The preliminary design for the new Cowichan Lake weir is ready to be presented.
The preliminary design and information are now posted on cowichanlakeweir.ca and a live presentation that will be held on Dec. 10 on the same site will introduce the design and its particular elements, such as the weir’s fish passage.
The design is expected to be finalized by May, 2021.
Over a two-year period from 2017 to 2018, a public advisory group developed a water-use plan for Cowichan Lake and Cowichan River that provides a long-term solution for storing water on the lake in order to maintain sufficient water flows in the river into the future, taking into consideration the climate change projections for the watershed.
The key recommendation of the advisory group is to construct a new weir with an increase of 70 cm of elevation above the existing weir.
The current weir, located at the mouth of Cowichan Lake in the Town of Lake Cowichan, was built in the 1950s to provide industrial water storage for the Catalyst pulp and paper mill in Crofton.
The original purpose and design of the weir was to store the necessary water based on the need for process water to run the mill’s operations.
But the weir was not designed to hold the additional and necessary volume of water to sustain the river flows that are now needed, nor does it meet today’s engineering standards required for expansion of storage capacity.
The control structure — including the weir, boat lock, and gates — is no longer capable of satisfying the current and future needs.
In 2019, after one of the worst droughts in the region in decades, Catalyst had to begin pumping water into the Cowichan River over the weir on Aug. 29 for several weeks to maintain water flows in the river and save the river’s fish populations.
It was the first time the company has had to take such action since the weir was first constructed.
According to the CVRD’s website, the preliminary design of the new weir will not only store adequate water to sustain the river flow, but will also allow regulated extraction from the system, in particular during dry seasons.
Upgraded monitoring systems will be used and designed to allow for the structure to be managed within very tight environmental constraints to be adaptive and responsive to environmental and climatic conditions.
The new structure will also be designed to adjust to a potential emergency release of water due to the necessity to store water much earlier in the season.
This is a much higher level of control than the existing infrastructure is capable of and will require a much more refined control structure moderating the spilling of the limited water resources.
The existing weir will also have to be carefully removed at or about the same time as the new infrastructure is built.
This will require environmental impact analysis and engineering to identify both the best process to do this and if any repurposing of the existing system is possible.
Project manager Leroy Van Wieren said a number of studies have yet to be completed, and some bureaucratic details still have to be dealt with before shovels go into the ground to construct the new weir.
He said he expects the construction of the new weir, whose total cost has yet to determined, should begin in 2024, and it should take less than a year to complete.
The live online presentation on Dec. 10 (visit cowichanlakeweir.ca for a link to the presentation) will run from 6 p.m. to 7 p.m., and a Q and A will follow from 7 p.m. to 8 p.m.
The call-in number is 1-844-992-4726, and the call-in access code is 146 385 7474.