Flagstaff addresses flood damage after record rainfall
Gov. Doug Ducey issued a declaration of emergency last month after a 200- to 500-year rainfall event hit the Museum Fire burn scar in Flagstaff on Aug. 17 and flooded streets. It was the largest rainfall event in the area to date.
Restoration and mitigation efforts being discussed by the city will soon be underway.
The number of private properties in Flagstaff with interior or exterior damage from the multiple flood events is now at 88. The city of Flagstaff estimated the cost of damages to be just over $1 million. In addition, 33 public properties were damaged, adding up to $2.3 million.
The Museum Fire ignited on July 21, 2019, and was not fully contained until Aug. 12 of that year, burning 1,961 acres within the Dry Lake Hills area just above Flagstaff.
A couple of years later, on Aug. 17, about 2 to 3.5 inches of rain fell within one to two hours on the Museum Fire burn scar. Gauges on the south and west sides recorded 1.14 inches within 15 minutes and 1.06 inches at the east gauge. In addition, 1.22 inches of rain fell on Linda Vista Drive and 1.5 inches on downstream neighborhoods.
The post-wildfire flood came down Mount Elden, along Paradise Road and Grandview Drive, across Cedar Avenue, through the Sunnyside neighborhood, and over Route 66. Mount Elden Estates, Grand View and Sunnyside neighborhoods experienced flooding. Many corner homes experienced the worst of the flooding and accumulated mud and debris. Flows were approximately 1 to 2 feet deep.
As a result of the flood, roads closed, storm drains and culverts clogged, yards filled up with mud and debris, and 14 homes had water inside. The hallways of Killip Elementary School flooded with 2 to 3 inches of water as well.
According to Sarah Langley, analyst for the City of Flagstaff, the flood damage is unlikely to exceed thresholds for assistance from FEMA. This means homeowners will not receive the aid of low-interest loans and are encouraged to secure insurance for flood damage.
External Affairs Officer for the U.S. Department of Homeland Security, Veronica Verde, explained in an email to The Arizona Republic, “If an incident is of a severity and magnitude that resources needed to recover are expected to exceed local, state, or tribal government capability, the state can request a Joint Preliminary Damage Assessment (PDA) from FEMA to validate damage and evaluate impact.”
Thus far, FEMA has not been asked
by Arizona to perform a PDA for the Aug. 17 flood event.
However, after the first flood in July, Coconino County secured $600,000 in funding from the National Resources Conservation Service for emergency channel stabilization in Mount Elden Estates. The project, which was completed before the Aug. 17 flood, included rock structure placement, minor grading and area cleanup to decrease serious erosion.
Government officials showed foresight in the post-wildfire situation. With modeling technology, the exact path of the flood was predicted and the public informed by mail.
Paula Swenski, a resident in Sunnyside neighborhood, said her neighbors had called her the crazy sandbag lady, but as an ex-wildland firefighter for the forest service she recognized the flood risk of a scorched earth as well.
“I took all that information in and realized I’m right in the floodplain. I believe the rest of the community didn’t digest that reality and most folks are renters in my neighborhood,” Swenski said.
Officials told residents specific actions they could take to protect themselves and their property. Swenski noted that after two seasons of dry weather, they were advised to not remove sandbags and more would be provided if not in place already.
“I noticed all throughout Sunnyside not many people had put sandbags up and I scratched my head over that and thought, ‘Wow, okay. Folks just aren’t listening.’ They just didn’t believe it could happen. All the sandbags you see now in place were post-flood. So I think the government did the best they could under the circumstances,” Swenski said.
Swenski’s house is positioned higher than those on the other side of the street, so her property was not touched by the water, but she feels assured the sandbags will prevent future damage.
According to Swenski, “looky-loos,” or non-local traffic, driving through the neighborhood to look at the flood created wakes that pushed the water farther onto the sidewalk.
Officials address future flooding
On Aug. 27, during the Coconino County Engineering Summit, several agencies streamed their report of the August flooding.
In attendance were engineers from multiple consulting firms, the City of Flagstaff, Flood Control District, Federal Emergency Management Agency, Arizona Department of Water Resources, Department of Transportation, and the U.S. Forest Service.
Deputy County Manager and Flood Control District Administrator, Lucinda Andreani, started the summit by saying there were high level ideas that came forward and tremendous brainstorming, but they still need to look at the feasibility of the concepts.
Feasibility criteria that will be considered are technical, financial, legal, environmental and cultural, according to Andreani. Everything requires a costbenefit analysis and once feasibility is determined then restoration and mitigation projects will be accepted or rejected.
According to Langley, the city is working on mitigation for 5- to 25-year post-wildfire storms while “the current drainage structure is built to manage the 100-year flood event from normal non-fire flows.”
Andreani similarly said, “All those factors of feasibility won’t let us design to every storm. What we do will help reduce the impacts during larger storms but it won’t eliminate them.”
At the summit, it was determined that forest and watershed restoration are the first key steps and fundamental to all other projects. The Schultz Fire, which burned 15,000 acres in 2010 and triggered dozens of floods that killed a 12-year-old girl, provided understanding for actions to take with the Museum Fire floods.
Every storm is unique so the summit team is watching how the watershed is impacted and what that looks like downstream.
Andreani said that “52% of the watershed burned and if the remainder of that watershed burns, anything we design downstream will be compromised.” The first priorities are mitigation upstream for this reason, but also because infrastructure changes are costly, she said.
“The objectives at the top of the watershed are to reduce sediment load, the large woody debris coming downstream and plugging the system, restore the forest in non-burn areas and place an alluvial fan,” said Julie Leid from Peak Engineering, also present during the summit.
Alluvial fans do not require as much maintenance because their primary purpose is for sediment and debris removal. Sediment removal helps the systems in place function better than in the conditions of flows right now, Leid said.
Channel stabilization is another mitigation strategy, but it is challenging because the terrain in the upper watershed is so steep that machinery and equipment cannot access it to perform work, according to Leid. Channel stabilization might not work well for the Museum Fire flood area and Spruce Watershed because there’s not many wide channels with gradual grades.
The U.S. Forest Service has approved channel widening and possibly a permanent barrier at the top of Paradise Road. “This is great news and work that we can move on very soon” said Leid.
For mitigation downstream, Leid said, “We need to look for bypass and additional conveyance at the Linda Vista crossing.” The conveyance would be an underground storm drain or pipe that goes east or west of Grandview Drive, behind Mount Elden Middle School or through the city-owned parcel off Cedar Avenue.
Attenuation is being considered at East Park Way as well. Attenuation is where water is held back and slowly released over an extended period of time.
In north Sunnyside, detention is underway at Killip Elementary School. Detention basins provide flow control through storage and attenuation of storm water runoff.
Other mitigation ideas for Sunnyside are to maintain the 60-inch storm drain, harden the channel to help with erosion and efficiency and add conveyance east or west in the neighborhood where there are not underground infrastructure conflicts. Possibilities for south Sunnyside include detention on the undeveloped area of Route 66.
According to Andreani, in order to restore the area, the Emergency Watershed Protection Program needs to be refunded through the Natural Resources Conservation Service. The EWP Program is administered by NRCS and helps local communities quickly recover after a natural disaster.
Since July 2019, the county’s Flood Control District has spent $3.4 million on mitigation and emergency response efforts in the Museum Flood area. The City has also spent $1.8 million since July 13.