By Marcy Stamper
A slow-moving thunderstorm that dropped torrential rains on the Methow Thursday night and Friday morning (Sept. 5–6) submerged the record for the wettest 24-hour period in September in both Winthrop and Mazama. The rain also unleashed dense slides of mud and debris, closing Highway 20 and several U.S. Forest Service roads and making area rivers resemble chocolate pudding.
By the end of the first week of September, it was already the sixth-wettest September in Winthrop in more than 100 years, and the fourth-wettest in Mazama in 65 years, according to the National Weather Service. August was also extra-wet for Mazama – the fourth-wettest for that month – according to Katherine Rowden, a hydrogeologist with the Weather Service.
The amounts of rainfall recorded in a 24-hour period – 1.35 inches in Winthrop and 1.78 inches in Mazama – were impressive even for the damper regions of Washington, where a University of Washington atmospheric scientist was forecasting “just amazing amounts, broad areas receiv[ing] 1 to 2.5 inches.”
The rain let loose a mud and debris flow that blocked the road to Harts Pass just below Deadhorse Point with rocky muck almost 5 feet deep, according to Jennifer Zbyszewski, wilderness and facilities program manager for the Methow Valley Ranger District. The slide landed on the west end of Lost River Road near the River Bend campground, blocking that road with mud and rocks 5 feet deep, she said. The Forest Service cleared both roads on Friday (Sept. 6) and more than a dozen campers were able to drive out, she said.
The Methow and Twisp rivers were churning high and dark brown on Friday, as mud and sediment coursed down from mountain streams. The water cleared considerably over the weekend, but some areas were still being stained by muddy flows early this week.
Little Bridge Creek was still depositing a brown cascade in the Twisp River, about 8 miles west of town. Zbyszewski said they have not found the source of the mud and silt running into the creek.
The road to Little Bridge Creek is blocked by rocks and logs and is difficult to navigate even in a four-wheel-drive vehicle, but Zbyszewski said that slide was not big enough to account for the amount of mud in the creek. The Forest Service expects to clear that road later this week.
“It’s interesting to think about how dynamic the landscape is,” said Zbyszewski. “We get used to seeing the hillsides with trees and dirt, but this is part of geology and hydrology. It will stabilize, harden and revegetate, and the creek will return to normal sediment levels.”
Although wildfires can make slopes less stable, with fewer roots to hold soil in place, the Forest Service is not aware of any slides or erosion in areas that burned recently, said Zbyszewski.
Risks to endangered fish
The sediment deposited in the rivers comes at a sensitive time for spring Chinook, which are in the midst of spawning and on the federal endangered list. While the fish are well adapted to normal river cycles, high water and extra sediment this late in the year can pose problems for the fish, said Brian Fisher, program manager and aquatic ecologist with the Methow Salmon Recovery Foundation.
With a six-week spawning period that started in early August, many of the fish have already laid their eggs, making the eggs vulnerable to being carried downstream by rapidly flowing water. The redds, where eggs are deposited, can also be smothered if too much sediment settles on them, cutting off oxygen, said Fisher.
Those fish that have yet to lay their eggs will be more fortunate, because the fish clean sediment from the gravel before depositing the eggs, said Fisher.
“This is the kind of event that means bad things for this year’s spring Chinook, but it won’t wipe out all of them,” he said. Those fish that do survive will have less competition for food.
With between 5,000 and 8,000 eggs per redd, hundreds will probably hatch and many will make it to the ocean. Even if only two fish ultimately survive to reproduce, that is sufficient to replace the population, said Fisher.
Other road damage
On West Chewuch Road near Andrews Creek (about 5 miles before the road’s end), a major rock flow blocked the road, gouging out sections of pavement, and ultimately landed in the river, said Zbyszewski. The obstruction was cleared on Friday.
On Twisp River Road, a 2-foot-deep mudslide cut off the road near the Poplar Flat campground, about 21 miles west of Twisp. The Forest Service expects to have that cleared by Thursday (Sept. 12).
There is still some damage further up Harts Pass Road, where debris blocked a culvert near Cache Creek, causing water to flow across the road, but it remains passable, said Zbyszewski.
Highway 20, currently open as far as Rainy Pass, was expected to re-open for through traffic by noon on Friday (Sept. 12).
There were only isolated instances of flooding and no serious damage elsewhere in Okanogan County, according to county Emergency Manager Scott Miller.
The county commissioners did declare an emergency on Friday to allow the immediate removal of a tree that was leaning precariously over the street near the county courthouse in Okanogan, he said.