Lock Conditions 12 Aug 2020

I dove the lock last evening… I have been working at updating information on the HydroElectric Plant and wanted to do a quick check of current conditions. It was my first dive of the season – with all the changes in my pandemic existence this summer – and I noted several changes.

The first was the really, really slow current. I noticed it as soon as we entered the water. Getting to the canal was easy and moving down the wall and turning to drift was also very easy. Of course there was current… but it was just hardly noticeable.

Right now, water level is at its usual low (it has been for most of the season). River current is also very low, for 2 reasons. Downstream, outflow at the Cornwall Dam remains fully open to ease Lake Ontario levels – this keeps the water level low in Morrisburg. Upstream, the Iroquois Dam has all gates open – this keeps river flow consistent and quiet.

As a result, the approach drift to the locks is slow and, while flow still diverts at the structures and is faster there, it remains calmer than usual, allowing divers a few moments to get their bearings when they need to stop.

We went over the new norm (since 2018) of the HE Plant sluice gates: very low gates now that the upper timbers are all gone, with extended silt hills on their downstream sides. It’s easy to slip over them without worrying about being pulled upward toward the (relatively close) surface.

Back eddies remain strong inside the headpond making the downstream swim somewhat strenuous. No change there.

The next surprise I encountered was as I went over the wall where the turbine water flow would have exited. This short foundation wall sits at about 12 feet (as usual). Normally, when you slide over it and descend, you bottom out at about 32 feet. Well… I went over… and looked at my computer… 25 feet. What? Put my hand down onto… silt… maybe 27 feet. What? I looked from the wall towards the north… another wide, low silt hill that seemed to obscure a lot of the debris and posts that I expected there. As I swam around a bit in the atrocious visibility of the area, I noted a large tree stump sitting on the bottom… not at all where I was accustomed to spotting it. Hmmm.

All the main landmarks were there, but changed or covered. And such terrible viz! Why? Here are my “scientific” thoughts. (1) There is virtually no current beyond the HE Plant foundations. Nothing new there, but… (2) There is one heck of a lot of silt piled up… so there’s probably a lot wafting around in the water too. (3) The weeds in the outlying areas seem lower to me. In fact I was astonished on the swim in to the beach how low and thin they were for this time of year – still lots but definitely not as thick or high (by this time I’m accustomed to brushing them aside as I move through them and they normally almost reach the surface of the water) Typically, those weeds trap a lot of silt. Is the change in them because of the warmer water? I thought it’d be the other way around. Most days have been sunny and hot.

Anyway, something to ponder. Will it stay this way if the summers stay overly warm? Will the silt gradually get washed away with time? I simply do not know.

Anyway it was an interesting dive. Over to you guys.