Climate change will bring more flood waters downtown. How much will the $52 million Jackson Creek diversion help?

This article is part of our Creek Week series — an exploration of our local creeks and subwatersheds. In previous articles, we profiled Bears Creek and Harper Creek, mostly from an environmental perspective. We also offered tips on how to protect creeks. In this article, we focus on Jackson Creek’s potential to flood the downtown, and the consequences of that flood risk for urban planning.

In 2004, Peterborough was hit by a storm the likes of which few residents could have thought was possible. 

At one point overnight, more than 150mm of rain fell in less than two hours, overwhelming municipal stormwater systems. Creeks burst over their banks, liberating themselves from their fixed routes to pour into basements and wreak havoc on our urban infrastructure. 

Now, nearly two decades later, this flood ought to be remembered not as a random weather event, but as a harbinger of the storms we can expect to see more of as a result of climate change.

Considering this, the timing of Peterborough’s flood was perhaps beneficial. When it comes to flood-related climate adaptation, “the City of Peterborough is maybe a little bit ahead of the curve because of our experience with the 2004 flood,” the City’s infrastructure manager Michael Papadacos told Peterborough Currents in 2020.

In the years following the flood, the City “put a lot of effort into developing flood reduction master plans,” Papadacos said. Those plans identified the key choke points along creek routes, and suggested infrastructure improvements to increase the creeks’ capacity during heavy rainfall. Many of those improvements have already been implemented, but others have yet to be funded and built.

This year, the City broke ground on the single biggest project recommended by those flood reduction plans: the diversion of Jackson Creek underneath Bethune Street. 

When Jackson Creek overflowed in the 2004 flood, it caused extensive damage downtown. The diversion project, which costs more than $52 million and is funded by all three levels of government, will help to protect the downtown from future floods by building a new storm sewer underneath Bethune from Murray Street to Townsend Street. When Jackson’s volume swells during future storms, the Bethune sewer will offer the creek extra capacity along a second route. 

The Bethune diversion is designed to safely accommodate what’s known as a 100-year flood — that’s the kind of large storm that has a 1 percent chance of occurring in any given year. The 2004 flood, for comparison, was more than double the strength of a 100-year flood.

The term “100-year flood” itself is a bit misleading. It only describes a probability, and so 100-year floods can happen more than once per century. Whatsmore, climate change is likely already accelerating the frequency not just of 100-year floods but of even bigger storms as well. There have been calls to do away with the term “100-year flood” altogether.

“There’s always going to be a bigger storm,” acknowledges Ian Boland, the City’s senior watershed project manager. “Ideally, if you had as much money as possible, you could design for 500-year events.”

Boland said the infrastructure being installed under Bethune Street is as big as the roadway could possibly allow, and it’s a feasible solution given the cost-benefit analysis. “We’re putting in a sewer that we feel makes sense and is designed to alleviate quite a bit of flooding through the downtown area.”

But given the very real possibility that Peterborough will face floods that exceed Jackson Creek’s capacity even after the Bethune Street diversion is completed, it’s worth asking what else can be done to flood-proof the downtown, and what kinds of development should be permitted there.

Building in a floodplain

If you look at some of Peterborough’s historical maps — like the 1878 map, for example — you’ll see that Jackson Creek didn’t always flow in the single channel that now dictates its route through the downtown.

Instead, it diverged into multiple parallel streams with small islands in between as it flowed toward Little Lake. But as Peterborough grew, the shape of Jackson Creek was constrained to make room for urban development. The creek was forced into smaller and smaller underground tunnels that are insufficient to convey the stormwater of a major rain event.

This 1878 map of Peterborough illustrates the original braided nature of Jackson Creek. Note how it diverges into multiple channels and takes up more space than it does today. (Source: City of Peterborough Museum and Archives)
And this 1875 illustrated map also reveals how much more room Jackson Creek was previously afforded in downtown Peterborough, and how much more of the creek remained above ground. (Source: York University Digital Library Map Collection)

Now, we live with the consequences of burying Jackson Creek underground, and we have to make trade-offs because of it. Densifying the downtown core is a key priority in Peterborough’s recently adopted Official Plan, for example, but provincial policy generally prohibits development in a floodplain.

Peterborough isn’t the only community in this bind. “Most historic downtowns are in a flooding hazard,” said Jennifer Clinesmith, who until recently was the planning and permitting manager for the Otonabee Region Conservation Authority, or ORCA. (She is now the director of campus planning and development at Trent University. Peterborough Currents spoke to her before the change.)

To account for this, the province allows municipalities to identify special policy areas where the rules around development in a floodplain are relaxed a little. “By loosening the rules you do have increased [flood] risk,” Clinesmith said, but the province permits the extra risk “so that these historic downtowns don’t become stagnated.”

Peterborough’s downtown was identified as a special policy area in 1995, and so development in the Jackson Creek floodplain can still happen, but not without extra mitigations. 

As the owner of Ashburnham Realty, Paul Bennett has had to navigate the rules governing special policy areas. To get their 5-storey development on the corner of Hunter and Aylmer approved, Ashburnham had to propose building it on an elevated platform without a basement, for example. “It took a lot of design work and a lot of time and effort,” Bennett said of the process. “That comes with a cost, and in some cases it makes sites totally undevelopable.”

Floodplains have a “massive impact” on the investment decisions that developers make, Bennett said, and the presence of the Jackson Creek floodplain downtown “really dictates a lot of how our city can potentially grow going forward.”

Considering this, it’s important to map out where exactly Jackson Creek is likely to flood in major storms. So … how big is the Jackson Creek floodplain downtown, and where exactly are the floodlines? Those questions, it turns out, are not as easy to answer as you might think.

How big is the floodplain, anyway?

Near the western edge of Peterborough, more than five kilometres upstream from downtown, there’s a slab of concrete that intersects Jackson Creek. It’s about 40 metres long, and in the middle of it there’s a 4-metre slot for the creek to pass through.

This is the Jackson Weir, and in major storms it holds water back in the Lily Lake wetland to prevent it from rushing downstream all at once.

The Jackson Weir in summer 2021. By only allowing the creek to pass through its slot in the centre, the weir regulates how much water can flow downstream toward the city core. In major storms, this mechanism holds water back in the Lily Lake wetland to protect the downtown from flooding. (Photo: Will Pearson)

The Jackson Weir is a key flood reduction measure for the Jackson Creek subwatershed. But it’s also a source of uncertainty due to one crucial question: When we calculate how much water the next major storm will send down Jackson Creek toward the downtown, should we assume the worst case scenario and plan for the weir to fail? Or should we assume the weir holds and spares the downtown from the worst possible result?

According to Clinesmith, the current provincial guidelines around this are clear: “When you’re mapping a floodplain, you need to assume that any structures that are there to hold back water will fail during the flood,” she said.

These rules are laid out in the province’s technical guide for mapping flooding hazard limits, which came into effect in 2002.

But the Jackson Creek floodplain was last mapped in the 1990s, before those guidelines were established, according to ORCA’s CEO Dan Marinigh. That means the current floodplain map assumes the weir will hold, which is contrary to provincial policy. ORCA is “preparing updated regulatory floodplain mapping for Jackson Creek using current methods and provincial guidelines,” Marinigh wrote to Peterborough Currents. He didn’t want to speculate on how the shape and size of the floodplain might change as a result of the updated approach. 

Jackson Creek approaching the intersection of Aylmer and Brock Streets. (Photo: Will Pearson)

The same issue applies to the Bethune Street diversion project. As a human-built structure, its flood-reduction impacts likely won’t be incorporated into the updated mapping of the floodplain.

To developers or potential developers downtown, that’s a frustration. The Jackson Creek floodplain “really hinders what we can and can’t do as a community,” Paul Bennett said. “Whether it’s a police station, or a new art gallery, or arenas, those kinds of things are big footprints. And they’re next to impossible to locate anywhere near or on a floodplain.”

The way Bennett sees it, new infrastructure that adds capacity to the creek and reduces flood risk should shrink the floodplain maps and make more development possible. That way, the project “would spur growth [and] pay for itself,” he argues. “If you’re investing all this money [to reduce flood risk] you should be able to adjust the floodplain.”

But as it stands, the Bethune diversion won’t lead to a floodplain adjustment, unless provincial policy changes. So it’s natural to ask: Is there a different way to address flood risk downtown?

Can we fully protect the downtown from flooding?

A sewer diversion was first recommended as part of the Jackson Creek Flood Reduction Master Plan in 2010. At the time, the idea was presented by AECOM Canada Ltd., the consultants who wrote the plan, as the most feasible solution to downtown flood risk — but not the most effective or environmentally friendly solution.

In its report, AECOM also presented another option: naturalizing Jackson Creek and expanding its channel on both sides. This would involve the City appropriating about 50 properties that border the creek downtown and likely demolishing the structures on them. Then, the City could return the creek to something like its natural state, which would provide enough capacity to accommodate peak flow during floods.

AECOM noted that naturalizing Jackson Creek would be the only way to fully protect the downtown from flooding in major storms. It would also prove beneficial for aquatic health and provide social benefits, their report said. Trails could be built alongside the newly exposed creek, for example.

But AECOM determined the plan to be too tricky to pull off. “While this may be a cost-effective solution over a very long term planning horizon, it represents a very significant initial cost, with considerable social disruption,” their report stated. City council agreed, and pursued the sewer diversion instead.

But that doesn’t mean naturalizing and daylighting Jackson Creek is off the table. While such a project would likely take decades of sustained political effort, the City seems ready to at least consider it. The new Official Plan approved by city council last month states that the City will “consider opportunities for rediscovering/daylighting Jackson Creek in the Central Area through the creation of open space.”

During consultations for the Official Plan, some citizens recommended starting the process by having the City purchase properties along the creek as they become available. 

Building the downtown on top of Jackson Creek is what created the flood risk we now face there in the first place. It seems appropriate, then, that eliminating that flood risk requires us to unbuild parts of downtown, and to relinquish our efforts to control the creek.

When I spoke to Clinesmith this summer, one comment she made stuck with me. “Water wins,” she said. “It’s going to flow where it wants to flow.”

“And I think we have a long tradition and history of thinking that we can engineer our way out of it,” she continued. But these engineered solutions only work to a point, she said. Better urban planning takes a different approach: “Instead of trying to impose your will and your wishes on the environment, you look at it [and ask] what can it actually support?”

The Bethune diversion is expected to be completed in late-fall of 2022. After that, it might be time to begin the long, hard work of letting Jackson Creek flow where it wants to flow.

This article is a part of Creek Week, a series about the creeks and subwatersheds of Peterborough. Read the rest of the series here.


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