Thursday, September 10, 2009

burn area

Image from NASA Earth Observatory

By Guy McCarthy

While an army of firefighters battles the 250-square-mile Station Fire, scientists and technicians are trying to map and quantify how much ash, mud and rock could pour out of the burned-out San Gabriel Mountains the next time heavy rains fall.

A U.S. Geological Survey Landslide Hazards team is using NASA satellite images to prepare a burn-severity map that will show probability, volume, and locations of likely debris flows and mudslides, said Sue Cannon, a USGS project manager in Golden, Colo.

"The San Gabriels have a significant history of debris flow activity after fires," Cannon said in a telephone interview. "There are so many humans at the base of the mountains who could be impacted. We want to do this quickly."

Hazard technicians plan today to start field-checking images they received from the earth-observing LANDSAT satellite on Tuesday, and they hope to have a final report and map ready for public safety agencies by next week, Cannon said.

Six years ago Cannon helped lead a team that prepared a similar report within weeks of the October 2003 Old and Grand Prix fires, which denuded a 40-mile mountain front from Upland, below the east San Gabriels, to Highland, below the San Bernardino Mountains.

The need for timely and accurate assessment of potential post-fire dangers was underscored on Christmas Day 2003, when torrential rains on burned watersheds unleashed flash floods and debris flows that killed 16 people -- including nine children -- in Waterman and Cable canyons.

Other mapping specialists working on the Station Fire and post-fire hazard studies include support technicians from Redlands-based ESRI, a producer of geographic information systems software used by the Defense Department in Iraq and Afghanistan, as well as by public safety and fire agencies in the United States.

"We have provided tech support for many of the cooperating agencies on the Station Fire," Russ Johnson, ESRI's director for public safety and homeland security programs, told City News Service. "We have provided them with USGS topographic base data for areas considered at risk.

"We will be providing the same kind of support for rehabilitation teams and burned area emergency response teams," Johnson said. "They will be able to extract from GIS (geographic information systems) imagery areas that have the most risk of debris flows and mudslides."

While the Station Fire continues burning east in wilderness areas of the Angeles National Forest, county flood control engineers are assessing the potential for post-fire mud flows from burned areas above densely populated hillside communities in La Canada Flintridge, La Crescenta and Tujunga, said Kerjon Lee, a spokesman for the Los Angeles County Department of Public Works.

Thousands of homes below the Station Fire burned areas are protected by flood control channels and basins, according to Public Works maps and records.

But many other homes built in the past 40 years may be at risk, said Doug Hamilton, an Irvine-based engineer and former consultant to the U.S. Army Corps of Engineers, which designed and built many of the flood control structures intended to protect Los Angeles from erosion disasters.

"My concern is the proximity of the fire along the edge of development that's built in the 70s, 80s and 90s," Hamilton said. "They've never seen a post-fire erosion event.

"I see these houses cut into the side of the mountain," Hamilton said. "They're built according to building code, but it's frightening to look at. If there's heavy rains, a lot of these houses are going to be difficult to protect."

The likelihood of heavy rains this fall and winter remains unclear, but local, state and federal agencies must plan for worst-case scenarios regardless of forecasts.

The El Nino pattern that sometimes serves as an accurate predictor for Southern California's winter rain season appears "weak to moderate" right now, which makes the forecast difficult to call, said Bill Patzert, a climatologist at the NASA Jet Propulsion Lab in La Canada-Flintridge.

"But all you need is a couple storms and it's a big mess," Patzert said. "Whatever we get in the way of rain, it's going to be a mess. The areas that burned, some of them hadn't burned in 40 to 60 years. One part hadn't burned in a hundred years."

Sen. Barbara Boxer, D-Calif., Tuesday encouraged U.S. Agriculture Secretary Tom Vilsack to ensure the U.S. Forest Service focuses on erosion mitigation efforts in denuded watersheds before the advent of winter rains.

"Erosion from steep hillsides will threaten water quality and often cause mudslides that damage property downstream and can seriously exacerbate flooding, as debris, mud and rocks clog flood basins," Boxer wrote in a letter to Vilsack, whose department oversees the Forest Service.


USFS Station Fire statement this afternoon:

Post Fire Watershed Rehabilitation Activities

Incident: Station Fire Wildfire
Released: 31 min. ago

What is ahead for the Angeles National Forest

The Station Fire is the largest in Los Angeles Countys recorded history and the largest in the history of the Angeles National Forest, which was established in 1892 as the Timber Land Reserve and later changed to Angeles National Forest.

As the Station Fire subsides, the ongoing concern for the forest lands north of Los Angeles heightens. Winter rain within the burned area can pose an ongoing threat to natural resources, life and property. In order to address those concerns ahead of time, the Angeles National Forest has assembled a Burned Area Emergency Response (BAER) Team to assess the damage to the watersheds, soil and natural and cultural resources. The team is comprised of specialists that are highly experienced in conducting rapid watershed assessments and analyses and include soil scientists, hydrologists, geologists, biologists, geographic information specialists, archeologists, botanists, silviculturists, and civil engineers.

The intense heat from wildfires can cause the soil to "seal" itself and water will not easily penetrate it. The water runs rapidly down streams and canyons which could cause potential flooding, mudslides, and debris flows. The BAER Team will assess the post-fire watershed conditions for any potential emergencies and recommend immediate treatments for the National Forest System lands.

The Angeles National Forest provides the Los Angeles Basin with 35% of its water supply. Four watersheds have their origins on the Angeles NF and those watersheds have all experienced different degrees of burn activity within the Station Fire. An assessment of these burned watersheds will need to be undertaken by the BAER Team to determine what methods of treatment will be effective.

Methods used after a fire to help slow the flow of water and mud slides could include erosion control protection measures, road drainage treatments, and cultural heritage resource sites protection.

Another area of concern for the Angeles National Forest is the wildlife that has been displaced. These animals have fled to the communities surrounding the forest. People can expect to see an increase in raccoons, skunks and other animals in their neighborhoods. As the forest cools down, the animals will begin to return to their normal habitat.

The Angeles National Forest will establish a cooperating group that will be able to provide a forum for local cities, towns, county, cooperating agencies; such as Natural Resources Conservation Service, LA Department of Water and Power, and Los Angeles County Flood Control to provide input into the assessment process.


NASA text with satellite image:

Two weeks after an arsonist ignited the drought-dry forest north of Los Angeles, the Station fire had become the ninth largest fire in California since 1933. On the morning of September 8, 2009, the fire had burned more than 250 square miles (about 650 square kilometers) of land, according to the Station Fire Incident Report from September 8. This image, captured by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite on September 6, shows the extent of the burned area. The newly charred land is black in this false-color image, which was made with near infrared light. Plants are dark red, and man-made surfaces, particularly the dense urban centers of Pasadena and Burbank, are blue and white.

The burned area covers much of the San Gabriel Mountains, edging down into residential areas northwest of Pasadena. Smoke rolls off the eastern edge of the burned land. The fire was still burning, just over 50 percent contained when the image was taken. According to the incident report from September 8, the fire was pushing east into forest with no recorded fire history. The fire had previously burned through tall, thick forest that had not seen fire in the past 40 years.

The image also illustrates why fighting the Station fire has been so difficult. The fire burned over steep mountains riddled with canyons. The rugged landscape looks wrinkled, particularly in the burned area where plants no longer soften the ridgelines and canyons. The steep terrain and the fire’s extreme, unpredictable behavior led to the death of two firefighters. Nine other firefighters have been injured fighting the fire, reported the Los Angeles Times.

South and east of the fire, the Mount Wilson Communication Facility and Observatory was still surrounded by unburned forest. The historic, 105-year-old observatory hosts two large telescopes, once the world’s largest, and other instruments to study the Sun and the Universe beyond. Mount Wilson also contains communications towers that serve much of the Los Angeles region. The image shows that the fire approached the facility on two sides, but left the forest around the observatory intact.


NASA Earth Observatory page here

USFS statement on InciWeb here

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