Stormwater is water from rain, snow, and ice melt. Managing stormwater, and where it goes, is important and helps reduce flooding.

Climate change and the increasing frequency of extreme weather makes it even more important to understand how stormwater drains around your home.  

Drainage and lot grading around your home

Stormwater features on or near your property

Homes are designed with several features to help direct water away from basements and yards. Your home may have one or more of the following features to keep stormwater away. 

  • Lot grading involves the sloping of land to help rain and snow-melt flow away from homes toward a designed discharge point.
  • Swales are drainage channels along the side and/or rear property lines that help keep water away from your home.
  • Catchbasins receive water from swales and take it to a storm sewer in the street through a pipe. Catchbasins are designed to allow for ponding that will slowly disperse as the storm sewer system’s capacity becomes available.
  • Overland flow routes are the flow paths that water takes during major rain events when the storm sewer exceeds capacity. These paths are generally found between properties.
  • The drainage apron is a depression located at the rear of a dwelling, approximately four metres from the rear foundation wall. The area between the house and the small depression will gently slope downwards allowing surface water from the rear of the lot to be directed towards the swales in the side yards.
  • Infiltration trenches can be found underground at the rear of new lots. These trenches are filled with materials that help speed up the rate water soaks into the ground.

Maintaining lot grading

The increasing frequency of extreme weather makes it even more important to understand how lot grading protects your home from stormwater and flooding. 

  • Ensure there is a 2% slope away from your foundation
  • Ensure swales and overland flow routes are kept clear
  • If you’re moving into a newly built home, ensure you receive a copy of the lot grading plan from the builder or developer

The homeowner is responsible to make sure that water continues to flow away from their foundation and does not impact neighbouring properties. Regular lot maintenance will ensure lot drainage always works as designed.

Contact the City's Geomatics Division at before making any changes to a lot grading plan.

Renovations at home or in the backyard

If you wish to change the grading on your property, contact a drainage contractor or landscaper to understand the impacts and risk prior to undertaking any work. Building pools, sheds, fences, raised gardens, and walkways can all impact drainage around your home and your neighbourhood. Certain renovations and landscaping materials can also prevent surface water from soaking into the ground.

Contact the City's Building Division at prior to building a shed, pool or other structure in your backyard to determine permitting requirements.

Help avoid flooding around your home

  • Do not remove or fill swales around your home
  • Do not block a catchbasin
  • Do not discharge water from downspouts or sump pumps directly onto sidewalks, stairs, walkways or neighbouring properties
Stormwater management ponds

What is a stormwater management pond?

A stormwater management pond is an engineered structure constructed to gather rainfall and surface water runoff. The pond temporarily stores water and then releases it at a controlled rate. A single pond can provide erosion and flooding control while enhancing water quality.

Through a combination of landscape and structural features, stormwater management ponds allow sediment and contaminants to settle out of runoff before it is released into a natural watercourse. Stormwater ponds also hold back water in order to release it at a controlled rate during large storms. Controlling the flow of stormwater protects downstream lands from erosion and flooding.

In addition, stormwater ponds are constructed to be an attractive feature with an environmental benefit. Stormwater management facilities are designed to be surrounded by natural vegetation and to provide habitat for birds and animals.

How can you help?

  • Do not skate or toboggan on stormwater management ponds.
  • Do not pour anything down the catchbasin that you would not want in a stream or river.
  • Properly dispose of pet waste.
  • Recycle and safely dispose of hazardous waste such as used oil, paint, paint thinners, and batteries.
  • Use eco-friendly salt alternatives for melting ice and snow.
  • Do not release unwanted household fish, game fish or aquarium pets into the pond (contact pet store where purchased or The Ministry of Natural Resources for proper disposal).
  • Drain pools and hot tubs only after they are free of chemicals and salt.
  • Use a commercial car wash or use eco-friendly car wash soap, and ensure your vehicle is not leaking fluids.
Protect natural buffers

Stormwater ponds are designed to mimic a natural system; therefore, it is important to allow a natural buffer to grow around the perimeter of the pond. The natural buffer is made up of native plants and grasses and should not be mown or trimmed. It is important to note that the property lines for homes near stormwater ponds do not extend to the water's edge. These buffer areas should not be mown or altered.

Reduce or eliminate the use of fertilizers and pesticides

The use of pesticides or fertilizers in grassed lawns around stormwater ponds should be limited or eliminated completely. These chemicals are easily carried away by runoff into the stormwater pond which can cause algae blooms and negative impacts to the downstream natural watercourse. Where possible, use organic alternatives to chemicals and plant native species that require low maintenance and no pesticides.

Curb the salt

During the winter, salt can be an effective way to melt ice on our sidewalks, walkways, steps and parking lots. When snow melts, the salt eventually washes into our creeks, rivers, wetlands, lakes and ground water.  Too much salt can be a nuisance as it ruins your shoes, boots and pants, harms fish in local creeks and irritates your pets’ feet. 

Reducing salt use can help reduce our impact on the environment. 

Remember, "only rain down the drain."

What you can do to help curb the salt:

Shovel First:   

Shovel snow from walkways and driveways before it is trampled and packed down.  

Proper Storage:  

Store salt and de-icing materials on an impermeable pad under a cover (e.g. under a roof or in sealed container).

Control Drainage:   

Direct downspouts and piled snow drainage towards grassed areas to prevent ice forming on paved areas.

Use Salt Alternatives:  

Reduce salt use by using sand or natural clay cat litter for traction.

Proper Use:  

Salt should never be used to melt snow piles rapidly. Salt is most effective between 0and -10C.

Plant wisely

Planting native species of trees, shrubs, grasses and flowers has numerous benefits. These species can dramatically reduce the amount of water used for irrigation, chemicals used for pest control, and fertilizers used for growth. Information on native landscaping species can be obtained from the Upper Thames River Conservation Authority.

Properly dispose of yard waste

Dumped yard waste in natural areas or around stormwater ponds can have an adverse affect on the health of the natural system. Dumped materials smother natural vegetation, may contain harmful chemicals, and non-native plant seeds.  The best solution is to compost leaves, grass clippings, and weeds on your own property. The City of London has yard waste collection days for brush and leaves throughout the year.

Mosquitoes and stormwater ponds

Stormwater management ponds are designed in such a way to prevent mosquito breeding. Mosquitoes need shallow water depths and standing water; where as stormwater ponds are deep and water is moving, (water from the ponds is typically draining below the surface which impedes mosquotoes from laying their eggs)

If you have any concerns or would like to report mosquitoes please contact the Middlesex Health Unit.

For more information, please contact, or call 519-661-2489 x 4574 

Rain gardens

What is a rain garden?

A rain garden is a shallow garden with enhanced soils and a rock reservoir designed to collect rainwater from roadways, parking lots or other hard surfaces.  They can be planted with a combination of shrubs, grasses and flowers.

Compared to a similar sized patch of lawn, a rain garden allows for 30% more water to soak into the ground!

Rain gardens provide stormwater control at the source, or where the rain falls.  Rain gardens are designed to mimic nature in an urban setting, increasing infiltration to native soils and removing pollutants prior to releasing surface runoff to the Thames River.  Rain gardens can also provide an aesthetic landscape feature. 

Benefits of a rain garden

  • Limits the amount of water that enters the storm sewer.
  • Reduces the potential for flooding drainage problems and stream bank erosion by slowing the water down and reducing flow into the waterways.
  • Removes pollutants that run from yards, parking lots and roads straight into the waterways.
  • Restores and recharges groundwater.
  • Are low maintenance. They are planted with beautiful, hardy plants that require little to no watering.
  • Attracts birds, butterflies and beneficial insects, such as mosquito-consuming dragonflies.
  • Enhances the beauty of the surrounding neighbourhood.

Building a rain garden at home

 A rain garden only requires four elements:

  • A source of stormwater runoff, such as a downspout or sump pump discharge.
  • An absorbent soil mix with lots of compost.
  • Full or partial sun.
  • Native plants that are both water-tolerant and drought-tolerant. Properly constructed rain gardens are designed to allow overflow in a large rain event and hold standing water for no more than 48 hours.

Place the rain garden in full or partial sun at least 3 metres from the house to ensure water won’t seep into the ground around the home, but no more than 9 metres from the downspout.

Your rain garden should not be placed over a septic tank or where water pools in your yard.

Soil in the rain garden is a special soil mix that is a combination of compost and sand which allows the water to infiltrate quickly.  There should be about 60 centimetres thickness of rain garden soil added which leaves room for plants.

Create an inlet for water to travel into the rain garden. Add small stones at the inlet into the garden to slow the water entering. This will help reduce erosion.

Create an overflow. The overflow should be created on the downhill side of the garden; add small stones at the overflow as was done at the inlet.

Plant rain garden friendly plants. These plants like water and to be dry.

Ensure plants are mulched with at least 5-10cm layer.

Rain garden size

To find out how large your garden should be, start by measuring the footprint of your house (the area of your first floor).

Identify the percentage of water runoff that will feed into the garden from the nearest downspout. Most houses have four downspouts,each collecting 25% of the runoff.

Multiply your home's footprint by the percentage of roof runoff to determine roof drainage area. Next, divide the roof drainage area by six.

This calculation sizes a garden to hold 2.5 centimetres of roof runoff in a garden that will be 15 centimetres deep but dug to about 85 centimetres to allow room for amended soil. A deeper rain garden can be smaller.

Keep your soil type in mind when deciding on the size of your garden. A garden with clay soil absorbs water more slowly than one with sandy soil, and therefore should be larger. The garden should be level so that water is spread evenly across its length. Don't forget to call before you dig!


100m2 (area of home)*0.25=25m2

25m2/ 6=4.17m2

Based on a house that is 100m2 the rain garden should be 4.17m2

For more information, please contact, or call 519-661-2489 x 4574 

Low impact developments

The City promotes and encourages low impact development or best management Practices in the design and construction of stormwater management systems both for new development and in municipal infrastructure projects. low impact development practices incorporate “green infrastructure” such as infiltration basins, green roofs, bioretention swales, engineered wetlands, and rain gardens to support the functions of traditional “grey infrastructure” such as storm sewer pipes and outfalls.  

In stormwater management, low impact development systems generally increase infiltration of rainwater runoff to minimize the overland flow volumes, recharge groundwater systems, and improve the water quality before it reaches a stormwater management facility or open watercourse. Implementation of low impact developments are evaluated on a case-by-case basis since the selected practice will depend on geotechnical and other site specific conditions.   As of 2016 the City has been incorporating low impact developments into design and construction projects  which will increase in future to optimize the water resources system as well as to increase the resiliency of infrastructure to climate change.

To learn more about leading Stormwater Management low impact developments in Ontario, please see the resources of the Credit Valley Conservation Authority or the Ontario Ministry of Environment and Climate Change Stormwater Management Planning and Design Manual.

Clean Water and Wastewater Fund Projects

The Environmental Services Department is beginning construction work related to the 23 projects that received provincial and federal funding as part of the CWWF program.  Each of these projects will benefit either the water, wastewater or stormwater systems in the City. A list of these projects is provided below.

Project IDProject Name
LON- 001            Design: Dingman Creek Subwatershed Stormwater Infrastructure
LON-002     Reclamation and Naturalization of Existing Urban Watercourses - Rehabilitation Plan Preparation
LON-003Applegate Stormwater Management Facility
LON-004Design and purchase of Organic Rankine Cycle equipment for Power Generation and Waste Heat Recovery Systems & Biosolids Optimization at Greenway Pollution Control Plant
LON-005East London - Sanitary Servicing Study
LON-006Conduct Facility Improvement Studies at 4 Wastewater Treatment Facilities across the city
LON-007Treatment Plant Energy Reduction With Turbo Blowers - Supply and Install
LON-008Design and Construction of Flood Protection Measures at the Vauxhall Pollution Control Plant
LON-009Design and construction of odour control upgrades at 4 Treatment Plants  across the City
LON-010Design and Construction of Technology Upgrades (Supervisory Control and Data Acquisition (SCADA) and Security) at 30 Wastewater and 14 Water locations across the City
LON-011Purchase and Install of Variable Frequency Drives at 4 Sanitary Pump Stations
LON-012Purchase and Install Solids and Floatables Management equipment at 8 Locations (Pumping Stations and Treatment Plants)
LON-013Mornington Area Storm Drainage Servicing - Environmental Assessment
LON-014Sewer Separation Program Acceleration  -Design and Construction
LON-015Sewer Separation and Infrastructure Renewal - Planning and design for future projects and construction of one high priority project
LON-016Sewer Relining Program Acceleration - Design and Construction
LON-017Arva Water Pumping Station Optimization and Energy Efficiency - Planning Study
LON-018Trunk Watermains Syphons and Pipeline - Inspections and Condition Rating
LON-019Trunk Watermain Cathodic Protection Upgrades - Design and Construction
LON-020Watermain Cleaning and Relining -  Design and Construction
LON-021Cathodic Protection Program - Inspection, Design and Construction
LON-022Design for Water, Wastewater and Stormwater Infrastructure Renewal in London
LON-023Springbank Reservoirs No. 1 & 3 Protective Membrane Condition Assessment

For more information, please contact Infrastructure Canada at 613-960-9251, toll free at 1-877-250-7154, or email    


Last modified:Wednesday, April 03, 2024