VOLUME OF SLOPE FAILURES CAUSED BY HURRICANE MARÍA IN PUERTO RICO USING LIDAR AND SFM

Hurricane Maria triggered tens of thousands of mass wasting sites across Puerto Rico in 2017. Sediment liberated at slope failure sites and transported into the fluvial system is important for the local system, especially given the limited storage capacity at many vital mountain freshwater reservoirs. In recent years, the reduction in capacity has contributed to widespread water rationing during the annual dry season.

The use of LiDAR and SfM datasets for the detailed study of landslide size, geometry, and volume change was undertaken as a pilot study for change detection at selected mass wasting sites in the island. Both the USGS and the NASA G-LiHT LiDAR datasets were collected before and after the passage of the hurricane. Additionally, Unmanned Aerial Vehicle (UAV) imagery was collected from three of the largest mass wasting sites on the island. The UAV imagery was converted to Digital Surface Models using the SfM technique. Each of the UAV sites included several Ground Control Points that were surveyed with RTK GPS/GNSS base-rover antennas. LiDAR data and SfM generated models were used to calculate volume change at 19 sites in the municipalities of Naguabo, Lares, Barranquitas, and Río Grande.

The results were compared with area-volume scaling-values for shallow and bedrock constants (Larsen et al. 2010). The values from the LiDAR and SfM analyses show that the published area-based scaling values may not be reliable for volume estimates for the sites in Puerto Rico, however the number of sites explored (n=19) is very small. Future work will include much more change detection analyses using a complete polygon inventory of failure sites from the event. It will also be important to better understand the efficiency and timing of sediment movement downstream of landslide scars in order to make projections for future extreme events. In addition, the local area-volume relationship will be explored with regards to other important site-specific factors such as local geology, soil, and slope.