294-5 Mapping Where the Land Meets the Sea: Determining Shoreline Positions from Lidar Data while Maintaining Consistency with Historical Practices

Session: Geologic Mapping (Posters)

Presenting Author:

Authors:

Abstract:

Researchers at the Bureau of Economic Geology, The University of Texas at Austin, conduct projects updating rates of shoreline movement along Texas Gulf and bay shorelines. A key component of these studies has been adapting methods for extracting a shoreline proxy position from lidar digital elevation models (DEM) that are consistent with historical mapping practices. Previous studies determined shoreline position as the land-water interface (wet-beach/dry-beach boundary) at the time aerial photography were taken. Shoreline positions extracted from a 2024 lidar data were chosen and verified by visually comparing a range of shoreline proxy contour elevations with the wet- and dry-beach boundary as shown on imagery acquired during the airborne survey and National Agriculture Imagery Program photography. We also used beach profiles and GPS-mapped shorelines acquired for the Bureau’s Texas High School Coastal Monitoring Program near the dates of the survey to compare the observed wet-beach/dry-beach positions at representative long-term monitoring sites. For a study examining shoreline change in the Galveston Bay system, the recent shoreline position was mapped by extracting an elevation contour from lidar DEMs and manually digitizing the water/land boundary from aerial photography. The elevation contour selected for the shoreline proxy approximated water levels at the time of the lidar surveys based upon analysis of tide gauge data from sites located throughout the Galveston Bay system.

The process of rigorously evaluating the shoreline proxy elevation that best matches the wet-beach/dry-beach boundary includes comparing extracted elevation contours with the wet-beach/dry-beach position as expressed on aerial imagery, beach profiles, and ground-based GPS-mapping relevant to each lidar survey. The extracted elevation contour should be reevaluated with each lidar survey to ensure that the shoreline proxy represents the best approximation of the wet-beach/dry-beach boundary at the time of the survey and not necessarily the elevation that was used during a previous survey. This approach ensures that the extracted elevation best represents current conditions and remains consistent with historical mapping of the shoreline position using the wet-beach/dry-beach boundary as depicted on aerial photographs.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9289

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.