The Idlewild dam rehabilitation project is on pace for construction in August, as city staff are soon hoping have a finalized plan in order to tender out a contract by July.
The Idlewild dam was decommissioned last spring, after city council received a report warning of the potential for a dam breach, which could cause a flooding disaster downstream of Joseph Creek.
"The most critical mode of failure of the dam was identified as overtopping, which raises the water level over the dam crest significantly increasing the volume of water stored behind the dam if a breach occurred," read the report—Dam Breach Inundation Study. "Other modes of failure identified include the low hydraulic capacity of the spillway, its potential for debris blockage and increased storms combining also identified as the most likely to occur — and capacity in Joseph Creek being reduced or used up by overtopping flows, which would increase the extent of flooding by the breach."
According to an administration update from CAO David Kim, the design planning of the rehabilitation project is well underway, including geotechnical work and modelling to determine creek flows. An archaeological impact assessment is also scheduled for the site.
Mike Matejka, the project manager for the City of Cranbrook, said the dam structure and the concrete spillway is past it's lifespan.
"The main reason that the project needs to be undertaken is because of the condition of the existing dam, in particular, the old concrete spillway," said Matejka, "so that's something that is in poor condition, it's past it's lifespan and it is undersized, so that means it can't pass as much water as it should, so if there was to be an extreme storm event, what we have to do right now—as you see up there right now—is lower the water to anticipate that, which isn't ideal.
"We will be looking to install a new spillway which would have a much higher capacity so it will be able to pass any foreseeable amount of water that does come down."
With the spring runoff occurring earlier than usual, Matejka is hoping that will mean an earlier start to the project itself.
"Timelines are restricted as far as the construction goes based on the timing of the spring runoff," Matejka said, "so we've been fortunate this year that the runoff has been fairly mild and it did happen much earlier than anticipated, about three weeks earlier, so that does give us the opportunity to start work a little bit earlier. "
We are working to try to get some of the design and the tender out maybe a little bit earlier so we can have a contract or a contractor in place sometime around the middle of July."
In order to do the work, the city will have to install a new bypass to ensure the creek flow through the park to below the dam.
"That is something we have to ensure, is that we maintain the flow to Joseph Creek below the dam and the new bypass will allow us to do that in a safe way such that we can undertake the construction without having any additional risks of the water going through the existing dam and spillway," Matekja said.
While much of the focus is on the dam structure, city staff are also in the process of creating an Idlewild Park Master Plan to illustrate and describe future development of the park.