Post-Wildfire Debris Flow and Large Woody Debris Transport Modeling from the North Complex Fire to Lake Oroville, CA, USA

A combination of debris flow modeling, hydrologic and hydraulic modeling, and large woody debris transport modeling are used to assess the magnitude of LWD transported from medium and small watersheds to Lake Oroville. Debris flow modeling, triggered by a 1-year rainfall intensity, from 13 watersheds, transported 1,073 pieces (1,579.7 m3) of LWD entrained from the ground in tributary streams to the Middle Fork of the Feather River and deposited on alluvial fans. Large woody debris transport modeling was performed for 1-, 2-, 5-, 25-, 50-, 100-, and 500-year flows. The LWD transport ratio increased with discharge as expected. A 2-year event was capable of transporting LWD to the reservoir with a transport ratio of 25% with no removal of LWD and 9% with removal of LWD greater than the cross-section width (simulating woody debris jamming). The 500-year event produced transport ratios of 58% and 46% in non-removal/removal scenarios.