Missoula County, Army Corps of Engineers seek repairs and mitigation from Clark Fork flooding

EVE BYRON eve.byron@missoulian.com | Posted: Tuesday, December 11, 2018 1:53 pm

Changes in the Clark Fork River and subsequent flooding during the past decade are prompting Missoula County to take a two-pronged approach to repair damages and lessen future impacts.

On Tuesday, the county signed a cooperation agreement with the U.S. Army Corps of Engineers to restore flood control measures — in particular, a levee in the Orchard Homes area — that was damaged during the spring flooding.

The levee sustained an estimated $1 million worth of damage from the high water, according to Chief Public Works Officer Greg Robertson. Impairments along about 805 linear feet include “scouring,” in which portions of the levee were washed away when topped by floodwaters; the loss of large “toe rocks” that are placed at the base of the levee for stabilization, and a 6-foot-long crack.

Under the agreement, the county will cover $193,780 in costs, which is about 20 percent of the overall repairs, Robertson said. The county can either provide cash or “in kind” contributions to the work.

“The agreement doesn’t preclude the county from doing some work, but most of the repairs are on the river side and it’s probably best to allow the Corps to do that,” Robertson said, adding that the work will take place in March and April 2019.

Meanwhile, the county is asking the city to sign a letter that requests assistance from the Army Corps of Engineers to “develop a range of structural and non-structural alternatives” to address the flooding of residences and private property in the Orchard Homes and Tower Street areas.

“For years we have been dealing with a changing river,” the letter states. “The Clark Fork has risen above flood stage several times in the last decade. Each time, the depth and period of inundation has increased. New areas, outside of the mapped floodplain, are now underwater during relatively minor recurrence intervals and the outlook will continue to worsen.”

Commissioner Jean Curtiss noted that the flood stage used to be 10.5 feet, but flooding now regularly occurs once river flows reach 7.5 feet.

About 65 residences, mainly in the Orchard Homes area north of Third Street, were evacuated in May due to the highest flows in the Clark Fork River in 100 years. The melting snowpack that hovered around 150 percent of average in the surrounding mountains was the main source for the floodwater.

Commissioners Dave Strohmaier and Cola Rowley added that as the climate changes, with warmer days earlier in the spring that melt the snowpack faster and lead to flooding, the county needs to figure out how to prevent homes from water damage.

“We need to prepare for projected outcomes in the future based on the modeling,” Strohmaier said. “What we’ve seen in the past is now a good indicator of what the future will hold for us.”

Curtiss expects that if some type of structural solution is warranted, it probably would be placed on the city’s open space off of Tower Street.

Robertson expects the bulk of the cost of the work will be covered by the Corps, since it’s already done some of the digital mapping that’s a large part of the study for potential solutions. He said if the Corps decides to go through its Section 205 Program, it will cover the first $100,000 for the study; under the Section 2 Program, the Corps and the city/county split the costs of the study.

“This has to be a joint project, because the city of Missoula has to be a willing partner in any potential solution,'' since buying out dozens of homes would be cost prohibitive and use of the city's open space land north of the levee would make more sense, Robertson said.

“This letter doesn’t commit you to anything,'' he added. "It simply gets the process going.”

Strohmaier said this seems like a “prudent next step.”

“We heard at the public hearing, loud and clear, that the public wanted some kind of plan,” Strohmaier said. “This would at least help identify and give us some options, for sure.”

Robertson added that if they get a plan with agreed-upon options, they can pursue federal hazard mitigation money to implement it.

“That opens opportunities to pay for this,” he said.

Ginny Merriam, spokesperson for the city of Missoula, said the letter is on the mayor's desk and he plans to sign it.