Post-wildfire hydrogeomorphic risk management assessment

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We continued to monitor streamflow and precipitation at an existing hydrologic monitoring network at the Grizzly Creek Fire, CO. Through analysis of this long-term dataset, managers may better plan for infrastructure impacts multiple years post-fire. Next, to evaluate the performance of existing post-fire decision criteria and assess potential improvements, we developed the Post-fire Decision Criteria Assessment Framework. We applied this framework to the Grizzly Creek Fire, CO (2020) and specifically evaluated the decision criteria for highway safety closures applied by the Colorado Department of Transportation (CDOT) to Interstate (I-) 70 within Glenwood Canyon, CO between Dotsero and Glenwood Springs in the first three years post-fire (2021-2023). We defined the infrastructure impact (referred to as ‘impact’) as any instance where I-70 was closed by the Colorado Department of Transportation beyond the end of the precipitation event for maintenance or cleanup associated with flooding or sediment. We
identified a total of 20 safety closure decisions reported by CDOT over the study period and classified each decision into one of three performance categories: true positive (preemptive closure and impact occurred), false positive (preemptive closure and no impact occurred), and false negative (no preemptive closure but impact occurred, resulting in emergency closure). We found that the performance of the safety closure decision criteria varied over the study period in alignment with the Colorado Department of Transportation’s aim of protecting travelers’ safety while reducing unnecessary safety closures without impact. Decisions that resulted in compromised traveler safety or unnecessary closures were considered poor performance. We identified that precipitation-based metrics including precipitation event depth and short-term intensity (i.e. 15-minute) were significant indicators of impact to I-70. Soil moisture-based metrics may be a good secondary indicator but further analysis with a larger dataset is needed. This framework is applicable across burned watersheds and to other infrastructure impacts of interest, such as for water intake shutdown.