Storm sewers carry rainfall and other surface runoff directly to the nearest creek, stream or river, frequently with limited or no treatment. Everyone plays a role in preventing pollutants from entering the storm sewer system and damaging the water ecosystem. Over time, stormwater collection has graduated from being concerned only with draining excess water away as quickly as possible, to flood and erosion prevention in waterways to restoring water quality before releasing to nearby waterways.
Various practices are used to manage stormwater runoff throughout its journey from rain to river. Stormwater management begins with lot-level controls where rain first drops. It then proceeds to conveyance controls which help transport stormwater. Finally, end-of-pipe measures treat stormwater before it is discharged into our local waterways.
The City of Ottawa maintains a network of culverts, storm sewers and municipal drains that transport stormwater to nearby creeks, lakes or rivers. In Ottawa, the stormwater system includes:
- More than 2,700 km of storm sewers
- More than 300 stormwater management facilities including 158 stormwater ponds, 12 stormwater pumping stations, underground storage, bioswales, and oil and grit separators
- 1,200 km of municipal drains in rural areas
Lot-level controls are measures implemented at individual private and public lots that help reduce the volume of runoff coming from properties and the amount of pollutants carried by runoff. Effective and sustainable stormwater management starts at the source where rain falls. To help protect our water supply, visit how to reduce your stormwater impact.
Typical lot level measures include:
- Downspout redirection: Downspout redirection diverts flows from roof tops to areas such as grass, gravel, or infiltration trenches. This reduces the quantity of stormwater that must be treated by reducing the amount of stormwater flowing onto impervious surfaces such as driveways which drain directly to the storm sewer system.
- Rain barrels and cisterns: Rain barrels and cisterns capture roof runoff and temporarily store it for reuse. This practice reduces runoff and pollutants, and can provide a benefit in terms of reduced water consumption.
- Rain gardens and other absorbent landscaping: Rain gardens are designed to absorb and clean stormwater by capturing runoff in human-made depressions lined with water thirsty (hydrophilic) plants and soil that encourages infiltration. This lot-level measure decreases peak flows through additional on-site storage and reduces pollutants released into the stormwater system through plant/ground absorption.
Conveyance controls are used to treat, limit and/or control storm water before reaching the municipal storm sewer. Typical conveyance control measures include:
- Catch Basins: Openings along curbs and parking lots where rainwater enters the storm sewer system designed to capture heavy debris and grit. Storm sewer catch basins are usually marked with a fish to remind people that stormwater eventually makes its way into nearby waterways.
- Bioswales: Vegetated, shallow, open channels designed for conveyance and treatment of stormwater runoff, particularly from roadway drainage. Grass swales can sometimes reduce runoff volumes and pollutant loads by filtration through the vegetation. Plants are often selected due to their ability to filter sediments and nutrients.
- Infiltration Trenches: Long, narrow, rock-filled trenches that receive stormwater runoff from roadways or landscaped areas. These trenches are effective in removing fine particles and associated pollutants.
- Perforated Pipe Systems: Perforated pipes have tiny holes that allow water to filter into the surrounding soil. This measure reduces the quantity of stormwater runoff that is managed by the stormwater collection system.
- Oil-Grit Separators (OGS): An oil-grit separator (OGS) uses separate chambers to remove coarse sediments (grit), oils and other buoyant pollutants (floatables).
- Inlet Control Devices (ICDs): Much like an hour glass, ICDs are engineered to only allow a certain amount of stormwater over time. ICDs are located throughout various storm water entry points and help manage stormwater quantity when storm sewer capacity is exceeded. ICDs prevent stormwater from discharging at critical points in the stormwater collection system and redirect it to parking lots, parks, or underground storage.
- Street Cleaning: Streets are a significant contributor of pollutants to urban runoff. Street cleaning can reduce this impact. The City of Ottawa uses tandem street cleaning machines that use brooms and vacuums to prevent debris from entering our stormwater system.
- Smart About Salt Program: During the winter, the City manages the use of rock salt on roads and parking lots. While this is a necessary tool to help combat Ottawa’s fluctuating winter climate, it is important to ensure we understand the impact of using too much salt. That is why the City has partnered with the Smart About Salt Council to become an active participant in the Smart About Salt Program.
End-of-pipe measures treat and/or control stormwater before it flows back into natural waterways. End of pipe measures used in Ottawa include:
- Biofilter: A biofilter uses grass or other dense plants to filter out sediment and nutrient material before re-entering local waterways. As stormwater passes through the plants, pollutants are removed. Biofilters provide treatment for pollution but do not control the amount of stormwater passing through them.
- Underground Storage Tanks: The use of underground storage tanks help control the flow of stormwater and aid in preventing flooding, erosion and combined sewer overflows. Stored water is released back into the storm sewer system at a reduced rate, decreasing the stresses placed on downstream stormwater infrastructure.
- Stormwater Ponds: Stormwater ponds receive stormwater runoff and hold the water back for a period to allow pollutants to settle before they are discharged into a watercourse. The controlled release rate also helps prevent flooding and erosion.
There are three main types of stormwater ponds in Ottawa:
- Dry Ponds: Designed to be dry most of the time and temporarily detain water to prevent overloading the storm sewer system during large storms. The stored water is released back into the storm sewer system at a reduced rate, preventing downstream flooding. These facilities are often incorporated as depressions in parks or adjacent to roadways.
- Infiltration Ponds: Collected stormwater filters into the ground, improving water quality as it slowly passes through the soil. These ponds are also capable of recharging or replenishing the groundwater table. Suitable sandy soils are required for these special facilities and are not common in the Ottawa area.
- Wet Ponds: Water levels in wet ponds rise and fall with each storm, but they always hold a certain volume of the water and may include man-made wetland features. Wet ponds are intended to mimic natural lakes and often have healthy aquatic ecosystems including fish, bird and waterfowl populations. Never consume any fish caught from a stormwater pond.
- Stay out of stormwater ponds. Recreational activities such as swimming, wading, and fishing are prohibited for your own health and safety. These ponds contain surface pollutants such as oil, metals, and feces
- Stay off the ice in the winter as water levels and flows change rapidly making skating or other activities extremely dangerous
- Protect your pet’s health and safety by keeping them out of stormwater ponds
Reducing your impact on stormwater
We all play a part in reducing the impact of stormwater in our community. Help keep stormwater clean by following these tips:
- Vacuum, sweep, and use rags or dry absorbents on your driveway - don’t hose it down
- Select native and adapted plants that require less fertilizer to minimize runoff
- Apply lawn and garden chemicals sparingly and according to directions. Ontario's province-wide pesticide regulation prohibits the sale and use of most pesticides for cosmetic purposes on lawns, gardens, park and schoolyards.
- Deposit yard waste in your green bin to prevent catch basin blockages
- Wash vehicles at a car wash so that cleaning products do not flow directly into the storm sewers or ditches
- Check underneath your car to ensure engine fluids are not leaking
- Dispose of chlorinated and salt water pool wastewater using the City’s pool maintenance tips.
- Keep litter, pet waste and debris out of street gutters, storm catch basins and ditches so they are not washed directly into streams, rivers, lakes and wetlands
- Always pick up after your pets. Stormwater will carry feces into local waterways increasing the total E. Coli and bacteria levels
- Dispose of used oil, antifreeze, paints and other household chemicals at a household hazardous waste depot or Take it Back! retailer, not into catch basins or ditches
- If you’re unsure of how to dispose of any chemicals or household hazardous materials, consult the City’s Waste Explorer
- Take part in cleanup initiatives such as the great Canadian Shoreline Cleanup or Ottawa’s very own bi-annual GLAD Cleaning the Capital!
- If you spot someone pouring harmful material into a catch basin, call 3-1-1
- Ensure cigarette butts are disposed of safely in a designated spot. More than 85,000 cigarette butts were gathered as part of Ontario’s Great Canadian Shoreline Cleanup in 2014.
- Don’t feed geese and other wildlife. One bird’s dropping can contaminate up to one acre of water
Soak it up and slow it down:
- Maximize infiltration of rain into the soil to recharge groundwater and protect aquifers for the future.
- Reduce peak stormwater flows through rainwater-harvesting and natural landscaping. Feed your garden not the storm drain!
- Redirect your downspout to drain away from hard surfaces such as asphalt or patio stones onto grass, gardens, or an infiltration trench
- Install a rain barrel to use rainwater at a later date
- Plant trees, shrubs and ground cover to reduce soil erosion
- Keep stormwater on your property through smart stormwater landscaping such as building a rain garden or infiltration pit
- Reduce the amount of impermeable surfaces on your property such as patio stone or asphalt and replace with permeable options such as interlock, gravel, or grass
For other ways on how you can do your part, please see the resources below:
Stormwater: Frequently asked questions
What is stormwater runoff?
Stormwater runoff is rain or melting snow that collects on the surface or flows into sewer pipes instead of seeping into the ground.
Runoff will either:
- Soak into the ground
- Get absorbed by plants
- Flow along the surface to the nearest sewer or waterway
In urban areas, we have a greater amount of runoff since we have decreased our natural ability to soak up water. When fields and forests are replaced with roads, parking lots and buildings, less rainfall can soak back into the ground and more water collects on hard surfaces. This increased runoff quickly drains via paved surfaces and storm sewers to local streams and rivers. For a brief video explanation, visit the Eastern Subwatersheds Stormwater Management Retrofit Study.
Why should I care about stormwater?
When we replace plants with pavement, we decrease the city’s natural ability to soak up stormwater. This means that when it rains, less water soaks into the ground and more water collects on the surface. A small storm can cause a surge in the levels and flows of rivers and streams which can lead to flooding and erosion.
In addition to increased volume and speed, the runoff picks up pollutants like dirt, oil, and animal waste as it flows over the surface and decreases the quality of our local waterways. Eventually, all stormwater reaches the Ottawa River which is the drinking water source for Ottawa and many downstream communities. With extreme weather events becoming more frequent, managing stormwater is even more important to reduce flooding and protect water quality.
How does stormwater become polluted?
Rain or melted snow falls on roofs, driveways, parking lots and roads and travels as runoff to reach a waterway. This runoff collects various pollutants (dirt, phosphorous, metals, nitrogen, animal waste) and debris (grass-clippings, garbage, cigarette butts) as it flows over these surfaces, resulting in polluted water.
What is the difference between a storm, sanitary, and combined sewer?
In Ottawa, we have three types of sewers:
- Storm sewers carry rainfall and runoff directly to either a stormwater pond or the nearest creek, stream or river, generally without treatment.
- Sanitary sewers gather wastewater from homes, businesses and industrial sites, and transport the waste through a network of sewers to the Robert O. Pickard Environmental Centre for treatment.
- Combined sewers carry both wastewater and runoff to the Robert O. Pickard Environmental Centre for treatment. These sewers are located in the downtown core and can overflow into local waterways if stormwater exceeds their capacity.
What does the fish symbol on a sewer grate mean?
Storm sewers are often marked with a fish symbol to remind that it drains to local rivers and streams. The fish symbol is there to remind the public that what goes down the drain can harm our rivers and streams. Remember: Only rain goes down the drain.
How does the City manage and treat stormwater?
Stormwater management has been applied to new urban developments in Ottawa since the 1980s. Over the last few decades it has evolved to include improving water quality and reducing the total amount of runoff by designing sites to allow more rainfall to soak back into the ground. Stormwater facilities such as man-made ponds, culverts and catch basins are built to temporarily hold water.
Ponds also provide water quality treatment via filtration to remove pollutants or and debris. The “cleaned” water is then slowly released back to the natural waterway, mimicking the natural runoff rate and quality. This helps prevent flooding and stream bank erosion.
In older areas of the city, stormwater runoff drains directly to creeks and rivers with no treatment or control of any kind. The continued discharge of uncontrolled stormwater runoff to the Ottawa River and its tributaries has been recognized as an important issue for the City to address. The City launched the Ottawa River Action Plan (ORAP) in 2010 to improve and protect the health of the Ottawa River and its tributaries.
What happens to stormwater in rural areas?
In rural areas, stormwater runoff infiltrates through a greater amount of impermeable surfaces. However, runoff can be subject to agricultural by-products such as excess fertilizer, pesticides and manure. The runoff from agricultural operations can have an impact on surface water sources such as groundwater, streams, lakes, and rivers. The Ottawa Rural Clean Water Program provides funding to improve surface water and groundwater quality.