St. Lawrence River Water: Level and Flood Control Structures
January 7, 2012 • 7:52PM

This project would add a much needed regulation system for one of our most important waterways, by adding various water control structures on remaining water bodies that feed into the St. Lawrence seaway. This project, as well as the "Water From the North" project found in an earlier post, was designed and submitted by F. Pierre Gingras, who has made articles about them available for this posting on this blog. F. Pierre Gingras is a specialist in industrial engineering, whose role among other studies was the chief cost and planning engineer for Hydro-Quebec dam construction and maintenance for more than 17 of the 35 years he has been involved in the construction of hydroelectric projects. ---Michael Kirsch

Present and Future Situation

To an important degree, the water level of the different parts of the St. Lawrence River has always been managed by adjusting the water flow. However, according to climate change experts, a reduction of some 20% to 30 % of annual water flow is foreseen in the Great Lakes area in this century. This area is already being affected by a form of drought.

From the environmental point of view, there are some 18,000 kilometers of shoreline and up to 1 000 square kilometers of wetlands involved, in many cases in some of the richest areas like Georgian Bay or the Lake St-Pierre wetlands reserve. Moreover, in recent years, newspapers have frequently reported the difficulties of several towns with their water supply, water intakes being sometimes almost at the level of the water line.

We must acknowledge that large volumes of water will be less and less available just to maintain water levels, in a situation where the water needs of the riparian populations will increase year after year. Moreover, the optimum use of spring flood water will be increasingly important, we just can let this important volume of water be ignore anymore.

Hypothesis: Management of the Entire St. Lawrence River Basin

The objective of the project is to manage the water level independently from the flow available, an alternative that seems has never been fully studied before.
It is possible to consider the overall arrangement of the St. Lawrence River as a series of about ten water basins or lakes, of which only four are already managed by control dams, in terms of water level and flow. This study will try to give an appreciation of how the four or five other lakes or reservoirs could be equipped with water control structures. The general arrangement of each site will be sketched and a planning and a cost estimate for each project will be outlined.

From upstream to downstream, the four major basins that are already controlled are first, Lake Superior, managed by the Sault Ste-Marie dam; then Lake Erie, controlled by various structures in the Welland-Niagara area; then Lake Ontario, managed by the Long-Sault Dam at Cornwall; then Lake St-François, the last to be controlled, managed by the Valleyfield and Beauharnois dams.

Downstream from Valleyfield, one does not find now any possibility to manage the water level of this important section of the St. Lawrence River, already suffering damage done by the St. Lawrence Seaway which acts rather like a drainage canal. The downstream part of the St-Lawrence River, located in Quebec province, will be the most affected by the flow reduction foreseen.

To avoid this situation, this study presumes that five control structures would be added for the following basins: Lakes Michigan and Huron at Sarnia, Lake St-Louis, the Laprairie basin, and the river sections from Montreal to Sorel and from Sorel to Portneuf.

The conceptual studies of the Portneuf, Sorel and Lachine Rapids projects will try to demonstrate how feasible it could be, technically and economically, to build these water control structures to manage the water level and flows independently one from the other. We understand that there will still be several studies to be done to ensure that ice control and fauna and wildlife needs will be properly met, although money is already included in the following estimates for those purposes.

Technical description of each project (downstream to upstream)


The first project of the “St. Lawrence River steps”, the Portneuf Dam, would be located about 1.5 kilometers upstream of the village of Portneuf. The upstream water level would be that of high tide, at elevation 4 meters, so as not to cause any significant land submersion and to make sure that the Lac St-Pierre wetlands, the most important wetlands of the entire St. Lawrence River basin, will be duly protected from now on.

This 3.2 kilometer long dam includes two main spillways totaling 30 gates, 10 meters high by 14 meters in width, with a capacity of 27,000 CMS (cubic meters/second) and a navigation lock of 350 by 40 meters, with a water depth of 12.5 meters, quite able to accommodate ships of more than 100,000 tons. The concrete structures are located in shallow waters to reduce the cofferdam works as the excavated material is for the most part directly used for the dam’s construction. The rockfill parts of the dam have a volume of 2,500,000 cubic meters with a length of 2,500 meters and an average height of 7 meters. The rockfill dams have a sheetpile core. The concrete works have a volume of 400,000 cubic meters.
The cost of the project is estimated at $1.1 billion, at the end of the works in the year 2022, with an amount of $710 million included for inflation and interest costs. A 20 % reserve is also included.
A road could be added on the dam. There will also be a large volume of surplus excavated rock available, quite enough to build one kilometer of wharf, maybe for the important aluminum plant of Deschambault located less than 3 kilometers distant.


The same general technical concepts are applied to this second site of 2.4 kilometers in length. The navigation lock is identical. The upstream water level would be limited to the highest flood waters of 9 meters, a water level that could be managed according to seasonal water preferences. The spillway is divided into two structures totaling 36 gates with a depth of 12 meters and 14 meters width. These structures have a concrete volume of 440,000 cubic meters and the rockfill volume of the structures is some 3,960,000 cubic meters.

A very important highway would be built on the dam, with the north shore highway 40 being less than 3 kilometers away while the highway 30, on the south shore, is less than 500 meters. The two ferryboats would not be needed any more. Once again, some two kilometers of wharfs could easily be added within the project.
The project estimate is $1.167 billion at the end of the work period in 2024. Built in a single day, without interest and inflation, the cost would be $896 million.

Laprairie Basin

To maintain the normal water level of the Laprairie basin at about a meter higher, a crest and two spillways would be needed in front of “Habitat 67”, at a cost of some $525 million. This 12 kilometer long basin, of which no shorelines are natural but have all been created by backfilling over a period of more than a hundred years, does not, at first sight, justify such a large investment. A more detailed study could be done later.

However raising the water level to the elevation of the St. Lawrence Seaway, namely about at 12.6 meters elevation, would allow opening the Seaway dike, thereby giving access to the Laprairie basin and the St. Lawrence river to the south shore populations.

Lachine Rapids

To maintain the water level of the important Lake St.Louis at its normal elevation of 21.18 meters, and protect the shorelines from Beauharnois to Dorval and La Salle, a 2 meter high crest would be built at two kilometers downstream from the Mercier Bridge. This is still two kilometers upstream of the rapids, which is important to environmentalists. A bridge would also be needed for this crest construction and its maintenance.

The capacity of this spilling crest being the future average flow of 7,200 CMS, a spillway of 8,800 CMS capacity would still be needed to discharge the maximum spring floods as estimated today. This estimate spring flood should be reduced with the construction of a control dam at Sarnia and with the effect of climate change. The spillway would be built on the south shore, equipped with 11 gates of a width of 14 meters and a height of 8 meters. An important discharge canal of 5 kilometers is required, with a width of 125 meters and a solid volume of 9.5 million cubic meters of excavation. This material could be used to build and improve a shoreline of some 25 kilometers long along the south shore of the St. Lawrence River and the Seaway dike where a community of several hundred thousand could be created all along this future magnificent shoreline.

The cost of the Lachine Rapids project is estimated at $857 million at the end of the construction period, in the year 2021.


This study does not describe in detail the works needed at Sarnia because the precise conditions of the foundations and of the shorelines were not available. But, with a height of less than 3 meters, we may assume that the general arrangement would be about the same as for the Portneuf and Sorel projects. It appears that the most interesting site could be just upstream of Lake St. Clair.

This project was supposed to be built a long time ago according to the original studies of the St. Lawrence Seaway. Maybe it was forgotten because the value of water was not as important in the fifties and sixties. The value of water and the present low level of Lakes Michigan and Huron make things quite different today. With a combined area of 114,000 square kilometers, these two lakes, once under control, would ensure that every drop of spring runoff would, from now on, be used efficiently and that the shorelines, from Chicago to Georgian Bay, could be fully restored over the years.


With management of water levels completely independent of the released flow through these nine or ten basins and/or lakes of the St. Lawrence River (instead of only four or five of them as now), no matter what the quantity of water available it would at last be possible to maintain water levels and the environment of the 18,000 kilometers of shoreline and of the more than a thousand of square kilometers of wetlands of the St. Lawrence basin. Moreover, from now on, every drop of water could be used with the utmost efficiency.

With the drying effect of climate change, it seems that average water levels, could eventually be lowered by as much as one or two meters in certain sections of the St. Lawrence River. Not maintaining the water level of these basin and lakes could hamper the operations and the profitability of the St. Lawrence Seaway to a very important degree. Moreover, with this new way of controlling water levels, regular dredging of the Seaway and the shorelines protection works will become a lot less necessary, bringing large operational savings.

Allowing the Port of Montreal, already the seventh most important port of North America, to accommodate ships as large as 100,000 tons capacity, means that several thousand jobs would be added. There might also be a future again for the petro-chemical industry of Montreal, especially with the probable petroleum extraction from the St. Lawrence Gulf area.

With independent water level control, all water needs of the populations of the Great Lakes area could be met by the St. Lawrence basin. Theses water needs do not require a great proportion of the regular water flow. For instance, a flow of 100 CMS equals a quantity of 100 gallons a day for each person of a 20 million population. So, if needed for the populations, a flow of several hundred CMS could conceivably be diverted from the St. Lawrence basin without important impacts on the environment.

The best way to make sure that freshwater will never be lacking is to stop sending so much to the sea!

Moreover, combined with another project called “Water from the North”, which would divert a flow of 800 CMS from the James Bay area to the St. Lawrence watershed, it becomes easier to make sure that the downstream half of the St. Lawrence river will not be damaged by becoming too stagnant.

The profitability of this whole project, including the dams and control works needed at Portneuf, Sorel, Lachine Rapids and Sarnia, at an estimated cost of some 4 to 5 billion dollars at the end of the construction works, appears sufficient to justify further studies by the Government of Canada, which has the principal responsibility for these matters.
The soundness of the St-Lawrence Seaway, as designed sixty years ago, explains why it seems now so easy to complete or update it to meet the most recent requirements of environment, water management, recreation and navigation.

F Pierre Gingras, nov. 2011
Author’s Rights Reserved

* Please follow the Commenting Guidlines.