Developing Multiple Lines of Evidence to Decrease Drainage-to-Surface Area Ratio for Effective Stormwater Control...

Area of Science:

• Environmental Engineering
• Urban Hydrology
• Horticultural Science

Background:

• Bioretention units are crucial for managing stormwater runoff.
• Sizing bioretention stormwater controls involves balancing multiple design objectives.
• Previous research has not fully elucidated the impact of unit size on vegetation health and performance.

Purpose of the Study:

• To evaluate the drainage-to-surface runoff ratio for sizing bioretention stormwater controls.
• To assess the impact of bioretention unit size and aspect ratio on vegetation growth and soil conditions.
• To determine optimal sizing for bioretention areas prioritizing vegetation health and stormwater infiltration.

Main Methods:

• Constructed and instrumented hydraulically isolated bioretention units of varying sizes and aspect ratios.
• Monitored soil moisture content using water content reflectometers (WCRs) and thermistors.
• Conducted vegetation surveys and analyzed planting media for organic matter and phosphorus content.

Main Results:

• Smaller bioretention units (higher watershed-to-surface area ratios) exhibited superior shrub growth due to more frequent root zone saturation.
• Plants in larger units, especially away from the inlet, often relied solely on direct rainfall, indicating underutilization of the stormwater control volume.
• Smaller units showed greater buildup of organic matter and phosphorus, suggesting enhanced pollutant retention.

Conclusions:

• Undersized bioretention controls can be effective for promoting healthy vegetation and achieving stormwater infiltration.
• Municipalities can utilize smaller rights-of-way for bioretention, contributing to stormwater management and other environmental benefits.
• Distributed bioretention systems, capturing frequent rainfall events, should be integrated into municipal stormwater management plans.