high water?

[Hunter216]

Latest IJC prediction.
They have been gradually increasing outflow as the risk of flooding from Ottawa River was decreasing but made a big reduction yesterday to allow Hydro-Quebec to do the annual install of the safety boom. The outflow is supposed to go back to increased levels early next week. I’m hoping they get it to last summers 2 month long high of 10,400 and get rid of some of this excess

 

[Hunter216]

IJC press release. Doesn't look like I’ll get my wish. Time will tell.

“In previous years, the Lake Ontario summer outflow reached 10,400 m3/s (367,000 cfs), but with Lake Ontario water levels expected to be lower this year, it is unlikely that this outflow rate will be achieved this year. With water levels lower, there is less capacity in the channel to move water without an increase in velocity that would impact navigation and recreation and cause detrimental river erosion.”

Link to full txt of press release:

IJC’s International Lake Ontario-St. Lawrence River Board announces that better water conditions downstream allow outflows to be set for navigation | International Joint Commission

Thanks to favorable weather and water supply conditions, in conjunction with recent actions taken by the International Lake Ontario-St. Lawrence River Board to increase Lake Ontario outflows, the board no longer needs to limit outflows to alleviate flooding risks downstream.

www.ijc.org

 

[Will Gilmore]

“In previous years, the Lake Ontario summer outflow reached 10,400 m3/s (367,000 cfs), but with Lake Ontario water levels expected to be lower this year, it is unlikely that this outflow rate will be achieved this year. With water levels lower, there is less capacity in the channel to move water without an increase in velocity that would impact navigation and recreation and cause detrimental river erosion.”

I'm afraid I don't understand this statement.
With less water in the channels, increasing the speed of the current would result in reducing channel levels even more. There is limited water, no matter how fast you want to move it. You can't get more outflow without increasing inflow on the other end, no matter how fast you move the water.

-Will (Dragonfly)

 

[Davidasailor26]

I'm afraid I don't understand this statement.
With less water in the channels, increasing the speed of the current would result in reducing channel levels even more. There is limited water, no matter how fast you want to move it. You can't get more outflow without increasing inflow on the other end, no matter how fast you move the water.

-Will (Dragonfly)

I think what they’re saying is that since the water depth is lower they can’t let as much volume of water out. For example, if you let a specified volume of water through the channel when the channel is 10 feet deep, that will result in a current of x knots. Let that same volume through a channel that’s 8 feet deep and the current will be 20% faster, which may impact navigation.

I don’t think that paragraph automatically means that there will be too much water in the lake though. I just think it means they’ll be letting less water out because there’s less water in the lake. Basically a statement on how to interpret future outflow data.

 

[Hunter216]

I'm afraid I don't understand this statement.
With less water in the channels, increasing the speed of the current would result in reducing channel levels even more. There is limited water, no matter how fast you want to move it. You can't get more outflow without increasing inflow on the other end, no matter how fast you move the water.

-Will (Dragonfly)

I am struggling with the “logic” of the statement as well. In 2019 they had the outflow at 10,400 from June 14 - Aug 19 and the seaway was open so that flow rate was “safe”.

Yes the Lake Ontario level was higher during that entire period than it is now but I don’t picture the “channel” as V shaped but more U shaped so I don’t really get the velocity changing dramatically.

I was hoping they could/would take advantage of the relatively good conditions on Lake Ontario and St Lawrence this year to go to the max they considered safe last year. It would cause a rapid reduction of the level on the entire Lake shoreline so the risk of flooding/damage is vastly reduced and provide a bigger cushion for rapid increases due to rainfall.

I know that sounds self serving but if you could protect the entire lake and not cause harm downstream then why not.

I trust that the IJC has lots of engineering expertise at their disposal so will have to trust that they are doing what they can to mitigate the overall risk.

 

[Hunter216]

I think what they’re saying is that since the water depth is lower they can’t let as much volume of water out. For example, if you let a specified volume of water through the channel when the channel is 10 feet deep, that will result in a current of x knots. Let that same volume through a channel that’s 8 feet deep and the current will be 20% faster, which may impact navigation.

I don’t think that paragraph automatically means that there will be too much water in the lake though. I just think it means they’ll be letting less water out because there’s less water in the lake. Basically a statement on how to interpret future outflow data.

This sort of makes sense to me, however the "channel" is anything but consistent so I guess they have to factor in where the most hazardous sections are and balance the risk.

I found this site - page full of interesting factoids:

Discharge Measurements on the St. Lawrence River

www.lre.usace.army.mil

 

[Will Gilmore]

The biggest problem I have is with the concept of faster water with less volume: Is there a driving system in place? The only way to increase the outflow of the water while maintaining the same slope, regardless of cross section, is to add more volume. Reducing the volume of a river does not speed it up and there is no way to speed it up without driving it some how.

Dropping the level of a river and then talking about erosion means you are only considering erosion of the banks underwater, below the higher waterlevel mark. These banks are still under attack from erosion by the water regardless of how much water is above them. How can you have lower water levels and higher rates of erosion?

I'm certainly no canal/lock engineer and am not trying to pretend to be. I don't follow their logic at all. I have worked as a furniture design and production engineer, I've engineered computer systems and networks and some my share of logic coding in various languages including AutoCAD's AutoLISP, and this logic does not compute.

-Will (Dragonfly)

 

[DArcy]

the flow rate is
F = S x A
Where
F is the flow rate in m^3/s
S = the speed of the water in m/s
A = the cross sectional area of the river

Remember that A is going to be lower the lower the water level, linearly propertional for a rectangular cross section. That means a lower water level needs a higher speed to maintain the same flow rate.
It makes sense to reduce flow rate for lower water level.

 

[Hunter216]

The biggest problem I have is with the concept of faster water with less volume: Is there a driving system in place? The only way to increase the outflow of the water while maintaining the same slope, regardless of cross section, is to add more volume. Reducing the volume of a river does not speed it up and there is no way to speed it up without driving it some how.

Dropping the level of a river and then talking about erosion means you are only considering erosion of the banks underwater, below the higher waterlevel mark. These banks are still under attack from erosion by the water regardless of how much water is above them. How can you have lower water levels and higher rates of erosion?

I'm certainly no canal/lock engineer and am not trying to pretend to be. I don't follow their logic at all. I have worked as a furniture design and production engineer, I've engineered computer systems and networks and some my share of logic coding in various languages including AutoCAD's AutoLISP, and this logic does not compute.

-Will (Dragonfly)

I’m been pondering on this

So here’s the logic of the IJC statement as
I see it. However with the caveat that I’m like a broken clock - only right twice a day

Outflow from the lake is what is being released from the dam on the river. Max last year was 10,400, setting right now is 9,000 down from 9,650 as they needed to reduce flow to install safety equipment at the dam

The supply of that water is lake level - river level - reservoir at the dam.

To my logic anything downstream of the dam if it was set to 10,400 should be the same as last year as the same quantity of water would be in the channel flowing to the ocean so to me no increase in any risk.

So that leaves upstream. I can sort of understand that if the supply level is lower that would mean the “size of the pipe” carrying the water would be “smaller” than last years higher lake level. If you move more water through the smaller pipe it would have to move faster so MORE current - higher risks.

If my logic is sound we are talking about a relatively short section of the river. Kingston to Cornwall ~ 160km. Kingston to Quebec City would be ~ 500km. Even then part of that 160km is relatively flat broad channel.

I wonder how much more current the 10,400 - 9,650 = 750 would cause???

 

[Will Gilmore]

Without raising the water level, where does the increased current come from?

-Will (Dragonfly)

 

[Hunter216]

Without raising the water level, where does the increased current come from?

-Will (Dragonfly)

Last year the lake level was higher so the stretch of the river from the lake to the dam was also higher. In other words the depth of water in the channel was greater.

In my “logic” - thinking of that as a certain size of pipe let’s give last years pipe diameter a value of 1. Now the water level is lower so the size of the pipe is <1.

If the outflow of the dam is 10,400 in both years the water will need to move faster through the smaller pipe.

 

[Will Gilmore]

If the outflow of the dam is 10,400 in both years the water will need to move faster through the smaller pipe.

Ok. No arguement with any of that except, how does that condition happen? Same canal both years, same output but different current? What's driving the faster current while keeping the output the same with lower water levels?

-Will (dragonfly)

 

[Hunter216]

Ok. No arguement with any of that except, how does that condition happen? Same canal both years, same output but different current? What's driving the faster current while keeping the output the same with lower water levels?

-Will (dragonfly)

Actually the canal IS different in the fact that the “height” of the water last year was greater than this year. If the output stays the same and the height can’t increase the water has to move “faster”.

 

[Will Gilmore]

Actually the canal IS different in the fact that the “height” of the water last year was greater than this year. If the output stays the same and the height can’t increase the water has to move “faster”.

How does that happen?

-Will (Dragonfly)

 

[Davidasailor26]

How does that happen?

-Will (Dragonfly)

Think of it this way - Imagine you have a 12” pipe just below the surface of a pool, with a cap on the end away from the pool. Drill a 1” hole near the bottom of the cap. The hole will let water out at a certain flow rate, and water will need move through the pipe at a certain speed to keep up with that flow.

Now, lower the level of the pool until only 6” of pipe is submerged. You’re only using half the pipe, so it’s like having a smaller pipe. The outlet hole is still the same size, so the outflow volume is still the same, but with a “smaller” pipe the water must travel at a faster speed to replace the water that’s flowing out.

 

[Will Gilmore]

Thank's David. So the pipe is not free flowing. Of course I knew that, I just wasn't thinking of it like that. Gotcha. That all makes sense now.

-Will (Dragonfly)

 

[danstanford]

Sorry, I don't buy it. I am on board with David's explanation but I don't think it is an appropriate analogy to this situation. The only reason (other than a higher water level in the lower containment vessel(Atlantic)) water levels would rise would be that the resistance to flow would be sufficient to raise the water level in the river. In other words, there becomes a balance between velocity and depth that is in balance with the resistance to flow. For every amount of volume there will be a height and a velocity.
Using the same tools as David's example, imagine it this way. The pipe leading out of the pool has no cap and the water level is half way up the outflow pipe and the same amount of water is being added to the pool as is flowing out of the pipe. Add water to the pool at a faster rate and the level of the pool will increase slightly and the velocity will increase both to some degree. Slow the rate of the water coming into the pool and the level of the pool will slowly lower till the flow out the pipe matches the flow into the pool. The river has no fixed aperture so as the water volume released from the dam increases the velocity increases and the level rises till the height exceeds the banks and flooding occurs.
That makes sense to me and I genuinely look forward to seeing it in a different way if I am wrong.
Dan

 

[Davidasailor26]

Sorry, I don't buy it. I am on board with David's explanation but I don't think it is an appropriate analogy to this situation. The only reason (other than a higher water level in the lower containment vessel(Atlantic)) water levels would rise would be that the resistance to flow would be sufficient to raise the water level in the river. In other words, there becomes a balance between velocity and depth that is in balance with the resistance to flow. For every amount of volume there will be a height and a velocity.
Using the same tools as David's example, imagine it this way. The pipe leading out of the pool has no cap and the water level is half way up the outflow pipe and the same amount of water is being added to the pool as is flowing out of the pipe. Add water to the pool at a faster rate and the level of the pool will increase slightly and the velocity will increase both to some degree. Slow the rate of the water coming into the pool and the level of the pool will slowly lower till the flow out the pipe matches the flow into the pool. The river has no fixed aperture so as the water volume released from the dam increases the velocity increases and the level rises till the height exceeds the banks and flooding occurs.
That makes sense to me and I genuinely look forward to seeing it in a different way if I am wrong.
Dan

I think in your interpretation you’re using the “pipe” to represent the river below the dam. I agree with you that for that section increased flow rate increases both velocity and height, because there is no fixed outlet aperture. But I was using the “pipe” as the section of channel above the dam, and the “cap” as the dam. If you increase the size of the aperture (open the dam), the only ways to provide the extra water for that increased outflow are either increasing the speed of the water through the pipe (more current) or increase the size of the pipe (higher lake level). The lake level is lower this year, so the current will be faster.

 

[danstanford]

I think in your interpretation you’re using the “pipe” to represent the river below the dam. I agree with you that for that section increased flow rate increases both velocity and height, because there is no fixed outlet aperture. But I was using the “pipe” as the section of channel above the dam, and the “cap” as the dam. If you increase the size of the aperture (open the dam), the only ways to provide the extra water for that increased outflow are either increasing the speed of the water through the pipe (more current) or increase the size of the pipe (higher lake level). The lake level is lower this year, so the current will be faster.

Thanks David, I agree with the conclusion. Perhaps I have not understood the issues at play and therefore jumped over the initial question unfairly. It has been my understanding that the issue with lowering the level of Lake Ontario has been the flow rate and levels below the dam.
Thanks for taking the time to respond.
Dan

 

[Hunter216]

In the recent statement the IJC has two concerns about increasing the flow rate to 10,400. Velocity and erosion.

“With water levels lower, there is less capacity in the channel to move water without an increase in velocity that would impact navigation and recreation and cause detrimental river erosion.”

I think we have agreed on the increased velocity - navigation part.

I’m not so sure about their erosion as I don’t find it consistent with what they did this winter.

At one point they had the flow at the dam up to 10,700 AND the lake level was LOWER than it is now. To me that would create an even greater increase of velocity and therefore erosive capability so I’m back to pondering again

The seaway in open now but was not in the winter so maybe big ships moving through combined with a faster current causes the increased erosion??