Forest officials say road did not cause slump
Flathead National Forest officials say their investigation of a remote hillside slump on the east side of the Swan Range concluded that it was not caused by improper drainage from an adjacent road.
The Forest received a report about the slump on Forest Service Road 547 from Keith Hammer of the Swan View Coalition on July 21.
The slump, which ran down into Sullivan Creek, is about 3.5 miles west of the West Side Hungry Horse Reservoir Road. The forest road is gated and closed to motorized vehicles but open to hikers and mountain bikers. It’s an important route for hunters and berry pickers, Spotted Bear District Ranger Deb Mucklow said.
Flathead Forest hydrologist Craig Kendall and civil engineer Shawn Boelman traveled to the scene on July 22. In their report, they described a total of “14 mass failures caused by channel erosion” between the confluence of Ball Creek and the Sullivan Creek Bridge — about five per mile.
Other than two smaller slumps, the slides are not near the road. Kendall and Boelman said the Ball Creek Fire burned through the area in 2003, which contributed to erosion in the stream.
“The lack of forest canopy makes more water available for soil moisture and shallow groundwater flow,” they said. “A rapid assessment of nearby drainages reveals that burned areas in similar settings — valley and stream morphology — have more mass failures than unburned areas.”
Kendall and Boelman also closely examined the road near the slump and found that it was level above the slump and not contributing to the slump 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.”
What they did find, however, was erosion 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.
Hammer, however, disputes the Forest Service findings.
“The evidence shows the road was a contributing factor in how and to what degree this hillside failed,” he said in a letter released last week. “The Forest Service expects the public to believe that a mass failure of this magnitude had nothing to do with the road — even though the failure’s apex is currently in the roadbed adjacent to the deepest portion of the road cut slope and the flattest, least drained stretch of ditch. This is not a simple matter of Sullivan Creek nibbling away at the toe of the hillside slope.”
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 sufficient funds to repair the road anytime soon. It also has no plans to “decommission” the road — which essentially would destroy it — as it could be used for management projects in the future, Mucklow said.
“We’ll keep it in the road system at this time,” she said.
Meanwhile the Swan View Coalition and Friends of the Wild Swan continue to push to have the road either repaired or decommissioned.
“It’s much better to make the investment in removing these roads rather than suffer the consequences,” said Arlene Montgomery, program director of Friends of the Wild Swan. “This landslide is an unnecessary setback for water quality and native fish habitat.”