Sponge Cities

Can innovations stop surface runoff from killing our waters?

George Le Masurier

Photo by Center for Neighborhood Technology, CC, cropped from original

The Department of Fisheries and Oceans slapped a ban on both personal and commercial shellfish harvesting throughout Baynes Sound recently because of heavy rainfall, which came “after a prolonged dry spell,” so would “adversely affect marine water quality.”

It’s a regular notice the DFO issues around most urbanized regions of Vancouver Island in the fall, and it usually lasts for more than a few days.

Why? Because every time it rains after a dry period, it’s as if a giant toilet flushes animal feces, fertilizers, pesticides, oils, road salts, heavy metals and other contaminants into municipal stormwater systems, which in turn send torrents of polluted water directly into watersheds, killing fish, eroding property and making waters unsafe for shellfish harvesting.

This is not a new problem. For the past 100 years, urban development has replaced natural vegetated land with impervious surfaces like roads and parking lots. This has diminished the amount of rainwater absorbed into the ground and reduced the dispersal of precipitation back into the atmosphere from trees (which do the heavy lifting) and other plants, via a process called evapotranspiration.

As a result, surface runoff has become the primary means of rainwater drainage.

To control flooding, Vancouver Island municipalities, like other local governments around the world, invested millions of dollars over time in underground infrastructure to channel rainwater runoff into rivers or streams. This not only polluted these waterways and killed wildlife, but the increased volume and speed of the moving water caused erosion and other flooding risks by altering the natural hydrologic cycle.

Humans have an order to their development process: first we log it, then we farm it, then we pave it

Comox’s Golf Creek is a prime example. Eighty-six per cent of the once flourishing natural stream flowing into Comox Harbour has been buried beneath residential streets, a shopping mall, and a retirement housing development. It’s polluted after heavy rains and a downstream property owner is currently suing the town over erosion caused by the creek’s sudden fast flows and large volumes.

“Humans have an order to their development process: first we log it, then we farm it, then we pave it,” says Chris Hilliar, a former Department of Fisheries and Oceans officer in Comox. “Fish can get along with forestry, if it’s done right; they can get along with farming, if it’s done right; but, concrete and pavement are killers, a death knell to streams and the aquatic life within them.”

Stormwater runoff is the main reason why many urban streams are devoid of fish or linger on aquatic life-support, and why these streams can pose a public health risk for children who play in them. Runoff is also the top non-point source of oil from human activity into North America’s oceans, according to the National Research Council. And it has been identified as the source of polychlorinated biphenyls (PCBs) that are harming British Columbia’s killer whale population, according to another NRC paper.

The situation is reversible

A shift in thinking about traditional methods of handling stormwater began to occur during the 1980s and 1990s, toward constructing wetlands and ponds to detain rainwater long enough for contaminates to settle out and allow some water to infiltrate back into the ground. This gave hope that there was a means of cleaning our streams and extending the life of municipal infrastructure.

Today, there’s been a further shift toward a recognition that nature itself cleans and controls rainwater better than any engineered solution. This new emphasis attempts to imitate nature with pervious surfaces, downspout disconnection, rain gardens, bioswales, green roofs and rainwater harvesting.

The prospects have excited many municipal engineers and environmentalists.

The city of Courtenay has narrowed roadways (reducing impervious surface area) and added rain gardens to capture runoff and encourage infiltration. The city plans to develop its first Integrated Stormwater Management Plan in 2019 that could set a new, greener standard for stormwater management in the municipality.

“sponge cities” describe the capacity of an urban landscape to absorb rainwater naturally.

Victoria has created a new utility tax to fund its future cost of maintaining stormwater infrastructure and to encourage residents and developers to adopt green infrastructure and low-impact development designs. In most communities, stormwater infrastructure costs are paid out of general revenue. Victoria residents are now taxed separately for the stormwater that leaves their property. In other words, the more impervious surfaces and the fewer onsite mitigations you have, such as rain gardens and rock pits, the more you will pay.

It’s the theory behind Chinese landscape architect Kongjian Yu’s “sponge cities” concept, a way to describe the capacity of an urban landscape to absorb rainwater naturally. Major world cities have jumped on the idea. Berlin, Germany, adopted a city-wide Sponge City Strategy in 2017.

Since 2009, Toronto, Ontario has required buildings over 2,000 square metres to have green roofs, which use several layers of soil to grow plants that capture and release rainwater, slowing the rush of water through the city’s stormwater pipes.

The list and variety of innovations for managing stormwater through green infrastructure is long and growing.

The change may seem to be coming too late for streams that are almost entirely buried and channelized. But challenging initiatives like the 100-year plan to restore Bowker Creek in Victoria and the campaign to save the Morrision Creek headwaters between Courtenay and Cumberland may someday restore fish in our streams and keep our waters open to shellfish harvesting.

George Le Masurier is a retired journalist and newspaper executive. This article is from his website www.decafnation.net and reprinted as part of a collaboration with the Watershed Sentinel.

5 Issues/yr — $25 print; $15 digital