Living in a Flood Vulnerable Area:
Downstream of G. Ross Lord Dam
Reducing flood risk in the Don River watershed
Use the information on this page to help you understand and prepare for flooding if you live downstream of G. Ross Lord Dam in the City of Toronto.
1. KNOW YOUR RISKS
Living Downstream of G. Ross Lord Dam
Living downstream of a Toronto and Region Conservation Authority (TRCA) flood control dam means being part of a community safeguarded by flood control infrastructure.
Flood control dams are essential for protecting communities during heavy rainfalls and flooding.
However, they also come with certain risks, making it essential to stay informed, prepared, and aware of potential hazards.
G. Ross Lord Dam, managed by TRCA, is one of the largest dams in the Greater Toronto Area and was designed to protect residents living along the West Don River, specifically the Hoggs Hollow community within the City of Toronto.
About G. Ross Lord Dam
The G. Ross Lord Dam was constructed as part of the 1959 TRCA Flood Control Works Program, in direct response to the flooding caused by Hurricane Hazel in 1954.
The dam consists of an earthen embankment and two concrete spillways to control flow.
On October 15-16, 1954, Hurricane Hazel brought unprecedented rainfall and severe flooding to Toronto, resulting in 81 deaths and leaving thousands homeless.
The devastation from this storm highlighted the urgent need for flood control measures, leading to the establishment of the Flood Control Works Program and the construction of the G. Ross Lord Dam in 1973.
Learn more about Hurricane Hazel.
G. Ross Lord Dam: Map
Select the image below to view the full-sized map.
G. Ross Lord Dam: Quick Facts
- Location: Dufferin Street and Finch Avenue, Toronto
- Date of Construction: 1973
- Status at Dam: The G. Ross Lord Dam structure is in good shape but is classified as very high hazard, meaning it poses significant risk if it fails. TRCA continues to invest in studies and preventative maintenance to ensure long-term safety.
Why G. Ross Lord Dam Matters
Flood control dams are important structures that help keep communities safe from flooding. They hold back large amounts of water during a storm and release it slowly after the storm passes, ensuring that downstream areas don’t get too much water all at once.
How Do Dams Work?
Flood control dams are large structures built across rivers to block and store water. They stop the water from flowing too fast and store it in a reservoir.
The dam reservoir is normally kept very low. During rain events or as snow melts, the reservoir stores water. After downstream water levels return to normal, the gates at the dam are opened to slowly lower the reservoir back down to the normal level, so that it is ready for the next storm.
G. Ross Lord Dam can provide flood protection for most expected rain events. However, during extreme storms beyond the capacity of the dam, the reservoir can exceed safe levels and the gates must be opened to prevent the dam from overtopping, causing a failure. The opening of the gates can cause flooding downstream.
Learn more about TRCA FLOOD CONTROL INFRASTRUCTURE.
Downstream of G. Ross Lord Dam:
Yonge York Mills Flood Control Channel
G. Ross Lord Dam works in conjunction with the Yonge York Mills Flood Control Channel.
The channel, built in 1959, was constructed to reduce the risk of flooding in the Hoggs Hollow community. The dam was later constructed in 1973 to further increase flood protection.
Flood control channels increase the amount of water that can flow through them by straightening the watercourse and removing obstacles that can slow the water down.
TRCA owns the channel from Yonge Street to Donino Avenue.
Learn more about TRCA FLOOD CONTROL INFRASTRUCTURE.
Public Safety and Dam Operators
Always stay away from flood control dams. If you are in danger, call 911 immediately.
Dams and reservoirs can be very dangerous, especially during and after heavy rainfall or snowmelts. The water near them can be deep and fast-moving. It’s important to stay away from dams and their surrounding areas.
G. Ross Lord Dam operators may change how much water passes through the dam at any time, without warning, making the area downstream hazardous. This can also happen during periods of dry weather.
Learn more from TRCA about DAM SAFETY.
What TRCA is Doing to Improve Dam Safety
- Regular Inspections: TRCA conducts monthly, quarterly, and annual dam inspections to monitor structural integrity and identify maintenance needs.
- Infrastructure Improvements: Ongoing upgrades to dams and flood related infrastructure help to keep dam conditions safe.
- Improved Communication with Municipal Staff: We’ve improved coordination with local emergency management teams to ensure quick, informed decision-making during an event.
- Dam Emergency Plans: We’ve developed dam emergency plans.
- Additional Monitoring Tools: We installed cameras at key locations to provide real-time monitoring and improve situational awareness during weather events. View trcagauging.ca.
What Types of Flooding Can Affect Residents?
Did you know that there are several types of flooding? Different levels of government are responsible for different types of flooding. To find out who to contact during a flood, see BE PREPARED.
- Riverine flooding occurs when the water levels of rivers rise, overflowing their banks. Reducing riverine flood risk is under the mandate of Conservation Authorities like TRCA.
- Urban or Pluvial flooding consists of street flooding, basement flooding, and flooding of other low-lying areas due to the overflow of local drainage systems. Municipalities are responsible for managing this type of flooding.
Flooding Can Happen at Any Time of Year
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WINTER: A rise in the water level or a thaw can break winter ice into large chunks, which can lead to jams behind structures such as bridges, culverts, and crossings. |
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SPRING: Rivers and streams can experience high flows in the early spring, as rising temperatures melt the winter’s accumulation of snow, causing water levels to rise. |
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SUMMER: Intense, localized downpours from thunderstorms can quickly lead to flooding in smaller creeks. |
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FALL: Large wet weather systems, including tropical storms such as Hurricane remnants (like Hurricane Hazel in 1954), can last for several days. Prolonged and heavy precipitation, on top of already saturated soils, can cause rivers to rise. |
How Will I Know If Flooding Is Forecasted?
TRCA operates a Flood Forecasting and Warning Program to support municipal partners during storm events and fulfill responsibilities delegated by the Ontario Ministry of Natural Resources.
The program provides advice on timing and severity of potential flooding, helping protect lives and property while also educating the public about flood risks.
To help residents stay safe, TRCA provides resources and guidance for flood preparedness. Learn what steps to take before, during, and after a flood by exploring our Emergency Management and Safety Resources.
Sign Up for Flood Messages
In order to provide support to our municipal partners during storm events, TRCA runs a Flood Forecasting and Warning Program.
The program provides advice and warning to municipalities for the forecasted timing and severity of potential flooding events from rivers and streams.
Active flood messages from TRCA can be viewed directly in two ways: on our website or on X.
Real-Time Water Level Information
TRCA has dozens of water level gauges on rivers and streams at important locations throughout the Greater Toronto Area as part of its Flood Forecasting and Warning Program.
Explore real-time water levels at at G. Ross Lord Dam, including live camera views, at TRCAgauging.ca/G.RossLordDam.
Public Notification of Dam Emergencies
– Only Available for G. Ross Lord Dam
Public notification of flooding related to dam emergencies will occur via multiple channels:
- TRCA’s Flood Forecasting and Warning message channels.
- Published on our website and sent out via e-mail (to self-subscribers) and on social media.
- If you live near a river, be aware of TRCA’s messaging as flood related information is delivered this way even in cases that are not considered dam emergencies.
- For a dam emergency posing an immediate threat to life, TRCA will request an Alert Ready message broadcast from the Province of Ontario through Emergency Management Ontario.
- Alert Ready is the national public alerting system which interrupts television and radio broadcasts, as well as delivers to LTE-connected and compatible wireless devices, with an emergency alert tone and brief description. Check your phone’s compatibility HERE.
- Evacuations for an emergency at G. Ross Lord Dam would be implemented by Toronto Police Services and Fire, and should be taken seriously. There may be very little notice to evacuate. If you receive notice to evacuate do so immediately. The time water takes to travel from the dam to downstream areas is very short and the speed and force of water can damage structures and pose a threat to life and safety. Move away from the river, towards higher ground outside the impact area. It may be necessary to move by foot.
2. BE PREPARED
When it comes to flood preparedness, everyone – homeowners, landlords, renters, and condo owners – has a role to play. You can take steps to prepare; just select a category below to find out more.
3. STAY INFORMED
Use the following sources to stay informed during a flood:
| • Check your local weather online, or on radio or television before you leave the house |
| • Check Environment Canada’s public weather alerts |
| • Sign up to receive TRCA flood messages |
| • Check your local municipal and public transit social media links (below). |
Social Media Alerts and Notices
Additional Resources
| • TRCA.ca/Flood |
| • Safety Around Dams |
| • TRCA Flood Forecasting and Warning Centre Page |
| • Ontario Power Generation (OPG) Water Safety |
| • Living Near Dams |
| • Emergency Management Ontario |
| • Ontario’s Emergency Management and Civil Protection Act: Disaster Recovery Assistance for Ontarians |
| • Public Safety Canada: Flood Ready – Tips for overland flooding and first steps to prepare your home |
| • Flood Smart Canada – Created in partnership with the Insurance Bureau of Canada, this resource is designed to help Canadians better prepare for flooding. |
| • Intact Centre on Climate Adaptation: Flood Protection Resources |
| • Institute for Catastrophic Loss Reduction: Flood Resources |
Information About Flood Insurance
Frequently Asked Questions
Can G. Ross Lord Dam handle all major storm events?
The dam is designed to manage large storm events.
However, it’s important to understand that the capacity of the dam depends on many factors, including the storm’s intensity, duration, and timing.
While the dam can handle a significant amount of rainfall and help manage water flow, it may not fully “hold back” a major storm event like Hurricane Hazel.
Instead, its primary function in such events is to delay water flow, reducing the risk of immediate downstream flooding and allowing more time for communities to respond.
What’s the difference between “safely passing” a flood versus “holding back” a flood?
When we talk about managing a flood with a dam, there are two key actions:
- Safely passing a flood means that, when necessary, water is released through the dam gates to avoid water levels rising to a point where they might flow over the top (overtop) of the dam. By releasing water in a controlled way, we can manage the flow downstream, even in intense storms, ensuring the structural integrity of the dam and protecting downstream areas.
- Holding back a flood means retaining water in the dam reservoir to reduce immediate flow downstream. However, during major storms, the dam reservoir can only hold a certain amount before reaching its capacity. At that point, to prevent overtopping, controlled releases might be required to “safely pass” the stormwater downstream.
Does water from G. Ross Lord Dam impact Lake Ontario levels?
G. Ross Lord Dam has no noticeable impact on Lake Ontario water levels.
Where does water going to the dam come from?
- Rainfall and Snowmelt: Precipitation is a major contributor, with rainwater and melting snow running off the land and flowing into rivers, creeks, and streams that feed into the dam reservoir.
- Streams and Tributaries: The dam watershed includes various smaller water channels like creeks and tributaries, which carry water from surrounding areas and flow into the main river or reservoir at the dam.
- Runoff from Urban and Rural Areas: When it rains, water runs off streets, fields, and other surfaces within the watershed. This surface runoff collects and channels into streams and rivers that eventually lead to the dam. This location is near the lower end of the Humber River watershed.
How much impact do hard surface developments and permeable surfaces have on flooding?
Hard surfaces do not allow water to infiltrate, so runoff can be seen on paved surfaces even during small rain storms.
However, larger rain storms can quickly exceed the infiltration capacity of permeable surfaces and create runoff.
One reason Hurricane Hazel had the impact that it did was because there had been a lot of rain in the days before the Hurricane, which meant that the ground had no more capacity to absorb additional water.
What do I do and how do I know if there is an emergency at the dam?
- If you are in immediate danger, call 911.
- If emergency officials order an evacuation, follow the instructions provided by the first responders.
- There is no set amount of time given for evacuation because delays in information dissemination can occur. For instance, if someone is not tuned into the TV, radio, or other alert systems, they may not receive an immediate evacuation notice. The best course of action is to evacuate as soon as a notification is received. This notification will come from your local municipality.
- A TRCA flood duty officer monitors the weather and stream gauges, allowing them to track changing water levels closely. While some storms, like hurricanes, can be anticipated, other events like thunderstorms are much harder to predict, adding to the importance of quick response upon notification.
- Sign up to receive TRCA flood messages.
Contact Information
Questions? Please contact:
TRCA’s Dam Outreach Project Team
Email: Dams@trca.ca