2016 NOAA Mean High Water Shorelines of the Puerto Rico coast used in Shoreline Change Analysis

Overview of the methods used to extract shoreline features in Puerto Rico and the islands of Vieques and Culebra: This data release uses the contour method of shoreline extraction. Described in Farris and others (2018), the contour method extracts the elevation of average MHW value from DEM data using ArcMap tool “Contour List” with the MHW value chosen for the contour. The resulting shorelines are polyline shapefiles.
The average MHW for Puerto Rico was calculated using NOAA’s vdatum tool (v4.0.1; https://vdatum.noaa.gov/) to model the regional surface using local MHW values based on the PRVD02 vertical datum.

Definition of average MHW for Puerto Rico: The height of MHW was determined from vdatum provided by NOAA. (https://vdatum.noaa.gov/). We continued the practice set out by Weber and others (2005) of using one MHW value for a continuous section of coast (as opposed to using a continuously varying value). This value is always within 6 cm of the value returned by vdatum at any point along the coast. The MHW value ranges from 0.09 m to 0.19 m from all tide observation stations in Puerto Rico, Vieques, and Culebra. Taking the mean from each of those MHW observations results in 0.13 m. This is the contour value used to delineate the shoreline and is recorded as the contour attribute in this shapefile.

Contour Shoreline extraction: A suite of ArcGIS tools (ArcGIS version 10.7.1) were compiled into a series of in-house models with ArcGIS ModelBuilder and used to help automate the contour method of shoreline extraction. First, the MHW shoreline elevation (0.13 m NAV88) was extracted from the DEMs using the ArcGIS Contour List tool (ArcToolbox > Spatial Analyst > Surface > Contour List). This step was iterated for each individual DEM in the study area. As a result, individual shapefiles were created for each DEM.

Contour Shoreline smoothing: Each contour shoreline was generalized using the Smooth Line tool (ArcToolbox > Cartography > Generalization > Smooth Line), applying the PAEK algorithm with a 5 m tolerance. The shoreline features were then merged (ArcToolbox > Data Management > General > Merge) into one feature class.

Contour Shoreline date calculation: The date for each shoreline is required to identify the dataset, and is used for shoreline change analysis with DSAS (Himmelstoss and others 2018). The date for each contour shoreline was calculated using the corresponding lidar point cloud tile index shapefile.
The tile index shapefile was downloaded from the 2016 NOAA NGS Topobathy Lidar bulk download page (https://chs.coast.noaa.gov/htdata/lidar4_z/geoid18/data/8463/). The dates associated with the tile index in the attribute table were used to apply the date to the contour shoreline features. In some instances, however, there were multiple tiles to one shoreline feature as some tiles were overlapping. In this case, the average date was calculated and applied to those shoreline features.
To do this, the date field from the tile index was converted to the Julian day (in this case, Julian day refers to the day of the year number).
In order to spatially join the tiles to the contour shorelines and calculate the average date, some modifications to the tile index shapefile was required. A “Count” field was added and calculated with a value of 1 in the tile index shapefile. Then, the contour shorelines were split where they intersected with the tile boundaries. This was done by creating a separate point shapefile where the contours intersected with the tile boundaries (ArcToolbox > Analysis > Overlay > Intersect) and then split the contours at these intersection points (ArcToolbox > Data Management > Features > Split Line at Point).
Each of these split contours were then spatially joined to the corresponding tile index or indices within which they fell (ArcToolbox > Analysis > Overlay > Spatial Join). The sum of the Julian day and Count fields was designated as the merge rule when spatially joining the tiles to the contours.
The summed Julian day field was divided by the summed Count field to derive the average Julian day for each of the contour shorelines. The average Julian day was then converted back to a date as a text field, compatible with DSAS.

Contour Shoreline attributes: Additional attributes are added UNCY (see Horizontal Positional Accuracy Report), PROXY (MHW), AGENCY, TYPE (lidar), METHOD (contour).

Contour Shoreline edits: The shoreline was then manually edited with the lidar data displayed with categorized elevation values to highlight the MHW values and a modern base map image for reference. Segments of the contour that did not fall near the open ocean MHW were removed.

Final coordinate transformation from "NAD_1983_NSRS2007_StatePlane_Puerto_Rico_Virgin_Isls_FIPS_5200" to "GCS_WGS_1984".