In a Nutshell: Overview of post-fire flooding including how flood mitigation structures impacted downstream flow.

Presenter: Rebecca Beers, Research Scientist, Arizona Geological Survey at University of Arizona

Description: The 2019 Museum Fire burned nearly 2,000 acres of steep forested terrain abutting Flagstaff city limits in northern Arizona. In addition to the immediate fire danger, post-fire flooding posed a significant threat to the downstream community and critical infrastructure, prompting a multi-agency cooperation to evaluate post-fire runoff and geomorphic change during the recovery period (Fall 2019 to present). Uniquely, the burn scar experienced two record-dry monsoons in 2019 and 2020 with minor runoff, followed by a significantly wet monsoon in 2021 resulting in multiple post-fire flow events and damage to areas identified to be at risk. The timing of these flow events proves relatively rare as most burn scars in the Southwest experience their first major runoff events between a few weeks and months following fire, with severity of runoff events generally decreasing with time as the scar recovers. This presentation provides a detailed, multi-year documentation of geomorphic change and recovery in the Museum burn scar throughout its unusual recovery history. Additionally, in response to the 2021 flood events, flood mitigation structures were constructed on the floodplain below the Museum scar; the impact of 2022 monsoonal runoff on these structures is currently being evaluated in context with watershed recovery and will be available for future discussion.

Hosted by the Southwest Fire Science Consortium.