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Post Wildfire Flash Flood and Debris Flow Guide

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Post Wildfire Flash Flood and Debris Flow Guide National Weather Service Post Wildfire Flash Flood and Debris Flow Guide Created by National Weather Service Los Angeles/Oxnard August 2015 www.weather.gov/losangeles Weather-Ready Nation Purpose of this Guide Post wildfire flash flooding and debris flows are a realistic threat in Southern California for homes and communities located within or along a wildland urban interface that has experienced a recent wildfire. It is crucial to plan and prepare for this type of hazard to prevent and reduce the loss of life and property, and to develop community resilience. The National Weather Service Office in Oxnard, CA has prepared and printed this comprehensive guide in a user-friendly manner with step-by-step guidance on what to do before, during, and after floods that could potentially follow recent wildfires. It is imperative for you to take time to develop a family disaster plan, review emergency prepara- tions and checklists regularly, build disaster supply kits in waterproof, easy-to-carry containers, and stay aware of current weather situations. Monitor statements, watches, and warnings issued by National Weather Service offices and listen to NOAA weather radio and local media broadcasts. The Emergency management community and its partners are committed to keeping Southern California residents safe when there is a threat of flash flooding and debris flows following wildland fires. We ask for your help as well by reading and studying this guide to prepare. You may also visit Weather-Ready Nation at www.nws.noaa.gov/com/weatherreadynation to learn more about NOAA’s initiative about building community resilience in the face of increasing vulnerability to extreme weather events. This guide was prepared by the National Weather Service Forecast Office in Oxnard, CA through funding provided by the NWS Advanced Hydrologic Prediction Service (AHPS). Visit us at www.weather.gov/losangeles. You can also find us on Facebook www.facebook.com/NWSLosAngeles, Twitter www.twitter.com/NWSLosAngeles, and YouTube www.youtube.com/user/NWSLosAngeles. Additional USGS information can be found at: http://landslides.usgs.gov/research/wildfire/ _______________________________________________________________________________ Los Angeles/Oxnard Weather Forecast Office NWS Los Angeles/ Oxnard, CA Southern California Post Wildfire Page 2 Flash Flood and De- 520 North Elevar Street bris Flow Guide Oxnard, California 93030 www.weather.gov/losangeles Phone: (805) 988-6610 NWS Los Angeles/Oxnard, CA Southern California Post Wildfire Page 1 Flash Flood and Debris Flow Guide Acronyms used in this Guide CA - California EAS - Emergency Activation System FEMA - Federal Emergency Management Agency NOAA - National Oceanic and Atmospheric Administration NWS - National Weather Service TADD- Turn Around Don’t Drown USGS - United States Geological Survey WEA - Weather Emergency Alert WRN - Weather-Ready Nation Front cover photo: Camarillo Springs, CA; December 12, 2014; Photo courtesy of the County of Ventura Office of Emergency Services Back cover photo: La Canada Flintridge, CA; February 6, 2010; Photo courtesy of the United States Geological Survey NWS Los Angeles/Oxnard, CA Southern California Post Wildfire Page 2 Flash Flood and Debris Flow Guide What is a Debris Flow? Before fire and rain After fire Soil is trapped on steep rocky hills by vegeta- During summer’s fire season, vegetation is tion. burned, causing sediment to roll down steep hills. Within a few hours or days, channel bottoms are loaded with loose sediment. Rain and runoff During an intense rain, the water and runoff move sediment in the steep channels, producing de- bris flows. Additional post wildfire flash flooding and debris flow web page sources: http://tinyurl.com/ye78vmw http://tinyurl.com/obvoo78 December 24, 2003 Devore, CA Debris Flow Video from the United States Geological Survey (USGS): http://tinyurl.com/nkogbel USGS Emergency Assessment of Post Debris Flow Hazards http://tinyurl.com/pezpzfe Graphics courtesy of Raoul Rañoa http://tinyurl.com/pspptm7 Copyright © 2014. Los Angeles Times. Reprinted with permission. NWS Los Angeles/Oxnard, CA Southern California Post Wildfire Page 3 Flash Flood and Debris Flow Guide Flood After Fire Fact Sheet Floods are the most common and costly natural haz- BE FLOODSMART – REDUCE YOUR RISK ard in the nation. Whether caused by heavy rain, A flood does not have to be a catastrophic event to thunderstorms, or the tropical storms, the results of bring high out-of-pocket costs, and you do not have flooding can be devastating. While some floods de- to live in a high-risk flood area to suffer flood dam- velop over time, flash floods—particularly common age. Around twenty percent of flood insurance after wildfires—can occur within minutes after the claims occur in moderate-to-low risk areas. Property onset of a rainstorm. Even areas that are not tradi- owners should remember: tionally flood-prone are at risk, due to changes to the landscape caused by fire. The Time to Prepare is Now. Gather supplies in case of a storm, strengthen your home against Residents need to protect their homes and assets damage, and review your insurance coverages. with flood insurance now—before a weather event No flood insurance? Remember: it typically takes occurs and it’s too late. 30 days for a new flood insurance policy to go WILDFIRES INCREASE THE RISK into effect, so get your policy now. You may be at an even greater risk of flooding due Only Flood Insurance Covers Flood Damage. to recent wildfires that have burned across the re- Most standard homeowner’s policies do not cov- gion. Large-scale wildfires dramatically alter the ter- er flood damage. Flood insurance is affordable. rain and ground conditions. Normally, vegetation An average flood policy costs around $600 a absorbs rainfall, reducing runoff. However, wildfires year, rates start at just $129 a year for homes in leave the ground charred, barren, and unable to ab- moderate- to low-risk areas. sorb water, creating conditions ripe for flash flooding Plan Ahead. Plan evacuation routes. Keep im- and mudflow. Flood risk remains significantly higher portant papers in a safe, waterproof place. Con- until vegetation is restored—up to 5 years after a duct a home inventory; itemize and take pictures wildfire. of possessions. Flooding after fire is often more severe, as debris Everyone is at risk for spring flooding, yet many re- and ash left from the fire can form mudflows. As main unprotected. Just a few inches of water can rainwater moves across charred and denuded cause tens of thousands of dollars in damage. The ground, it can also pick up soil and sediment and average flood claim in 2010 was approximately carry it in a stream of floodwaters. These mudflows $28,000, and without flood insurance, many must can cause significant damage. cover the costs to repair or rebuild on their own. For example, in June 2011, the Las Conchas Wild- Residents should consider their risk and the conse- fire charred more than 150,000 acres in New Mexi- quences of a flood event, and make the choice to co. One month later, heavy rains flooded the burn protect themselves. area, prompting a Presidential Disaster Declaration. Visit FloodSmart.gov (or call 1-800-427-2419) to learn more about individual flood risk, explore cover- age options and to find an agent in your area. NWS Los Angeles/Oxnard, CA Southern California Post Wildfire Page 4 Flash Flood and Debris Flow Guide Flood After Fire Risks Floods are the number 1 natural disaster in the almost anywhere, but the most commonly af- United States. Flooding causes damage and fected states are Arizona, California, Idaho, Ne- destruction across all regions, wiping out vada, Oregon, and Washington. homes and businesses. However, many resi- Heavy Rains dents and business owners are unaware that they qualify for flood insurance. You can take Excessive amounts of rainfall can happen steps to reduce the financial impact of flooding throughout the year, putting your property at before disaster strikes. risk. Properties directly affected by fires and those located below or downstream of burn are- One important step is understanding your risk. as are most at risk for flooding. Wildfires dramatically change landscape and ground conditions, which can lead to increased Flash Floods risk of flooding due to heavy rains, flash flood- A flash flood is a rapid flooding of low-lying are- ing, and mudflows. as in less than 6 hours, which can be caused Residents and business owners are urged to by intense rainfall. Flash floods are known to purchase flood insurance now to guarantee fi- roll boulders, tear out trees, and destroy build- nancial protection from flooding. There typically ings and bridges. is a 30-day waiting period before flood insur- Mudflows ance takes effect. But the Biggert-Waters Flood Mudflows are rivers of liquid and flowing mud Insurance Reform Act of 2012 allows for an ex- on the surface of normally dry land, often ception to the waiting period in certain cases caused by a combination of brush loss and sub- where property is affected by flooding on sequent heavy rains. Mudflows can develop burned Federal land that is a result of, or is ex- when water saturates the ground, such as from acerbated by, post-wildfire conditions. For more rapid snowmelt or heavy or long periods of rain- information, please contact your insurance fall, causing a thick, liquid, downhill flow of agent. earth. Mudflows are covered by flood insurance Flood after Fire: The Risks but are different from other non-covered earth You may be at an even greater risk of flooding movements where there is not a flowing char- after a wildfire. Normally, vegetation absorbs acteristic—such as landslides or slope failures. rainfall, reducing runoff. However, wildfires leave the ground charred, barren, and unable to To learn more about your risk for flooding and absorb water, creating conditions ripe for flash how to prepare for floods, visit flooding and mudflow.
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