Raising Ste Agathe dike no small feat: engineers
A multi-year, multimillion-dollar plan to raise the dike that protects Ste Agathe when the Red River spills its banks continues to take shape, but the project isn’t without its engineering challenges, members of the community heard last Tuesday at a local forum.
About 20 people attended the first of two back-to-back information sessions held in the Ste Agathe Culture and Community Centre. The sessions followed an initial round of consultations held in December.
Preliminary designs were presented by a trio of engineers, who talked candidly about the work ahead as they endeavour to raise the town’s dike to protect against a one-in-200-year flood event.
Jared Baldwin, a project engineer with Manitoba Transportation and Infrastructure, said the town’s existing 20-year-old dike was built to a flood protection level (FPL) of 1997 plus two feet, which today equates to one-in-100-year flood protection.
The dike raise project was prompted by a pair of 2014 reports that recommended the province adopt a 200-year FPL standard for all provincial flood protection infrastructure.
That will cost billions of dollars, so Baldwin said the province is starting with the biggest trouble spot: the Red River corridor between Emerson and Winnipeg.
Ste Agathe residents in December identified several problems with the existing dike, including poor internal drainage, snow buildup, trespassing, and off-road vehicle use.
Property owners whose yards back onto the dike are also concerned about unsightliness. Those who live outside the dike are worried their property values will plummet and their insurance premiums will increase. There are also smaller challenges, like to integrate the community’s new boat launch into the upgrades.
Engineers with the consulting firm KGS Group are trying to draw up a low-maintenance design that addresses those problems while also improving river access. The creation of new recreational paths, and gated culverts to prevent back-flooding, are also priorities.
Baldwin said he wants to minimize the amount of land required to raise the dike, reduce any environmental effects, improve internal drainage, and minimize disruptions to local property owners.
The current dike, which is roughly 10 kilometres in circumference, provides varying levels of protection around the community. Bruno Arpin, a project manager with KGS Group, said different solutions will be needed in different places.
Some sections will need to be raised less than one metre, while others will need to be raised by two to three meters. Portions of the northeast corner of the dike, will be relocated slightly to improve internal drainage.
“We’re seeing an increased frequency of high-water events, so we want to ensure that…we take that into consideration,” Arpin said.
Baldwin said the project will involve raising the existing dike section by section, designing new sections of dike where none currently exist, and stabilizing the riverbank where needed.
Three options were presented for a new 1.1-kilometre section that will run along the eastern edge of the dike from the Provincial Road 305 bridge to Cheyenne Avenue. Project engineers said they’re deciding between an earthen dike, a mechanically stabilized earth wall dike, or a bin wall dike made with sheet piles.
The goal is to complete the bulk of the work by March 2025, when promised federal funding that will cover up to 50 percent of the total cost will expire. The ballpark total cost of the project has yet to be announced.
Much of the preliminary field work, including surveys and soil sample analysis, has already been done. The project’s preliminary design will be completed in the next two months. Residents will then have a chance to view and respond to the preferred design.
Raising Highway 75 and Provincial Road 305 is not part of the project’s scope, attendees were told.