URGENT! - Dam Debris (Fall 2021)

The following was relayed via CRCA regarding debris accumulation in the dam. Photos are included at the end of this post.

Description of the Debris Accumulation
Operations staff don’t have anything else to add to the description that I provided in my December 6th e-mail (excerpt below) of the November 7th accumulation of concern:

“…debris accumulation at the dam, which was abnormally high this year and contributed to some operational difficulties. Operations staff who cleared a large accumulation of debris on November 8, 2021, described most of the debris as appearing “to be trimmed branches and construction debris from homeowners on the lake, not beaver activity or other natural processes”. The blockage was so great that a follow up visit was necessary to clear the rest of it. The blockage also had a considerable effected on water level and discharge control at the dam. Staff describe this as being the first time since 2013 that they’ve had to struggle with debris at this location.”

Impacts on Operation & Safety
Operations staff more recently noted the following, regarding the impact of the debris:

“I would say the big impact is that when logs are placed in the dam to hold back water, that they need to sit flush together in order to work as intended, and that the branches and debris that get caught between logs allow leaks. Not only does this mean that the dam is not functioning as intended, it also means pulling logs back out, clearing debris, and re-seating them. This leads to unnecessary operator fatigue and also spending much more time at the site then needed (impacting other work we need to get done). The debris clearing is physically intense work.”

I would add that because of the magnitude of the accumulations this year, there have been times that we’ve had to clear the debris via access from below (underneath the roadway). It’s my experience that it used to be debris accumulations were much more manageable, necessitating only a quick raking from above to clear a few sticks prior to stoplog adjustments. As such, larger accumulations have greater Operator safety implications.

Impacts on Water Level & Flood Management
From a water level management and discharge perspective I will add that the debris accumulation and associated discharge restriction resulted in prolonged elevated water levels following rainfall at the end of October. Water levels above the Upper Compliance Level necessitated our intervention to clear the blockage to facilitate the fall drawdown to stabilize water levels prior to winter freeze-up. Under more extreme conditions (e.g., heavy rainfall or spring freshet) reduced discharge capacity from similar blockages could result in very high lake levels and complicate efforts to balance high-water impacts upstream and downstream, which is typically done with appropriate stoplog adjustments informed by experience and analysis based on an unobstructed water control structure.

Photos



Spring 2022 Update:

These pics show dam debris from last summer, as well as lake debris that has breached the Sydenham dam and made its way into the Milhaven Creek. The two tangles are partially impeding the creek flow and continue to accumulate debris. We are in discussions with Conservation Authority about their removal.

Each of us remaining vigilant about making sure our cuttings and construction materials remain out of the lake will help minimize this in future seasons/years - leaving predominantly natural decay in the dam that is easier for each of us and the CRCA to manage, and much more sustainable for the environment.

New photos taken April 1, 2022:
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