I just wanted to thank everyone for making the December 10 virtual presentation regarding the Weir Preliminary Design a success. Most importantly we had over 100 participants and you really added value with all of your great questions. Under the ‘Weir Design’ TAB on this website you can see the presentation and hear the Q&A session. Although we ran out of time, we did address most of the questions and I am hoping it addressed yours. If not, please send me your question through this site. I will do my best to respond over the next couple of weeks.
I would also like to apologize for those who did not receive enough notice regarding this meeting. Apparently some of the letters were delivered well after the meeting date. I take responsibility.
The primary reason for raising the weir is for environmental flows to support fish habitat and create a better environment for salmon in particular. Our Heritage Cowichan river has seen much degradation in it’s fish bearing capability over the past 100 years primarily due to development and climate change. This project is just one of the ways we can help protect one of our finest assets in the Cowichan Valley.
Although not required for fish health or fish passage, items like a walkway over the weir, hydroelectric power, lighting, and recreation are items of interest to people in the area. I agree we need to find the balance between a basic functional design and a design that is pleasing, educational and supports the local community. We will continue with the design in the new year and consider what we have heard.
Stay safe, take care and Best of the Holiday Season to you! Leroy.
The current ‘Weir’ actually has several distinct and unique elements making it the WEIR as we commonly describe it today. From north to south it is a collection of a boat lock, a concrete dam, a concrete sill across the weir Island, a gate structure with 4 independent gates, a fish ladder and finally a concrete sill into the south abutment. Only the gates control the flow during the control period (from April to October). During the winter months (November to March) the gates are laid down and are considered fully open. The concrete dam and sills give us the elevated water supply for us to control but they do not control the flow volume.
As we design a new elevated weir one of the questions is whether or not any of the existing structures can be reused. We have determined that we cannot reuse the concrete dam, the concrete sills nor the fish ladder. They have deteriorated over the past 63 years but most importantly they are at the wrong elevation. It appears that both the boat lock foundation and the gate foundation can be reused and would save considerable costs of demolition and rebuilding new. The health of those concrete structures will be verified over the next couple of weeks.
The design is becoming clearer as we near our Preliminary Design deadline. We will share that information with you on December 10. Stay tuned.
While I am not the right person to give you all the facts and figures on why a new weir is necessary, I can point you to few places to get all the information you need at the end of this posting. Essentially the weir is needed to support environmental (i.e. fish) flows due to climate change which has resulted in greatly reduced precipitation (including snow) in our valley. A new weir is not required to ensure water supply to Crofton’s pulp and paper mill. Their existing water license and the current weir have secured that supply since 1957 and that will continue into the future, regardless of a new weir.
I can tell you that the current structure, built in 1957, does not meet todays engineering standards or Dam Safety requirements. That doesn’t mean it isn’t safe, it just means that it requires regular reviews, inspections and that maintenance is necessary. It also means that it is not as robust as it would be if we apply today’s standards. Data of precipitation, flooding, earthquakes, seismic activity are much more robust now than 65 years ago. The understanding of science, geology, engineering, material technology has also progressed substantially over the past several decades. One would certainly expect changes to engineering and design standards over time particularly as populations have increased around water bodies.
The following are a couple of links to websites with much more information on why we need the weir:
Will the new weir raise the winter high water levels or won’t it?
One of the more common questions I have heard is regarding lakefront owners concern for flood levels. Many of the older structures were built before the current development rules (to build above the 200 year flood level) came into place and as such some of those buildings see flood conditions on occasion. They don’t want to see an increase in frequency or higher flood elevations if possible.
This brings up the question on whether or not the new weir will impact flooding conditions. Well, this is exactly one of the concerns we are trying to determine within our current projects (Weir Design and Shoreline Assessment). The shape, location and operability of the weir along with modelling historical, current and future hydrologic conditions will help us determine the impact the new weir would have during every part of the year. The answer, at this point, is we do not know yet. The weir is in the middle of it’s design process and has to account for a number of design inputs with the priority being a structure that optimizes environmental (fish) flows and fish passage from river to lake and vise versa.
The current weir is submerged throughout the winter months and the gates are laying flat on the river bottom. In the winter high water condition you can’t even tell a weir exists as it is submerged and the water easily passes overtop. That is because the weir itself is flooded due to the restriction at the Greendale Trestle where the river canyon narrows and the river bed rises. After the weir is taken off of control in early November the river flow, and therefore the elevation of the lake, is controlled by other restrictions such as the narrow valley at the Greendale Trestle. The new weir will also be submerged during the wetter winter months – as such it should become the narrow valley that continues to control flooding conditions. Our analyses will help us determine whether or not that is true.
We had our kick off meeting in the field yesterday with KWL consulting engineers who have expertise in water resource engineering. The team included a geomorphologist, a coastal engineer, a professional surveyor and a water resource engineer. The size, complexity and type of this assessment is unique. The work at Cowichan Lake will be a challenge but we have the expertise who can tackle it. Consider the variability of a lake of this size with changing beach slope angles, different geology, varying vegetation, changing winds, protected bays, exposed points, creeks and streams of all sizes as well as the work humans.
As we seek to determine the current natural boundary we need to consider a few factors: 1. The presence of water: how often water reaches a certain point on the shoreline influences what types of vegetation can grow at different elevations. 2. The action of water: the energy of waves along the shoreline depends on the exposure of the shoreline to prevailing winds or boat wakes. This wave energy determines how shoreline are eroded and vegetated over time. 3. The character of the current shoreline (slope, substrate type, vegetation) not only influences the location of the current natural boundary but also plays an important role in how the natural boundary could change as a result of the proposed upgrades and operation of the Cowichan Lake Weir.
Over the next several weeks measurements and photographs will be taken to capture existing conditions to ensure we have a solid benchmark from which to start our analyses. Our BC Professional surveyor will be using his years of experience to record the current natural boundary and key access points along the shoreline. Others will record beach substrate such as gravel, sand, mud, rock and vegetation. This new information along with existing photographs, and high resolution LiDar (light detection and ranging using laser light) data and other databases we will create a clear picture of what exists today. This information, along with a new weir design, climactic data, hydrological modelling will help us determine future impacts of raising the weir.