digital Shoreline Analysis System (DSAS) version 5.1, an ArcGIS extension developed by the U.S. Geological Survey. Long-term rates of shoreline change were calculated using a linear regression rate based on available shoreline data. A reference baseline was used as the originating point for the orthogonal transects cast by the DSAS software. The transects intersect each shoreline establishing measurement points, which are then used to calculate rates. This dataset consists of shoreline change rates calculated with DSAS v5.1 and stored as a new transect layer. Original measurement transects are cast by DSAS from the baseline to intersect shoreline vectors, and the intersect data provide location and time information used to calculate rates of change.
  1. How might this data set be cited?
    Bartlett, Marie K., 20230526, Long-term shoreline change rates for the Virginia coastal region, calculated with and without the proxy-datum bias using the Digital Shoreline Analysis System version 5.1: data release doi:10.5066/P9DHOFXU, 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.

    Bartlett, Marie K., Henderson, Rachel E., and Farris, Amy S., 2023, USGS National Shoreline Change — A GIS Compilation of Vector Shorelines and Associated Shoreline Change Data for Coastal Virginia from the 1840s to 2010s: data release doi:10.5066/P9DHOFXU, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Bartlett, M.K., Henderson R.E., and Farris, A.S., 2023, USGS National Shoreline Change — A GIS Compilation of Vector Shorelines and Associated Shoreline Change Data for Coastal Virginia from the 1840s to 2010s: U.S. Geological Survey data release, https://doi.org/10.5066/P9DHOFXU.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -76.0670
    East_Bounding_Coordinate: -75.2369
    North_Bounding_Coordinate: 38.0273
    South_Bounding_Coordinate: 36.5490
  3. What does it look like?
    https://www.sciencebase.gov/catalog/file/get/641c6393d34e807d39b63fc4?name=VA_rates_LT_browse.JPG (JPEG)
    Map view of dataset
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date:
    Ending_Date: 2017
    Currentness_Reference:
    ground condition at the time of shoreline source data
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector digital data
  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):
      • String (3288)
    2. What coordinate system is used to represent geographic features?
      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 18
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: -75.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      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 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?
    VA_rates_LT.shp Attribute Table
    Rates of long-term shoreline change are calculated by DSAS and stored in the transect file, using the distance measurements between shorelines and baseline at each DSAS transect. These attributes are for long-term rates with and without bias applied. The shapefiles will have LT for long-term in filename. Rate calculations without bias applied will have "_NB" In the attribute field title. (Source: U.S. Geological Survey (USGS))
    FID
    Internal feature number. (Source: Esri) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: Esri) Feature geometry. Rates are polyline shapefiles.
    BaselineID
    Unique identification number of the baseline segment. If BaselineID=0 no transects will be generated. Used by DSAS to determine transect ordering alongshore if multiple baseline segments exist. (Source: USGS)
    Range of values
    Minimum:1
    Maximum:14
    GroupID
    Optional field to aggregate transects on the basis of physical variations alongshore (for example, tidal inlets, change in coastal type, or hard stabilization features). This value was assigned by the user as an attribute to a baseline segment and results in a group average being reported in the DSAS summary text file. (Source: USGS)
    Range of values
    Minimum:1
    Maximum:8
    TransOrder
    Assigned by DSAS based on ordering of transects along the baseline. Used to allow user to sort transect data along the baseline from baseline start to baseline end. (Source: USGS)
    Range of values
    Minimum:1
    Maximum:3672
    Azimuth
    Assigned by DSAS to record the azimuth of the transect measure in degrees clockwise from North. If a transect position has been adjusted during the editing process, the azimuth value in the attribute table is updated automatically. (Source: USGS)
    Range of values
    Minimum:0.32
    Maximum:359.84
    ShrCount
    Number of shorelines used to compute shoreline change metrics. (Source: USGS)
    Range of values
    Minimum:3
    Maximum:12
    TCD
    The Total Cumulative Distance (TCD) is the measure in meters along shore from the start of the baseline segment with an ID=1, and measured sequentially alongshore to the end of the final baseline segment (Source: USGS)
    Range of values
    Minimum:0.0
    Maximum:217485.29
    SHAPE_Leng
    Length of feature in meter units (UTM zone 18N, WGS 84) (Source: USGS)
    Range of values
    Minimum:63.116
    Maximum:2763.621
    LRR
    A linear regression rate-of-change statistic was calculated by fitting a least-squares regression line to all shoreline points for a particular transect. Any shoreline points that are referenced to HWL were adjusted by the proxy-datum bias distance (meters) along the transect to correct for the offset between proxy-based HWL and datum-based MHW shorelines. The best-fit regression line is placed so that the sum of the squared residuals (determined by squaring the offset distance of each data point from the regression line and adding the squared residuals together) is minimized. The linear regression rate is the slope of the line. The rate is reported in meters per year with positive values indicating accretion and negative values indicating erosion. (Source: USGS)
    Range of values
    Minimum:-17.60
    Maximum:18.61
    NB_LRR
    The LRR without the bias applied. Decimal values may be positive or negative, which is used to indicate landward (negative) or seaward (positive) direction from baseline origin. Reported in meters per year. (Source: USGS)
    Range of values
    Minimum:-17.49
    Maximum:18.71
    LR2
    The R-squared statistic, or coefficient of determination, is the percentage of variance in the data that is explained by a regression. It is a dimensionless index that ranges from 1.0 to 0.0 and measures how successfully the best-fit line accounts for variation in the data. The smaller the variability of the residual values around the regression line relative to the overall variability, the better the prediction (and closer the R-squared value is to 1.0). (Source: USGS)
    Range of values
    Minimum:0.0
    Maximum:1.0
    NB_LR2
    The LR2 without the bias applied. (Source: USGS)
    Range of values
    Minimum:0.0
    Maximum:1.0
    LSE
    This quantity is the standard error of the regression, also known as the standard error of the estimate. To calculate it, the distance between each data point and the regression line is calculated. These distances are squared then summed. The sum is divided by the number of data point minus two. The square root is taken of the result. These are positive decimal values in meters. (Source: USGS)
    Range of values
    Minimum:2.3
    Maximum:588.5
    NB_LSE
    The LSE without the bias applied. (Source: USGS)
    Range of values
    Minimum:1.9
    Maximum:584.68
    LCI90
    The 90 percent confidence interval (LCI90) is calculated by multiplying the standard error of the slope by the two-tailed test statistic at the user-specified 90 percent confidence. This value is often reported in conjunction with the slope to describe the confidence of the reported rate. For example: LRR = 1.2 and LCI90 = 0.7 could be reported as a rate of 1.2 (+/-) 0.7 meters/year. These are positive decimal values in meters. (Source: USGS)
    Range of values
    Minimum:0.04
    Maximum:62.46
    NB_LCI90
    The LCI90 without the bias applied. These are positive decimal values in meters. (Source: USGS)
    Range of values
    Minimum:0.03
    Maximum:62.85
    Entity_and_Attribute_Overview:
    The entity and attribute information provided here describes the tabular data associated with long-term shoreline change rates. Long-term rates incorporate the known unidirectional offset between proxy-based high water line features and datum-based mean high water line features (the proxy-datum bias). Please review the individual attribute descriptions for detailed information. All calculations for length are in meter units and were based on the UTM zone 18N WGS 84 projection. This region has two shapefiles describing rates, long-term (~168 years) and short-term (~20 years).
    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)
    • Marie K. Bartlett
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    Marie K. Bartlett
    U.S. Geological Survey
    Geologist
    384 Woods Hole Rd
    Woods Hole, MA
    United States

    508-457-8700 x2306 (voice)
    mbartlett@usgs.gov

Why was the data set created?

This dataset describes the long-term (up to 168 years) shoreline change rates for the Virginia coastal region, used to maintain a national assessment of shoreline change.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 2022 (process 1 of 4)
    A polyline, midshore baseline was constructed using standard feature creation tools in Esri's ArcMap v10.7.1. The baseline was positioned to follow to the overall orientation of the shorelines alongshore (see larger work citation, VA_baseline.shp, VA_shorelines.shp). This was done so that the transects, which are generated by the Digital Shoreline Analysis System and extend from the baseline, would intersect roughly perpendicular to the general trend of the shorelines. The baseline was constructed in UTM zone 18N (WGS 84) coordinate system. This process step and all subsequent process steps were performed by the same person - Marie K. Bartlett Person who carried out this activity:
    Marie K. Bartlett
    U.S. Geological Survey
    Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x 2306 (voice)
    mbartlett@usgs.gov
    Date: 2022 (process 2 of 4)
    Transect features were generated in a personal geodatabase using DSAS v5.1.2020.0720.0030. Parameters Used: baseline layer= VA_baseline, baseline group field=NULL, shoreline layer= VA_shorelines, transect spacing=50 meters, search distance=1000 meters, land direction=right, shoreline intersection=seaward, File produced = VA_transects_LT. Some transects were manually edited for length, moved, or deleted in an edit session using standard editing tools in ArcMap v10.7.1. For additional details on these parameters, please see the DSAS help file distributed with the DSAS software, or visit the USGS website at: https://woodshole.er.usgs.gov/project-pages/DSAS/
    Date: 2023 (process 3 of 4)
    Shoreline intersects and rate calculations performed for long-term rates with and without bias. Parameters Used: Shoreline layer = VA_shorelines, shoreline date field= Date_, shoreline uncertainty field name=Uncy, the default accuracy = 5.1 meters, shoreline intersection = seaward, stats calculations = [LRR], shoreline threshold = 3, confidence interval=90%. Files produced = VA_trans_LT_rates_20230321_135326, VA_trans_LT_intersect_20230321_135326. All shorelines have an uncertainty value listed in the attribute table that provides the horizontal uncertainty associated with the shoreline, regardless of the method used. The shoreline database contains both MHW and HWL shorelines thus a proxy-datum bias (PDB), stored as a line feature class appended to the reference baseline, is applied during rate calculation. For more information about the origin of the PDB see Ruggiero and List (2009). Rate statistics are presented with and without the PDB applied, denoted in the attribute field with “NB_” or “No bias”. The bias uncertainty values are stored within the bias feature attribute table.
    Date: 2023 (process 4 of 4)
    The rate feature classes were exported to shapefiles in ArcMap v10.7.1 by right-clicking the transect layer > data > export data. Coordinate system: UTM Zone 18N (WGS84)
  3. What similar or related data should the user be aware of?
    Hapke, Cheryl J., Himmelstoss, Emily A., Kraztmann, Meredith G., List, Jeffrey H., and Thieler, E. Robert, 20120423, National Assessment of Shoreline Change: Historical Shoreline Change along the New England and Mid-Atlantic Coasts: Open-File Report 2010-1118, U.S. Geological Survey, Reston, VA.

    Online Links:

    Himmelstoss, Emily A., Farris, Amy S., Henderson, Rachel E., Kratzmann, Meredith G., Ergul, Ayhan, Zhang, Ouya, Zichichi, Jessica L., and Thieler, E. Robert, 2021, Digital Shoreline Analysis System (version 5.1): U.S. Geological Survey Software: software release version 5.1, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Use the first two links to access the software. The third link directs to the DSAS project page. Current version of software at time of use was 5.1.
    Himmelstoss, Emily A., Henderson, Rachel E., Kratzmann, Meredith G., and Farris, Amy S., 20211019, Digital Shoreline Analysis System (version 5.1) User Guide: Open-File Report 2021-1091, U.S. Geological Survey, Reston, VA.

    Online Links:

    Other_Citation_Details:
    Refer to the DSAS user guide for more information about attribute requirements, accuracy reports, and feature creation.
    Ruggiero, Peter, and List, Jeffrey H., 200909, Improving Accuracy and Statistical Reliability of Shoreline Position and Change Rate Estimates: Journal of Coastal Research vol. 255, Coastal Education and Research Foundation, n/a.

    Online Links:

    Other_Citation_Details: ppg. 1069-1081

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

  1. How well have the observations been checked?
    The attributes of this dataset are based on the field requirements of the Digital Shoreline Analysis System and were automatically generated by the software during the generation of the transect layer or during the calculation of shoreline change rates performed by the software.
  2. How accurate are the geographic locations?
    The uncertainty of the linear regression rate is estimated by the elements LR2, LSE and LCI90. See the attribute definition of each for more information.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    This dataset contains the transects automatically generated by the DSAS software application that were used to calculate shoreline change rates for the region. Additional transects may have been generated but did not intersect the minimum requirement of three shorelines. Shoreline change rates data are provided where there are available shorelines to compute change metrics. Though the full database of shorelines was utilized (1849-2017), gaps in shorelines or lack of lidar data in certain areas may mean that not all transects will incorporate every shoreline date in the rate calculations.
  5. How consistent are the relationships among the observations, including topology?
    These data were generated using DSAS v5.1. The transects automatically generated by the software were visually inspected along with the shoreline data prior to rate calculations. Sometimes transect positions were manually edited within a standard ArcMap edit session to adjust the position at which individual transects intersect the shorelines to better represent an orthogonal position to the general trend of the coast over time.

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 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 originator of the dataset. These data are not to be used for navigation.
  1. Who distributes the data set? (Distributor 1 of 1)
    U.S. Geological Survey
    Attn: USGS ScienceBase
    Denver Federal Center, Building 810, Mail Stop 302
    Denver, CO
    United States

    1-888-275-8747 (voice)
    sciencebase@usgs.gov
  2. What's the catalog number I need to order this data set? The dataset contains the polyline shapefile of Virginia long-term rates of change (VA_rates_LT.shp and other shapefile components), browse graphic (VA_rates_LT_browse.JPG), and the FGDC 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. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), and have been processed successfully on a computer system at the 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. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: These files (.cpg, .dbf, .prj, .sbn, .sbx, .shp, and .shx) are a collection of files with a common filename prefix and must be downloaded and stored in the same directory. Together they are the components of the shapefile. Additional files of the same name included are FGDC CSDGM-compliant metadata in XML format. in format Shapefile (version ArcGIS 10.7.1) Esri Polyline Shapefile Size: 0.29
      Network links: https://www.sciencebase.gov/catalog/item/641c6393d34e807d39b63fc4
    • Cost to order the data: None.

Who wrote the metadata?

Dates:
Last modified: 19-Mar-2024
Metadata author:
Marie K. Bartlett
U.S. Geological Survey
384 Woods Hole Rd
Woods Hole, MA
USA

508-548-8700 x2306 (voice)
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. The contact instructions were updated on 20240319.
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/SB_data_release/DR_P9DHOFXU/VA_rates_LT.faq.html>
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