Lake Levels – High Water Mark

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.

8 thoughts on “Lake Levels – High Water Mark

  1. So the HWM will be reached sooner with the higher weir meaning that our properties will experience prolonged flooding?

  2. Upon further thought the earlier and prolonged HWM will result in prolonged erosion of our property. Will property owners be given leeway in installing erosion protection for our properties without having to through the Riparian Protection development applications?

    1. An earlier and prolonged HWM has not yet been determined. This will be part of our modelling and analysis.
      This Shoreline Assessment Project is being done to inform the public, a future water license holder and application approvers. Riparian Area Regulations remain in place – this project cannot determine whether or not changes to the regulations would be supported.

  3. The higher weir will mean the HWM is reached sooner in the fall winter than in the past meaning that there will be earlier and prolonged flooding for property owners. This then leads to a longer period of erosion. Will property owners such as us, with elevations below the HWM and only 50cm above the new weir be given concessions to allow for addition of erosion protection to our property without having to go through a Riparian Protection development permit process?

    1. An earlier and prolonged HWM has not yet been determined. This will be part of our modelling and analysis.
      This Shoreline Assessment Project is being done to inform the public, future water license holder and application approvers. Riparian Area Regulations remain in place – this project cannot determine whether or not changes to the regulations would be supported.

  4. I believe that the Mill in Croften should be paying for all the work on the Weir. Also, the lake water levels will, No Dout be a problem. Absolutely, No One can say how bad it Will be. Only guessing takes place! Also, The mill can use water from the ocean. Of course they will have reasons why they dont,
    Also, the amount of Salmon Fry killed by weir pump has never bees disgussed. Business obviously does not care. $$$$$, is all that matters!

  5. Will we be hearing of your shoreline assesment soon? I’m curious how much water your going to hold in my yard. Also why are you leaving the weir gates open and draining the lake gates should operate April 1st according to current license there is plenty of water in the river for emerging fry. Common sense would be to raise the gates and retain as much water as possible for later summer months when it is needed your own modeling shows gates closed and water flowing over the weir at this time but that never seems to be the case. Yes there is snow on Heather MTN and sporadically here and there but that may not even make it to the lake as one or to small heat waves will dry that up quick. Also if your concerned about fish address the logging issues it’s out of control right down to the stream edges. They leave a tiny little ribbon of trees along the creeks,rivers,streams allowing no filtration of sediment from clear cut hill sides. Or shade to keep the water cool. Then comes winter rains Wich has no retention in the hills. down go the little ribbon of trees left causing bank erosion increase in stream flow and speed as well as piles of gravel and sediment. Weir design should have more control gates to relieve the lake of winter water influx to the lake. As the current gates are no were near adequate. A lake full to your new 70cm increase combined with snow in the hills followed by an atmospheric river and many will be affected. It happens just look at 2019 2020 lake Cowichan town had some issues. And north Cowichan mayor should consider were there water comes from and were there sewer go’s before before building his Langford style developments it’s not sustainable.

    1. The shoreline assessment work is progressing well. We are still in the data collection and modelling mode of analysis. This work will be reviewed by our Steering Committee in June. We plan to have another virtual public meeting on July 8th where we will share the results of the final weir design and introduce our preliminary shoreline assessment work.
      The weir is meant to be overtopped during winter high water conditions. The gates remain fully open during the ‘off control’ period from November to March and the ‘controlling’ feature become the river valley itself.

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