Homeowner s Mitigation Projects Spared Home from Mudflow Damage

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Myra Hall
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Homeowner s Mitigation Projects Spared Home from Mudflow Damage Full Mitigation Best Practice Story Los Angeles County, California Los Angeles County, CA - In the summer and fall of 2009, Southern

1 Homeowner s Mitigation Projects Spared Home from Mudflow Damage Full Mitigation Best Practice Story Los Angeles County, California Los Angeles County, CA - In the summer and fall of 2009, Southern California was plagued with a series of 63 wildfires fueled by three previous years of drought. Although the fires ignited as early as July 2009, before the normal beginning of fire season, temperatures exceeding 100 degrees Fahrenheit and low humidity, together with large amounts of dead vegetation, made conditions ripe for massive fires, even before the arrival of the annual Santa Ana winds. Altogether, 336,020 acres were burned, leaving barren soils on steep terrain adjacent to residential areas a perfect combination for dangerous mud and debris flow potential when the rainy season arrived. Rain falling on a scorched landscape gathers dirt, rocks, and debris from the naked hillsides and mixes them into a cement-like slurry that can cover the area the size of several football fields. These mudflows can race down canyons and across basins at up to 35 miles per hour, leveling everything in their path. On August 29, 2009, the residents of Paradise Valley, a small neighborhood perched on a picturesque hillside in La Cañada Flintridge (and immediately adjacent to the Angeles National Forest) awoke to the smell of nearby smoke from the Station Fire. The same fire had approached their area two days earlier, then returned that Saturday even closer. The silence was eerie, said Olivia Brown, eight-year resident of Paradise Valley, the crackling, the popping [of the fire] no other sounds. The fire line on the steep hill behind their house dropped burning embers, red-hot rocks, and other fire debris into their back yard. Three days later, after returning from their mandatory evacuation, they found scorched spots in the grass where embers had dropped. It was then that the Browns made the important decision to protect their home from the inevitable mud and debris flows that would follow with the following rainy season. Flooding danger was on everyone s mind. Olivia Brown knew, One day it could happen and it came. Mrs. Brown, the head of the Safety Committee for their Home Owner s Association, decided that their home s safety was a first priority. Mrs. Brown said their mitigation plans came from common sense knowledge of how the water and debris would flow downhill, directly at their house, unless they did something to redirect it. The Browns learned about mitigation measures that could be taken by attending community meetings and listening to representatives from the United States Geological Survey and city government. They also consulted with one county engineer and three private engineers before starting their projects. Getting to work quickly, the family built check-dams into the terraces on the steep hillside angling up from the back of their house; they drove heavy, seven-foot-long rebar down to bedrock (four feet below the surface) to hold the heavy landscaping ties. Next, they screwed flat steel bars across the faces of the wood to hold them firmly together (top to bottom, and side to side). At the top of their property, they anchored diversion walls (also of wood and steel posts) angling from the middle out to the sides of their yard to catch basins at the bottom of the hill on each side of their back yard. The Browns realized that everything on the hillside above their home was a potential projectile when the rains began. Across the back of their house they placed a barrier wall of heavy plywood and thick steel vertical bars deeply anchored into concrete. This was topped with heavy chain-link fencing to catch and deflect any falling boulders from landing on the house. Thick plastic sheeting covering the wooden part of the barrier, extended out into the yard several feet, and was anchored by a row of sandbags. Between the bottom concrete/wood terrace and the barrier wall, they placed another row of sandbags to catch any runoff that penetrated the terraces. Sand bags at the sides of the house also created a drainage route for all the water and debris to safely divert around the house from the catch basins instead of through or under. The hot tub, decorative plants, and furniture, which formerly graced their back yard, were now replaced by these mitigation measures. Except for the upper diversion walls, none are visible from the front of their house. Generated on Wed Nov 10 14:06:39 EST 2010 Page 1 of 5

2 In early December 2009, the first round of heavy rain and winter storms hit California. El Niño conditions continued to trigger a series of fierce storms which caused deadly avalanches, flooded streets and set off mudflows and rock slides in January. Some areas received more moisture in a week than during the entire rainy season of 2008/2009. On January 18, the first of a series of powerful Pacific storms pounded the region with rain, unleashing mud and debris flows that prompted evacuations, flooded businesses, toppled trees and electrical lines and caused hundreds of traffic collisions. In the early morning of February 6, a slow-moving rain storm hit the area and dumped about two inches of rain onto the hills above the Paradise Valley community. All night the Browns heard the rain and kept checking their back yard. Pickens Canyon (across the street from their house) was running full. Water and debris was coming down the hill behind the house. The Mullally catch basin, perched over Paradise Valley, was gathering runoff and debris from the fire-denuded hills over the neighborhood and soon overtopped that morning. About 5:00 AM, the Browns heard the roaring of the storm and were alarmed at the amount of water and debris pouring past the front of their house in the street. The debris flow sprayed high into the air as it hit the K- rails (concrete traffic dividers), which had been placed on a nearby road but not yet anchored. The force of the water was so powerful, it was visibly moving the 2,000 pound concrete structures down the street. Of the 66 homes in their community, one house was so severely damaged that it had to be demolished. Nine other houses were severely damaged. Numerous cars and trucks were washed out of driveways into piles of crushed metal further down the road to wedge against houses and trees. At one home, the garage door collapsed under the heavy debris flow when the Mullally catch basin overtopped. The full force of the muddy, debris-filled water ripped the garage off the front of the house. A section of that garage, along with the car which had been parked inside, was washed into a neighbor s yard. Evacuation of the neighborhood occurred with the discovery of a broken gas line to one of the damaged homes. When residents were allowed to return, the Browns found their mitigation work had done its job. Although they had mud and debris to clean out of their backyard catch basins and from behind the sand bag barriers, no water had entered their home. Had their mitigation projects not been in place, all the water, mud, and debris that accumulated in their catch basins would have inundated their living space. Surrounded by damage and destruction, they were grateful that their home had been spared. Based on the current approximate market valuation of their home ($800,000) and the cost of their mitigation work ($10,000), the cost to benefit ratio of the project is 1:80. In other words, for every dollar spent, 80 dollars were saved. And because they could prove that what they did protected their home from damage, their cost was partially reimbursable by their homeowners insurance. Grateful for the success of their back yard mitigation project, Mrs. Brown said, I knew when we moved in, that hillside would always be a concern, but after the fire the concern became all-consuming until we got the work done. Homeowners should consult with local officials and engineers if they believe they have a potential debris flow hazard. A valuable resource is the United States Geologic Survey Circular 1325, The Landslide Handbook A Guide to Understanding Landslides. Appendix C. Introduction to Landslide Stabilization and Mitigation, discusses specific mitigation measures for debris flows Activity/Project Location Geographical Area: FEMA Region: State: County: City/Community: Single County in a State Region IX California Los Angeles County La Canada Flintridge Generated on Wed Nov 10 14:06:39 EST 2010 Page 2 of 5

3 Key Activity/Project Information Sector: Hazard Type: Activity/Project Type: Structure Type: Private Mudslide/Landslide Retrofitting, Non-structural Wood Frame Activity/Project Start Date: 09/2009 Activity/Project End Date: Funding Source: Ongoing Homeowner Activity/Project Economic Analysis Non FEMA Cost: Cost: $10, (Actual) Activity/Project Disaster Information Mitigation Resulted From Federal Disaster? Value Tested By Disaster? Tested By Federal Disaster #: No Yes No Federal Disaster specified Year First Tested: 2010 Repetitive Loss Property? No Reference URLs Reference URL 1: Reference URL 2: Main Points No Main Points were entered. Generated on Wed Nov 10 14:06:39 EST 2010 Page 3 of 5

4 fire line behind house hillside behind house backyard projects torrent of muddy water in front of house pile of debris and cars Generated on Wed Nov 10 14:06:39 EST 2010 Page 4 of 5

5 homeowner explains process Generated on Wed Nov 10 14:06:39 EST 2010 Page 5 of 5

Landslide Mitigation (BYUI)

Landslide Mitigation (BYUI) The general principle behind landslide mitigation is stabilization. Slopes that are too steep are shallowed or strengthened. Loose rocks can be bolted or cemented into place.