By Petitcodiac RiverWatcher Georges Brun
Editing: Monique Arsenault
Do you know that the tidal bore ends at Turtle Creek?
If you visit the area where the Petitcodiac River reaches Turtle Creek during the winter months, you might be able to spot the distance between 4 or 5 successive tides, indicated by breaks in the ice. These breaks show where the Petitcodiac River’s tidal bore ends its journey. Once it has made its way under the causeway and through the tidal control structure, the bore reaches different stretches upstream depending on the strength of daily tides. The breaks in the ice are the result of water pressure that pushes upwards on the ice. You can see one of these breaks in the image below, which clearly shows where a bore ended.
One question I would like to run by my readers is the following: if the tidal control structure and the causeway between Moncton and Riverview was replaced by a bridge, would the bore go further?
The Gates Are Too Low
The tidal control structure beneath the causeway linking Moncton and Riverview was built between 1966 and 1968.
This control structure is part of the land and not the river itself. It was in operation until April 2010 when the Provincial Court decided that the province should open the floodgates to help the migration of many species of fish and facilitate a more natural flow.
Although the river is doing increasingly well since the opening of gates, expanding and regaining its natural flow downstream, it is shrinking more and more upstream. The tidal control structure is contributing to this problem. Here is why.
The water level at high tide can be quite elevated in winter, even more so when water is covered with a sheet of ice. Melting ice and snow, heavy rains, as well as local and regional temperature variations all influence the river’s flow.
The tidal control structure’s gates are only partially open. The opening could be made much larger. You can see the height of the gates in the photo below, taken at a low tide.
The gates could be raised by at least one meter.
Currently, the gates are not high enough to allow the river to flow naturally during very high tides in the winter and spring. The ice sheet on the river has a hard time passing through, often hitting the gates, which impedes its passage and slows down the river’s flow.
The Control Structure Acts Like a Funnel
The control structure hardly exceeds 50 meters in width while the river downstream is about 400 meters wide. Imagine all that volume of water trying to make its way through such a tight space! The control structure acts like a funnel, reducing the river’s strength and preventing it from flowing as naturally as possible.
Without the Passage of Ice and an Adequate Volume of Water, the River Will Continue to Narrow Upstream
The passage of ice is important to support the natural drainage and erosion process that needs to take place in the river. Without this process, the river will continue to narrow upstream. In the image below, we can see that the river is becoming narrower in Riverview, where the artificial lake once was. In winter, sediments accumulate and freeze, requiring lots of heat and a greater volume of water to be eroded.
Gravel Deposits Upstream
Finally, note the accumulation of gravel near the control structure, left by melted ice. Gravel accumulates when the ice is unable to pass through to the other side of the control structure under the causeway and is thus pushed back, dropping sediments along the banks of the river.
The Solution: Remove the Control Structure
Opening the causeway gates in 2010 has certainly helped the river regain its natural flow. However, I believe that the control structure’s gates could be lifted even higher to allow a greater volume of water to pass through. I also hope that we can one day completely remove the causeway and control structure and replace them both with a bridge of adequate height. The tidal bore could thus continue its journey much further than Turtle Creek. Over time, the river’s natural erosion process would help widen the river where the artificial lake once was. We would thus enjoy the beauty and health of our river, now longer, wider and more majestic, having regained its former glory.