# Long-Term Analysis of Wave Climate and Shoreline Change along the Gulf of California
## 3 Materials and Methods
### Extraction and Shoreline Analysis  
The High Water Line (HWL) is widely used in the investigation of shoreline change to represent the shoreline [38]. It is defined as the highest run-up of the last high tide [39] that is visually discernible in satellite images [16]. Its demarcation in the images is difficult due to the lack of knowledge of the oceanographic conditions at the time of the satellite image acquisition. Nevertheless, it has been shown that the wet/dry line (on a rising tide, it is equal to the maximum run-up limit; on a falling tide, it is equal to the part of the beach that is still wet [16]) closely approximates the HWL [40; 41]. For these reasons, in this paper, the wet/dry line from the Landsat images was used as an approximation of the HWL inland/outland horizontal displacement. It was manually digitized from each satellite image in ArcGIS 10.5. Given the latter and the resolution of the images, the objective of the analysis was to evaluate the erosion and accretion long trends and not the precise quantification of the shoreline displacements based on the position of the HWL.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Spacecraft ID/Sensor** & **Acquired Date** & **Path/Row** & **Pixel Resolution** \\ \hline  & 1978-11-05 & 036/043 & 60 m \\  & 1978-11-05 & 036/044 & 60 m \\  & 1978-10-01 & 037/042 & 60 m \\  & 1978-10-01 & 037/043 & 60 m \\  & 1978-10-02 & 038/041 & 60 m \\  & 1978-11-08 & 039/040 & 60 m \\  & 1980-10-19 & 039/040 & 60 m \\ Landsat 2-3/Multispectral Scanner System (MSS) & 1980-10-02 & 040/039 & 60 m \\  & 1981-10-26 & 033/044 & 60 m \\  & 1981-10-27 & 034/043 & 60 m \\  & 1981-11-15 & 035/043 & 60 m \\  & 1981-11-15 & 035/042 & 60 m \\  & 1981-11-16 & 036/042 & 60 m \\  & 1981-09-23 & 036/041 & 60 m \\  & 1981-09-23 & 036/042 & 60 m \\  & 1981-11-17 & 037/041 & 60 m \\  & 1981-10-14 & 039/039 & 60 m \\  & 1981-09-27 & 040/038 & 60 m \\ \hline  & 2019-10-31 & 031/044 & 30 m \\  & 2019-10-22 & 032/043 & 30 m \\  & 2019-10-22 & 032/044 & 30 m \\  & 2019-10-29 & 033/042 & 30 m \\  & 2019-10-29 & 033/043 & 30 m \\  & 2019-10-04 & 034/042 & 30 m \\  & 2019-10-20 & 034/044 & 30 m \\  & 2019-10-11 & 035/041 & 30 m \\  & 2019-10-11 & 035/042 & 30 m \\ Landsat 8/Operational Land Imager (OLI) & 2019-11-14 & 033/044 & 30 m \\  & 2019-10-20 & 034/041 & 30 m \\  & 2019-10-16 & 038/039 & 30 m \\  & 2019-10-04 & 034/043 & 30 m \\  & 2019-10-16 & 038/038 & 30 m \\  & 2019-10-25 & 037/040 & 30 m \\  & 2019-10-25 & 037/039 & 30 m \\  & 2019-10-25 & 037/038 & 30 m \\  & 2019-10-18 & 036/041 & 30 m \\  & 2019-10-18 & 036/040 & 30 m \\ \hline \end{tabular}
\end{table}
Table 1: Historical Landsat images used in the shoreline position analysis.  
Shoreline changes were analyzed using DSAS (version 5.0), which is a software extension for ArcGIS(r), developed by the USGS to calculate shoreline change rates from multiple historic shoreline positions [19]. To use DSAS, a geographic database was created that combined digitized shorelines and a baseline in front of the coast, then cross-shore transects every 100 m were generated along the west and east coasts of the GC. End Point Rate (EPR) statistics were calculated for each transect (the EPR being the division of the distance between the shoreline position at different dates by the difference in years of the shoreline position) using the shoreline positions indicated in Figure 3[42]. The EPR obtained for the GC coast was further divided into 4 categories (Table 2).  
Finally, the shoreline change in the study area was evaluated for each state for two main reasons: (1) in order to facilitate the analysis and interpretation of the calculations, and (2) due to the availability of images for the study area, which were not homogeneous in time and space, and, thus, different periods of time were available for the analysis on each state (Figure 3).