Stormwater and drainage

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Stormwater facts and figures

Stormwater begins as rainfall and melting snow/ice. Stormwater on the ground is called runoff. In undeveloped areas, runoff will either soak into the soil, get absorbed by plants, evaporate or find its way to the nearest body of water.

In developed areas, hard surfaces like roads, roofs, driveways and parking lots prevent water from seeping into the ground. Instead, stormwater runoff flows to catch basins while picking up contaminants like motor oil, animal waste and cigarette butts along the way. Storm sewers carry the dirty water to stormwater outlets draining to creeks, streams and rivers. During a big storm, storm sewers can get overloaded and contribute to flooding.

Stormwater management reduces the risks caused by uncontrolled runoff. Municipal infrastructure like stormwater ponds temporarily hold water back. These man-made ponds collect runoff and slow down the flow. Dirt and other pollutants can settle and be broken down by plants and bacteria. Cleaner water leaves the ponds at a controlled rate, and there is less danger of flooding and erosion downstream.

In suburban and rural communities, stormwater ponds blend into the landscape. Some look like natural lakes and are a habitat for fish, ducks and birds. Others are designed to be dry most of the time; they simply look like a depression in a park or field. During a storm, they will fill up with rainwater to relieve the downstream drainage system. Other ways to manage stormwater are, for example, rain gardens, oil and grit separators, underground storage tanks, culverts and roadside ditches.

All residents, properties and businesses in Ottawa benefit from stormwater management. It keeps streets and basements dry, local waterways healthy and our drinking water sources clean. The City of Ottawa operates and maintains:

  • More than 2,700 km of storm sewers
  • 111,000 catch basins
  • 1,600 stormwater outlets
  • 133 wet ponds
  • 100 dry ponds
  • 83 underground facilities
  • 12 stormwater pumping stations
  • 1,200 km of municipal drains in rural areas
  • More more than 6,000 culverts, mostly in rural areas
Visual: A rain cloud appears over an urban, suburban and rural neighbourhood. Stormwater infrastructure benefits everyone in urban, suburban and rural neighbourhoods.

Visual: Water and property tax bills appear. That’s why all residents pay their share on their water bills or property taxes.

Visual: Animated rendering of a waterway, ditch, creek, and home flood. Culverts and ditches divert water runoff from our roads, fields, and creeks towards streams and rivers, which helps prevent flooding.

Visual: Animated rendering of a pond and waterway. Stormwater ponds help limit soil erosion and act as natural filters for our waterways.

Visual: A plant, fish and duck appear. They’re also a natural habitat for plants, fish and birds.

Visual: A storm cloud icon appears. Stormwater management is an important investment to prevent flooding and preserve our waterways.

Visual: The City of Ottawa logo appears.

Frequently asked questions about lot grading

The grade of your property is designed to direct water away from your home towards ideal areas for drainage. Keep these frequently asked grading questions in mind before starting any landscaping projects.

Why is lot grading important?

Proper lot grading keeps surface water away from your home. Your lot should be sloped away from the home to allow all surface water to soak into the ground or flow to the property line. Changes to the grade of your lot can significantly impact how water flows across your property. This can damage your foundation, causing erosion or flooding basements and streets.

What am I responsible for as a property owner?

Property owners are responsible for maintaining the lot grade elevations established by the original grading plan. When hiring private contractors for landscaping or yard alteration, ensure that they respect the intended drainage design when carrying out work. This will reduce additional costs and stress that stems from improper lot grading.

Where can I obtain the grading plan for my property?

If a grading plan exists, residents can review the original plan by submitting an Access to Building Permit Records request. If there is no grading plan on record, please call 3-1-1 for additional grading inquires.

What is a violation of the site alteration by-law?

Any action that negatively impacts the intended drainage of a lot violates the site alteration by-law.  Swales are not to be filled, piped, or obstructed by any landscaping feature such as sheds or gardens. Consult the Site-Alteration By-law before altering your lot.

I’m planning minor landscaping, how do I know if I am violating the site alteration by-law?

Small gardens are permitted just as long they do not interfere with the intended drainage of your property.  Do not fill in sloped swales or depressions. Never cover a catch basin, they are designed to help remove excess water from your lawn.

Why do I have a catch basin in my backyard?

Catch basins assist both you and properties abutting your lot in removing excess water. Never block a catch basin as that may increase the chances of local flooding. Never pour anything down a catch basin as this leads directly to a nearby waterway. To find out how to dispose of household hazardous waste, please consult the Waste Explorer.

Where should water be redirected?

Water from a downspout should flow onto your property and soak into the ground. Never direct water onto a neighbour's property, a sidewalk, right of way or easement. If space is limited, redirect water to the intended drainage point. Your downspout should be directed away from your home to a permeable surface such as grass. Extend your downspout at least four feet away from your foundation while respecting your neighbour’s property.

Water is pooling on my lawn, is this normal?

Your lot is designed to allow water to infiltrate back into the ground while draining excess water away from the property. This recharges ground water aquifers and reduces the strain on the municipal storm sewer system. If water has not disappeared after 48 hours, please call 3-1-1.

What should I do if my neighbour’s downspout drains on to my property?

Speaking with your neighbour is the first step. Inform them on how their drainage may negatively impact your property. If this does not work, call 3-1-1.

If you still have grading inquiries that have not been answered, please call 3-1-1 for more information.

Ditches and drains

Municipal drains

There are over 700 municipal drains in Ottawa. Most municipal drains are located on private property in rural agricultural areas and are either ditches or closed systems such as pipes or tiles buried in the ground. They were constructed to improve the drainage of agricultural land by serving as the discharge point for private agricultural tile drainage systems. But, they also remove excess water collected by roadside ditches, residential lots, commercial lands and any other properties in rural areas. Municipal drains are created under the authority of the Drainage Act (provincial legislation) and municipalities in Ontario are required to administer the Act on behalf of the Province. If you have an inquiry about a municipal drain, contact the City of Ottawa by calling 3-1-1. For more detailed information on municipal drains, see the Municipal Drains Fact Sheet.

Tile drains

Tile drainage consists of corrugated plastic tubing, clay and concrete drain tile installed beneath the surface of agricultural land to remove excess subsurface water for a healthy crop root system. The tile drain outlet must be kept clean and in good condition for the drainage system to function properly. The benefits of tile drains include:

  • Crop productivity / increased profitability
  • Farm efficiency / best management practices
  • Reduces soil erosion

In Ontario, the Tile Drainage Act provides loans to agricultural property owners to help them finance tile drain projects through the Tile Loan Program. Applications can be picked up at any Client Service Centre. Applications are reviewed and sent to Council where a by-law is adopted. The application for the loan must be completed and the by-law adopted before the tile drainage system can be installed.


Municipal culverts are part of a drainage system, usually made of corrugated steel, crossing under a road, rail or an embankment.

Culverts are also used under driveways which cross a ditch, and permitted by City’s Private Approach By-law. Driveway culverts belong to the homeowner. Approval to install a driveway culvert is required and contractors must meet the City’s insurance requirements.

Procedure for Culvert Private Approach Permits

  • Private Approach Permit applications are available on at any Client Service Centre.
  • Pre-construction inspections of ditch conditions are conducted by the Roads Department, who will recommend location and size and may include special conditions.
  • The Roads Department also does the post-construction inspections to ensure compliance with by-law regulations and any special conditions.
  • Approvals are not required for any repairs which are the sole responsibility of the homeowner.


The application cost for permanent or temporary private approach varies according to the following categories:

  • Private access
  • Commercial, industrial, multi-residential access
  • Temporary access
  • Closure

Catch basin locator map

The City of Ottawa has over 100,000 catch basins to provide drainage to our roadways and greenspaces. As a critical component of the city storm collection system, keeping catch basins clear of debris (leaves, ice, snow, etc.) is important. Find the location of your nearest catch basin using the interactive map and help keep our system operating effectively. 


The catch basins depicted in this interactive map are derived from existing and collected engineering drawings for the City of Ottawa's Geographic Information System and are protected by copyright. The locations of this infrastructure information are approximate, and should not be used for construction purposes.