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

Historical shoreline data covering the coast of South Carolina from the previously published National Assessment of Shoreline Change: A GIS compilation of Updated Vector Shorelines and Associated Shoreline Change Data for the Southeast Atlantic Coast (USGS data release, https://doi.org/10.5066/F74X55X7.) were compiled and merged into a single feature class within a personal geodatabase in ArcMap v 10.7.1. The data were projected in ArcToolbox v10.7.1 > Data Management Tools > Projections and Transformations > Feature > Project. Parameters: input projection = geographic coordinates (WGS84); output projection = UTM zone 17N (WGS 84); transformation = none. Historical shoreline data covers date range 1852-2000 and includes one lidar-derived shoreline (2000). See associated source metadata (https://www.sciencebase.gov/catalog/item/58b89084e4b01ccd5500c2ac) in larger work citation for complete process steps for historical shoreline delineation. This process step and all subsequent process steps were performed by the same person - Marie K. Bartlett

The datum-based, MHW shorelines (see larger work citation, SC_shoreline_2010 and SC_shoreline_2017_2018) and historical shorelines compiled for analysis (SC_historical_shorelines) were confirmed to have the same attribute fields required for use in DSAS before they were merged into a single feature class using Esri's ArcToolbox > Data Management > General > Merge, filename= SC_shorelines. Some shoreline segments from 1962 and 2000, and one segment from 1925 were removed from the dataset prior to analysis because they represented the wrong feature.

Transect features were generated in a personal geodatabase using DSAS v5.1.2020.0720.0030. Parameters Used: baseline layer= SC_baseline, baseline group field=NULL, shoreline layer= SC_shorelines, transect spacing=50 meters, search distance=1000 meters, land direction=right, shoreline intersection=seaward, File produced = SC_transects_LT. Some transects were manually edited for length, moved, or deleted in an edit session using standard editing tools in the editor toolbar, 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://www.usgs.gov/centers/whcmsc/science/digital-shoreline-analysis-system-dsas

Long-term rate calculations performed producing rates with and without the proxy-datum bias correction. Parameters Used: Shoreline layer = SC_shorelines, Shoreline date field = Date_, shoreline uncertainty field name = Uncy, default accuracy = 5.1 meters, shoreline intersection = seaward, stats calculations = [LRR], shoreline threshold = 3, confidence interval=90%. Files produced = SC_trans_LT_rates_20230504_120014, SC_trans_LT_intersect_20230504_120014. 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. Uncertainty for historical shorelines (1852-2000) is found in Kratzmann and others, 2017, which is listed as a source citation in this metadata file. The historical 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 (see larger work citation, SC_bias_feature). For more information about the origin of the PDB see Ruggiero and List (2009), which is cross-referenced in this metadata file. Rate statistics are presented with and without the PDB correction applied, denoted in the transects/rates attribute table with “NB_” or “No bias”. The bias uncertainty values are stored within the bias feature attribute table.

The rate feature class was exported to shapefiles in ArcMap v10.7.1 by right-clicking the transect layer > data > export data. Coordinate system: UTM Zone 17N (WGS84)