The Shadowy St. Joe River is losing its signature shade trees.
Hundreds of cottonwoods that once lined natural levees along the lower St. Joe River are gone. Uprooted by erosion, the big, old trees washed away. A few linger as driftwood on the remaining mudflats, but even the mudflats are vanishing.
Over thousands of years, the St. Joe River deposited silt that created a system of parallel levees stretching into Lake Coeur d’Alene. Old postcards depict watery avenues with sunlight filtering through leafy canopies.
But the trees and the levees that support them have lost ground to erosion from powerboats and an artificially high summer lake level.
“If nothing is done, the Shadowy St. Joe as we know it will disappear,” said Dave Lamb, a lake ecologist for the Coeur d’Alene Tribe.
The tribe hopes to halt the worst of the erosion with help from Avista Corp. As part of its Spokane River dam relicensing project, the utility agreed to pay $100 million over the next 50 years for restoration work on tribal lands. Part of the money will be used to shore up the levees.
As a first step, the tribe and Avista hired a consultant to measure erosion rates. Bruce Stoker, a geologist who runs a company called Earth Systems in Monroe, Wash., spent two months surveying the levees.
“The bottom three miles of the Shadowy St. Joe are gone,” said Stoker, as he rode up the St. Joe on a pontoon boat, past levees that had eroded into barren mudflats or had vanished under water. “In the next 50 years, the next two miles could disappear, too.”
The Coeur d’Alene Tribe, which owns the southern third of Lake Coeur d’Alene, hopes to avoid that scenario. Their ancestors fished from the levees and harvested water potatoes from shallow waters along the banks.
Ecologically, the intact levees farther upstream are tremendously rich habitat, said Lamb, the lake ecologist. Moose and deer feed on red osier dogwoods and willows that sprout on the levees. The intersection of land and water also attracts beaver, muskrat, osprey and great blue herons.
Last summer, Stoker camped on his boat next to the levees. The sound of tiny teeth kept him awake.
“These levees are just bursting with life,” Stoker said. “There were so many little mammals in the grass that you could hear them all chewing.”
The area’s beauty also attracts people. In the early 1900s, steamboats chugged up the St. Joe River on scenic excursions. A rusted wood stove, still visible on the shore, attests to the levees’ long popularity with campers.
Avista’s Post Falls Dam on the Spokane River went into operation in 1906, allowing the utility to control Lake Coeur d’Alene’s water level by regulating flows over the dam. To enhance recreation, the utility started manipulating summer lake levels.
Between Memorial Day and Labor Day, the utility shoots for lake levels of 2,128 feet above sea level. The higher water creates better boating conditions and deeper dock access for hundreds of property owners along the lake and the upper Spokane River. But the manipulation also keeps wetlands underwater three to four months longer than nature intended.
Under natural conditions, Lake Coeur d’Alene would typically cover roughly 30,000 acres during the dry summer months. Nowadays, the lake covers 41,000 acres, and the high pool extends farther up the St. Joe River.
Wakes from increased boat traffic also contribute to erosion, said Stoker, the consultant. Counts estimate the volume of boat traffic up the St. Joe River each summer is 5,000 to 6,000 roundtrips.
The Coeur d’Alene Tribe supported a high summer pool in Lake Coeur d’Alene as part of Avista’s dam relicensing process. In return, however, the utility agreed to pay a settlement for flooding the tribe’s land and establish the $100 million fund for restoration work.
Now that erosion rates have been established for the levees, Avista and the tribe will work together to identify priority areas for erosion control, said Meghan Lunney, Avista’s aquatic resource specialist.
Stabilizing the levees will be done with rocks and vegetation, including planting young cottonwoods, Stoker said.
In some areas of the St. Joe, the cottonwoods are surviving but not reproducing. The bare, moist dirt that cottonwood seeds once fell on as the waters retreated isn’t available anymore.
“Cottonwoods are adapted for living along rivers, but they need exposed dirt for a nursery,” Stoker said. “There’s not enough unsaturated soil to germinate the seeds.”