Flow through media

Practices which infiltrate surface runoff through an engineered soil or filter media, and discharge through an underdrain include stormwater planters and some forms of bioretention. The maximum flow rate from the BMP may be limited by the hydraulic conductivity of the mmedium, or by the properties of the perforated pipe.

The maximum flow rate through a bed of filer media (Q_max) may be calculated: $Q_{max}=K_{m}\times A_{p}\times \left({\frac {\sum d}{d_{m}}}\right)\times 3.6\times 10^{-3}$

Where:

• K_m is the hydraulic conductivity of the filter media (mm/hr),
• A_p is the area of the practice (m²),
• Σ d is the total depth of bioretention components over the perforated pipe (mm) (e.g. ponding/mulch/filter media/choker layer), and
• d_m is the depth of the filter media (mm).

Example calculation

$Q_{max}=50mm/hr\times A_{p}\times \left({\frac {\sum d}{d_{m}}}\right)\times 3.6\times 10^{-3}$

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

A perforated pipe used to assist the draining of soils.

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

A parameter that describes the capability of a medium to transmit water.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.