QGG STANLEY A. SCHUMM AWARD: CHANNEL REFILL PROCESSES FOLLOWING POST-FIRE DEBRIS FLOWS, PINALEÑO MOUNTAINS, ARIZONA, USA

In the Pinaleño Mountains in southeastern Arizona, fire severity has increased substantially while high severity fire recurrence intervals have decreased, leading to a change in landscape response to precipitation events. This altered landscape response to precipitation has led to an increase in surface runoff and increased debris flow activity. In general, debris flow initiation processes have been thoroughly investigated; however, the longer-term processes acting on the landscape between debris flow events are poorly understood. These processes are imperative to study because they influence how quickly the debris flow-scoured channels refill with sediment, directly influencing debris flow recurrence intervals. In the Pinaleño Mountains, we studied four drainages to better understand landscape response to fire. Specifically, we investigated how the landscape is currently responding to the 2017 Frye Fire and subsequent debris flow events. We chose to study the 2017 events to determine how quickly scoured channels are refilling with sediment, therefore setting the stage for subsequent debris flows. We also investigated the history of debris flow events in the Pinaleño Mountains using stratigraphy exposed by the recent 2017 debris flow events. Our research intends to: (1) determine the interval of channel filling prior to the 2017 debris flows in Wet Canyon and Ash Creek, (2) identify surface processes that have delivered sediment to the Wet Canyon channel in the past, (3) determine which processes are currently delivering sediment to the scoured channel in Wet Canyon, (4) estimate channel margin sediment volume availability in Wet Canyon, (5) estimate sediment volume remaining in the unscoured channels of Twilight Canyon and Frye Canyon, and (6) determine the rate of sedimentation in Wet Canyon represented by the stratigraphic record exposed by its recent debris flow. For our study, we used GIS-based reconnaissance, radiocarbon dating of charcoal samples, structure-from-motion surveys, as well as shallow seismic and ground-penetrating-radar surveys. Preliminary results suggest that the 2017 post-fire debris flow events are unprecedented, which may imply a new state governing the longer-term processes acting on the landscape and alter debris flow recurrence intervals on the Pinaleño Mountains.