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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<sub>max<max>'') may be calculated:
<math>Q_{max}=3.6 \times 10^{-3}\times K_{m}\times A_{p}\times \left (\frac{d_{pd}+d_{m}}{d_{m}} \right )</math>
{{Plainlist|1=Where:
*''K<sub>m</sub>''' is the hydraulic condcuvitiy of the filter media (mm/hr),
*''Aand
<math>Q_{p} = A_{p}\times K_{sat}\times </math>
{{Plainlist|1=Where:
*''K<sub>sat</sub>'' is the saturated hydraulic conductivity of the filter media (mm/hr), and
*''A<sub>p</sub>'' is the area of the practice (m<sup>2</sup>).}}