One of the biggest concerns I hear are to do with lake levels, particularly in the winter at peak water levels or often referred to as the High Water Mark (HWM).
As is turns out the Government of Canada has been recording lake levels and river flows for decades. This can be found on their website at http://www.wateroffice.gc.ca and look for station 08HA009 where it will show you current water levels and you can search historical data as well. The graph is referenced as: Real-Time Hydrometric Data Graph for COWICHAN LAKE NEAR LAKE COWICHAN (08HA009) [BC]
This data shows us that before the existing weir was constructed in 1957 the HWM averaged 164.16m from 1953 to 1956 and has since averaged 164.01m for the 61 years from 1957 to 2018. The lowest HWM was 162.33m in 1978 and the highest HWM was 165.39m in 1968.
The current weir crest height is at 162.37m. With an average HWM of 164.01m you can see that the weir is actually submerged (by 1.6 meters or 5 feet) during the high water season. I took a few photos a couple of weeks ago and the flow over the weir is hardly noticeable as the water flows completely over it, across the weir island and around the south side. The flow control shifts downstream to the natural river valley close to the Greendale Trestle and it is the river valley that then controls the HWM as the valley narrows and the river bottom rises. Similarly the new weir (at 163.07m) will be submerged during the high water season and shouldn’t impact annual High Water levels.
With longer, hotter and dryer summers becoming the new norm it will be important to hold back some more of these winter waters for release through the summer months.