Dysentery, typhoid, and cholera were just a few of the diseases that stalked our cities before the modern sewer. Before we tunnelled our way under those cities in the last century and a half. The project was to pipe unwanted water, from sinks, toilets, and storms away from our homes as fast as possible. The goal was to save lives and property.

For the last century and a half, we’ve done a pretty good job of it. Engineering water transfer with such speed and success we forget about the sheer miraculous scale of it. But now the very efficiency of engineered water transfer is bringing its own risks to people and property.

In it’s simplest form, here’s what happens: a storm hits a major city like Toronto. Water rushes off hundreds of thousands of roofs, onto the paved sidewalks, into the paved streets and down into the concrete maze under our feet. It surges through the pipes and into the lake.

Photo by Scott Schiller

Simple enough and that’s what most people see. What you don’t see is what’s important. The water carries with it everything in its path including; car oil, detergents, cigarette butts, dog poo, plastic, and garbage. When the surge is powerful enough it overrides the sewage treatment system. For example, in July 2013, a powerful storm hit Toronto and dumped over a billion litres of raw sewage into Lake Ontario in just over 24 hours.

Introducing Green Infrastructure

Over the last few decades, there’s been an architectural and engineering movement aiming to slow the waters down. To crack open our concrete cities and let some of the water through to the soil instead of forcing it through the sewers and into the lake.

Slower water would cut the risk of overriding the sewer system. Letting the water into the soil would allow for micro-organisms to do their job of cleaning the water before it re-enters the system.

Green Infrastructure, as opposed to our current grey infrastructure, begins with the simple planting of more trees and creating urban park space. It then ramps up to the more technically challenging green roofs and green walls. Branching out to the exotic, bioswales, urban landscaping designed to mimic natural filtering systems.

With increased erratic weather and climate change forecasts predicting more precipitation in Toronto and other Great Lakes cities the problem is set to magnify. But there are many problems in moving towards green infrastructure as well.

To start with, green infrastructure demands a bit of a magpie approach. You need to pick up a lot of different skills to make it work: engineering, soil ecology, hydrology, urban planning.

“We’ve siloed a lot of these things. Especially at the municipal level. You need public works, department of transportation, urban forestry, parks, and even more departments that need to get together and work collaboratively,” Janet McKay, Executive Director and Founder, LEAF (Local Enhancement and Appreciation of Forests).

One person who does have the magpie mentality, at least when it comes to picking up his academic credentials, is Professor Paul Mankiewicz from New York’s Gaia Institute. His background includes biogeochemistry, developmental plant ecology, and biophysics.

“Partly it’s a generational thing. You have older engineers who aren’t really familiar with the way soils work.”

Mankiewicz is responsible for designing dozens of green roofs and other green infrastructure projects across New York. His work includes a project at a Bronx plastic and glass recycling plant that diverts a million gallons of grey water a year that is now filtered through natural soil buffers. That means there are a million gallons of dirty water that aren’t going into the Bronx River on that one project alone.

He points out that Toronto is sitting on glacial till. And that sort of soil is perfect for absorbing water and acting as a natural filter. The problem is the water can’t get to it.

Even the most straightforward moves, such as planting more trees on urban sidewalks comes with a heap of problems. Apart from shade and aesthetics the tree, in theory, would suck up moisture and the ground around the tree would let water get back into the soil instead of rushing into the sewer.

But as LEAF’s Janet Mackay points out, real estate is prime under the cement.

The fight for space in a concrete world

“There’s competition for space. There’s pipes, cables, all the things we need to make the city work. Trees come in as an afterthought. Roots need room and a proper soil system.”

In an ideal world, the one we’re very far from, environmental engineer, Imitaz Shah, would have us use Water Balance Analysis. The theory calls for development to be based on the needs of the particular soils we’re building on. An idea that largely remains an ideal. “Human beings, we’re kind of selfish when it comes to development. We don’t respect nature.”

So much of our cities are already paved over and there’s fierce competition for both sidewalk space and the ground underneath it. The virgin territory in the urban landscape is the rooftop. Green roofs are designed to slow and filter the water. Keeping it out of the sewers.

Photo by Jeremy Wilburn

On the financial side, there is money to be saved in the green roof cutting heating bills, saving on air conditioning and reducing the load on the city’s sewage infrastructure.

Unlike wind or solar power, there’s nothing new or particularly contentious about a lot of these ideas. The engineering is relatively straightforward. But for the vast majority of urban dwellers looking out their windows, you won’t see a green roof, a bioswale or a green wall.

Mankiewicz says we just haven’t hit the tipping point yet.

“These things are not difficult or expensive to build. It is just a matter of having the will. And having models to point at. We need to see this done on a whole block, a whole community. Without having something to point at, it’s just talk.”

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