DOI: 10.5061/dryad.n5qb383/36
title: Imperial Beach Characteristics

description: Characteristics of Imperial Beach. MOP DEFINITIONS: The beach site locations are defined using MOP lines. Backbeach locations of each line (spaced 100m apart in the alongshore) and the corresponding offshore locations in 10m depth are included, as well as the MOP site names, index number, and the angle of the line relative to true north. REGIONS: The monitoring schemes at each beach evolved over time with consistently surveyed regions spanning between 1.6 and 2.7km alongshore. Region outlines, and MOP site names and index numbers within each region are provided, as well as times with minimal nourishment influence. SECTIONS: Beaches were split into sections spanning 700-900m alongshore. Location outlines, MOP sites and index numbers, and times of minimal nourishment influence are provided for each section. Additionally, features (e.g. pier, jetty, shoal) are listed. The sections that are labeled as 1D, have a coherent seasonal cross-shore sand exchange signal along the profile, as identified with empirical orthogonal function analysis. During times of minimal nourishment influence, these 1D sections are recommended for testing 1-D cross-shore beach profile evolution models. Note that cobble may be present even in 1D sections, especially when subaerial sand levels are eroded. PIER AND JETTY LOCATIONS: The locations of the pier and two short jetties are included. NOURISHMENT: Sand nourishment placement locations and start and end times are provided. The nourishment placement outline is defined as the bulge in the 2m contour (relative to MSL) location between the pre and post-nourishment surveys. HARD SUBSTRATE: Subaerial substrate is monitored by the ATV driver, however, offshore substrate is difficult to identify. Areas with underlying hard substrate erode to minimum levels significantly less than adjacent sandy areas. Specifically, these areas are defined as areas with mapped minimum surface greater than 30cm relative to the time- and alongshore-averaged mapped profile in the alongshore uniform sections. These locations agree qualitatively with limited available sidescan sonar which helped to identify the hard substrate as cobble shoal. VOLUMES: For each survey, maps are used to estimate sand volumes relative to the minimum surface. The minimum value in each mapped grid point over the study period is used to calculate the minimum surface. The total volume is estimated over the survey area, while subaerial volume is calculated over an area which extends from the mean shoreline position (average location of the intersection of the profile with MSL) to the backbeach. Estimates are provided for each beach, region and section. Volume estimates are discarded if more than 10% of the mapped area has NMSE&gt;0.2. BEACH WIDTHS: Beach width is calculated along each MOP line as the positive slope intersection of the MSL contour with the mapped profile where NMSE&lt; 0.2. If more than one intersection is found, the most offshore MSL position is used, as long as no negative slope intersection is seaward of it. Alongshore-averaged beach widths are provided for each beach, region and section when less than 10% of MOP lines were missing estimates.