wetlands for stormwater management

As cities continue to grow and develop, managing stormwater effectively has become a critical challenge. While traditional stormwater management systems, such as stormwater management facilities (SWMFs) and underground pipes, play a vital role in controlling runoff, they can be complemented by natural solutions like wetlands. Wetlands offer a sustainable, multifunctional approach to stormwater management by enhancing water retention, improving water quality, and reducing the risk of flooding while boosting ecological function. By effectively utilizing wetlands alongside existing infrastructure, cities can create more resilient and adaptive stormwater management systems.

the role of wetlands in stormwater management

Wetlands are either natural or constructed ecosystems that act as sponges, absorbing and filtering stormwater while reducing the impact of flooding. Their multifunctional role in stormwater management includes:

• Flood Mitigation: Wetlands slow down and store excess rainwater, reducing the risk of flash flooding in urban areas. Their ability to retain water helps in managing peak storm events, preventing overwhelmed drainage systems and infrastructure damage.

• Water Quality Improvement: These ecosystems act as natural filters, capturing and breaking down pollutants such as heavy metals, oils, pesticides, and fertilizers. By allowing sediments and contaminants to settle before water re-enters rivers and groundwater systems, wetlands improve overall water quality and reduce the burden on municipal water treatment facilities.

• Erosion Control: Wetlands stabilize soil and reduce erosion by slowing down water movement and trapping sediments. The presence of dense vegetation in wetlands further reinforces banks and shorelines, preventing degradation due to heavy rainfall and runoff.

• Groundwater Recharge: Wetlands can help maintain groundwater levels by allowing stormwater to percolate slowly into underground aquifers. This natural recharge process is essential for maintaining water supply in urban and rural areas, particularly during dry seasons.

• Temperature Regulation: Water bodies in wetlands help moderate local temperatures by cooling the surrounding environment. This function is particularly beneficial in urban areas where impervious surfaces contribute to the heat island effect.

• Biodiversity and Habitat Creation: Wetlands support a diverse range of plants, animals, and microorganisms, fostering rich ecosystems. They provide breeding and nesting grounds for many species, enhancing urban biodiversity and supporting ecological balance.

wetland retention potential for urban development

Not all wetlands can practically be utilized within the stormwater management drainage system. Several competing factors, such as planning objectives, engineering constraints, economic considerations, and development logistics, often limit opportunities for wetland retention. Early assessment of wetland retention potential is crucial for prioritizing high-value systems.

Determining a wetland’s retention potential requires assessing several factors, including basin quality, habitat connectivity, and upland conditions. Typically, wetland specialists conduct both desktop and field studies to validate retention potential.

From a policy perspective, Alberta follows a three-tier approach to wetland management: Avoid, Minimize, and Replace. These strategies can be described as follows:

• Avoid: Preserve wetland basins in situ, ensuring pre-development catchment flow patterns are maintained.

• Minimize: Maintain wetland basins while supplementing them with treated stormwater replenishment systems to preserve pre-development flow patterns.

• Replace: Modify or remove wetlands and where possible attempt to replicate lost ecological function through stormwater management wetlands or other compensatory measures.

strategies for wetland utilization into stormwater management

Developing stormwater management strategies that align with the wetland policy directives, meet planning and engineering regulatory requirements, and remain economically viable can be challenging.

The following five-strategy framework can be a helpful tool to help teams navigate these complexities:·

• Strategy 1 – Preserved Natural Wetland SWMFs: an avoid/minimize strategy where the existing wetland basin is preserved by creating an adjacent SWMF that offers hydroperiod matching feedwater to supplement natural processes, in parallel with stormwater management services. This approach is often applied for high class wetlands or crown wetlands as there is significant capital, maintenance, and land costs associated.

• Strategy 2 - Integrated Natural Wetland SWMFs: an avoid/minimize strategy where the existing wetland basin is integrated into an adjacent SWMF with basin modifications. The integrated wetland operates through a shared water reservoir and/or through a shared feedwater system, in series with stormwater management services. This approach is often applied when land development functional requirements coincide with wetland basin water levels and when ecological function can practically be integrated.

• Strategy 3 – Constructed Wetland SWMFs: a minimize/replace strategy where the existing wetland basin is removed and replaced with a constructed wetland system that aims to replace lost ecological services through design best practices. This approach is often applied when land development functional requirements prohibit feasible integration with the wetland basin.

• Strategy 4 – Wetland Removal SWMF: a removal strategy where the existing wetland basin is removed but a SWMF with some ecological function is constructed at the wetland’s original location. This approach is often applied for low class wetlands.

• Strategy 5 – Wetland Removal SWMF Offsite: where the wetland is eliminated without replacement, and a SWMF is developed elsewhere. This is used when the wetland’s location does not support feasible stormwater management functions, or a higher retention value wetland is nearby which can more practically be included in the stormwater strategy.

Wetlands can provide a sustainable and environmentally friendly approach to stormwater management when thoughtfully balanced with planning, engineering, and logistical factors. By identifying wetlands with high retention potential and deploying practical strategies, cities can effectively meet stormwater management needs while enhancing environmental sustainability and urban placemaking. This holistic approach ensures that wetland systems not only serve as natural stormwater solutions but also contribute to resilient urban development, biodiversity conservation, and long-term climate adaptation.