Bio Station fights shoreline erosion with innovative gravel beach
| August 12, 2020 1:00 AM
Bio Station fights shoreline erosion with innovative gravel beach
University of Montana physical lake ecologist Dr. Mark Lorang stood on the shore front of the Flathead Lake Biological Station enthusiastically taking pictures of the beach. “I wish I could have been down here filming it when it was happening,” he said.
Lorang was referring to a brief, intense storm that had rolled through the previous night. Its waves had rearranged the biological station’s newly completed erosion control beach, and Lorang wanted to see how it had fared. He had meticulously designed this beach to protect a portion of the station’s shoreline, and its completion meant part of a decades-long plan had finally come to fruition.
The beach was constructed in March when things at FLBS were quiet. For the people working at the bio station during beach construction, the sound of heavy machinery and delivery of truckload after truckload of gravel was a change of pace.
Abigail Schmeichel who started working as a K-12 educator at the station in January said it was an interesting process to watch. Over the course of almost two weeks, truckloads of cobble and gravel were transported continuously from Polson and Woods Bay.
“Every day from 8 to 5 p.m. you could hear the trucks going, beeping, backing up and turning around,” Schmeichel said. “It definitely spiced up the week.”
Schmeichel had a front-row view of the beach construction from her FLBS apartment and went to check out the process frequently. She said the addition of the beach is nice from a user standpoint. The slope of the bank into the water is less steep, and the gravel is easier to walk on.
But the beach wasn’t installed for aesthetics and recreational use, although they are a happy byproduct. It has a very functional purpose. It’s called a “dynamic equilibrium beach” – a beach designed to prevent shoreline erosion and help restore habitat.
Lorang, a former FLBS faculty member, has studied Flathead Lake for over 30 years. His research led him to design soft structure beaches made of varying particle sizes (i.e., gravel and cobble) that can absorb and dissipate incoming wave energy, thus preventing damaging erosion.
The bio station beach is made up of varying sizes of rocks that were placed strategically at low water. First, a mix of larger cobbles and gravel was placed lower down on the exposed shoreline. That was followed by a smaller cobble mix above the previous layer. And finally on top of all that, a large amount of pea-sized gravel was deposited, extending up towards the trees. When the lake’s water levels were brought up in June, only the easy to walk on smaller gravel was left exposed.
When waves break on the gravel, it is pushed around as it absorbs the energy. A big storm at a high water level will create a berm or beach crest built up by the largest waves tossing larger rocks on top of the smaller gravel. The waves dynamically reshape the gravels into a beach that can break the waves and dissipate the erosive energy. It will take subsequent larger storms to rearrange the beach again.
Ultimately, Lorang has installed a soft structure that mimics what natural beaches do.
Flathead Lake water levels are controlled by the Seli’š Ksanka Qlispe’ Dam, formerly known as Kerr Dam, near Polson. Lake levels fluctuate as much as 10 feet throughout the year. In the summer the water is purposefully kept at a high level or “full pool” for recreational purposes.
The UM station has lost 1.6 acres of shoreline property since the regulation of Flathead Lake’s water level began in 1938. Lorang has designed and helped install about 2.5 miles of dynamic equilibrium beaches on Flathead Lake’s shoreline since 1989.
Traditional and most commonly used methods for preventing erosion are hard structures such as seawalls, large barriers usually made of concrete and riprap – a field of large boulders or objects. Historically, large car bodies have been used along river banks, creating “Detroit riprap.”
These methods have some drawbacks, Lorgan said. The energy of a wave is what causes erosion. That energy doesn’t dissipate when it hits a hard structure like a concrete wall but is reflected back into the lake where it interacts with other incoming waves.
Lorang said beaches moving and being reshaped is a part of natural processes. It’s normal to see these beaches change after storms. That’s the point of a dynamic structure: It can adapt and change to the variable wave and storm conditions while dissipating the wave energy that causes shoreline erosion.
These beaches have been slow to grow in popularity, and Lorang thinks that people have this perception that a changing or “dynamic” beach means something bad.
But essentially, Lorang is simply providing the right volumes and distributions of gravel material so that the waves can do the work of mimicking what natural beaches do. And natural beaches change over time. Lorang said this method of designing with nature just doesn’t have enough credibility, yet.
“The first thing people do when they buy property out here is stake out their boundaries. Usually that means cutting down trees and building a seawall,” Lorang said.
In total, about 460 feet of FLBS shoreline was transformed, with close to 1,020 cubic yards of cobble and gravel. In weight that’s about 1,020 Toyota Corollas or 510 medium-sized hippos.
The beach was built with money the bio station was awarded in a recent class-action lawsuit for shoreline damages caused by dam-regulated lake levels, according to Tom Bansak, FLBS associate director.
Bansak said the station wants their beach to serve as a model of how Lorang’s beach design works over time.
FBLS officials and Lorang have future plans to protect more of its shoreline with this kind of erosion control, Bansak said. This includes the adjacent Yellow Bay Unit at Flathead Lake State Park, which sits on FLBS property. The park is open to the public and sees a lot of summer users on its shrinking shoreline. Station personnel want to enhance the visitor experience by helping to restore and protect the park.
“From a recreational standpoint, you can’t use half the state park, right? Because you have to fight through the brush to get to the water,” Bansak said.
Flathead Lake State Park manager Amy Grout has been in talks with the bio station about an erosion control beach. Yellow Bay is one of six units around the lake that make up Flathead Lake State Park. Grout said the idea of Yellow Bay having one of Lorang’s beaches is exciting. She has been park manager for five years, and within the last year she has noticed notable erosion at Yellow Bay.
“A beach would allow for more usable area of the shoreline for the public,” she said.
The challenge for Yellow Bay is finding the funding. While Grout is on board with putting in a beach, the money isn’t there. She said the Flathead parks have many facilities that need repairs and upgrades, and those take priority. Finding funding will be a challenge, but the bio station and partners are looking to philanthropy to help foot the bill.
Standing on the new bio station beach, Lorang commented on how the beach has already changed shape, hypothesizing why a curve was created here or debris was deposited there. He wants Whited to fly a drone over to take aerial photos of the beach to document the changes made before and after the storm.
“I’ve been doing this for 40 years, and I still get excited about beaches,” Lorang said.