Both damaged areas may see floods, erosion, debris flows
The Crescent Mountain and McLeod wildfires burned more than 77,000 acres of U.S. Forest Service land in the Methow Valley last summer, leaving thousands of acres vulnerable to increased flooding, erosion and weed invasions.
The Forest Service has allocated $332,330 for emergency treatments designed to reduce risks in the areas damaged by the fires. Emergency measures to manage post-fire threats to natural resources, human life and safety, and Forest Service property (including roads, trails, bridges and campgrounds), were recommended through a process called Burned Area Emergency Response (BAER).
The funding for post-fire treatments includes $141,180 for the McLeod Fire, which burned northeast of Mazama, and $191,150 for the Crescent Mountain Fire, which burned in the upper Twisp River drainage west of Twisp. Post-fire risk assessments been completed for both areas by BAER teams, which include hydrologists, soil scientists, engineers and other experts.
A recently completed assessment of the McLeod Fire burn area identified areas within the 24,412-acre fire perimeter that burned most severely and present the greatest potential for increased runoff and erosion. “The Goat Creek and Button Creek drainages stand out as those with the highest magnitude of change from pre-fire to post-fire conditions,” the BAER report said.
“Risk to forest personnel and forest users is elevated based on potential impacts from flooding, debris flows, hazard trees and rockfall along trails and road in the Goat Creek and Button Creek/Eightmile drainages,” the report said. “Individuals who may find themselves in portions of the burn area along any of the drainages or roads affected by fire are at risk during storm events.”
A BAER assessment of the Crescent Mountain Fire was completed last month and was reported in the Oct. 31 issue of the Methow Valley News.
When slopes are burned bare of vegetation during wildfires, and severely burned soil is damaged so that it repels rather than absorbs water, the potential for post-fire runoff and erosion increases dramatically. Sediments may move downstream and damage roads, trails, campgrounds and houses, and put wildlife and water supplies at risk.
Treatments recommended by the BAER team are intended to stabilize roads and trails, protect infrastructure like bridges, and prevent spread of weeds in the national forest. They are also intended to protect human safety by temporarily closing selected roads, trails and campgrounds, and by installing signs warning of post-fire hazards.
Some of that work is underway in both the Crescent Mountain and McLeod fire areas, including installation of warning signs, said Deborah Kelly, a public information officer for the Okanogan-Wenatchee National Forest. “Because of the urgent nature of it … the goal is to get out there as soon as possible, and it’s a bit of a race with the weather,” she said.
“A lot of the trail work will probably happen next spring. Weed treatment will be done next spring and summer,” Kelly said. The Forest Service will contract for the road work, which will be done as weather permits.
Mosaic of severity
The McLeod Fire was ignited by lighting on Aug. 11 and spread through a combination of slow creeping and short runs, spotting and burnout operations, resulting in a mosaic of fire severity on Forest Service land. Through field studies and satellite images, the BAER team found that 728 acres burned with high severity, 7,059 acres burned with moderate severity, 9,624 acres burned with low severity, and 7,001 acres within the fire perimeter were unburned.
About 5,540 acres were found to have burned so severely that the soils have become water-repellent, or “hydrophobic,” which contributes to erosion and runoff. The BAER report found 21,575 acres within the fire perimeter had moderate or high “soil erosion hazard erosion ratings,” with an erosion potential of up to 6.8 tons per acre and a potential of producing up to 4,321 cubic yards per square mile.
Based on models of probability and volume of debris flow, much of the burned area presents a moderate risk, and the Hurricane Creek sub watershed was rated as a high risk, the report said.
“Debris flows are very likely to occur in the steep tributaries to streams within the McLeod Fire area. Within the burned area, some watersheds show past debris slide/debris flow activity and it appears likely these areas could experience future debris flows.”
Approximately 28 percent of the Eightmile sub-watershed, and 6 percent of the lower Lost River sub-watershed, are within the McLeod Fire perimeter, the BAER report found.
The report recommended a range of treatments to roads, trails and campgrounds to protect resources, property and human safety. Within the fire perimeter there are approximately 45 miles of Forest Service system roads, with an additional 7 miles directly below the fire perimeter that are at elevated risk of damage, the report said.
Recommended road treatments include improving drainage, installing armored dips to divert water and minimize damage to road surfaces, removing selected culverts, inspecting roads after storms, inspecting bridges and culverts, and installing hazard warning signs. Three miles of roads within the fire perimeter are suitable for passenger cars, and treatments were recommended on 1.5 miles of those roads.
There are about 10 miles of trails within the McLeod Fire perimeter on the Methow Valley Ranger District. Of those 10 miles, 1 mile had high soil burn severity, 3 miles had moderate soil burn severity and 6 miles had low soil burn severity or were unburned.
Due to the high risk of falling trees, rolling rocks and flash floods, temporary closure was recommended for the Goat Creek trail, Copper Glance trail, and Roundup Creek trail to protect public safety.
Treatment to prevent erosion of trails included cleaning existing drainage features, installing rolling dips and water bars, removing berms, stabilizing banks and improving stream crossings.
The BAER team also recommended seasonal closures for two campsites at Honeymoon campground that are close to Eightmile Creek due to a “high risk … for flooding at these campsites.” The team also recommended closing a campsite along the creek in the Ruffed Grouse campground. Backcountry camps located near streams or in flood plain areas below burned areas are at increased risk of flooding and debris flow, the report noted.
Warning signs reading “Entering Burned Area” should be posted in key locations to alert travelers to dangers such as falling rocks and flooding, the report said.
To prevent the spread of invasive weeds, the report also recommended early detection and rapid response to prevent invasive weeds from becoming established in fire damaged areas, particularly on bulldozer lines constructed as part firefighting efforts.
Information on BAER and reports and maps can be found at centralwashingtonfirerecovery.info.