Changes

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]].  

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 from the BMP may be limited by the hydraulic conductivity of the medium, or by the properties of the perforated [[pipe]].

The maximum flow rate through a bed of filer media (''Q_max'', L/s) may be calculated:

The maximum flow rate through a bed of filter media (''Q_{max, m}'', L/s) may be calculated:

<math>Q_{max}=\frac{K_{m}\times A_{p}\times \left (\frac{\sum d}{d_{m}}  \right )}{3600}</math>

<math>Q_{max, m}=\frac{K_{m}\times A_{p}\times \left (\frac{\sum d}{d_{m}}  \right )}{3600}</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*''K_m'' is the hydraulic conductivity of the filter media (mm/hr),  

*''K_m'' is the hydraulic conductivity of the filter media (mm/hr),  

===Example calculation===

===Example calculation===

A [[stormwater planter]] with footprint of 8 x 1.5 m is planned to received runoff from an adjacent rooftop. The initial design for the planters includes 750 mm depth of filter medium, 50 mm rock mulch, and a further ponding of 300 mm. The underdrain pipe will be embedded into high performance bedding or similar, with a strip of geotextile over the top to prevent migration of the filter media into the pipe. The lab test states that the medium has a hydraulic conductivity of 25 mm/hr. The maximum flow through the medium will be calculated and a comparison made with the maximum flow through the pipe to see....:

A [[stormwater planter]] with footprint of 8 x 1.5 m is planned to received runoff from an adjacent rooftop. The initial design for the planters includes 750 mm depth of filter medium, 50 mm rock mulch, and a further ponding of 300 mm. The underdrain pipe will be embedded into high performance bedding or similar, with a strip of geotextile over the top to prevent migration of the filter media into the pipe. The lab test states that the medium has a hydraulic conductivity of 25 mm/hr. The maximum flow through the medium will be calculated and a comparison made with the maximum flow through the pipe to see....:

<math>Q_{max}=\frac{25 mm/hr\times 12\ m^{2}\times \left (\frac{1.1\ m}{0.75\ m}  \right )}{3600\ s/hr}=0.12\ L/s</math>

<math>Q_{max, m}=\frac{25 mm/hr\times 12\ m^{2}\times \left (\frac{1.1\ m}{0.75\ m}  \right )}{3600\ s/hr}=0.12\ L/s</math>