Bank erosion a growing concern on Flathead River

By AVERY HOWE 

For the Hungry Horse News

“We had heard a lot from landowners in recent years about concerns with erosion,” Flathead Conservation District resource conservationist Samantha Tappenbeck said. “These are riverfront landowners that are contacting us and saying, ‘We are losing a crazy amount of ground to erosion that’s unprecedented.’”

Tappenbeck led a community meeting on the results of a 2022 FCD study determining recreational boating’s impact on erosion in the Flathead River on Thursday, Aug. 28. A large group of participants gathered at the Diamond B Ranch, directly next to the river, to share their sometimes heated viewpoints on how watercrafts and erosion could be handled.  

The last study on Flathead River erosion was done in 2010 by Flathead Lake Biological Station, which measured 13 miles of moderate erosion and 6 miles of severe erosion compared to 9 miles of no erosion; excluding stabilized shorelines. A FWP study showed hours boating on the lake during the summer months more than quadrupled from 1992 to 2008. The study concluded there was likely increased erosion due to this activity.  

Tappenbeck noted that both studies are over a decade old, leaving a large information gap over a timespan where multitudes of people have moved to the Flathead Valley. Landowners reported to FCD the accelerated loss of acreage, threats to structures, and a perceived recreation increase. 

Tappenbeck reminded the crowd that erosion is not a new factor in the Flathead; drivers include lake level, freeze and thaw, river current, development near streambeds, waves and wakes. The banks of Flathead River are sandy and prone to erosion in many places. Riprap and armoring have been common practice throughout history. “Detroit riprap,” cars pushed into the river around the 1940s to stabilize the bank, are still visible in some places along the river. 

“But these days I think we are seeing extraordinary erosion,” Tappenbeck said. 

She showed photos of fully vegetated banks on the Flathead River undercut, where root systems should be enough to stabilize the soil, irrigation intakes washed out and fence lines threatened by the water line.  

Streambank erosion is estimated to contribute 20-30% of suspended solids and 60% of nutrient loading in the Flathead River. DEQ’s Total Maximum Daily Loads document reported erosion as a major contributor to pollutants in Flathead Lake. The Flathead-Stillwater Restoration plan also identifies stream bank erosion as a priority for restoration. 

It is difficult to measure erosion from specific drivers, Tappenbeck said. The 2022 FCD study looked to address the concerns of landowners reporting loss of property by measuring the wake energy produced by various types of boats on the Flathead River. Four stations were set up on the lower 21 miles of the river, starting at one mile upstream of Flathead Lake. Each was equipped with a pressure transducer and a video camera; data was collected for wave events and correlated to recreational watercraft when applicable by comparing timestamped video of the river. They collected information from July-Sept running 8 a.m. to 9 p.m. 

Station 3, the second most northern, went out for unknown reasons, possibly a lightning strike. Of the remaining data collected, the number of discrete wave events measured decreased moving north, away from Flathead Lake.  

The study found that the height of a wave generated was more influential on the wave energy, the force hitting the shoreline, than the number of waves. Consistently, wake boats produced the highest waves with 1.09 feet the largest height recorded. The number of wake boats recorded at Station 2 was 101 between July 7-23, with pontoons at 105, bowriders at 71, speedboats at 54, fishing boats at 52 and personal watercraft at 24.  The number of discrete wave events was higher on weekends, holidays and evenings. 

Zac Andrews, a riverfront property owner, suggested that anecdotal evidence regarding property owners’ experiences should not be regarded as scientific evidence. Runoff, climate change, wind and other factors were not considered in the study.  

“Erosion happens no matter what, and boats contribute, but the boats are contributing a very little bit to the total amount,” Andrews said. He proposed that bank stabilization should be prioritized regardless of the cause of erosion and education for boaters, to keep them further from shore, should be implemented to minimize conflicts.  

Several audience members complained of the cumbersome process to put riprap in place along the Flathead River, which requires cooperation from multiple organizations. A set of rules to streamline the engineering process for shore stabilization was suggested.  

At the same time, commenters reiterated stories of waves from boats taking off grass and trees from their lawns every summer. Concern was raised about the relocation of Sportsman’s Bridge fishing access site, which will begin in early 2025 and was presumed by commenters to increase boater activity. The new location off Oldenberg Road would cover roughly 18.2 acres, provide access to around 1,000 feet of Flathead River shoreline and include a two-lane boat ramp, 38 truck-trailer parking spots and 10 standard vehicle parking spots.  There was disappointment that a monitoring station had not been placed at Sportsman’s Bridge or closer to the lake for the study.  

It was suggested that FWP law enforcement was not adequate to deal with any regulations that could be put in place on the river. Education, it seemed, was the preferred way to deal with boaters and their wakes.  

“We’re not asking to regulate, but something has to get figured out with some of this stuff,” FCD board member Mark Siderius said. “There’s people in this room who have been here for generations... It has to be a good neighbor thing, or it is going to get regulated by those outside of the area and I don’t think any of us are going to like those regulations.” 

There are no definitive plans to continue the FCD wake study, grant money is not currently available. No recommendations are being made. The FCD Board meets the second and fourth Mondays of every month at 1 p.m. and are open to the public virtually via Zoom or at the USDA/FCD  in Kalispell. For more information, visit https://flatheadcd.org/fcd-meetings/.