Lake Sammamish level concerns homeowners
May 3, 2011
County announces plan to unclog lake-to-river transition
King County environmental managers plan to tackle the high water level in Lake Sammamish, after aquatic weeds and sediment clogged the outlet from the lake to the Sammamish River.
The problem — although centered at county-run Marymoor Park along the lake’s northern shore — reflects a common complaint among lakeside residents in Issaquah and Sammamish about the water level.
“It’s really important that we remove these things. Particularly at the north end up around Marymoor Park is a real problem, and it’s spread to the rest of the lake,” Save Lake Sammamish founder Joanna Buehler said. “For real control, you need everybody around the lake to work on it.”
The effort calls for yanking invasive plants, increased mowing near the transition zone from lake to river and enacting other steps along the lake in order to address levels along the shoreline.
County Executive Dow Constantine said the series of steps is necessary to reduce seasonal flooding along the lake.
“We are taking immediate action to provide relief for lakeside residents who have to deal with high lake levels — particularly during the wettest months of the year,” he said in a statement released in March.
The transition zone from lake to river includes a fixed-concrete spillway and a steep section of channel downstream from the weir. The area is designed to pass flood flows quickly downstream, help hold water in the lake for summer recreation and enable fish to pass upstream, including salmon returning to the Issaquah Salmon Hatchery.
In order to address the water level, county workers could also remove accumulated sediment from the transition zone. Crews also plan to mow the area each year, and as late in the season as possible, in order to reduce vegetation before the rainy season. The dense vegetation impedes flows from the lake to the Sammamish River.
County collaborates for lake
Doug Williams, spokesman for the county Department of Natural Resources and Parks, said some of the backup in the channel comes from invasive species, such as Brazilian elodea, a popular aquarium plant, and Eurasian watermilfoil, a feathery plant.
The plan also calls for “revaluating the potential for removal of accumulated sediment,” though Williams said county staffers must be careful not to disturb habitat for spawning fish in the process.
“We’re hoping this can get water moving a bit more quickly,” he said.
Soggy conditions also caused the water level in the lake to rise.
“All it takes is a couple wet springs or a particularly wet year to really fill up the lake, and it slowly drains,” Issaquah Surface Water Manager Kerry Ritland said.
In addition to the efforts, the county is working alongside Redmond municipal government on a proposed project to modify the transition zone to create more capacity in the river.
“This proposed action plan will protect private property, address salmon habitat needs and also meet the requirements of our maintenance agreement with the Army Corps of Engineers,” County Councilwoman Kathy Lambert, the Issaquah, Sammamish and Redmond representative, said in a statement. “Bringing in partners, such as the city of Redmond, will help to ensure the success of our long-term plan for the weir and the water levels on the lake.”
Dwight Martin, owner of D.K. Martin Custom Homes and a Sammamish resident, conducted a study on the weir and the affect of the structure on the lake.
Martin also serves on the citizen advisory group for the city’s upcoming Ordinary High Water Mark study.
Sammamish is in the bidding process for a study to determine the average water level on the lake — a key number in the city’s shoreline environmental regulations.
‘Lake is like a bathtub’
Lakefront homeowners petitioned the Sammamish City Council to conduct a new study instead of accepting the 28.18 feet set by Bellevue after a 2004 study. Residents had been pushing for the city to use 27 feet — the number used by U.S. Army Corps of Engineers for many years.
Martin said clearing any blockages just past the weir should make for a more accurate study and cut down on the times when heavy rains lead to a high water level, flooded docks and eroded shorelines. The homebuilder also praised the county’s responsiveness to his concerns.
“Sometimes, when citizens approach government they wonder if anyone is going to listen,” he said. “To the county’s credit, we came to them and said, ‘This is what we’re seeing,’ and they responded.”
Theories abound about the root cause for the high water level in the lake.
“There is an effort by King County to get to the bottom of if there are improvements that need to be done to improve the flow,” Ritland said. “There are theories — whether it’s more development or weeds in the Sammamish River that are slowing down the water or Bear Creek kind of backing up into the lake. It’s kind of a mystery.”
Environmentalists blame interrupted watersheds and additional construction near tributary streams for some of the problems, because development adds impervious surface.
“The lake is like a bathtub, and it used to be that it was just fed by Issaquah Creek, which puts in about 70 percent of the inflow, and then you have all of these other little creeks, like Tibbetts, Lewis, Ebright, Vasa — and they’re all very small,” Buehler said. “But they have contributed to the lake water flow.”
Rainfall exacerbates the problem, as runoff flows from neighborhoods and roads into tributary streams, rather than being absorbed into the ground.
“What has happened is, with the build-out, every one of these little streams has become, basically, like a fire hydrant, every time it rains,” Buehler said.
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