Mosquito Creek
In September of 2017 the Eagle Creek Wildfire burned 48,000 acres of rugged and densely vegetated terrain in the Columbia River Gorge, near Cascade Locks Oregon. Studies have shown that in steep mountainous terrain, this type of event can trigger large debris flows, however the timing and scale of such events is still highly unpredictable. In early 2018, airborne LiDAR was collected by NCALM for baseline monitoring of the wildfire area, knowing there would be widespread mass wasting events taking place in the near future. Due to the extreme terrain in the region, an interstate, railroad, and historic highway are all built along the Columbia River shoreline. In January 2021, significant precipitation events across the Eagle Creek wildfire area led to increased debris flow activity, with over 20 documented from Mosquito Creek alone, with its largest debris flow crossing the historic highway and railroad, nearly reaching Interstate-84. Within hours, Elevate was contracted by ODOT and a geotechnical engineering firm to collect reconnaissance imagery to better understand where the material came from and whether there was more unstable material upslope. Leveraging high resolution RGB and thermal infrared imagery it became clear there were numerous springs contributing to headwall erosion 1,400 feet above and 2,300 feet away from the highway. A high zoom camera was used to conduct a more detailed inspection of the source area, locating a fresh 5-foot high headwall 50 feet upslope from the springs, indicating there will be more debris flow events in the very near future. This critical information gave the geotechnical engineer onsite enough information to keep the historic highway closed, and initiate an emergency contract for a geotechnical engineering firm to investigate and address these issues.
Material covering the historic highway and railroad after a large debris flow in January 2021.
A shaded relief map derived from UAS LiDAR is overlaid by a false color raster illustrating the elevation changes that occurred between 2018 and March 2021. Cool colors indicate where the elevation decreased and warm colors indicate where the elevation increased.
Elevate was part of the team tasked with solving this problem. and temporal remotely sensed data to monitor this active site. In March 2021 high resolution imagery and high density LiDAR was collected to capture baseline data of the current conditions within the Mosquito Creek drainage. Due to the extreme relief of the Columbia River Gorge, flight planning was essential in order to get data coverage across the entire area and within the deep narrow canyon where debris flows were channeled. Additional analysis using the historical (2018) LiDAR was critical for accurately characterizing the dangerous and dynamic processes taking place within Mosquito Creek. It provided context to the geologists and engineers so they could understand the volume of material that had been mobilized, where it was being deposited, and begin to design a mitigation system. Over the next 2 years, Elevate captured an additional 3 data sets of the project area, providing critical elevation and as-built models to the engineers designing a diversion berm. This system was constructed to divert future debris flows away from the historic highway and railroad, and into a containment basin, which could be safely accessed to haul material off-site.