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Tracking Beach Change
In partnership with the U.S. Geological Survey (USGS), we use aerial photos and Structure from Motion (SfM) technology to understand how and when dunes are shifting.
For the images below: red means beach loss; blue means beach gain.
How does Structure from Motion (SfM) work?
By finding common, recognizable features in multiple pictures—like a unique rock formation, a distinct crack in a cliff face, or a specific log on the beach—a specialized computer program can figure out the 3D location of those features.
To get the raw data for SfM, a plane or drone captures overlapping photos of a stretch of coastline.
Piecing Beaches Together
After capturing a 3D model at one point in time, we can repeat the process a month later or after a major storm, beach nourishment...anything. Then we can compare the 3D models from different points in time. This allows us to calculate:
- Volumetric change: Changes in the volume of material lost or gained on the beach, dune or cliff face. We get a precise number, for example, "the beach lost 500 cubic meters of sand".
- Elevation change: We can also create a map that shows exactly where the landscape rose (accretion) and fell (erosion), and by how much.
- Visualizing the change: By overlaying the 3D models, you can visually compare the before and after states. You can see new landslide scars on a cliff or observe how a sandbar has shifted.
By repeating this process regularly, we can build a historical record to better understand what makes beaches grow and what makes them shrink.
The Moving Shoreline Project
We're developing a custom, community-driven monitoring program to track dune and beach change at Ocean Beach in San Francisco. Please reach out to get involved in this cutting edge citizen monitoring project!
