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SCI-DEM: A Method for Generating Digital Beach Surfaces from Tide and Waterline Timeseries
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Authors
Ben Howey,
Natalie Tripp Foulds,
Michael Reinwald 
,
Ketron Mitchell-Wynne,
Zane D'Amico,
Mercedes Stringer,
Benjamin Freeston
Abstract
We present SCI-DEM, a method for deriving Digital Elevation Models (DEMs) of intertidal beach surfaces, profiles and beach widths from time-series waterlines using low-cost coastal CCTV cameras and modelled water levels. SCI-DEM builds on two established components: a waterline extraction method built on a semantic segmentation model, and a camera-pose-estimated homography, used to georeference each waterline. The SCI-DEM-specific contribution is the spatiotemporal aggregation of the resulting waterline time series: over a two-week moving window, waterlines are cleaned, intersected with fixed cross-shore transects, tagged with modelled water elevation (astronomical tide plus sea-level anomaly), and fit with shape-constrained monotonic regression under automated quality control; profiles passing quality control are combined into intertidal DEMs, mean-high-water (MHW) shoreline contours, and per-transect beach-width estimates. We validate SCI-DEM against RTK-GNSS beach-profile surveys at two camera deployments in Southern California, Torrey Pines and Oceanside Harbor South Jetty, and demonstrate its beach-width product at a third, Ehukai Beach Park (Hawaii), a microtidal beach with no survey programme. At all three sites an independently produced CoastSat satellite-shoreline record is shown alongside the camera series. Camera-derived and surveyed profiles agree to a mean absolute vertical residual of 0.09 m (1 October 2024), 0.15 m (20 May 2025) and 0.10 m (6 October 2025) at Torrey Pines and 0.11 m (1 October 2024) and 0.18 m (6 October 2025) at Oceanside Harbor South Jetty. The resulting beach-width time series reproduce the in-situ MHW crossings to within 3.0 m at Torrey Pines and 2.2 m at Oceanside Harbor South Jetty, and follow the same seasonal trends as the tidally corrected CoastSat record. SCI-DEM is currently running on over 60 live cameras. The method offers a cost-effective route to continuous, high-temporal-resolution beach-profile and beach-width monitoring that complements (and densifies) episodic physical surveys.
DOI
https://doi.org/10.31223/X59V4B
Subjects
Environmental Monitoring, Geomorphology, Oceanography
Keywords
shoreline detection, digital elevation model, beach morphodynamics, coastal video, intertidal zone, monotonic regression
Dates
Published: 2026-10-27 09:16
Last Updated: 2026-10-27 09:16
License
CC-BY Attribution-NonCommercial 4.0 International
Additional Metadata
Conflict of interest statement:
All seven authors are employees of Surfline/Wavetrak, Inc., which operates the camera network and the SCI-DEM method described here, and which funded the work; no external funding was received. Co-author B. Freeston is the named inventor on US Patent 10,891,481 B2, assigned to Surfline/Wavetrak, Inc., which discloses the broader automated ocean-sensing framework within which SCI-DEM was developed.
Data Availability:
The validation reference data (SANDAG beach-profile surveys) is publicly available from SANDAG's Shoreline Monitoring Program (https://www.sandag.org/projects-and-programs/environment/shoreline-management/monitoring-program).
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