UAV Lidar-Based Debris Basin Capacity Assessment Following the 2025 Eaton Wildfire and the Presidents' Weekend Storm, Los Angeles County

In the aftermath of the January 2025 Eaton and Palisades wildfires in Los Angeles County, assessing the capacities of debris basins is critical for forecasting potential hazards associated with upcoming rain events. This report provides a low-cost, efficient assessment of debris basin capacities using UAV-based lidar surveys to provide high-resolution topographic data. We conducted surveys of 14 debris basins in the Eaton Fire area to quantify the change in capacity following the Presidents’ Day weekend storm event (February 13-14, 2025). For some basins, we conducted repeat surveys following the storm to assess if significant dewatering had occurred (i.e., to better measure debris volumes vs. water volumes). We found that the storm delivered approximately 480,000 cubic yards of debris to the 14 surveyed basins, filling the basins to amounts ranging from 12 - 59% of their design capacities. The results from this study are intended to support emergency management agencies by (i) prioritizing debris basin cleanouts, (ii) calibrating and validating debris flow models for the burned catchments, and (iii) forecasting potential debris flow risks for upcoming storm events.