Restoration of Lake Waterloo through the use of bioretention areas

In 2017, Innovert Design was hired by The Friends of the Lake Waterloo Watershed (ABVLW) to develop a bioretention area pilot project. The objective of the project was to reduce external phosphorus (P) inputs to Lake Waterloo (QC). Bioretention areas are designed to reduce urban runoff, which accounts for one-half of all external P inputs. Increased urban runoff is an impact associated with climate change. The study recommends the single-family solution, i.e., a standardized design solution consisting of bioretention areas tailored to the varied settings of single-family residences. This solution was considered to be the most engaging for residents, who will be directly involved throughout the entire design and installation process. The project to install bioretention areas requires a very high level of social acceptance and engagement.

Understanding and Assessing Impacts

To assess the impacts of runoff in urban areas, this report gathers 11 analyses that were conducted to compare the three bioretention area options, namely the single-family dwelling option, multiple family dwelling option and roadside option:

  • hydrology and hydraulics
  • geotechnical
  • environmental
  • technical elements of bioretention areas
  • impact of seasons
  • maintenance requirements
  • social impacts and sustainable development impacts
  •  functional
  • preliminary risks
  • preliminary economic analysis
  • life cycle

On the basis of these studies, the single-family dwelling bioretention area solution was selected. With this option, the pilot project can be implemented within a shorter timeframe than the roadside solution. In addition, the possibility of duplicating the design is very appealing given the high percentage of single-family dwellings in the City of Waterloo. This solution has the potential to reduce phosphorus and is very engaging for residents. However, the results of the preliminary risk analysis and life cycle analysis were poor.

Identifying Actions

The main objectives of the design were to install bioretention areas in existing urbanized areas and to standardize the design so that the project could be more easily implemented by residents.
The single-family dwelling bioretention area solution was selected, with a number of changes made for design phase to more effectively meets the needs identified. The preliminary cost estimate was too high, which raised concerns that citizen participation would be lower, and since this is a major aspect of the project rollout, the team developed a modified single-family solution. By relocating the pilot project to neighbourhoods farther upstream in the municipality (as opposed to properties along the lake), the installation of a drain is no longer required since the higher quality soils can more efficiently drain the water. As a result, the costs were cut almost in half, yet the bioretention areas will still have a major impact on urban runoff and the health of the lake.


The following aspects were considered in standardizing the design:

  1. It is important to position the single-family bioretention areas near the roof gutter outlet, in a location that will not be contaminated by de-icing products in the winter, at a reasonable distance from the septic tank, if applicable, and in a naturally low area.
  2.  The area of bioretention areas must account for at least 5% of the total area of the lot in order to have a real impact.
  3. Configuration: grade of 2:1; a 200 mm storage area to accumulate water, but that also allows for evaporation and settling of sediments; presence of a filter strip upstream of the storage area to reduce the maintenance of the bioretention area and to pretreat the runoff.
  4. Select plants that have good phosphorus absorbing properties and that are resistant to flooding and deicing products.
  5. Soil layer thickness: the total height of the bioretention area can range from 450 mm to 1200 mm. Typical bioretention areas have 50 mm of mulch to prevent erosion and clogging, 150 mm of soil to support the vegetation (mixture of sand, compost and topsoil) to more effectively absorb nutrients such as nitrogen and phosphorus, and 300 mm of granular material to temporarily store water. It is important to respect the principle of filters to prevent clogging of this layer.

Outcomes and Monitoring Progress

The proposed solution reduces urban runoff and external phosphorus inputs. Simulations have shown a 50% reduction in the runoff water depth and 50% reduction in phosphorus in the runoff.

The solution is:

  1. cost-effective: 925 m2 lot and the price rises to $3,500 for a 46 m2 garden. The total price could be further reduced by organizing periods devoted to the installation of the bioretention areas in the municipality. The costs associated with the necessary machinery could be split among the participants, there would be less loss of materials because it would be easier to share materials among residents and one resource person could be available for a group of citizens to guide them in implementing the project.
  2. attractive and aesthetically pleasing for citizens: beautifying one’s lot increases its property value and generates new ecosystems that will provide suitable habitat for birds and butterflies.
  3. increases the quality of the lake so that all residents of Waterloo can enjoy this natural resource.

Next Steps

The project to install bioretention areas requires social acceptance, as well as a very high level of citizen engagement, which is critical to duplicating the pilot project and maximizing the environmental impacts. The creation of a design methodology in order to standardize the solution is a special challenge that will increase the citizens’ collective expertise and power to take action as part of this great project to rehabilitate Lake Waterloo. Climate change impacts, the changing seasons, the presence of rock outcrops and the lack of available empirical data are additional challenges that had to be addressed by the InnoVert Design team to meet the needs of the ABVLW.

The next steps are as follows:

  1. Present the bioretention area project to the municipalities and obtain their approval
  2. Submit a proposal for an incentive program for residents, in collaboration with the municipalities
  3. Examine the possibility of using existing bioretention area projects as pilot projects for reproduction (e.g., ABVLW_Aire_Biorétention_Plage de Chambourg and ABVLW_Aire_Biorétention_L_Orée des Canton)
  4. Secure social buy-in of the project by citizens (through information sessions, development of a web-based platform for providing, creating posters with a catchy slogan, etc.)
  5. Create an outreach showcase for ABVLW that could advise citizens in their individual efforts to restore the lake. Become and example for other Quebec municipalities that, despite their limited means, could focus on major projects.


Link to Full Case Study (in French only)