Stormwater Design for Greenfield & Infill Sites
29 May 2025
The Critical Role of Stormwater Design in Greenfield and Infill Development: Safeguarding Water Quality
As urban development continues to expand, developers and engineers face growing challenges in managing stormwater effectively—particularly on greenfield and infill sites. These sites, whether undeveloped land or underutilized urban areas, present unique opportunities and challenges for sustainable development. A well-executed stormwater design is not only essential for site performance and regulatory compliance but also plays a pivotal role in protecting water quality and promoting long-term environmental resilience.
Understanding Greenfield vs. Infill Development
Greenfield development involves building on previously undeveloped land—typically rural or agricultural areas—where natural hydrologic systems are still intact. Conversely, infill development focuses on repurposing or intensifying use within already urbanized zones, where impervious surfaces and aging infrastructure often dominate.
Both contexts demand strategic stormwater management to minimise runoff impacts, maintain pre-development hydrology, and ensure compliance with local and national water quality standards.
Why Stormwater Design Matters
Unmanaged stormwater runoff from impervious surfaces—roofs, driveways and roads, and parking lots—can lead to:
- Increased flooding risks
- Erosion and sedimentation of nearby streams
- Transport of pollutants (nutrients, hydrocarbons, metals) to surface and groundwater
- Degradation of aquatic ecosystems
In both greenfield and infill developments, thoughtful stormwater design mitigates these issues by mimicking natural hydrologic processes, reducing runoff volume, and improving water quality before discharge.
Key Stormwater Strategies for Modern Development
Low Impact Development (LID) Techniques
LID aims to replicate natural infiltration and evapotranspiration, often through:
- Bioretention systems (rain gardens, bioswales): Capture and treat runoff via filtration and plant uptake.
- Permeable pavements: Allow water to infiltrate through surfaces that would otherwise be impervious.
- Green roofs: Retain and slow rainfall, reducing peak discharge rates.
- Vegetated swales: Convey runoff while promoting infiltration and pollutant removal.
Detention and Retention Systems
- Detention basins temporarily store runoff and release it slowly to reduce downstream flooding and erosion.
- Retention ponds hold a permanent pool of water and allow sediments and pollutants to settle before discharge.
Source Control and Pretreatment
Design strategies often include forebays, oil-grit separators, and sediment traps to remove debris and coarse solids before water enters treatment systems.
Maintaining Water Quality
To protect water quality, stormwater systems must be designed with treatment objectives in mind, including:
- TSS (Total Suspended Solids) removal
- Nutrient load reduction (nitrogen and phosphorus)
- Temperature moderation to prevent thermal pollution
- Hydrocarbon and heavy metal removal in urbanized infill areas
Designers use modelling tools like the MUSIC and DRAINs to simulate hydrology, pollutant loads, and BMP (Best Management Practice) to ensure regulatory compliance and system efficiency.
Operation and Maintenance: A Long-Term Commitment
Effective stormwater management doesn’t end at construction. Maintenance plans are critical to system longevity and function. Clogged bioretention media, silted inlets, or vegetation overgrowth can compromise performance. Effective choice of stormwater management systems is important in ensuring ongoing operation and easy maintenance. Land owners and site managers must schedule routine inspections, sediment removal, and vegetation management to maintain treatment efficacy and hydraulic capacity.
Partner with Stride Consulting Engineers for Sustainable Solutions
Stormwater design is a cornerstone of responsible greenfield and infill development. By integrating sustainable drainage systems and prioritizing water quality treatment, developers can reduce environmental impacts, meet regulatory demands, and contribute to resilient, livable communities. Whether designing from a blank slate or retrofitting an urban lot, stormwater management must be a deliberate and technically robust component of every development project.
Planning a new development? Contact Stride Consulting Engineers for expert stormwater design and permitting support.
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