Avista has begun work on the Post Falls Dam, which is in need of some much-needed repairs.
The southern spillway on the dam was built in 1906 and holds back the water that keeps Lake Coeur d'Alene at its summer elevation. However more than a century of raging spring runoffs have taken their toll on the dam.
Before work can begin on the southern spillway Avista has to to build a coffer dam, which will require diving to the bottom of the 30 foot channel and welding steel in place to hold back the water so workers can get to the dam.
“Well after we dredge and prepare the foundation we have to start setting up the sheet pile and the template structure, the steel template structure,” Avista project manager Mary Jensen said.
In the middle of the coffer dam, which is being built by Kunney Construction, there's a platform for the crane that will do the heavy lifting on the project, including lifting into place the 2,500 sandbags that will help hold it in place and keep most of the water out.
“We know we're going to have seepage, we're going to deal with it. we're going to meet water quality standards and we're going to have a series of systems in place to take care of the seepage,” Jensen said.
Once the water behind the coffer dam is drained off crews will begin the process of replacing spill gates so water levels can be regulated more efficiently.
“Currently it takes about two and a half hours to open up all six gates. We need a crew of three Avista workers to open or close the gates so this process will allow us to have automatic gates and at a touch of a button be able to open the gates,” Jensen explained.
Avista also wants to get a look at the spillway's concrete and make sure it's structurally sound. The Post Falls Dam makes enough power for 14,000 homes and if it failed we'd lose more than just electricity.
“It keeps Lake Coeur d'Alene a lake. If it wasn't in the way, half of the year it would be at quite a low elevation and we wouldn't have the great recreation that we do without the dams in the summertime,” Jensen said.
Avista expects to have the dam construction project wrapped up by next March.