What are bioretention systems?

A bioretention system consists of a soil bed planted with suitable non-invasive (preferably native) vegetation. Vegetation in the soil planting bed provides uptake of pollutants and runoff and helps maintain the pores and associated infiltration rates of the soil in the bed.

How do bioretention cells work?

A bioretention cell is a stormwater best management practice (BMP) designed to capture and treat the first flush of runoff from impermeable surfaces. In a bioretention cell, the first flush is captured and infiltrated into the soil profile, where it is treated and released to the local ground or surface water.

How do bioretention basins work?

Bioretention basins are landscaped depressions or shallow basins used to slow and treat on-site stormwater runoff. Stormwater is directed to the basin and then percolates through the system where it is treated by a number of physical, chemical and biological processes.

What is a bioretention swale?

Bioretention swales are shallow, vegetated, landscaped depressions with sloped sides. They are designed to capture, treat and infiltrate stormwater runoff as it moves downstream.

Is a rain garden bioretention?

Description. A rain garden is a bowl-shaped garden designed to capture and absorb stormwater. Bioretention areas (also referred to as bioretention cells or rain gardens) use soil, plants and microbes to treat stormwater before it is infiltrated or discharged.

What benefit does a bioretention garden provide?

Bioretention areas enhance the landscape in a variety of ways: they improve the appearance of developed sites, provide wind breaks, absorb noise, provide wildlife habitat, and reduce the urban heat island effect.

What is the purpose of Bioswale?

Bioswales are vegetated, shallow, landscaped depressions designed to capture, treat, and infiltrate stormwater runoff as it moves downstream.

How do you size a bioretention basin?

The minimum size for any bioretention facility should be 10 feet wide (perpendicular to incoming sheet flow direction) and 15 feet long. The depth of the facility’s planting soil (reference Figure 11.1) should be approximately 30 inches, or the diameter of the largest plant root ball plus 4 inches.

How effective are Bioswales?

According to the American Society of Landscape Architects (ASLA), a 4-meter bioswale can reduce about 25% the of total rainfall runoff. The effectiveness of bioswales extends to their ability to filter stormwater naturally.

What is grass swale?

A grass drainage swale is an open channel that collects water from hard surfaces and allows it to percolate into the ground, reducing the amount of runoff leaving the road or property. The grass covering the side slopes and swale bottom provides a filtration surface for the water and helps to reduce the flow velocity.

How deep should a rain garden be?

between four and eight inches deep
A typical rain garden is between four and eight inches deep. A rain garden more than eight inches deep might pond water too long, look like a hole in the ground, and present a tripping hazard for somebody stepping into it.

How are bioretention systems used to filter runoff?

Bioretention systems can be used to filter the runoff from both residential and nonresidential developments. Concentrated inflow from a drainage pipe or swale must include adequate erosion protection and energy dissipation measures. Bioretention systems are most effective when they receive runoff as close to its source as possible.

What should the construction specifications for bioretention be?

Given that the construction of bioretention practices incorporates techniques or steps which may be considered non-traditional, it is recommended that the construction specifications include the format and information discussed below.

When do bioretention BMPs need to be installed?

Proper construction techniques are critical to achieve long-term functionality of bioretention systems. Construction sequencing is imperative; infiltration BMPs need to be installed as close to the end of construction as possible.

How to check soil permeability for bioretention?

When designing Bioretention practices without underdrains and with drainage areas greater than 0.5 acre, designers should verify soil permeability by using the on-site soil investigation methods provided in Appendix A of the manual (Infiltration and Soil Texture Testing Methods).