Storm and Sewage Systems

Storm and Sewage Systems

Student Author: 
Teresa Tran & Lara Isaac
May 2015
Mona El Khafif

Storm events in Toronto are the cause of catastrophic environmental and property damage including basement flooding and bypasses of raw sewage. These events are occurring with increasing frequency and severity. The problem Toronto is facing is caused by the compounded problems of insufficient sewer plant capacity, high impermeable ground area, high population density, and a combined storm and sewer system. As population increases, the baseline pressure on the sewage system increases, and storm events, which are also worsening due to global climate change, cause sudden catastrophic stress. Storm damage is particularly damaging in downtown Toronto where the stormwater and sewage systems are combined, resulting in bypasses of storm water mixed with raw sewage. Consequently, Toronto’s beaches often have a Water Quality Advisory warning following storms because the lake is unsafe to swim in. This is a public health and safety and environmental concern.

This project uses GIS to show how weak points of Toronto’s storm and sewer management systems coverage to create the conditions for the “perfect storm” downtown in the combined sewer area by the convergence of the lowest elevation, the highest percent impermeable coverage, highest population density and combined storm/sewer system. Due to a combination of incidental circumstances and poor design, Toronto’s downtown is left in dire need of updates to its water infrastructure to avoid further damages and disasters.

Unfortunately, infrastructure changes are highly expensive, and experts recommend the construction of “soft infrastructure” to mitigate the impact of storm events and individual acts of conservation to reduce the proportion of raw sewage in the bypasses. Through community awareness and targeted design intervention, individuals and communities can avert the occurrence and reduce the severity of storm events and bypasses.

The need to address the problem of flooding has received widespread acknowledgement both in the press and in academia and is becoming a pressing design issue for landscape architects, urban planners, and architects, whom are able to avoid or minimize the impact of flooding through design. The prevailing research indicates the best and most cost effective methods are small scale construction of permeable surfaces, such as bioswales rather than sidewalks, and green roofs rather than ballast. By using other cities as precedents, Toronto can get inspiration and information on to modify its streetscapes to be more flood-resistant.

There is significant financial motivation for the city of Toronto to prepare for rather respond to extreme weather events. Recent history has seen an increase in flooding events both in Toronto and in other regions of Canada, such as the Calgary flood of 2012. With the projected population growth of 23% by 2030, Toronto’s flooding concerns can only increase- both form higher pressure on sewage infrastructure and greater quantities of property available to be damaged.

When it comes to water infrastructure, the biggest problem Toronto faces is the issue of bypasses which irreparably damage the ecosystem and water quality of Lake Ontario with toxic human waste. A reduction in the proportion of storm water diverted to sewers rather than absorbed or infiltrated is critical to avoid financial, ecological and public health damages. A combination of both natural and artificial factors are compounded to create this water crisis, and small, distributed changes to both the natural and artificial environments can help to solve this problem. Toronto’s storm water management challenges are manageable with good design.