July 13, 2011 in City

River channels to be filled

Avista work will enhance look of upper Spokane Falls
By The Spokesman-Review
 
Map of this story's location
Purpose of work

Avista Utilities, which controls the falls with a dam at the east end of Riverfront Park, is seeking to enhance the natural look of the falls while saving a majority of the river’s water for power generation at the park.

Repair work to restore the historic riverbed beneath the upper Spokane Falls will get started later this summer after the Spokane River drops to seasonal lows.

The Spokane hearing examiner on Monday approved a shoreline substantial development permit for the project.

The goal is to restore the river channel on the north and south sides of Canada Island in Riverfront Park so that the falls maintains its visual integrity during low water.

Avista Utilities, which controls the falls with a dam at the east end of Riverfront Park, is seeking to enhance the natural look of the falls while saving a majority of the river’s water for power generation at the park.

Channels were historically carved into the basalt bedrock of the river to convey sewage and to divert water to early-day mills.

Avista is going to hire a contractor to fill those channels with concrete structures known as weirs that will be anchored to the bedrock and made to match the native stone.

A limited amount of water – 300 cubic feet per second – will be sent over the falls. With the restoration, that water should give the look of a fuller falls.

“The project will spread water more evenly,” said Anna Scarlett, spokeswoman for Avista.

The project was outlined as part of Avista’s 2009 dam relicensing through the Federal Energy Regulatory Commission.

Under the license, Avista could have chosen to let 500 cfs pass over the falls in lieu of restoring the channel and spilling the 300 cfs over the falls.

The river last September dropped to a low flow of about 900 cfs.

The falls is considered a major natural asset in downtown Spokane, but in the past has been anemic or almost non-existent during low water.

The riverbed restoration is expected to improve fish passage during certain periods of the year, the hearing examiner said.

Work will include placing track vehicles into the river channel with a crane; fencing to protect the construction area; temporary bridges for traversing the terrain in the channel; temporary water diversion structures; and minor shaving of existing basalt.

Concrete would be pumped to each construction site, according to the hearing examiner findings.

Steel anchors with high-strength resin would be used to hold the structures in place.

Leftover concrete in hoses will be drained onto an impermeable membrane surrounded by absorbent booms and then removed by crane. Truck and equipment cleaning must be done away from the river.

Hearing Examiner Greg Smith is requiring ongoing maintenance as needed.

“The impacts of the placements of the weirs should be positive to the environment,” Smith found in his ruling.

Scarlett said that Avista is ready to seek a contractor for the job that could last into October.


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