Forest refutes road caused Sullivan slump

A Flathead National Forest investigation of a slump near Sullivan Creek concludes it was not caused by an adjacent road.

After receiving a report from Keith Hammer of the Swan View Coalition on July 21, the Forest conducted an investigation of its own on a slump off Forest Service Road 547. Forest Hydrologist Craig Kendall and civil engineer Shawn Boelman went to the scene the next day. The Coalition claimed the slump was caused by the road and the road should be decommissioned — essentially destroyed.

The slump, which runs down into the creek, is about 3.5 miles up the road from the West Side Hungry Horse Reservoir Road on the Spotted Bear Ranger District.

The road is gated and closed to motorized vehicles, but is still open to hikers and mountain bikers and is an important route for hunters and berry pickers, noted Spotted Bear District Ranger Deb Mucklow.

Kendall and Boelman said in a report there are a total of 14 “mass failures caused by channel erosion” between the confluence of Ball Creek and the Sullivan Creek Bridge, or about five per mile.

The other slides, save for two smaller ones, are not near the road. They note the Ball Creek Fire of 2003 burned through the area, which is contributing to the erosion in the stream.

"The lack of forest canopy makes more water available for soil moisture and shallow groundwater flow. A rapid assessment of nearby drainages reveals that burned areas in similar settings — valley and stream morphology — have more mass failures than un-burned areas,” they said.

They also closely examined the road near the slump and found that it was flat above the slump and was not contributing to the slump itself, by dumping runoff into the area.

“About 80 feet of road ditch drains toward the slide area, but there are no visible signs of surface runoff, scour, or deposition on the road prism at the slide location,” they said. “At this location, the road is at a high point and water does not drain toward the unstable areas. This provides evidence that slides occur in this area without receiving direct surface drainage from roads.”

They did find the slump was eroding at the toe of the hillside. The slump, they concluded, was likely caused sometime this spring or earlier summer, during a heavy rain or runoff event.

Sullivan Creek is an important bull trout spawning stream. Mucklow said the Forest Service closed the road in 2000 to meet grizzly bear security requirements under Amendment 19. The Forest does not have the funds to repair the road anytime soon.

The Forest also has no plans to “decommission” the road, as it could be used for Forest management projects in the future, Mucklow said.

“We’ll keep it in the road system at this time,” she said.