Frequently Asked Questions

Regarding Riverine Flooding

What do I do in the event of a flood?

BE PREPARED. The best way to prepare for a flood is to draw up a household emergency plan ahead of time. This plan should detail the actions you and your family should take before, during and after a flood event.

  • Listen for local Flood Messaging on the radio or local television station or visit the LRCA website
  • Know what the Flood Message Terminology means:
    • Watershed Conditions Statement
      • Water Safety – high flows, melting ice, unsafe banks, etc.
      • Flood Outlook – early notice of the potential for flooding based on weather forecasts
    • Flood Watch – potential for flooding
    • Flood Warning – flooding is occurring or imminent
  • Take heed of all Flood Messages.
  • Be aware of where the floodplain is on your property and what may be flooded.
  • Have an escape route planned.
  • Do not drive through water that has risen over roads. Roads or culverts could be washed out under the surface of the water.
  • Be prepared to evacuate if necessary. If requested to leave your home by local authorities do so immediately. Time permitting, take all medication and essential items as you may not be able to return to the residence for a period of time.
  • Have a plan as to where you will stay during a flood event.
  • Family members should stay in contact with one another so that all members of the family can be accounted for.
  • Do not store irreplaceable items in areas that may be flooded.
  • If safe to do so, move items stored near the watercourse or in lower levels to higher ground.
  • Have portable radios and flashlights to use in the event of power failure.
  • If on a well system, sample drinking water after the flood event prior to use, as it may be contaminated.
  • If flooding occurs in your home use extreme caution around electrical outlets and appliances.
  • If necessary shut off power and gas to your home.
  • After a major flood event consult with local experts regarding flood damage and remediation.

Is the floodplain registered on title for a property?

No, the floodplain is a natural hazard and is not registered on the title of a property.

Why are there homes built in the floodplain?

In general, new development is not permitted in the floodplain. Most homes that are located in the floodplain were built prior to any regulations or zoning restricting development in floodplains.

How are new home owners advised of a floodplain on their property?

During a Real Estate transaction, lawyers can do a search with the Conservation Authority for a fee. The Conservation Authority provides a written letter with a map that indicates the regulated area (i.e. Floodplain, Fill Regulated Area, etc.) which is then provided to their clients.

Home owners, prospective purchasers or Real Estate Agents can request a map of any property within the Area of Jurisdiction of the Authority or speak to a staff member directly.

How will I know if a flood is going to occur?

The Conservation Authority issues Flood Messages during flood events advising residents and local agencies of the potential for flooding. Messages are sent out to the Member Municipalities, media, affected agencies and are posted on the Authority's website (

Local media will advise the public of any issued Messages via radio or television. Residents who live along watercourses need to be aware of where the floodplain is on their property and be aware of their surroundings at all times.

When does flooding occur?

Flooding can occur at any time during any season.

Who owns the floodplain?

In most cases private citizens own the floodplain adjacent to rivers and streams.

What are Flood Damage Centres?

Areas that have residential dwellings located in areas that are prone to flood.

What is the Regulated Floodplain?

The main stream/river channel plus the area of land adjacent to the river or stream that is flooded (i.e. under water). The regulated floodplain is calculated using the greater of the Regional Storm or the 100-year storm.

In the LRCA’s area of jurisdiction, the regulated floodplain is defined in provincial legislation by the Regional Storm, which is defined as rainfall event (193 millimetres of rain in 12 hours), except for:

  • the main channel of the Kaministiquia River – the 100 Year floodplain applies, and
  • Lake Superior –the 100-year flood level plus wave uprush applies.

What is the Regional Storm?

The Regional Storm for Northern Ontario is a storm that occurred in Timmins, Ontario in 1961 in which 193 millimetres of rain fell in 12 hours. In most cases the Regional Storm exceeds the 100-year storm.

Many flash floods are localized situations, as was the case in Timmins on August 31, 1961. Temperatures during the afternoon were over 25°C, skies were cloudy, and an occasional roll of thunder could be heard. By 6:00 in the evening, heavy rain began which lasted for a couple of hours. Light rain commenced again about 9:00 p.m. and continued until 11:00 p.m., when it became a torrential downpour for over an hour. During the heavy rains thunder was continuous and accompanied by an occasional burst of hail. Although the downpour only lasted a few hours, it ripped roads apart, smashed houses, undercut foundations, and damaged personal property. A mother and her four children were drowned in a house on the bank of the creek.

When we calculate the floodplain, the impact is assessed as if the Timmins storm (Regional Storm) is centered over each of LRCA’s watersheds.

What is the 100-Year Storm?

The term “100-year storm” is used to simplify the definition of a rainfall event that statistically has a 1-percent chance of occurring or being exceeded in any given year, at any given place. A 100-year storm does not mean that it will only occur once every 100 years. 

What do I do in the event of a flood?

If you are concerned about current flooding conditions, please check our website for flood messages or contact our office at (807) 344-5857. 

What is floodplain mapping?

Floodplain mapping uses data and technical models to predict the path of floodwaters in the area known as the floodplain.  

In the event of riverine flooding, water levels rise resulting in the inundation of low-lying areas adjoining a watercourse that are not ordinarily covered by water. Such areas are known as floodplains. High water levels are often the result of extreme watercourse flows, which are produced by extreme rainfall and snowmelt (i.e., Regional storm).

Flooding poses dangers to people and property. A floodplain map shows where the flooding hazard is so that actions can be taken to protect public safety, reduce potential property damage, and protect the environment.

What is the difference between urban flooding vs. riverine flooding? 

Riverine flooding is what occurs when water levels of rivers, streams, and creeks rise and overflow their banks and spill onto adjacent areas. Conservation Authorities are responsible for determining the hazard from riverine flooding.

Urban flooding such as street flooding, and basement flooding, occurs when there is more water than the local drainage system (sewers and streets) can handle, or when there is a lack of a major overland flow route from a low-lying area. Urban storm infrastructure is the responsibility of municipalities.

The regulated floodplain mapping shows riverine flooding only.

How are floodplains mapped?

Floodplain maps are produced using a science-based method of field surveys and computer models. Background data is gathered on land use, topography, stream flow, and precipitation. Field surveys collect information on local infrastructure (culverts, bridges, etc.). Data is then entered into computer models to calculate stream flow and water levels during storm events at various locations along a watercourse. Review of technical work and modelling is completed to finalize the floodplain map.

Floodplain mapping is updated when new data is available, computer modelling techniques are improved, and changes to the landscape need to be incorporated. All these changes can affect the size and location of the floodplain area.

Can the regulated floodplain boundaries change?

Yes. As each of the variables change (topography, infrastructure, land use, weather data, stream flows, and hydraulic and hydrological modelling techniques), so too will the resulting floodplain boundary. Flood studies are updated and commissioned to ensure that floodplain boundaries are current and up to date as funding allows. When floodplain boundaries change some lands that were formerly within a floodplain could be removed and others added.

What standard was followed for updating floodplain maps?

Floodplain mapping updates were undertaken in a manner consistent with the Ontario Ministry of Natural Resources and Forestry’s (MNRF) Technical Guide – River and Stream Systems: Flooding Hazard Limit (2002). This guideline sets out provincial expectations on analysis approaches applied in mapping the regulated flood hazard. The MNRF guideline is used by all Conservation Authorities undertaking flood hazard mapping.