Bioretention Form & Function

In urban development, where built spaces reduce permeable square footage, stormwater management is increasingly important. Runoff moves quickly from buildings into municipal systems overburdening storm drains. In cases like these, the speed of runoff to drains and filtering pollutants from the runoff can be slowed using bioretention systems. Two main types of bioretention are infiltration and flow-through. Infiltration systems, such as bioswales, are sited on permeable ground allowing stormwater to percolate into the soil. Flow-through systems are used on non-permeable surfaces where filtration happens in the system, and runoff is held back and allowed to flow into drains slowly.

On-Structure Solutions

Flow-through bioretention can happen above or below ground or on-structure. In dense urban environments where real estate is at a premium, capturing the water on-structure frees up ground-level spaces for other development.

Reducing Build Times with Pre-Built Solutions

Site-poured concrete basins can create containment on rooftops, but for many new construction projects, a better option is to bring pre-built containment to the roof, reducing build times.

Essential Considerations

On-structure flow-through bioretention systems, careful calculation of size is essential. Local codes may specify volume requirements and offer formulas for calculating capacity. In many cases, a system of bioretention planters are needed to accommodate the required volume, or desired aesthetic.

Tournesol’s Bioretention

If you’re looking for a flow-through bioretention planter system built to spec, Tournesol’s experienced team can help you. We can design, engineer, and build bioretention systems based on regional requirements across the country. Our Bioretention Planters are offered in Powder-coated Steel or Glass Fiber Reinforced Concrete (GFRC) and can be manufactured to coordinate with other planters on site.

Bioretention planters act as structural stormwater controls. They capture, filter, and temporarily store and slow water runoff using soils and vegetation.

Five Steps to Get Started

1. Understand the volume of stormwater that your building will be required to capture.

2. Establish the desired location and footprint. Note how the building equipment, such as HVAC, will impact the size, shape, and location.

3. Material and color selection may depend on key design elements, planters, and site furnishings.

4. Select the right filtering/planting media. Media specifically formulated for bioretention systems may be available. Contact your municipality for recommended or required media.

5. Choose plants that tolerate variable watering conditions. Appropriate plants may be evergreen, but others may go dormant during either dry or wet seasons. Choose a mixture for increased appeal.

SETTING UP FOR SUCCESS - Planters That Work!

Plants that have caught our eye in Pacific Northwest bioretention planters include grasses, bulbs, wildflowers, and shrubs. Here are some of our favorites:

Grasses

• Idaho Fescue (Festuca idahoensis)
• Soft Rush (Juncus effusus)
• Tufted Hairgrass (Deschampsia cespitosa)

Flowering Plants

• Douglas Iris (Iris douglasiana)
• Oregon Iris (Iris tenax)
• Red Flowering Currant (Ribes sanguineum)
• Sunflower (Helianthus annus)
• Western red columbine (Aquilegia formosa)
• White Spiraea (Spiraea betulifolia var. lucida)

Low and Trailing Plants

• Beach Strawberry (Fragaria chiloensis)
• Blue-eyed Grass (Sisyrinchium bellum)
• Coastal Strawberry (Fragaria vesca)

Plants will need to be watered for at least two years to get established. If you choose to irrigate planters in dry seasons, you have more choices but take note that the most effective bioretention systems are dry before they take on stormwater. Additional factors for consideration are noted by the American Society of Landscape Architects and supplemental guidance may be found at your local county extension office or native plant society.