The need to design a new weir for Cowichan Lake was set in motion when, in response to increasing frequency of critically low summer flows in the Cowichan River, a partnership was formed by the Cowichan Valley Regional District (CVRD), Cowichan Tribes, the Cowichan Watershed Board and Catalyst Paper (a Paper Excellence company) to conduct a Water Use Planning study as per the Province of BC Water Use Plan (WUP) Guidelines.
A Public Advisory Group was formed and, beginning in the Fall of 2017 and finishing in the Spring of 2018, the group developed a Water Use Plan (WUP) for Cowichan Lake and Cowichan River that provides a balanced, long term solution for storing water on Cowichan Lake in order to maintain sufficient water flows in the Cowichan River into the future. The key recommendation of the WUP is to construct a new weir with an increase of 70 cm of elevation above the existing weir.
A condition of this recommendation is that an assessment be done to understand thepotential impacts to Cowichan Lake shoreline due to the additional storage, (go to the Cowichan Lake Shoreline Assessment Project page to learn more about this effort).
Work is currently underway to design a new weir for the Cowichan Lake that will store adequate water for future needs, while reflecting the visual, environmental and recreation goals of the community. Climate change is driving longer, hotter, drier summers, resulting in reduced water levels and flow in the Cowichan River. A new weir would result in maintaining water levels and river flows that will provide enough water to support:
- Fish spawning, habitat, and passage
- Flora and fauna in the Cowichan Estuary
- Recreation on the Cowichan River
- Sport fishing
- Water supply for surrounding community
- Water supply for industrial use
- Wastewater dilution requirements
The development of the new weir design is being funded entirely by the BC Salmon Restoration and Innovation Fund through a grant that was awarded by Fisheries and Oceans Canada to address the following key issues:
- Develop the necessary engineering designs, environmental impact assessments and geotechnical studies, cost estimates and tender documents to allow the partners or others to support a future water license application for a new structure.
- Design the temporary works and the removal of the existing infrastructure to reduce environmental impacts and allow for the potential beneficial reuse of systems components if applicable.
- Provide the necessary information to support future regulatory review.
You will be redirected to a secure server through the CVRD website to enter your information. Find the Weir Project Updates under Notify Me.
The existing weir located at the mouth of Lake Cowichan and in the Town of Lake Cowichan was built in the 1950’s to provide industrial water storage for the Pulp & Paper Mill in Crofton; now, Paper Excellence. The 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. The weir was not designed to hold the additional and necessary volume of water to sustain the river flows we now need, nor does it meet today’s engineering standards required for expansion of storage capacity. The control structure (weir, boat lock, and gates) is no longer capable of satisfying the current and future needs.
Current Weir Operation, Lake Levels, and River Flows
The images below from the WUP public meeting in October of 2017, illustrate how the demand for water in the summer is surpassing the supply.
New Cowichan Lake Weir Design
The new control structure 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. The new structure will be designed as per the BC’s dam safety requirements and will allow better management of the stored water.
Upgraded monitoring systems will be utilized 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 (anticipated to be late winter / early spring). 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.
In order for necessary implementation of the proposed capital works, detailed cost estimates will be required for investment purposes. Detailed tender documents will be provided for future implementation.
The new weir design is a multi-step process that begins by developing an understanding of the geotechnical profile and characteristics of the lake discharge area and moves through a structured process to determine both the optimum location and design of a new structure.
Detailed geotechnical studies and analysis will ensure that the new infrastructure is designed to meet the existing dam safety requirements. The dam and its attendant control features will also be designed to use remote sensing information and analytics to optimize both water and safety features. The Cowichan Lake Weir Design includes:
- Assessment of the existing structure, including gates and boat lock
- Site Selection for the new weir structure, the boat lock, and gates
- Preliminary and final design for the:
- Weir and fish passage
- Boat lock
- Mechanical and electrical systems
- Temporary works
- Environmental Impact Analysis during construction
- Decommissioning plan for the existing structure
- Preparing construction drawings, including specifications
- Preparing Cost Estimates at each design stage
- Preparing Tender package, including drawings and technical specifications
- Approvals (permits)