If you’ve visited the Nature Centre in the past eight months, you’ll have seen that we’ve had to close a section of the 4 km Wishart Trail. If you’ve been waiting patiently for the section to reopen and for the trail to return to a full loop, you’re in luck. As of this morning, March 21, the trail is reopened.
We thank everyone who abided by the signs and fencing, and acted accordingly to keep themselves safe. Those fences and signs were there for a reason.
So, what happened to require the trail closure? Why did it take so long to get to this point? Where do we go from here?
What Closed the Trail?
Think back to last spring and early summer. We got a LOT of rain in Central Alberta. So much so that we’d seen larger than normal erosion channels running lengthwise down many of the hilly sections of the Wishart Trail. These channels are of little concern as the material being moved is just lightly packed, surface gravel. Our Sanctuary Technician goes out with a shovel and rake, and pulls the material back into place.
Little did we know that last spring water was moving in two very unexpected ways, out of sight. Local geology was causing water to pool on a clay layer below the trail bed. At the same time, a previously-unknown, abandoned drainage pipe had ruptured. The sheer volume and weight of the water collecting on the clay layer combined with the ruptured pipe undermining the hill, caused what is known as a global slump.
When we think of a landslide, we typically imagine material sloughing off and tumbling downhill. In a global slump, the entire face of the hill rotates on the weak point and slides off in one cohesive piece. Large slumps on vegetated hills will often result in trees being relocated to the bottom of the hill, perfectly able to continue growing.
The slump at the edge of the Wishart trail created a number of challenges. The first and most critical was that it peeled away a few feet of trail along the edge of the slope. Following the slump, the trail edge now overhangs the slope. City of Red Deer Engineering and Parks & Public Works staff as well as Nature Centre staff were onsite almost immediately to assess the damage. In order to keep people safe from further sloughing and to keep them away from the crumbly edge of the slump, the decision was made to close the trail.
Fencing and signage was erected.
And then, from the public’s point of view, it seemed like nothing happened.
So, What was Happening?
Behind the scenes City staff and Nature Centre staff were figuring out a path forward. Critically, we needed to know A) why the slump occurred, B) would it happen again, and C) can we prevent it from happening again.
A team of consulting Geotechnical Engineers was retained with the aim of producing a geotechnical report that would answer all three of those questions. Over the fall and winter we held onsite meetings in the cold, took core samples with a huge boring machine, sent an remotely operated vehicle (ROV) armed with a camera up the drainage pipe, and collected a lot of data. We talked to Alberta Environment and Parks regarding groundwater and fish. We consulted with the Gaetz Lakes Sanctuary Committee regarding discharge water.
All the while, the Nature Centre’s Sanctuary Technician continued to reset fencing and replace signage as some people decided that fences and signs didn’t apply to them.
In February 2023 the consultant returned their report.
It said:
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The hillside will undergo a process called regressive flattening. Right now there are two vertical planes separated by the horizontal trail bed. The hillside “wants” to be one plane. The slump site will continue to slide until the hillside is one continuous slope. This is not a matter of “if it happens”. This will absolutely happen. The unknown piece is how long it will take. It could be as few as three – five years.
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Because of the regressive flattening, the trail will eventually slide into the valley below.
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The decommissioned pipe needs to be sealed in an attempt to prevent the slope from undercutting itself. This will slow, but not stop the flattening process.
Where Do We Go from Here?
We have been given the go-ahead to reopen the trail. Barriers will be installed to keep people away from the edge of the slump. The trail will become significantly narrower. You will likely be walking single-file through the slump site, possibly alternating with people going in the opposite direction.
This reopening is a temporary solution. Ultimately a permanent solution will need to be designed and built.
A retaining wall is one of the proposed solutions put forward in the geotechnical report. Given the cost and the sheer amount of negative environmental impact building a retaining wall would create, we are not pursuing this option. Building a retaining wall is hugely expensive and requires equipment that would be insanely difficult to get to the site.
Ultimately the affected section of the Wishart trail plus roughly an extra 100 metres will be decommissioned and permanently fenced off. The geological processes will be allowed to unfold and the trail will simply slump away. Interpretive signage will be installed to tell the story of what happened on the site.
We are going to reroute the trail to the east. The new trail will take you through the bush up and down a couple of staircases, and extend your walk by a hundred meters or so. You’ll see a new view of the Sanctuary and the city, and Central Alberta to the west. The exact route has not been fully vetted as myriad biologists, ecologists, engineers, Nature Centre staff, and the Sanctuary Committee all have to approve the route. And of course, the money has to be found for design and construction. As this project will take place on City-owned land, The City will fund the project. The Nature Centre is not asking for donations from the public.
Until this trail is built – be patient because we could be looking at the winter of 2024 or beyond – we ask that you stay inside the fencing and don’t go exploring to see for yourself. You will occasionally see our Sanctuary Technician at the slump site. They’ll be measuring, and taking photos; data that will be forwarded to City and consulting engineers so they can evaluate the ongoing stability of the slope. Feel free to ask questions when you see them on-site.
Here at the Nature Centre we are extremely appreciative of the time, energy, money and talent The City has dedicated to this project. From the outset the goal was to “get it right” the first time, rather than rush through to a solution. Personally, I am extremely thankful for my City colleagues and their willingness to jump in and solve this challenge.
As always, feel free to phone or email us at the Nature Centre. Share your experiences on the trails, show us your pictures, report problems that you find. Get outside, stay outside, and enjoy your time on the trails.
