By Ann McCreary
A report on the potential impact of the massive Carlton Complex Fire describes a high risk of erosion and debris flow to homes, roads, water systems, public utilities and fish habitat within or near burned areas.
The Burned Area Emergency Response (BAER) report published this week identifies threats to life and property from dams and ponds in Finley Canyon and the Leecher and Frazer creek watersheds that could potentially fill with sediment during storms and breech.
The spread of noxious weeds and invasive plant species is also identified as a threat in the wake of the July fires that roared through the Methow Valley and surrounding areas, burning 255,181 acres.
The report was prepared by a multidisciplinary team that surveyed the burned area. It summarizes potential post-fire risks to people and the environment, and recommends emergency stabilization and long-term restoration actions.
The intense fire destroyed vegetation and in some areas scorched soils so badly that they have become water-resistant, intensifying the risk of runoff during storms and snowmelt. The risks of flooding and erosion are expected to continue for up to five years.
Emergency measures costing $2.8 million are recommended to protect people, property and resources. They include installing flood diversion dikes and berms to protect homes and property; constructing dips in roadways to channel runoff and reinforcing roadside shoulders and slopes; placing flood warning signs along roads and highways; seeding burned slopes to restore vegetation and discourage invasive weeds; and monitoring and repairing dams and ponds that are at risk of failing during floods.
A survey conducted this month of properties at highest risk from future flooding and runoff has identified 42 homes or other structures — most of them in the Methow Valley — that need protection, said Craig Nelson, manager of the Okanogan Conservation District and assistant leader for the BAER team.
Many of the properties are located at the bottom of watersheds or draws, said Nelson. Those property owners are being contacted and will be eligible for assistance through a federal Emergency Watershed Protection Program, which helps pay for construction of diversions such as dikes, dams or dips in roadways to direct flash floods or mudslides away from homes and properties.
Only homes considered “defensible” qualify for the program, and work is expected to be done this fall, Nelson said.
Drainages identified in the BAER report as posing the highest risk from flooding and runoff to homes and outbuildings include Benson, Finley, Canyon, Cow, Texas, French, Frazer, Beaver, Squaw, Gold and McFarland creeks, and Black and Davis canyons.
To illustrate the increased risk of flooding and debris flows, the report provides a chart comparing sediment that would be produced in various drainages before and after the fire, based on a scenario of a 25-year, one-hour storm depositing .77 inches of precipitation.
For Benson Creek, one of the most heavily burned drainages, the report estimated that a total of 9 tons of sediment would have been produced in the drainage during the storm pre-fire, and a total of 1,101 tons produced after the fire — a 11,581 percent increase.
Beaver Creek would have seen 650 tons of sediment produced during the storm prior to the fire, and 11,884 post-fire, a 1,728 percent change. Texas Creek was projected to increase from 65 tons of sediment pre-fire to 1,250 post-fire, a 1,831 percent increase.
The report also charted the extent and severity of the fires in various drainages that pose risk of erosion and run-off.
High-severity fire means all or nearly all ground cover and surface organic matter is gone, only bare soil or ash is left, soil structure and stability is damaged or destroyed, and the soil may have become water repellant at the surface or deeper.
In Benson Creek, 85 percent (20,746 acres) of the total acreage was burned, 5,027 of them categorized as high burn severity. In Texas Creek 91 percent (6,524 acres) burned, 286 are high severity. In Cow Creek 100 percent burned (3,689 acres), 507 severely.
The survey found that of the 255,181 acres burned in the Carlton Complex, the largest portion — 98,753 acres — is private land. U.S. Forest Service lands burned in the fire total 79,795 acres; state lands, 69,885 acres; other federal property, 6,157acres; and tribal land, 590 acres.
Among the nearly $3 million in emergency measures recommended by the BAER report are:
• Place warning signs in areas of potential flooding along state and county roads.
• Protect homes and property from possible damage from 11 dams and ponds that could fail by inspecting, dredging sediment and debris, repairing the structures or performing controlled breaching of dams. The report notes that the state Department of Ecology has issued correction orders for two dams owned by the Washington Department of Fish and Wildlife, and the privately owned Rabel Dam in the Benson/Finley watershed.
• Improve drainage on state and county roads, including those already damaged in recent storms, through ditches and culverts, and by armoring road shoulders and slopes where water may flow over the roadway.
• Install berms or other diversions to protect utilities, wells, fish screens and irrigations systems from expected runoff and debris flow.
• Hand-seed bulldozer lines with native seed and aerial seed moderate to severely burned areas to discourage the spread of noxious weeds and invasive plants and to stabilize and rebuild the soil.
Among long-term restoration recommendations, the report suggests that people with property at risk of floods or runoff “consider relocating … to more secure locations that are not prone to additional debris flows, increased runoff and sediment.”
The report notes that “hundreds of miles of boundary fence and range fences” were lost in the fire, and an inventory should be conducted and fences replaced, with priority going to fencing sensitive areas and burned areas that that need longer recovery or seeding.
The rangeland and grazeable woodlands should be rested for two years to recover, the report recommends. Fire lines should be restored to prevent their conversion to new motorized roads or trails, and a variety of shrubs should be planted to support mule deer.
The BAER report is available at the Okanogan Conservation District website, www.okanogancd.org/sites/default/files/programs/Carlton%20Complex%20BAER%20Report.pdf.