Climate Projections Suggest More Winter Rains, Threatening More Flooding

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

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

Greater Infrastructure Investments Needed to Reduce Combined Sewer Overflows

By Michael Mezzacapo, IJC

cso graphic combined sewer overflows
Figure 1: A graphic depicting a CSO event in extreme weather. Credit: Michael Mezzacapo

Many older sewer systems in Canada and the United States mix stormwater runoff with raw or partially treated sewage and discharge the excess into the Great Lakes during periods of heavy precipitation. These discharges are known as combined sewer overflow events (CSOs). CSO systems can handle typical rain events (Figure 1) but during more intense rain events the capacity of the treatment plant and its connecting systems is exceeded, causing the excess water to be discharged to a nearby lake or river (Figure 2).

CSO runoff can contain contaminants, including pathogens like E.coli and chemicals and nutrients like phosphorus and nitrogen, which impact the drinkability, swimability and fishability of Great Lakes waters. Outflows from CSOs also have health and economic impacts, resulting in drinking water supplies requiring greater and more costly treatment and beach closures in order to protect human health. The IJC recommends zero discharge of inadequately treated or untreated sewage into the Great Lakes and connecting waters in its recently released First Triennial Assessment of Progress (TAP) under the Great Lakes Water Quality Agreement.

The TAP report notes that in just one year, 20 Great Lakes cities in Canada and the US released a combined total of 92 billion gallons of untreated sewage and stormwater to the Great Lakes, mostly via CSOs. That’s roughly equal to 147,000 Olympic size swimming pools. Between Canada and the US, there are about 291 cities in the Great Lakes basin with antiquated sewer systems which release CSOs, 109 in Canada and 182 in the United States. The map below shows the discharge in millions of gallons per year between 2005-2008 for 49 cities in the US and Canada.

csos map great lakes basin
Map showing the discharge volume of CSOs for 49 cities between 2005-2008 within the Great Lakes basin. Credit: GLEAM

The release of wastewater just above Niagara Falls this summer by the Niagara Falls Water Board sparked public outrage and government fines. The July discharge was highly visible, occurring during the peak tourist season. Citizens may be unaware of how frequently CSO events occur around the Great Lakes basin. In 2014, a US Environmental Protection Agency report cited 1,482 untreated CSO events in US states within the Great Lakes basin. Although the province of Ontario issues guidance to municipalities on CSOs, there are no comprehensive reports detailing these events. Releases may intensify as aging sewer systems are impacted by a changing climate due to precipitation pattern shifts and population increases.

An Aug. 15 discharge of sewage into the Niagara River
An Aug. 15 discharge of sewage into the Niagara River. Credit: Christine Hess

Citizens may not notice impacts from CSO discharges. The old adage of “out-of-sight and out-of-mind” often comes into play. Those that live directly on the shoreline and frequent beaches are most likely to notice the foul smells and discolored waters, while others who aren’t adjacent to CSO releases may not even be aware they are occurring, although many states require public notice of such events.  Ontario does not require public notice of such events, though some cities do notify the public.

More than 35 million people rely on the Great Lakes for drinking water, recreation and employment. CSOs have the potential to cause human illness over large sections of the population, not just those who recreate in the contaminated water. A study published in the Journal of Environmental Health Perspectives detailed a 13 percent increase in emergency room visits related to gastrointestinal illness in Massachusetts following extreme precipitation events in areas with sewers that discharged CSOs into drinking water sources. Another study co-authored by IJC Health Professional Advisory Board member Dr. Tim Takaro noted that drinking water systems can prevent illness by developing planning tools and building resilience and capacity into infrastructure for future events; the study was done in Vancouver, British Columbia.

The IJC has consistently expressed concern about the need to increase the governments’ attention to water quality and human health. The IJC recommends in its recent TAP report that older sewer systems that contribute CSOs to the Great Lakes be upgraded to separated sewer systems which do not combine stormwater and sewage. In its 14th Biennial Report in 2009, the IJC highlighted the safety risk to human health by exposure to contaminants from CSOs through fish consumption, drinking water and swimming.

To protect human health and reduce exposure to untreated and inadequately treated sewage, the IJC recommends in its new TAP report that Canada and the US determine an accelerated and fixed period of time by which zero discharge of inadequately treated or untreated sewage into the Great Lakes will be virtually achieved. Given the importance of public health and lake recreation to the Great Lakes public and local economies, the IJC recommends that sufficient resources be dedicated to proactively and systematically improve the capacity of city sewer systems to respond to extreme storm events, especially as related to combined sewer overflows, in the areas of planning, zoning and adaptation.

The Canadian and US governments have slowed needed investment on infrastructure since the 1970s and 1980s, due to increasing demands placed on municipal budgets in other areas. The need for increases in funding was highlighted in a recent US Clean Watersheds Needs Survey, which found that over the next 20 years, six of the eight Great Lakes states (Minnesota, Wisconsin, Illinois, Indiana, Michigan and Ohio), will need an estimated US$77.5 billion to upgrade wastewater and stormwater infrastructure, by separating stormwater and sewage with adequate treatment capacity.

Tackling CSOs will require a concerted and calculated effort between local, provincial, state and federal governments. Engaged citizens can voice their concern over CSO releases and the need to increase spending to upgrade aging infrastructure by writing their local, state, provincial or federal governments. Citizens should inform themselves of CSO events in their area and obey signage for beach closures and fish consumption advisories. Finally, you can also have your voice be heard by submitting comments through

Michael Mezzacapo is the 2017-2018 Michigan Sea Grant Fellow at the IJC’s Great Lakes Regional Office in Windsor, Ontario.