Part 1 (July 9 Daily Sun) covered the huge community response to the Museum Fire. This column discusses the science being done by U.S. Forest Service and Northern Arizona University to assess the watershed and determine the most effective ways to recover from this fire. These efforts involve collection of data -- lots of it -- to make informed decisions about the best ways to accelerate the watershed recovery process.
Even before the Museum Fire was contained, Forest Service specialists in soil science, hydrology, engineering, geographic information systems, wildlife, archeology, botany, recreation and geology started to survey fire impacts as part of the Burned Area Emergency Response (BAER).
The burn-area severity map was created based on flights to assess reflectance, coupled with transects to ground-truth soil and vegetation conditions.
Aerial mulching utilizing shredded wood from forest treatment operations was then carried out in the fall of 2019 by the Forest Service BAER team on 170 acres of the eastern and central burn scar. According to retired Forest Service soil scientist and monitoring team member Rory Steinke, “Mulching is done to slow water down on burned steep slope soil surfaces to protect soil productivity [and] reduce erosion, risk of flooding and debris flows downstream ..."
Rain and stream flow gauges and cameras were set up by Coconino County and the City of Flagstaff to establish a flood alert system, and flood modeling of the watershed was begun.
According to Joe Loverich at JE Fuller, the flood model incorporates watershed elevations and all the data collected by the Forest Service (e.g., soil types, vegetation reduction, extent of soil damage due to the burn) to estimate how much water would run down Spruce Avenue Wash given a certain amount of rainfall and how fast it falls. Rainfall amount, intensity and duration are the key variables: the wash can handle an inch of rain per hour but given more rainfall per hour (2 inches per hour or more for example), significant flooding will likely occur in the downstream neighborhoods of Paradise, Grandview and Sunnyside.
Rebecca Beers (2020 MS graduate of NAU’s School of Earth and Sustainability) is trying to better understand the current flooding hazard and how that hazard might evolve over time. Her work is funded by the USFS Rocky Mountain Research Station.
Rebecca initially made infiltration measurements to gauge the extent of watershed damage from the fire and measured erosion using both “rill” and “channel head” measurements to compare areas treated by aerial mulching versus those not treated. These measurements are being repeated over time to determine the amount and rate of change.
Rebecca is also using drones to make high-resolution 3D images of selected portions of the watershed. This technique allows detection of small changes resulting from erosion by assembling the images into 3D mosaics and comparing them using a computer program that can detect and quantify small differences. Her goal is to assess over time how the burn scar is changing in response to rainfall and debris flow events, and to gauge both the rate and nature of watershed recovery.
With support from the National Science Foundation, Ryan Porter at NAU leads a team of seismologists deploying an array of seismic listening devices (seismographs and geophones) to detect initiation of debris flows on the burned watershed. During 2019, they detected a small debris flow that fortunately did not reach town where it could do real damage. If the technique proves effective, seismographs could be another element in an early warning system for post-fire flood events.
The team has also set up motion-activated game cameras to catch a debris flow in the process of forming. It is only a matter of time before an actual debris flow rumbles by the cameras.
These studies take time to yield results, but in the long run they will help mitigate flood risk and accelerate the recovery from wildfires like the Museum Fire. In the meantime, we have to stay prepared for possible floodwaters by maintaining existing barriers in place.
Monitoring the watershed during the recovery process and continuing to help it recover at the fastest rate possible from this very impactful fire are both essential to putting the Museum Fire truly in Flagstaff’s past.
John Noll is a retired geologist and two-year volunteer Roving Ranger. Karen Malis-Clark is a 9-year Roving Ranger and former deputy public affairs officer for CNF, who comes out of retirement to assist with fire information. The authors thank Ed Schenck (City of Flagstaff’s storm water manager), Joe Loverich at JE Fuller, Ryan Porter and Rebecca Beers at NAU, retired Forest Service soil scientist Rory Steinke and the BAER team for their generous sharing of expertise about the Museum Fire.
The NPS/USFS Roving Rangers volunteer through a unique agreement between the Flagstaff-area national monuments and the Coconino National Forest to provide interpretive ranger walks and talks in the Flagstaff area each summer.
Submit questions for the Ask a Ranger to firstname.lastname@example.org.
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