Abstract:

Satellite imagery imported into ArcGIS software were used to delineate the shoreline (defined as the edge of vegetation) and calculate shoreline movement as a proxy for sediment stabilization. For at least 2 years prior to and for each sampling year of the study, the imagery for each of the plots was obtained with a minimum of 1 viable image per year for a total of 4 analyses over the project period. Changes in shoreline position were calculated using U.S. Geological Survey (USGS) Digital Shoreline Analysis System (DSAS) and used estimate erosion rates for each site.

Suggested Citation:

Joshua Goff, Just Cebrian. 2019. Analyses of shoreline movement to assess sediment stabilization from 2012-10-29 to 2017-09-08. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-0caw-d652

Purpose:

The purpose of this dataset is to delineate a historic shoreline position and calculate accretion/erosion rates.

Data Parameters and Units:

NetShorelineMovement.xlsx contains the following: OBJECTID: Unique identifier for each line of data TransectId: Unique identifier given to each transect during transect casting in DSAS (see Transects.shp). BaselineId: Unique identifier of each user generated baseline (see Baselines.shp). Site: The site in which each baseline is associated. Habitat: Habitat type in which data was collected. ShorelineId: Unique identifier for each shoreline. Corresponds to the date of the image from which the shoreline was delineated. Distance: The distance between the baseline and the shoreline expressed in meters. This distance is equivalent to the length of the segment starting at the origin of the transect at the baseline and the intersection of the transect with the shoreline. IntersectX: The x coordinate of the intersection of the transect and shoreline. IntersectY: The y coordinate of the intersection of the transect and shoreline. Tn-T(n-1) in years: The difference in shoreline dates expressed in years where T0 = 10/29/2012, T1=11/26/204, T2=8/25/2015, and T3=9/8/2017 Shoreline Diff: The difference in shoreline distance from the baseline between sequential time periods in meters. Rate of Change: Change in shoreline distance from baseline between sequential time periods divided by the change in time between shoreline dates. Attributes from shapefiles can be obtained from the metadata associated with these shapefiles.

Methods:

Google Earth Pro software was used to delineate historic shorelines at each study site (refer to Sites.shp for coordinates) in the Chandeleur Islands for 2012, 2014, and 2015 using imagery provided by Google Earth. These shorelines were imported (.kmz file) into QGIS where they were converted to shapefiles and reprojected to the project coordinate system, NAD 83 UTM 16N. The 2017 shoreline was delineated in QGIS using high-resolution orthoimagery obtained from USGS Earth Explorer (earthexplorer.usgs.gov). The bounding coordinates provided were used to search for relevant imagery. Shoreline change rates were calculated using the Digital Shoreline Analysis System (Thieler et. al., 2017) extension for ESRI ArcGIS software (ArcMap v10.3). Delineated shoreline shapefiles were imported into ArcMap, merged into a single shapefile (ACERShoreline.shp), and imported into a personal geodatabase. The attribute table was then modified to fulfil DSAS requirements. Within the geodatabase, a baseline layer was created. The baseline layer (refer to Baselines.shp) contains a 10 m segment oriented onshore and approximately perpendicular to each plot (n=12, refer to Sites.shp for plot position). For each baseline segment, 15 m transects were cast at 1 m intervals perpendicular to each baseline (n = 10, refer to Transects.shp). Net shoreline movement variables were then calculated using the DSAS extension (1 m uncertainty and 95% confidence). Relevant raw data were imported to an excel spreadsheet where erosion rates were calculated. For each shoreline date, the difference in date in years was calculated (Δt). Similarly, for each date, the difference in shoreline distance from the baseline was also calculated (Δd). Accretion/erosion rates were calculated by finding Δd/ Δt.

Provenance and Historical References:

Thieler, E.R., Himmelstoss, E.A., Zichichi, J.L., and Ergul, Ayhan, 2017, Digital Shoreline Analysis System (DSAS) version 4.0—An ArcGIS extension for calculating shoreline change (ver. 4.4, July 2017): U.S. Geological Survey Open-File Report 2008-1278.

Individual Files: