This article summarizes Civica’s Stormwater System Sustainability webinar, which explores innovative funding options for meeting the new CLI-ECA regulations. The focus of this post will be to examine the key challenges of stormwater management, as well as practical, low-cost solutions for sustainability. An overview of the webinar will be provided in two parts.
Stormwater Management and Sustainable Program Considerations
When devising a sustainable stormwater management program, there are several aspects to consider, including:
- Level of service
- Performance and cost
- Regulatory changes
- Funding strategies
- Environmental Impacts
- Safety concerns
- Future goals
- The impact of future urbanization
- Rainwater conveyance
- At-source controls
- End-of-pipe management
Key Challenges of Stormwater Management
What are the central challenges and pressures of today’s stormwater management systems?
- Lack of funding: Cities across the GTA and Southern Ontario are seeing a scarcity of funds to support stormwater management infrastructure.
- Introduction of stormwater rate programs: City councils are looking for alternative funding ways to cover the costs and generate revenue, such as by introducing new stormwater rate programs.
- Climate change considerations: Opportunity exists to link the need for these increased charges and fees to climate change. The changing climate conditions cannot be ignored, and by introducing new programs, municipalities are acting to recognize these environmental changes, mitigate risks, and close the funding gaps.
- Political challenges: Councillors and other politicians seeking to protect community resources may express skepticism about stormwater management programs. There could be concerns about the allocation of public funds, balance, priorities, etc.
- Stakeholder challenges: Community residents directly affected by stormwater and the fees of programs designed to address it may have concerns about the fair distribution of costs.
The Impact of Urbanization on Stormwater Systems
An increased focus on stormwater management exists as a direct result of urbanization. The development of forests and farmland changes the characteristics of runoff. While surface runoff is minimal on undeveloped land, it dominates the water balance on impervious surfaces, such as home or building rooftops, driveways, cars, roads, sidewalks, etc.
Therefore, the goal is to design controls to protect downstream by recreating pre-development runoff conditions. The balance of watershed protection, public safety, and cost is all-important in setting stormwater policies. Programs need funding to cover the cost of construction, maintenance, and repair of these stormwater systems.
Service-Level Considerations
At the service level, it is important to consider the environmental, community, and economic impact in balancing all aspects of stormwater management systems. Each element has an impact on both cost and performance.
Environmental
- Mitigation of downstream flow conditions to protect watercourse/receiver
- Erosion and sediment load to environment
- Public education related to understanding and use of stormwater system
Community
- Flood protection and public safety related to extreme rain events
- Use of infrastructure, resilience, and understanding of major/minor design concept
- Individual and private-owner participation with at-source options for management
Economic
- Life-cycle impact of maintenance, cleaning, remediation, and expansion of systems once new infrastructure is created
- Responsibility for costs, equitable share models, and recognition of stormwater as a separate and important community service
Rainwater Conveyance to Avoid Flooding
Rainwater conveyance is essentially a network of piping that carries rainwater from homes and other community buildings into underground storm sewer systems. This helps to reduce flooding risks during heavy rainfalls.
Local Roads and the Dual Drainage Model
A key element of stormwater management is the dual drainage model. Most urban stormwater systems feature two major elements: a minor system and a major system. Typically, the minor system is designed to accommodate the runoff for a five-year return period storm. It mainly comprises underground storm sewer pipes.
The major system is designed to accommodate a more severe 100-year storm event, and it includes the local roads. Also known as right-of-way (ROW), this stormwater drainage system is considered significantly more cost-efficient than the construction or replacement of piping infrastructure.
However, with the increasing intensity and duration of storms as a result of climate change, cities are seeing more ROW flooding, which, in addition to water accumulation on roads, can result in basement flooding in private residences.
This roadway flooding can further impact sanitary systems. The storm sewer system and the sanitary sewer system are two separate entities, and any combination of these two flows is a problem. Inflow into the sanitary system can occur during extreme events such as flash flooding or rapid snowmelt.
At-Source Control Considerations (LIDs) for Runoff Control
Low-impact development (LID) is a sustainable practice that uses land planning and engineering to mimic natural runoff conditions. Controlling runoff at the source is the most effective approach to long-term sustainability. While LID solutions may be challenging to install in existing urban areas, they can be especially useful and are becoming more widely adopted in existing and particularly in newly developed areas.
Every option that retains runoff at the source reduces the demand on the central stormwater collection and treatment systems. Some choices include:
- Rain gardens: Also known as bioretention cells, these are depressions that contain vegetation grown in an engineered soil mixture placed above a gravel drainage bed. They provide storage, infiltration, and evaporation of both direct rainfall and runoff captured from surrounding areas.
- Green roofs: These bioretention-cell variations convey excess percolated rainfall off the roof.
- Infiltration trenches: Narrow ditches filled with gravel, they intercept runoff from upslope impervious areas. These trenches provide storage volume and additional time for captured runoff to infiltrate the native soil below.
- Permeable pavements: These are excavated areas filled with gravel and paved over with porous concrete, asphalt, or paver blocks to make rainwater infiltrate at natural rates into the site’s native soil.
- Rain barrels: These containers collect roof runoff during storm events and can either release or reuse the rainwater during dry periods.
- Vegetative swales: These are channels or depressed areas with sloping sides covered with grass or other vegetation. They slow down the conveyance of collected runoff and allow it more time to infiltrate the native soil beneath it.
End-of-Pipe Management – Storm Ponds
The dominant approach to stormwater quality and quantity control over the last 20-030 years is the wet storm pond. A combination of storage for quantity control and sediment removal for quality improvement, the design goal is to meet treatment objectives and release flows to mimic pre-development conditions on the receiving watercourse.
Stormwater management ponds provide:
- Stormwater storage
- Permanent pool for sediment reduction
- Controlled release to mimic pre-development conditions
- Sediment storage for limited period based on design useful life
Choose Civica for Stormwater Management Solutions
Civica is a leader in municipal stormwater management solutions with extensive experience in LID design and drainage modelling. Stay tuned for part 2 of the webinar recap, which will take a closer look at the costs and funding strategies for stormwater management programs. For more information, please contact Civica today.
Learn more at:
Stormwater Management: Funding Alternatives for CLI-ECA Regulations
How Design Standards Impact Storm Drainage and Sanitary Maintenance Holes (Part 1)
How Design Standards Impact Storm Drainage and Sanitary Maintenance Holes (Part 2)
Flow Monitoring in Collection System Modelling (Part 1)
Collection System Modelling Utilizing Flow and Rainfall Monitoring Data (Part 2)