Bioretention is the process in which contaminants and sedimentation are removed from stormwater runoff. The main objective of natural rain garden media is to attenuate peak runoff and remove stormwater runoff pollutants.

There are a lot of technical factors that go into designing a rain garden, such as:

• Location

• Depth, dimension and spacing

• Drainage and Infiltration rate

• Media mix and media depth

• Surface finishing and plant selection

• Overland flow path

Azwood supplies the natural filter media required for a bioretention rain garden and works with civil contractors and councils to create a media specific to their project.

Each component of a rain garden is designed to perform a specific function and different rain gardens are required for different locations depending on rainfall.

A rain garden’s main job is to help remove pollutants and slow down stormwater flows.

Natural rain garden media provides a temporary holding capacity during a rain event which helps slow down the flow of water going into catchments. The water is filtered through the bioretention media which absorbs contaminants before the stormwater flows into the ground, pipes, drains and streams, and eventually to the sea.

The plants chosen for a rain garden system have been specifically picked for their ability to absorb nitrogen, phosphorus and other heavy metals.

The suitability of plant species will depend not only on their ability to remove heavy metals, but also on their capacity to tolerate conditions that may negatively impact plant growth. For example, plants in bioretention systems may be exposed to both wet and dry conditions, ponding and loading of fine sediments.

• Filter media

• Transitional layer material

• Drainage layer material

• Visual

• Environmental

• Land Value

• Stormwater management