WC132 SeptOct 2023 - Magazine - Page 17
Environmental quandary
When it comes to the options of a
“Rivers like to wander around. It needs be able to erode its banks
bridge or tunnel in this area of the
Fraser Delta, each has its environduring 昀氀oods and deposit at lower 昀氀ows. It needs to aggrade and
mental pros and cons. A bridge has
degrade the bed of the river. " - Jeremy Venditti
obvious issues we can all see. They
can impact air traffic, create light
pollution, and disturb surrounding
habitats, especially nesting grounds.
With many protected avian species
of the river until it’s no longer a natural channel.”
that call the Fraser Delta home, this has been a significant cause
With the project’s environmental assessment in its early stages
for concern.
and its completion estimated for 2025, knowing what precauThis, along with the questions on how a bridge would impact
tions must be taken to protect the river’s natural elements is a
surrounding agricultural land, is part of the reason why the original tunnel replacement plan for a 10-lane bridge was scrapped
matter of time.
in 2017. “It’s been very clear from communities up to this point
While this work progresses, studies such as those from Venditti’s lab have been working on measuring sediment flux from
that they did not want a 10-lane bridge,” said Transportation
as far as 75 kilometres upstream of the tunnel to understand
Minister Claire Trevena in 2018. “We’re going to be working
how much sediment is entering the Fraser Delta. Their findings
more aggressively on the approaches to the tunnel and working
show that the delta has a sediment deficit, but it’s not yet been
within the tunnel.”
determined why. “These are standard things that need to be done
The impacts of a new tunnel relative to a bridge may be less
obvious at first glance as they have more to do with the morphol- in the context of an environmental impact review.”
ogy of the river itself. Though the same above land issues may
Environmental stewardship
not exist, what happens below the water in the bed of the river
More projects like the replacement of the George Massey Tunnel,
can be equally as critical. The out-of-sight, out-of-mind perspective fails to acknowledge the dynamic nature of these ecosystems
also known as the Fraser River Tunnel Project, part of the Highand how interdependent they are.
way 99 Tunnel Program, will inevitably continue to take place
in and around the Fraser River. But rather than simply accepting
“Rivers like to wander around,” Venditti describes. “It needs
these engineering feats for what they are, Venditti says we should
to be able to erode its banks during floods and deposit at lower
be asking ourselves what kind of Fraser River we want.
flows. It needs to aggrade and degrade the bed of the river.”
“If you want one that conveys water and sediment out to
It’s this dynamic nature that makes building infrastructure in
the ocean, that’s no problem. The engineering community is
or around a river so unique.
perfectly able to provide a river, they’ll pass the water and protect
With a bridge, this kind of flow is possible because the pilings
communities from flooding.”
that go in the river don’t prevent the river bed from evolving in
We’ve seen these types of engineering projects around the
this way. However, an immersed tube tunnel, like the one that
world. From the Port of Rotterdam to the Panama Canal, we’ve
is currently in the procurement phase to replace the George
proven our capability to control the natural environment for the
Massey Tunnel, does. Immersed tube tunnels require dredging
purpose of human activity. However, taking a relatively natural
the bottom of the river, displacing the sediment, and placing
delta like the Fraser Delta and turning it into a concrete channel
fixed, cement boundaries on each side of the river at the tunnel
does not need to be the only way we solve challenges.
entrances.
“If you want a healthy, living river–one where you have relaThis ultimately changes the way sediment can move throughout
tively natural processes happening,” Vendetti says, “We can have
the river. While it’s unlikely these changes will cause any widespread erosion or environmental catastrophes, the exact impacts
that kind of river.”
won’t be known until we see them. And once we do, our choices
But the only way to have that is through gaining a deep understanding of where we’re at and where we want to go.
as to how we correct these potential impacts are limited with the
Striking a balance between creating a built environment in
most common solution being to add more infrastructure.
“If you start seeing erosion, you don’t take the tunnel out, you place of a natural one is not easy. But with every challenge comes
the opportunity to set an example of innovative thinking for
build more. You put more concrete in and more riprap on the
growing economies and populations around the world who will
side of the river preventing it from eroding in those areas,” Venditti explains. “What happens is progressively you start building
need to engineer solutions into natural spaces, too. The question
up more and more of that concrete and the riprap on the banks
is, how will they do it?
WAT E R C A N A D A . N E T
WATER C AN ADA • SEP TEMBER/OCTOBER 2023
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