Report includes suggestions for repairs, reduced risks
By Ann McCreary
A post-fire assessment of the Diamond Creek Fire identified potential “threats to human life and safety” along wilderness trails in severely burned areas, and in the communities of Lost River and Mazama, which are downstream of the burned area and could experience flooding.
More than half of the area in last summer’s Diamond Creek Fire burned at high severity or moderate severity, resulting in damaged soils and increased potential for erosion and flooding in the aftermath of the fire, the assessment by the U.S. Forest Service found.
A Burned Area Emergency Response (BAER) report released last week analyzed the impacts of the huge wildfire and made recommendations to address risks resulting from the fire. At the recommendation of the BAER team, $143,405 was approved by the Regional Forester in Portland, Oregon, for emergency treatments to mitigate risks.
The Diamond Creek Fire burned from July 23 through mid-October over an estimated 128,272 acres on national forest lands and in Canada, with 97,136 within the national forest north of Winthrop. The fire, which came to within 11 miles of Mazama and forced temporary evacuations in September, is probably still smoldering in some areas, said Molly Hanson, a Forest service hydrologist who led the assessment team.
The BAER team found that about 56 percent of the area within the national forest burned at high or moderate severity — more than 54,000 acres. The hotter a fire burns, the more damage it causes to soil as well as vegetation, causing soil to become water repellent. That, in turn, increases the likelihood that rain and snowmelt will produce flooding and erosion.
The potential for soil erosion during a significant storm increased 16-fold in the higher severity burned areas, the report said. A 25-year storm, delivering 3.3 inches of precipitation within a 24-hour period, would result in 16 tons of sediment per acre, compared to one ton before the fire.
“The increased erosion can result in downstream sediment delivery that bulks flows, resulting in increased flooding effects. This additional sediment may impair habitat for aquatic species,” according to a summary of the BAER report.
Increased stream flows
The fire burned in the headwaters of the Lost River watershed on national forest lands. Within that upper watershed, post-fire flows in Stubb Creek are expected to increase by 300 percent, placing the Stubb Creek Trail and a Forest Service cabin at risk from flooding. Ptarmigan Creek is expected to have a 200 percent increase in flows, the BAER report said.
Diamond Creek, for which the fire was named, drains into Lost River and is expected to have increases in post-fire flows of approximately 270 percent. Monument Creek, which flows into Lost River below Diamond Creek, is predicted to have increases in post-fire flows of about 150 percent.
“There is a high risk of increased flows in the upper watershed, which may translate into potential increased flows 11 miles downstream at the communities of Lost River and Mazama. There may be an increased risk of potential damage to a county bridge across the Lost River,” the BAER report said.
Hanson said Okanogan County has taken steps to stabilize abutments on the Lost River bridge. The report calls for coordination among agencies, including the National Weather Service and Okanogan County, to warn of potential flooding. Hanson said a stream gauge on Andrews Creek can help agencies predict when Lost River will rise. “The biggest flood risk would be snowmelt,” Hanson said.
The loss of soil through erosion can also impair the ability of the landscape to recover in the short and long term, especially in the most severely burned areas, the report said. “The burned areas may require up to five years to re-establish vegetation and hydrologically recover. The major concern for vegetative recovery and, in turn, hydrologic recovery, is in the high severity burn areas where tree canopy and groundcover has been lost.”
The Diamond Creek Fire burned through vast tracts of the Pasayten Wilderness, a popular destination for hikers, packers and hunters. Approximately 141 miles of Forest Service trails are within the fire perimeter, and the BAER analysis found that 41 miles of trails in high and moderate severity burn areas are at risk from increased runoff, erosion and debris.
Risks to travelers
Risks to travelers in the fire area including flooding and hazard trees and rock fall along trails and roads in the Lost River and Eightmile drainages, and on the trail system in the fire perimeter. Impacted trails include Hidden Lakes, Monument/Shellrock, Lake Creek, Larch Creek/Billy Goat, Andrews Creek, Chewuch, Diamond Jack and Boundary trails. Some bridges on those trails were burned in the fire, and others are at risk of damage from increased flows, the post-fire assessment said.
About $61,000 is expected to be allocated for drainage work on the 41 miles of most impacted trails, said John Rohrer of the Methow Valley Ranger District. Because the trails are within the wilderness area where mechanized equipment is not allowed, the work must be done by hand. Funding will likely help the ranger district hire additional trail crew members, Rohrer said.
A total of 955 additional drainage structures, such as water bars, should be installed on trails to accommodate the projected increase in runoff from adjacent moderate and high severity burn areas, with the goal of reducing damage to trail beds and downslope hillsides, the BAER report said.
The report also calls for placing signs at trailheads to warn trail users of potential hazards. “Because it’s wilderness we’re not closing it, so we will need to be posting on all trailheads saying people will be encountering hazard trees, stump holes, rolling debris,” Hanson said.
The report recommends further assessment of trail conditions in the spring to determine if hazards warrant closing some trails. It also recommends that the Forest Service hold an open house with other agencies in the spring to share information about fire impacts with the public.
Potential risks to threatened and endangered species were possible for bull trout and steelhead in the Lost River and Eightmile Creek due to the threat of increased erosion and sedimentation in critical habitats, the report found. Treatments to prevent trail and road erosion would help mitigate the risk, but natural recovery of groundcover was deemed the “most cost-effective approach to … stabilization.”
Most of the Diamond Creek Fire burned in wilderness, but the fire also burned in the vicinity of Forest Service Road 5130 along Eightmile Creek. A 4-mile segment of road is at high risk of damage from increased runoff and erosion, and drainage improvements and road stabilization work should be undertaken to reduce the risk of road failure, the report recommended.
At the Billy Goat Trailhead at the end of the Eightmile road, a pit toilet burned and the site will need to be cleaned, sanitized and covered to protect the public.
In the wake of the fire, noxious weeds can be expected to move into burned areas, and treatments to prevent them from becoming established were recommended by the BAER team. Whitebark pine trees, a sensitive, high-elevation species, burned within the fire perimeter but potential impacts were not clear, although some restoration planting might occur, the report said.
The most severe “stand replacing” fire occurred primarily in the northern portion of the fire, Hanson said. Photos taken during the BAER field studies show trail beds running through blackened landscapes of standing dead trees. Other areas burned in a more mosaic pattern, leaving some areas untouched, Hanson said.
The Diamond Creek Fire and other major fires of the past 20 years have burned about 65 percent of the 531,000-acre Pasayten Wilderness, one of the largest in the state. The Diamond Creek Fire has been determined to be human-caused.
BAER reports on the Diamond Creek Fire, as well as Jack Creek Fire, Jolly Mountain Fire, Norse Peak Fire and Uno Peak Fire, can be found at centralwashingtonfirerecovery.info.