Flooding Hazards: Prevent and Mitigate, or Compensate and Rehabilitate?
Millions of dollars have been spent on flood prevention measures to eliminate or mitigate the risks posed to public health and safety, damage to property, and the effects of flooding on the environment. However, flooding events are still common and compensation costs continue to escalate. In addition, floodwaters are often highly polluted with chemicals from flooded industries and households, sewage from overflowing septic systems and sewage treatment plants, and sediment from fields. Rushing floodwaters can erode stream banks and scour streambeds. Fish and other aquatic organisms are killed and their habitats are destroyed.
Flood management responsibilities are distributed across all three levels of government (federal, provincial and municipal), as well as delegated to Conservation Authorities (CAs.) A core responsibility – defining and updating the regulations, policies and guidelines on which municipalities, CAs, engineers, developers and the public rely to protect life, property and the environment – is distributed across several provincial ministries. These ministries must balance the costs of prevention and mitigation against the potential for loss of life, and the costs to repair and rebuild homes, businesses and infrastructure, and rehabilitate streams and habitats.
An ECO review of some of the current flood prevention and mitigation measures that are currently employed by the Ministry of Municipal Affairs and Housing (MMAH), Ministry of Natural Resources (MNR) and Ministry of Environment (MOE) suggests that strong development controls and well-designed stormwater management systems can significantly reduce the risk of flooding. However, exceptions to development controls, aging and/or inadequate stormwater management systems and flood control structures, and lack of support for innovative technologies and funding for flood management activities are increasing the risk that future rainfall events will overwhelm existing flood prevention and mitigation measures. As evidence mounts that storms are becoming more severe due to climate change, the ECO believes that bold pro-active steps are required to reduce the risk of significant flooding.
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Historical flooding events shape Ontario’s flood management policies
In Ontario, two rainfall events, in particular, have shaped Ontario’s overall flood management policies:
- In 1954, Hurricane Hazel swept through the Greater Toronto Area, killing 81 people, leaving 1,868 families homeless, destroying 20 bridges, and washing away numerous buildings across the region and crops in Holland Marsh. About 210 millimetres (8.3 inches) of rain fell in 12 hours on already saturated ground.
- In 1961, heavy rains falling during the “Timmins Storm” caused a small creek in Timmins to overflow its banks, destroying roads and homes, and undercutting foundations. Five people died. About 193 mm (7.6 in) of rain fell in 12 hours.
Some effective measures that reduce the flooding hazard
MMAH Provincial Policy Statement, 2005
One of the most effective ways of preventing flood damage is to prohibit development and site alteration in areas subject to flooding hazards. According to the MMAH’s 2005 Provincial Policy Statement (PPS), issued under the Planning Act, development is defined to include creation of a new lot, a change in land use, or the construction of buildings and structures, requiring approval under the Act. Site alteration includes grading, placement of fill and excavation. Under the PPS, municipalities “shall generally” direct development away from the following flooding hazard areas:
- areas adjacent to the shorelines of the Great Lakes-St. Lawrence River systems and large inland lakes that would be inundated in a 100-year flood, (i.e., a flood that has a one chance in one hundred of occurring or being exceeded in any particular year); and
- areas, called flood plains, adjacent to rivers, streams and small inland lakes that would be flooded by the greatest of (a) rainfall experienced during a major storm, such as Hurricane Hazel or the Timmins Storm, in the specific watershed, (b) the 100-year flood, or (c) a previous flood caused by ice jams.
Conservation Authorities – Regulations prohibit development near waterbodies and wetlands
A Conservation Authority is also able to prevent and/or limit development, if, in its opinion, the development interferes with the control of flooding. Development, under the Conservation Authorities Act (CAA), includes increasing the size of a building, grading, excavation and the placement of fill. Each CA, in its ‘development’ regulation, has identified the rivers, streams, lakes, wetlands, valleys and shorelines, including the flooding hazard areas identified under the 2005 PPS, where development is prohibited unless the CA has approved it.
MOE – Urban stormwater management
Effective management of urban runoff can reduce flooding. MOE’s “Stormwater Management Planning & Design Manual” (SWMP, 2003) states that runoff from post-development sites must not exceed pre-development levels for storms with return periods ranging from two to 100 years. According to SWMP, new development projects should manage runoff from average rainfall events using a variety of methods, such as directing runoff onto lawns, backyard swales and road gutters; and from larger events by directing runoff down streets, to large storm sewers, storage ponds and other structures before being discharged to a waterbody.
Opportunities to reduce the flooding hazard
Development and site alteration in flood fringe areas
The flood fringe is the area within the flooding hazard area where the water depth and velocity are lower than elsewhere within the area. The 2005 PPS allows some types of development (e.g., new residential housing and site alteration) in the flood fringe, if safety and flood proofing measures that protect life and property are used. However, these measures do not guarantee that areas within the flood fringe are safe from being flooded. When municipalities and/or CAs refuse to approve development and/or site alteration in the flood fringe, they often face considerable opposition because of economic interests or prior development in the area.
Since many older communities previously allowed homes and businesses to be sited in flooding hazard areas, the 2005 PPS allows municipalities to designate these areas as Special Policy Areas (SPAs) subject to provincial approval. SPAs provide municipalities with a way of controlling the nature and extent of development and site alteration activities to reduce the risk that changes will increase flooding in the area.
Managing runoff and unrestrained use of impervious materials
Managing runoff in older parts of cities is often very difficult using conventional methods. Precipitation falling on roofs, parking lots and roads built of impervious materials, such as asphalt, concrete, metal, brick and/or stone, becomes runoff that must be managed rather than infiltrating into the ground. Replacing agricultural lands with high-density commercial uses can increase surface runoff by 250 per cent and peak stream flows by 200 to 500 per cent. Although the SWMP encourages management of runoff locally, it does not encourage the use of porous materials for parking lots, walkways, etc., and other innovative methods of handling runoff on-site, such as green roofs. Furthermore, urban streets are often too flat to handle runoff or have low spots resulting in local flooding, and many homes and businesses have little or no pervious areas.
Aging flood control structures and inadequate stormwater systems
About one-quarter of Ontario’s 2,400 dams are more than 50-years-old and in need of maintenance and repair. Ruptures in older stormwater systems resulting in local flooding and street cave-ins are increasingly common. One-fifth of Toronto’s storm sewer system is more than 80-years-old, and some stormwater systems, such as those found in parts of Peterborough, were not designed to handle more than a one to two year return storm.
Funding of flood management initiatives cut in the 1990s
Between the 1950s and early 1990s, the federal and/or provincial governments funded various flood management initiatives, including the building, maintenance and operation of dams. They also funded the preparation of flood plain maps, which are used by municipalities to identify their flooding hazard areas. However, in the 1990s, provincial transfer payments to the CAs for flood management services, such as operating and maintaining dams, were cut by 87 per cent. Since 2000, the payments have remained flat at $7.6 million per year, less than one-half of the amount that Conservation Ontario has calculated is owed to CAs, according to its funding agreement with MNR. MNR also eliminated funding support for enforcement of CAA regulations and reviewing municipal plans.
Adapting to climate change
Flood management, including flood plain mapping, dams, stormwater systems, and municipal plans, are based on historical rainfall and flooding events. However, under the climate change scenario, historical events may be a poor predictor of future events. More frequent and intense precipitation events in Ontario are expected and anecdotal evidence suggests that municipalities have already experienced such events:
- Since 1996, three 100-year storms have hit the Ottawa area and the village of Carp to the west of the city.
- In 2002, the “49th Parallel Storm” in northwestern Ontario exceeded the rainfall depth of the Timmins Storm by a factor of at least two.
- In 2002, Peterborough experienced a 100-year storm, and just two years later, a 290-year storm in 2004.
- In 2004, Hurricane Frances dumped up to 150 mm of rain in 12 hours on eastern Ontario.
- On August 19, 2005, a 100-year storm dumped almost 175 mm of rain in less than one hour across the northern sections of the City of Toronto and York Region.
By 2090, Environment Canada estimates that the 100-year storm will be experienced every 50 years, based on a projected 15 per cent increase in rainfall across Ontario. Infrastructure with long service lives, such as dams, combined sewer systems and stormwater systems, are at risk of experiencing storms that exceed their capacity to handle the floodwaters. A recent climate change study included a recommendation that designers of future stormwater structures should assume storms that are 15 per cent larger than those experienced currently.
An increasing number of experts have begun to question the appropriateness of planning policies that allow development and site alteration in flooding hazard areas, and to raise concerns about aging infrastructure. Some are also questioning the appropriateness of relying solely on historical storm events to design infrastructure. Meanwhile, major infrastructure decisions are still being made based on historical data, and municipalities and CAs are struggling to prohibit development and site alteration in flood prone areas. The ECO urges MOE, MNR and MMAH to update current regulations, policies and guidelines so that today’s decisions don’t add to an existing legacy of infrastructure and development that will not be able to handle or withstand projected flood events.
| This is an article from the 2006/07 Annual Report to the Legislature from the Environmental Commissioner of Ontario. |
Citing This Article:
Environmental Commissioner of Ontario. 2007. "Flooding Hazards:Prevent and Mitigate, or Compensate and Rehabilitate?." Reconciling our Priorities, ECO Annual Report, 2006-07. Toronto, ON : Environmental Commissioner of Ontario. 197-201.
