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  • Bighorn Fire Flood Risk

    Bighorn FireThe Bighorn Fire has increased the risk of flash floods and mudflows in the foothills of the Catalina Mountains. Pima County residents living adjacent to washes downstream of the Bighorn Fire burn area should be aware of the increased risk of flooding due to the fire and take appropriate steps to mitigate that risk. Loss of vegetation and physical changes to the soil leave burned areas prone to increased runoff and erosion. This combination can cause flash floods and mudflows to flow faster and with more volume than normal flows during a typical monsoon storm. These flows, which can include ash, mud, and vegetative debris, increase flood risk for those who work and live in downstream areas. A post-fire flood video from the Canada Del Oro Wash following the Bighorn Fire is a small example of what can happen after wildfires.

    A debris flow in Canada del Oro Wash following a minor rainFlash floods may overtop wash channel banks and cause damage in adjacent areas, even beyond the limits of the regulatory flood. After the Aspen Fire on Mount Lemmon in 2003, flash floods and mudflows resulted in at least one reported fatality and caused extensive property damage in watershed areas downstream of the burn area. 

    Before the fire was even extinguished, the District was working with JE Fuller Hydrology & Geomorphology, Inc. to do floodplain modeling under pre-burn and post-burn conditions. This report is titled Bighorn Fire: Post-fire Flood Risk Assessment. For a comprehensive overview of the Bighorn Fire and flood preparedness plan, please see the County Administrator's July 22, 2020 memorandum "Big Horn Fire Flood Preparedness Plan"  

    For more information on post-fire flood hazards, please visit the Floods Follow Fires page.

    What can you do?

    Sign up for MyAlerts. The Pima County Office of Emergency Management’s MyAlerts (http://myalerts.pima.gov system allows the Regional Flood Control District to provide near real-time flood alerts to Pima County residents within certain watersheds. Residents who sign up for MyAlerts using addresses within these watercourses will receive messages about flood events in their area. This warning system is the most effective way for the Flood Control District to notify residents about flood events. Find additional information about the MyAlerts Flood Alert Messaging webpage at www.pima.gov/floodalerts.

    Get Flood insurance. Disaster relief for private property is almost unheard of and after the flood is too late to get flood insurance. The Flood Control District recommends that you acquire flood insurance immediately. The cost does not change due to the fire and you may be surprised how inexpensive it is, especially if your structure is not within a FEMA Special Flood Hazard Area. Ask your insurance agent about a Preferred Risk Policy. 

    The Bighorn Fire was officially declared contained on 7/23/2020. Property owners, renters and businesses have 60 calendar days from that date to purchase flood insurance that qualifies for a potential exemption to the usual 30-day waiting period for coverage.

    Pima County Board of Supervisors Chairman Ramon Valadez urges you to obtain flood insurance as well.

    Protect your structure(s). A common response to the threat of flooding is to protect ones entire property. However, frequently some of that land is necessary to convey flows and obstructing the flow path risks adversely affecting other properties. The best course of action is to identify ways to protect your residence from flood damage. The use of sandbags in the doorways, or small diversions just upstream of the residence is usually the most effective way to protect the residence while leave the rest of the property open to flow. Protecting more than just your structures may cause harm to your neighbors and leave you open to civil lawsuits. It may also be a violation of the Floodplain Ordinance, leaving you open to enforcement action and fines.

    Create an Emergency Response Plan. An Emergency Response Plan should include preparing “go bags” to help you and your loved ones get out of harm’s way quickly, the fastest route to high ground and safety, and keeping in contact with friends and family.


    Pima County is providing a limited number of sandbags for impacted properties, available at:

    • Department of Transportation facility at 1313 S. Mission Road (724-6410);
    • Brandi Fenton Memorial Park in the northwest dirt parking lot;
    • In Summerhaven on Carter Canyon Road at the north side of Snyder Road and Lason Lane; and
    • The Town of Oro Valley is providing sandbags at Naranja Park in the Christmas tree drop off lot located just north of the Archery Range along the entry drive.

    Post-fire Flood Maps

    Within the first week of the start of the Bighorn Fire, the District was already working with a contractor to develop floodplain maps accounting for the increased flood risk due to the fire. The District has obtained preliminary floodplain maps for the 100-year storm showing the area expected to be flooded by this storm in the aftermath of the fire. Additional maps may be found in the following report: Bighorn Fire: Post-fire Flood Risk Assessment

    It is extremely important to keep the following things in mind when looking at these maps:

    • The floodplain shown is based on computer modeling using the best available data.
    • The floodplains shown do NOT account for debris flows that may clog channels and divert flow in unexpected directions and/or intensities.
    • The floodplains shown do not account for walls, fences, and other similar improvements that may divert flow.
    • The floodplains shown do not account for storms larger than the 100-year storm. 
    • Damaging floods from storms smaller than the 100-year storm are expected. The affects of the Bighorn Fire may turn otherwise harmless storms into damaging floods.

    Post-Bighorn Fire Flood Inundation Maps


    Post-fire Flood Impacted Property Notifications

    Property owners with structures that may be subject to additional risk due to the effects of the Bighorn Fire have been notified by mail by the District. Those outreach packets included the following information:

    Notification letter to private property owners
    - Notification letter to business owners
    Flood After Fire infographic
    Floods Follow Fires fact sheet
    Preferred Risk Policies
    My Alerts brochure

    Notification letters were sent to properties in the following watersheds: Canada del Oro, Esperero, Finger Rock, Golder, Pima, Rooney, Sabino, Steampump, Sutherland, Valley View, and Ventana. The notifications for Steampump and Rooney washes were sent in cooperation with the Town of Oro Valley.


    The increased risk of flooding in the aftermath of the Bighorn Fire has received a lot of media attention. Some examples are provided below.

    • "Bighorn Fire Aftermath: Experts Warn of Higher Flood risk Near Burned Areas"  - AZ Star, June 16, 2020
    • "Bighorn Fire: County Preps for Flood Risk After Fire" - KGUN 9, June 17, 2020
    • "Floods Follow Fires: Leaders Prepare for Post-Bighorn Fire Monsoon" - KOLD, June 27, 2020
    • "Floods Follow Fires" - Pima County Sheriff's Department, July 2, 2020
    • "Experts say Pima County Residents Should be Concerned About Flooding amid Bighorn Fire" - KVOA, July 2, 2020
    • "Pima County Urges Residents to get Flood Insurance Ahead of Monsoon" - KOLD, July 2, 2020
    • Public Service Announcement from Pima County Supervisor Ramon Valadez
    • "Mt. Lemmon Tour Flood Concern" - Pima County Sheriff's Department, July 10, 2020
    • "Crews Prep Tucson-area Washes Before Monsoon Flooding" - KOLD, July 15, 2020
    • "Flash Flood Carries Bighorn Fire Debris Along Channel Outside Tucson" - UK News Yahoo, July 17, 2020
    • "Bighorn Fire Debris Begins to Flood Into Washes Amid Monsoon Season" - KOLD, July 17, 2020
    • "Bighorn Fire Debris Floods Canada Del Oro Wash" - KGUN, July 17, 2020
    • "Flash Food After the Bighorn Fire in the Catalina Mountains, Tucson, AZ" - Reddit Post, July 17, 2020
    • "TFD Warns Public About Runoff from Bighorn Fire" - KOLD, July 17, 2020
    • "Video Featuring Ash-mud Slide Filmed in Pima County Goes Viral" - KVOA, July 17, 2020
    • "Pima County Prepares for More Runoff From Bighorn Fire" - KGUN, July 17, 2020
    • "Blackened Runoff Seen in Tucson-area Wash May be Just the Beginning, Flood Experts Warn" - AZ Star, July 19, 2020
    • "Streaming River of Black Sludge Floods Through Arizona" - Live Science, July 20, 2020
    • "Flash Flood in Arizona Triggers Torrent of Wildfire Debris; officials Warn of Risks After Blaze Near Tucson" - Fox News, July 20, 2020
    • "Deadly River of Black Sludge Filled with Debris Filmed Flooding Through Arizona After Wildfires" - The Irish Sun, July 21, 2020
    • "What the Hell is this River of Black Sludge Oozing as a Result of Arizona" - Inside Wales, July 21, 2020
    • "Rain triggers a flood of steaming muck near Arizona wildfire. Officials warn it can happen again" - Erie News Now, July 22, 2020
    • "Bighorn Fire Aftermath: Official Warn of Flash Flood Danger, Close Mount Lemmon" - Tucson Local Media, July 22, 2020
    • "В Аризоне опасаются внезапных селей в пострадавших от природного пожара района ( Google Translate
    • "This Oozing Black River of Sludge Makes Its Way Through Arizona" - Interesting Engineering, July 23, 2020
    • "Hell Runeth Over" - The Cut, July 23, 2020
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    Regional Flood Control District

    201 N. Stone Avenue, 9th Fl.
    Tucson, AZ 85701

    Phone: (520) 724-4600
    Fax: (520) 724-4621

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