August 13, 2014 in City

Avista to fix Post Falls Dam’s south channel

By The Spokesman-Review
 
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Project manager Mary Jensen of Avista answers a question during a tour of a cofferdam at Post Falls Dam on Monday.
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The 108-year-old Post Falls Dam is undergoing renovations that will allow Avista utilities to respond faster to changing flows in the Spokane River.

As part of the work, the original spillway gates at the dam’s south channel will be replaced with gates that can be raised and lowered electronically on site or from the utility’s Spokane control center. The current gates require a three-person crew to raise and lower them manually, a 2 ½ to 3 ½ hour process.

“If water levels change on a Saturday, sometimes we can’t get a crew out until Monday,” said Mary Jensen, project manager for the south channel renovation work.

The $13.5 million renovation also will give the 1906 structure a face-lift. The south channel structure’s outer concrete layer will be sliced off and replaced with about 600 yards of new concrete.

“It’s basically keeping the old girl running,” Jensen said of the work.

A cofferdam and sandbags will hold back the Spokane River’s flow while the work is done on the south channel. Though the construction site is off-limits to the public, the work can be viewed from trails above the river at Q’emlin Park, which has remained open during the work.

Starting Monday, water will be drained from the river between the south channel structure and the cofferdam. That will allow crews to better evaluate the condition of the concrete below the waterline, Jensen said.

Working in the river required Avista to get permit approval from seven federal, state and local agencies.

The circular cofferdam will be anchored in place with about 300 dump truck loads of fill, said Tobin Smith, project manager for Kuney Co. of Spokane, which is the contractor for the dam work. All of the fill will be removed when the work wraps up in December. Landscaping around the site will be done next spring.

The Post Falls Dam complex regulates the level of Lake Coeur d’Alene for flood control and recreation, while generating enough electricity to serve about 13,500 households.

The dam’s powerhouse is located on the middle channel of the Spokane River. The structures on the north and south channels help control river levels.

Avista upgraded the middle and north channel stuctures during earlier renovations.


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