Get rid of the trees. That’s the U.S. Army Corps of Engineers’ edict across the West in the aftermath of Hurricane Katrina.
Trees are in the crosshairs as the Army Corps rates the flood-worthiness of the nation’s levee structures. After years of subjective interpretations and lax enforcement of national policies that prohibit woody vegetation on levees, the agency has begun cracking down, catching dozens of Northwest communities by surprise.
In Coeur d’Alene, the corps flagged mature Ponderosa pines along a dike road bordering Lake Coeur d’Alene and the Spokane River, saying the trees could topple during a flood, tearing holes in the levee, or creating seepage pathways along the roots. The levees passed decades of inspections – until this spring, said City Engineer Gordon Dobler.
In Missoula, the offending trees are cottonwoods along the Clark Fork River. In Pocatello, willows in the Porteuf River greenbelt. In King County, a mixed forest that contributes to habitat for endangered salmon and steelhead runs.
Community response has varied. The city of Missoula logged about a mile of its levees to comply with corps’ standards, which affect flood plain maps and insurance rates for residents and businesses. Other communities have compromised or fought to keep their trees, questioning the validity of the science behind tree removal.
“The corps has one set of standards that applies all across the country,” said Steve Bleifuhs, manager of King County’s river and floodplain management section. “It ignores regional differences and unique environments. … Every soil type is different, every vegetation type is different.”
In King County, cost could be $150 million
After King County cut down 500 trees along the Green River levees near Seattle to satisfy the Army Corps, the county spent $2 million on land purchases for mitigation required by the Washington Department of Fish and Wildlife for the loss of salmon and steelhead habitat.
Trees are crucial to watersheds, Bleifuhs said. Their shade helps cool water temperatures, so “you’re not cooking the fish,” he said. Trees also provide breeding grounds for the insects consumed by fish.
King County continues to work with the corps on the Green River’s levee system. However, the county has adopted its own vegetation management plan for the Cedar, Snoqualmie and White watersheds, which will keep trees on the levees. Meeting the corps’ requirements on 46 miles of levees would cost up to $150 million, the county estimates. And it’s a questionable policy, Bleifuhs said.
“We have a lot of anecdotal evidence around the performance of vegetation, how it reduces erosion on levees,” he said. “The root structure helps bind soil together.”
In California, three environmental groups sued the corps in June, saying the “vegetation-free” policy would require clear-cutting trees along 1,600 miles of levees in the Sacramento and San Joaquin watersheds, destroying habitat for threatened salmon, sturgeon and smelt.
Corps officials adopted the policy without “any environmental review … and without scientific support,” said the suit, which was filed by Friends of the River, Center for Biological Diversity and Defenders of Wildlife.
“There is substantial public controversy over the issue of whether vegetation has an adverse effect on levee performance in California,” the suit said. “Most of the studies … have concluded that vegetation is compatible with the flood control function of levees, or that vegetation actually improves public safety by reducing the potential for levee erosion.”
Corps reviewing its vegetation policy
Roger Smith, a retired civil engineer from Coeur d’Alene, often walks the dike road separating North Idaho College and the Fort Grounds neighborhood from Lake Coeur d’Alene and the Spokane River. The towering pines along the waterfront are an “aesthetic heritage feature” for the city, Smith said.
He was one of several speakers at Tuesday night’s City Council meeting who urged the council to seek options other than cutting down the trees – advice the City Council heeded and passed as a resolution. The Army Corps is in the midst of a two-year review of its vegetation policy, Smith and others noted.
“It would be a crime to remove those trees and have it come out a week later that they don’t need to be removed,” said Mike Kennedy, a Coeur d’Alene city councilman.
After levees in New Orleans failed in the aftermath of Hurricane Katrina in 2005, the Army Corps stepped up scrutiny of levees nationwide. Tammy Conforti, the Army Corps’ levee safety program manager in Washington, D.C., acknowledged that “vegetation … has gotten a lot of attention lately.”
In recent years, the corps has tried to create consistent standards for acceptable vegetation on levees, Conforti said. While the science is still emerging, “what we know is that large woody vegetation introduces some uncertainly to a levee, (but) we don’t know exactly how to quantify that uncertainty,” Conforti said. The corps is erring on the side of caution, because it inspects levees with the intent of protecting both people and property during floods.
Having levees “decertified” as flood-worthy by the corps can result in serious economic repercussions. After levees along the Walla Walla River in Milton-Freewater, Ore., were decertified, the Federal Emergency Management Agency remapped the area’s 100-year flood plain, including the city of 6,400 within the boundaries.
Selling homes became difficult, and the city couldn’t qualify for certain types of grants, said Linda Hall, the city administrator. Milton-Freewater appealed FEMA’s new flood plain boundaries, which softened some of the restrictions, while citizens passed a bond for structural levee repairs. The community is currently working with the Army Corps and the Umatilla Tribe on a vegetation management plan for the levees.
CdA examining options on levee
The Coeur d’Alene City Council took a nuanced approach Tuesday, authorizing the city’s engineer to begin other levee repair work outlined in the corps’ inspection report, while investigating options for keeping as many trees as possible. Coeur d’Alene has two years to address the levee deficiencies.
“Our goal is to keep that levee certified,” said Dobler, the city engineer. If the levee loses certification and the Fort Grounds neighborhood is re-mapped within the 100-year flood plain, flood insurance rates would likely shoot up and building restrictions could go into effect, according to FEMA officials.
Council members weighed practical considerations and aesthetic values during Tuesday night’s discussion. The massive pines shadowing the dike road are important to many city residents, they acknowledged. “That’s one of my favorite places in the whole world, and I’d hate to see it changed,” said City Councilwoman Deanna Goodlander.