Climate Projections Suggest More Winter Rains, Threatening More Flooding

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Kevin Bunch
April 05, 2018
lake erie starts here storm drain stencil

By Kevin Bunch, IJC

storm drain erie
Runoff from rain or snow melt in cities is channeled
to storm drains, which run directly to waterways or
treatment plants that can become overwhelmed
during storms. Credit: Tim Evanson

Projected changes to the Great Lakes region’s climate suggest milder winters will become the norm, bringing with them more rainfall. That’s going to put a strain on older infrastructure, leading to the possibility of additional combined sewer overflows and floods like those seen across the Great Lakes basin in late February 2018.

This year, a warm snap caused snowpack and ice cover to melt throughout the region. Several parts of the Great Lakes saw serious rainfall, exacerbating those issues. In older cities like Chicago, Illinois; Detroit, Michigan; and Brantford, Ontario, these conditions led to combined sewer overflows. Communities there still have old pipes that combine stormwater from runoff of melting snow and rain and sewage waste from homes and businesses. In normal circumstances, all that water is treated and released. But when too much water enters at once, it can overwhelm a treatment plant and divert dirty water directly into rivers and lakes.

“It’s a chronic issue right across older communities,” said Ellen Schwartzel, deputy commissioner of the Environmental Commissioner of Ontario. “(And) when you have milder winters, what used to be snowpack now comes in as rain and then you get these floods very early in the season. We may need to get ready for that kind of thing more often.”

Schwartzel added that global climate change models suggest increasing air temperatures will lead to more energetic storms on average through 2050. A joint research team from Michigan State University and the University of Michigan found that would play out as more frequent, intense storms, particularly as rainfall during winter months. Summer precipitation could potentially decline or simply increase less compared to other seasons.

Climate change has been one driver for more frequent combined sewer overflows and flooding, but Schwartzel said another is readily overlooked: human development. This can further strain combined sewer systems in older cities with growing populations, such as Toronto, Ontario.

Sprawling growth into undeveloped areas has its own impacts. When the landscape is paved over and built upon, that reduces the permeable surface area where precipitation and snowmelt can seep into the ground. Water is then stuck on these hard surfaces until it can run into stormwater drains and potentially contribute to an overflow. “Whenever you do get rainfall, you get these rapid runoffs,” Schwartzel said. “You get a flashy kind of watershed that you didn’t used to have.” At the same time, it means that in drier times, streams and rivers don’t have the same supply of groundwater to draw from, which also reduces water flows.

Cities Adapting With Green Infrastructure

With more frequent and intense storms and earlier snowmelts due to milder winters expected in the Great Lakes region, municipalities are turning to green infrastructure in response to increasing stormwater discharges , said hydrologist Ralph Haefner, deputy director of the US Geological Survey’s Upper Midwest Water Science Center. Also known as “low impact development,” this might involve using permeable concrete, green rooftops, rain gardens, swales, and other methods that can reduce  water runoff. “A lot of urban planners want more green space, more open areas, and more trees – they’re underestimated in their value for stormwater control and reduction,” Haefner said. “It’s just thinking about how the environment can accept the water that’s supposed to be there. Rather than channeling it out when it rains, how can we utilize it on site? Can we grow plants with it?”

cso ohio river
A combined sewer overflow along the Ohio River in 2011. Credit: Brett Ciccotelli

A growing number of municipalities are considering or implementing stormwater charges for property owners, too. Unlike traditional water bills based on how much water a property is using, the stormwater charge is based on how much runoff a property is contributing to the stormwater sewer system. For example, a parking lot owner may pay very little in a traditional water usage bill, but could see a bigger stormwater charge due to it being paved with asphalt. The money from those stormwater charges can provide a reliable source of funding for storm-related infrastructure, Schwartzel said, including general maintenance to build out separated stormwater and wastewater sewer lines – mitigating the problem of combined sewer overflows. A separated stormwater line can still discharge without treatment in heavy runoff events, but there would be a smaller amount of pollutants entering the water system and a smaller likelihood of an overflow to begin with. Haefner said some communities – Hamilton and Kingston in Ontario, and Toronto, Cleveland, Chicago, and Milwaukee – have opted to construct stormwater storage devices that can hold onto stormwater surges, allowing the water to slowly drain. That way, sewer systems aren’t overtaxed and those communities can avoid combined sewer overflows. These can be large underground tunnel systems or above-ground, reservoir-style “impoundments.”

Overflow Events Cause Public Health Dilemmas

Avoiding overflows is important not just to get around potential flooding, but for health and safety reasons. Haefner said that in conditions where there isn't an overflow, a combination of stormwater and sanitary sewer discharge is treated before being discharged. But when a combined sewer overflow occurs, this can flush pathogens, viruses and toxic chemicals into rivers and lakes. With people using waterfronts in the Great Lakes region to swim or go boating, these can cause health risks that users aren’t always aware of. Ontario and US states require reporting sewer bypasses to the state and provincial governments, but historically these aren’t generally required to be reported to the public.

The US Environmental Protection Agency recently issued a rule requiring public notification of combined sewer overflows into the Great Lakes, specifically for entities seeking new permits or renewing a permit to discharge those into the lakes.

Schwartzel said Utilities Kingston recently developed a map to alert residents to releases of contaminated water due to storms and how long outflows from the sewer system will be running.

“When people are aware that we’re doing this to our waterfronts we all want to enjoy, these patches of the Great Lakes, they begin to see the connection between these (bypass) events and the lack of funding,” she said.

stormwater storage
A stormwater storage system under construction in Toronto will hold water until treatment plants, such as the pictured Ashbridges Bay plant, can get to it. Credit: Timothy Neesam


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Kevin Bunch

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.