The threat of flooding is a hazard that many cities face across Canada and globally.  The impact can be small in scale (a community or a neighbourhood) or quite large (entire river basins or multiple municipalities).  However, it is important to recognize that not all floods are the same.

Types of Flooding

Before a Flood

During a Flood

After a Flood

Flood Preparedness (pdf 102 kb)

Types of Flooding

In Greater Sudbury, flooding can occur due to one of or a combination of these conditions:

Snow and Ice Melt Runoff

This is the most common type of flooding in Greater Sudbury.  During the winter, most of the precipitation is stored as snow or ice on the ground.  When the spring melt occurs, heavy runoff results from the rapid melting of the snow under the combined effect of sunlight, winds, and warmer temperatures.  This causes huge quantities of water to be released.  When the ground is frozen or paved over, the melting snow is unable to penetrate and runs off over the ground surface into streams and lakes, resulting in flooding.

Spring Rainfall

The impact of spring rainfall will vary depending on a number of factors including:

  • How much rain falls

  • How much melting occurred before a rain event

  • The water content of the existing snow on the ground

  • The ground conditions (frozen or unfrozen)

The worst-case scenario is above-zero temperatures combined with rain on frozen ground, or rain on snow with above-average water content.  These conditions provide the greatest threat for flooding.

Severe Summer Storms (Flash Flooding)

During high intensity thunderstorms, rainfall is often so heavy (torrential downpours) that the ground is incapable of absorbing the water quickly enough, resulting in very high runoff rates.  As a result, flash flooding may occur.  Flash flooding can occur in a matter of minutes or hours.

Ice Jams / Frazil Ice

Ice jams result from the accumulation of ice fragments that build up to restrict the flow of water and then act as a temporary obstruction.  Jams form during both the freeze-up and break-up periods, but it is usually the break-up jams that have the greatest flood potential.

Debris Jams

Debris jams typically occur at crossing structures and are triggered during extreme, high-intensity rainfall events where large quantities of organic and inorganic material are washed into streams.

Dam Break or Breach

When a dam fails and water is released from a reservoir, the flood wave travelling downstream can cause significant property damage and possible loss of life. 

Dam failures can be divided into two broad classifications:

  1. Failures caused by overtopping during extreme rainfall / snowmelt events, or failure of an upstream dam.

  2. Structural failures due to foundation problems (i.e.: deterioration of concrete, erosion of earth, etc.), geological conditions, or earthquakes.

Overtopping the crest of the dam (i.e.: dam breach), whether alone or in combination with a dam failure, can occur when an extreme hydrologic event or failure of an upstream dam causes large water inflows to exceed the capacity of the reservoir and its spillway.  Overtopping may also be caused by an accumulation of debris or ice that restricts flow through the dam’s spillway.

Urban Flooding

Urban flooding may occur when the rainfall exceeds the municipal storm drainage system’s ability to handle the volume of rain.  Urban flooding is common during flash flood events.  This type of flooding occurs in urban / built up areas during thunderstorm events because the surrounding ground surfaces are largely paved over, thereby decreasing the capability of the ground to absorb even small amounts of rainfall quickly enough.  During these types of events, the streets may become inundated, sewer systems may surcharge, and basements may fill with water.

Water Main Break

In extreme circumstances, water main breaks could result in large volumes of water being released and result in flooding.  During such situations the streets may become inundated, sewer systems may surcharge, and basements may fill with water, creating issues similar to floods caused by natural phenomenon.


Before a Flood

To reduce the likelihood of flood damage

  • Ensure downspouts include extensions that drain runoff water a sufficient distance from your home and any neighbouring properties.

  • Put weather protection sealant around basement windows and the base of ground-level doors.

  • Consider installing a sump pump and zero reverse flow valves in basement floor drains.

  • Elevate the furnace, water heater, and electric panel in your home.

  • Keep your eavestroughs free of debris.

  • Ensure your window wells have proper drainage.

  • Ensure the ground around your home slopes away from your foundation.

  • Avoid building in a flood plain.

  • Keep the sewage pipes between your house and the sewer main clean.

    • Avoid pouring grease, oils and kitchen wastes down the drain.

    • Do not flush dental floss down the toilet.  It can wrap around paper and other debris, catch on imperfections in your sewer pipes or in the sewage line between your home and the street, and cause a blockage.

    • Avoid planting trees and shrubs near the line that leads from your home to the sewer main.  Their roots can penetrate the lateral and cause the pipe to break or block.

  • Disconnect rain gutter downspouts, weeping tiles, and sump pumps from the sanitary sewer system.

    • In some older homes, rain gutter downspouts, weeping tiles and sump pumps are directly connected to the sanitary sewer system.  While this was once an acceptable practice, the municipal wastewater treatment system serves more customers today than in the past, leaving less excess capacity to process rainwater and snow melt.  These connects are illegal under municipal by-law and increase the risk of basement flooding.

  • Clear the storm sewer grates in front of your property of debris.

    • If there is a municipal storm sewer in front of your residence, check that the surface is clear of ice, leaves and other debris to prevent water from flowing back onto your property.

  • Reduce home water use during heavy rainfall events.

    • The more stress placed on the municipal sewer system, the greater the chances that you or your neighbours will have sewer backup problems.  Wait a few hours after a sever rainfall before starting laundry and dishes.

  • If you have a livestock farm, remember that livestock have a natural “move away instinct” to flash flood waters.  They generally seek higher ground if possible.  When purchasing or designing your livestock operation, it is important to allow livestock a way to reach high ground in each pasture.  Without access, livestock will fight fences and be at a greater risk of drowning.

If a flood is forecast

  • Take special precautions to safeguard electrical, natural gas or propane heating equipment.

    • If there is enough time, consult your electricity or fuel supplier for instructions on how to proceed.

  • Keep children and pets away from lakes, rivers, creeks, and low-lying areas which may be prone to flooding.

  • In a rural farm setting, sheltering livestock may be the wrong thing to do.  Leaving animals unsheltered is preferable because flood waters that inundate a barn could trap animals inside, causing them to drown.

If flooding is imminent

  • Turn off your furnace, gas, and electricity.

    • DO NOT attempt to shut off electricity if any water is present.  Water and live electrical wires can be lethal.

  • Move furniture, electrical appliances and other belongings to floors above ground level.

  • If you have time, bring in outdoor furniture.

  • Remove toxic substances such as pesticides and insecticides from the flood area to prevent pollution.

  • Disconnect eavestroughs if they are connected to the sanitary sewer system.

While flood insurance is not available in Canada, you can obtain sewer backup coverage.  Talk to your insurance provider about coverage options.


During a Flood

  • Listen to the radio for emergency information.

  • Only call 911 if you have a life-threatening emergency.

  • Keep children and pets away from flood water.

  • Be aware that flash flooding can occur.  If there is any possibility of a flash flood, move immediately to higher ground.  Do not wait for instructions to move.

  • Have your GO Bag Evacuation Kit with you in case you are instructed to evacuate.

  • If you need to evacuate, follow the routes specified by officials.  Don’t take shortcuts – they could lead you to a blocked or dangerous area.

    • Make arrangements for your pets.  If it’s not safe for you, it’s not safe for them!

  • Never cross a flooded area

    • If you are on foot, fast water could sweep you away.

    • If you are in a car, do not drive through flood waters or underpasses.  The water may be deeper than it looks and your car could get stuck or swept away by fast water.

    • Avoid crossing bridges if the water is high and flowing quickly.

    • If you are caught in fast-rising waters and your car stalls, leave it and save yourself and your passengers.


After a Flood

Care should be taken when re-entering your home.  Flood water is heavily contaminated with sewage and other pollutants that can pose a serious health hazard.

  • If you were evacuated, do not return to your home until authorities have advised that it is safe to do so.

  • Before entering a flooded building, make sure the building is structurally safe.  Check for foundation damage, buckled walls or floors, and make sure all porch roofs and overhangs are supported.  If in doubt, do not enter the building.  Make arrangements for a structural engineer to evaluate the building.

  • If the main power switch was not turned off prior to flooding, do not re-enter your home until a qualified electrician has determined it is safe to do so.

    • The main electrical panel must be cleaned, dried, and tested by a qualified electrician to ensure that it is safe.

  • Appliances that may have been flooded pose a risk of shock or fire when turned on.  Do not use any appliances, heating, pressure, or sewage system until electrical components have been thoroughly cleaned, dried, and inspected by a qualified electrician.

  • Use a flashlight to inspect for damage inside your home.  Do not strike a match or use an open flame.

  • If your basement is full of water, drain it in stages (about a third of the volume of water per day) as draining too quickly can structurally damage your home.

  • Contact a heating repair company to inspect your furnace and chimney.

  • Contact your insurance company and begin documenting damages.

  • Clean up contaminated areas using proper safety precautions.

  • Keep children and pets away from contaminated areas during cleanup operations.

  • Dispose of all:

    • Contaminated food including:

      • Contents of the freezer or refrigerator (meats, fresh fruit and vegetables).

      • Boxed foods.

      • Bottled drinks and products in jars, including home preserves (the area under the seal of the jars and bottles cannot be properly disinfected).

      • Cans with large dents or that reveal seepage.

    • Medicines, cosmetics, and other toiletries that have been exposed to flood water.

    • Contaminated insulation materials, particleboard furniture, mattresses, box springs, stuffed toys, pillows, padding, cushions, and furniture coverings.

  • Monitor the local media for information about clean up initiatives and instructions from the City and the Health Unit.