Larry Collins reports on the hazards faced by Southern California firefighters when floods and mud and debris flows follow wildfires. Four years after deadly fire storms swept across Southern California and burned thousands of homes, it happened again. In October and November 2007, an unprecedented...
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- Recognition of conditions contributing to mud- and debris-flow potential.
- Understanding that the first "wave" of mud and debris may not signal the end of the event, but merely the beginning. Frequently, multiple "waves" of mud and debris will follow the first. The ensuing waves may be larger than the initial flow.
- Do not commit personnel to hazard areas without establishing an upstream spotter (to warn of additional "waves"); a warning system; proper safety equipment; and an escape plan.
- Mud/debris flows (like water) generally follow the path of least resistance. They tend to follow stream beds. However, the large amount of solid material within them may block channels, diverting flows elsewhere, and completely changing the hydrology in a matter of seconds.
- A solid object is only 22% of its normal weight when it is being moved by a flow. Rocks and huge boulders may roll or even float in the flow.
- In some areas below major burns, entire neighborhoods may be buried.
- Severe flash flooding independent of debris flows is possible in adjacent areas that have not been burned. This may cause other problems for rescuers.
- Flooding and mudslides may completely block access to many areas. Bulldozers, helicopters, four-wheel-drive vehicles and other special transportation will be needed. In some cases, all these modes may be ineffective, and hiking in by foot may be required.
- Some events may create life-threatening conditions to rescuers. In these cases, all search and rescue efforts may be delayed until water and mud stops flowing, until hillsides can be secured, until daylight breaks or until weather conditions abate.
- In some cases, the most prudent action is total evacuation of entire canyons and other endangered areas as a precaution for the approach of major storms.
- Special equipment, tools and supplies will be required to conduct rescue operations when mud and debris flows occur. Required items may include plywood, screw jacks, pipe, four-by-four-inch and six-by-six-inch wood struts, airbags, umbilical air self-contained breathing apparatus (SCBA) systems, shovels, buckets, hammers, nails, "avalanche poles" and swiftwater rescue gear.
- Search-dog teams may save victims if promptly dispatched.
- There are effective methods to rescue victims buried in void spaces created by mudslides. All personnel should become familiar with the basic "game plan" for these rescues.
- Fire crews and other sources of manpower will be especially important to rescue efforts.
- Nighttime operations may be especially dangerous. Anyone who has operated at a nighttime rescue in the rain knows that visibility and communications may be extremely poor. Personnel efficiency is down due to wet, cold, muddy conditions. Upstream safety personnel may not see a wall of mud and debris until it is too late. Personnel committed to a rescue operation in the danger zone will be even less likely to escape in time if something goes wrong. The most extreme caution should be used for operations at night.
- Unified command is likely to be required because multiple agencies may be involved.
- A systematic approach should be used when homes and vehicles are buried. Thorough search, documentation of results and marking of sites should be accomplished. Use the international USAR collapse-site marking system adopted by the California Office of Emergency Services and FEMA USAR task forces.
- Victims may be alive inside structures buried in mud and debris, even if a structure is completely covered. Access via the roof may be necessary. This may require traditional truck company ventilation/access techniques (cutting through the roof with axes and chainsaws). Victims may be trapped in void spaces.
- Live victims may have "floated" to ceilings as mud entered a structure. Therefore, use only shallow chainsaw swipes when cutting through the structure into the living spaces to prevent injuring victims. Use search cameras to look before cutting when possible.
- Trench-collapse rescue materials and techniques may be required to make access and conduct rescue.
- Access may be made via helicopter, aerial ladder or multiple ladders laid over the mud to spread the weight of rescuers and prevent sinking, or plywood for the same purposes. Heavy bulldozers, front-end loaders and similar vehicles have been successful.
In December 1993, just as the new Mud and Debris Flow Safety and Awareness Course was being presented in areas affected by the firestorms, a huge Pacific storm approached Southern California from Alaska. The LACoFD deployed 10 swiftwater rescue teams, augmented by a reserve USAR unit (USAR-2). On the first morning of the storm, USAR-2, staffed by LACoFD Captains Scott Smith and Troy Flath, helped Truck 125's members teach the course to other stations in the Malibu area. Two hours later, severe thunderstorms occurred over the "Old Topanga Fire" burn area. Almost immediately, Malibu experienced serious trouble as several life-threatening situations occurred simultaneously.
The worst incident was a huge mud and debris flow that roared over the banks of Big Rock Creek, where many homes had burned. The creek is normally a trickling stream that crosses under the Pacific Coast Highway and drains into the Pacific Ocean. Now it had become a river of mud and boulders that washed down the canyon only minutes after the downpour struck. The mud and debris poured off the hillsides like brown lava, clogging the creek in several places. As the debris "dams" burst, they sent waves of debris down the canyon, turning the entire canyon into a torrent of mud and rock. The flood immediately clogged the channel under the Pacific Coast Highway and swept across the road, trapping people in cars and homes, which blocked the mud from going into the ocean, creating a damming effect that quickly raised the flood to the roof lines of some homes.
Battalion 5, Engine 70, Swiftwater 70, USAR-2, an LACoFD swiftwater/helo team-equipped copter and other units found dozens of people trapped in various predicaments. Extra resources (including front-end loaders from Los Angeles County Public Works) for access and rescue in the flowing mud) were requested, and full-scale rescue operations began. The most life-threatening situation appeared to be a couple whose Jeep Cherokee had been swept into the middle of the debris flow. Mud was up to the windows and rushing by at great speed. The Jeep was foundering adjacent to the point where the creek normally drops under the highway. If pushed into the dropout point, the vehicle and its occupants would be buried in 15 feet of slurry.
After sizing-up the situation and assigning a firefighter as upstream lookout, Smith coordinated as Flath and Firefighter Steve Linnel (Engine 70) donned swiftwater PPE and attempted to rescue the couple. A front-end loader was at the scene, and the Public Works driver volunteered to drive it into the flow with the two firefighters in the bucket. Flath and Linnel climbed into the bucket and the tractor drove into the flow. Mud and water were still rushing out of the canyon, and additional walls of debris were a constant threat, but they removed the couple to safety. Several front-end loaders were used to rescue other civilians from rooftops and second-story balconies. Smith conferred with the incident commander, who ordered the entire hazard area to be evacuated in case of additional, larger flows.
The Big Rock rescues offer a possible preview to some of the conditions that firefighters and other rescuers may encounter in areas burned by the 2007 firestorms. Conditions are ripe for mud and debris flows to occur in these areas during the next several winters. The BAER reports for Southern California's huge burn areas are clear in their warnings, which frequently include language like this: "The pre-fire condition of the watersheds already included possible risk from landslides, debris flows and rock falls. These hazards are part of the natural processes in this environment, and were present under pre-fire conditions.