When the rain falls and the Skykomish River rises, people living along Mann Road suddenly become islanders.
Flooding from the river and its tributary creeks and streams can make stretches of rural Snohomish County roads, including Ben Howard and Mann, impassable.
They’re located just outside of Sultan’s city limits, but the environment doesn’t necessarily recognize municipal boundaries.
“The impact to residents out on Ben Howard and Mann Road during flooding is something we certainly feel,” Sultan Mayor Russell Wiita said.
The Daily Herald has published plenty of stories about water over Ben Howard and Mann roads. In 2008, firefighters used a raft to rescue a man having a medical condition from a flooded home. In October 2019, emergency responders rescued someone from their vehicle. The road was closed again this February because of flooding.
Snohomish County has a plan: elevate a few locations of the road and install culverts so traffic and water can move safely and separately.
“We’re trying to raise the roads enough so that instead of statistically every other year it floods, we’re trying to get it every five years or so,” said Dave Lucas, Snohomish County floodplain services manager.
It costs the county about $30,000 to repair flood damage at three sites on Ben Howard and Mann roads in years with a lot of storms, Snohomish County project manager Oscar Fuentes said.
There isn’t enough data yet to declare if the river is flooding more frequently, but “it sure seems that way,” Lucas said. Snohomish County is working with the University of Washington Climate Impacts Group to gather and review information about how changes in the climate affect the flow.
The first of the two projects is to replace a Mann Road culvert at Haystack Creek, where the two pipes are failing.
In spring or summer 2021, crews are set to realign the stream, install a new concrete box culvert that is 18 feet wide and 4.5 feet high, and put up a new guardrail. A road segment of about 1,400 feet will rise about 3 feet. That project is estimated to cost $1 million, with work slated for spring or summer next year and expected to take between three and four months to complete.
County staff hope to start the more complicated and expensive project to elevate three sites and install culverts in 2023.
“These are the locations that cause the road to be closed first,” said Charlie Green, Snohomish County Public Works design engineering manager.
The most western location is a bit west of 311th Avenue Southeast/Mann Road, which crosses over the river to U.S. 2 and becomes Fifth Street in Sultan. Snohomish County staff proposed raising about 450 feet of Ben Howard Road there by about 2 feet; replacing an existing 12-inch culvert with a 6-feet by 8-feet culvert; and replacing a driveway culvert. The larger culvert allows for current stream flows in the area and would meet current fish passage standards.
“The road after the project is going to look pretty similar to what we see right now,” Green said.
After an analysis of the existing road, the county determined it would remove 4 feet of unsuitable soil in that stretch of road. All of that excavation and rebuilding the road base added to the project’s expense from its initial estimate several years ago of around $1.9 million, Green said. Raising the road in three sites now is projected to cost $5.1 million.
Closer to 311th Avenue Southeast, crews would elevate the second location’s stretch of 630 feet by about 5 feet, install a 24-inch culvert where there isn’t one now and replace the guardrail. There isn’t a stream there, so the culvert doesn’t have to meet fish passage requirements and is solely for stormwater and spillover from the river. About 2 feet of soil must be excavated there.
Crews would raise the third 650-foot section of Mann Road, known locally as Devil’s Elbow, by 6 feet, replace the guardrail, realign the stream channel and replace the existing 5-foot culvert with a 10-by-17-foot concrete box culvert.
“The stream realignment is just to make the culvert work better with the stream that’s there,” Green said.
The county ruled out elevating all of Ben Howard and Mann roads because of the prohibitive cost and potential to cause flooding elsewhere, Lucas said. Instead of preventing all of the roadway flooding in a known floodplain, county staff want to significantly reduce the amount of time it is impassable. For example, the proposed work at Devil’s Elbow could cut it from being under water on average 28 hours a year to eight hours.
“It’s good to see the county is taking steps to address it because we’ve seen, for as long as I can remember, these issues out there,” Sultan Mayor Wiita said.
County staff are set to present the projects and field questions during a virtual open house Tuesday. They want to give the area’s residents plenty of notice about the upcoming work and share their traffic plans for Mann Road, which has no other way in or out than from 311th Avenue Southeast and Ben Howard Road.
“We really want to get people in that area comfortable with that project and prepare for construction,” said Meghan Jordan, a county public works spokesperson.
People can call 253-215-8782 to listen and comment or join the Snohomish County Public Works meeting from 6:30 to 8 p.m. Tuesday, Oct. 20, via video conference at https://zoom.us/j/99098781458. The meeting identification number is 990-9878-1458.
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