Long Sault Dam is effectively the emergency spillway for the Moses-Saunders Power Dam. Normally, the entire flow of the St. Lawrence River would go through the power dam to maximize the production of electricity. For simplicity, I'm going to refer to these two dams as the Cornwall Dam. I've seen the "Cornwall Dam" reference in news articles. The slack pool created by these dams is called Lake St. Lawrence.
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| ijc.org Moses-Saunders Power Dam |
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| May 22, 2017, file photo from the International Lake Ontario - St. Lawrence River Board (source) |
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| Facebook, lots of gates are open because gates are closed at the power dam for routine turbine maintenance. Seeing this significant flow gives us great insight as to how big the flow is through the power dam. The river flow is more than the flow going over Niagara Falls because some of the flow of the Niagara River is diverted through powerhouses. Furthermore, the watershed for these dams is greater than the watershed for the Niagara Falls. |
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| New York Power Authority posted Surveyors and engineers calculate precise measurements during the construction of the St. Lawrence Power Dam in 1956. James Torgeson shared |
When they built a 9' navigation channel in an American river such as the Upper Mississippi, Ohio, Illinois, Tennessee, etc., they didn't dig down 9', they built a lock & dam to raise the level of the water to create a series of slack pools. To create the 26'+ navigation channel in the St. Lawrence river, these "slack pools" are big enough to be called lakes. Lake St. Lawrence is created by the Cornwall Dam and creates a pool 26'+ deep at the foot of the Iroquois Lock and Dam.
Unlike a 9' rise in water level, a 26' rise is significant enough that it flooded some of the towns that were on the original shores of the St. Lawrence River. I have already described how the entire town of Iroquois was moved up a hill.
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| Peter Joseph posted |
This image is part of an analysis of what the tanker got stuck on. It shows us that the part of Morrisburg that got flooded included some old locks. Specifically it was Lock 23 built in the 1800s.
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| OttawaRewind (source) |
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| Satellite |
The International Lake Ontario - St. Lawrence River Board (River Board) is responsible for controlling the flows through the Iroquois Dam and these dams. The power dam should have been designed so that the ideal river flow is the capacity of the powerhouse with no water going over the spillway dam. The effect of these dams on the river is significant enough that upstream is considered the "upper St. Lawrence River" and downstream is considered the "lower St. Lawrence River." The "upper St. Lawrence River" is basically Lake St. Lawrence. To determine the outflow of the dams, the River Board considers the need of the powerhouse, maintaining a minimum depth in the navigation channel, and water levels for Lake Ontario and the upper and lower St. Lawrence River. If water levels are too high, it increases erosion of the shoreline and it can flood property. If it is too low, then the water intakes for towns along the river provide an inadequate flow to the town. And people's boats can't reach their piers. When determining the outflow rate, the River Board must also consider precipitation in the watershed and evaporation from Lake Ontario. Water flow through the locks is negligible. If outflows are high, then commercial shipping is stopped because the river currents are too dangerous.
Three plans as to how to determine the river flow had been written: 1952, 1956, and 1958D. In 2014, work began a new plan "to improve ecosystem health and diversity on Lake Ontario and the upper St. Lawrence River....Allowing for more natural variations of water levels, the plan aims to foster the conditions needed to restore Lake Ontario and upper St. Lawrence River coastal wetlands and improve habitat for fish and wildlife. The plan will also frequently extend the Lake Ontario recreational boating season in the fall, better maintain system-wide levels for navigation and allow for a modest increase in hydropower production compared to the previous plan." Plan 2014 became effective Dec. 8, 2016. [ijc]
An additional issue the River Board must consider is the formation of a stable ice cover. When ice starts to form, the outflows are reduced to allow an ice cover to form. After a stable ice cover forms, the flows can be increased. Furthermore, if the Ottawa River is causing flooding in the Montreal area, outflows are reduced to reduce the extent of the flooding in the Montreal area. [ijc]
But in 2017, Mother Nature dumped a record amount of precipitation into Ontario Lake causing flooding.
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| InternationalLakeOntarioStLawrenceRiverBoatd |
Letting out enough water to lower Lake Ontario by 1 inch would raise the level of the river at Montreal by nearly a foot, says the International Joint Commission, which controls water levels. Letting less water out of the lake until the Ottawa River peaks "can prevent several feet of flooding in the Montreal area," said commission spokesman Frank Bevacqua. During nine days in April and May when the Ottawa River was high, the commission let less water out of Lake Ontario, Bevacqua said. The commission plans to start discharging more water from the lake as the water levels near Montreal begin to recede, Bevacqua said. [NewYorkUpstate-flooding]Below the above article is this drought information. But I think the flooding was May 10, 2017 and this drought article is current (Sep 7, 2018). I still get the printed Chicago Tribune delivered to my house, so I'm not experienced with reading "web news." But the juxtaposition of old and new articles does demonstrate that Mother Nature can have significant "mood swings."
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| A severe drought (orange) is now affecting parts of the Adirondacks, while 20 percent of New York remains in a moderate drought (tan) or is considered abnormally dry (yellow). (U.S. Drought Monitor) |
Evidently the water level in the lower St. Lawrence River is now low enough that they have been able to use the spillway and powerhouse to increase the outflow. But this creates another problem, low river levels on the downstream end of Lake St. Lawrence. An organizer of a Sep 11, 2018 meeting to complain about the low levels claims parts of the river are now down to the bare minimum needed to support commercial shipping --- something not seen since at least 1998.
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| NationValleyNews |
Dennis DeBruler Why don't they open the gates at the Iroquois Dam as well to match the flow being spilled by the Cornwall Dam to maintain the traditional height of Lake St. Lawrence? Especially since they want to get water out of Lake Ontario?
Dennis DeBruler I think I now understand. I'm looking at a photo at the downstream part of Lake St. Lawrence. As the flow increases, the "lake" turns back into a river and the water slopes downstream from Iroquois to Cornwall causing the water level to be significantly lower at the Cornwall end. Basically, the water management people have done such a good job for so many decades that people think they bought land on a lake instead of a river. At least they have the advantage that the exception is that the water goes down instead of up. Most people that live on a river get flooded, not drained, by abnormal weather. For example the Mid-Continental Railway Museum got hit this summer by the Baraboo River. They were still trying to recover from a 2008 flood. https://www.facebook.com/.../a.22924.../2293066620709671/...
Dennis DeBruler Even a true lake can be at the mercy of Mother Nature's precipitation moods. Lake Michigan varies by about six feet. When Lake Michigan went down after Chicago reversed the flow of their river, Wisconsin sued the sanitary district to reduce the flow. Water Treatment Plants were invented and a lock was installed at the mouth of the river to reduce the flow out of the lake. Later, when the lake went back up, Chicago was asked to open the locks and allow big flows again. Chicago refused because the outflow was a drop in the bucket compared to what Mother Nature was adding and because a heavy river flow would disrupt barge traffic.
Update Oct 2, 2018: the flow will be reduced so the water level near the Cornwall Dam should go up about 2 feet.
The international board said this week that it will temporarily decrease outflows significantly over two 45-hour periods during the first two weekends of October to provide an opportunity for residents of Lake St. Lawrence and upstream of that area to remove their boats and other equipment while the river level rises.
“These flow decreases will temporarily raise Lake St. Lawrence levels, which will assist marinas, yacht clubs and other recreational boaters in the area in removal of their boats prior to winter,” according to the organization’s statement. “The board acknowledges the concerns identified at recent meetings with the public in the area, and the board takes each concern very seriously. The exact amounts of the water level rises will vary depending on a number of factors, including location, winds and other secondary factors.”
[WaterTownDailyTimes]
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| CHRISTOPHER LENNEY / WATERTOWN DAILY TIMES Boaters are complaining that low river levels at the Patterson Street access site make it difficult to remove their vessels. |
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| Satellite |
After studying a satellite image, I noticed that the levels at Ogdensburg are controlled by the Iroquois Dam instead of the Cornwall Dam. The article says the flow reduction will raise the water level at Ogdensburg just three inches instead of the two feet expected near the Cornwall Dam.
South Stormont is another town near the Cornwall Dams that is complaining about the low water levels. It is not just a matter of the people along the shore refusing to convert to floating docks, the exceptionally low water levels is exposing hazards to navigation. They claim it is impacting commercial as well as recreational boats. “What if an oil ship gets punctured? It could be a disaster and that’s the point I’ve tried to get across to the IJC.” But I can't believe the River Board would jeopardize the 26'+ draft of the Seaway navigation channel. [CornwallSeawayNews] Of note, all tankers on the Seaway are required to be double hulled.
2020 Update: Because Lake Ontario has "unprecedentedly high water levels," the outflows of the dam are sometimes as high as 10,700 cfs causing Lake St. Lawrence to be even lower. "These high outflows have lead to extremely low water levels in municipalities immediately west of the dam on the shores of Lake St. Lawrence, such as South Stormont and South Dundas. In fact, water levels have been so low, that the Lost Villages, termed Canada’s Atlantis, have been uncovered. In 1959, 10 villages west of the Moses-Saunders Dam were intentionally flooded during the creation of the St. Lawrence Seaway, including the village of Aultsville. This week, it was once again possible to walk the streets of Aultsville thanks to the low water levels." [CornwallSeawayNews, source] I assume they don't have to worry about maintaining a shipping depth during the Winter because shipping shuts down.
The plan of 2014 that was implemented in 2016 allows higher highs. Many blame this plan for the floods in 2017 and 2019 that caused a lot of damage along the shoreline. Others say the floods are a result of climate warming. It sounds like New York is now planning on having floods: "From the Niagara River in the west to the Moses-Saunders dam on the St. Lawrence in the northeast, New York is spending $300 million on 135 shoreline-related projects." Since FEMA was mentioned, I assume that some of the $300m is coming out of federal taxpayer pockets. [ChicagoTribune] Because there have not been significant lows recently, cattails have invaded some of the wetlands. Work is now being done to get rid of them. [ChicagoTribune-sidebar]
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