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→Determine the active water storage depth of the practice
<math>d_{p}'=d_{p, max}</math>
<math>d_{p}'=d_{p, max}</math>
==Determine the active water storage depth of the practice==
==Determine the infiltration water storage depth of the practice==
* Step 4: Identify and calculate the active water storage depth of the practice, d<sub>a</sub><br>
* Step 4: Identify and calculate the infiltration water storage depth of the practice, d<sub>i</sub>, which is the depth of water stored in the practice that can drain by infiltration alone.<br>
For practices without an underdrain, the active water storage components include the surface ponding, mulch and filter media depths (i.e. total depth of the practice). The active water storage depth of the practice can be calculated as:
For practices without an underdrain, components contributing to infiltration water storage include the surface ponding, mulch and filter media depths (i.e. total depth of the practice). The infiltration water storage depth of the practice can be calculated as:
<math>d_{a}=d_{p}'+ (d_{m}\times n_{m}) + (d_{f}\times n_{f})</math>
<math>d_{i}=d_{p}'+ (d_{m}\times n_{m}) + (d_{f}\times n_{f})</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*d<sub>p</sub>' = Design surface ponding depth (m)
*d<sub>p</sub>' = Design surface ponding depth (m)
*d<sub>f</sub> = Depth of filter media (m)
*d<sub>f</sub> = Depth of filter media (m)
*n<sub>f</sub> = Porosity of filter media}}<br>
*n<sub>f</sub> = Porosity of filter media}}<br>
For practices with the underdrain perforated pipe elevated off the bottom of the storage reservoir, the active storage component is the depth of storage reservoir below the invert of the underdrain perforated pipe that can reliably drain within the specified drainage time. The active water storage of the practice can be calculated as:
For practices with the underdrain perforated pipe elevated off the bottom of the storage reservoir, infiltration water storage is only provided by the depth of storage reservoir below the invert of the underdrain perforated pipe, and only the portion that can reliably drain within the specified drainage time. So the infiltration water storage of the practice can be calculated as:
<math>d_{a}= f' t </math>
<math>d_{i}= f' t </math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*f' = [[Design infiltration rate]] of underlying native soil (m/h)
*f' = [[Design infiltration rate]] of underlying native soil (m/h)
*t = [[Drainage time]] (h). Check provincial or local criteria for drainage time requirements}}<br>
*t = [[Drainage time]] (h). Check provincial or local criteria for drainage time requirements}}<br>
For practices with the underdrain perforated pipe installed on the bottom of the storage reservoir and connected to a riser (e.g., standpipe and 90 degree coupling), the active storage component is the storage reservoir depth between the inverts of the reservoir bottom and riser outlet (i.e invert elevation of the 90 degree coupling) and is calculated the same way as above.<br>
For practices with the underdrain perforated pipe installed on the bottom of the storage reservoir and connected to a riser (e.g., standpipe and 90 degree coupling), the infiltration water storage is only provided by the storage reservoir depth between the inverts of the reservoir bottom and riser outlet (i.e invert elevation of the 90 degree coupling) and is calculated the same way as above.<br>
To boost drainage performance on fine-textured, low permeability soils, consider designing storage reservoirs even deeper than those calculated using the above approach, that many not fully drain between storm events, which increases hydraulic head and infiltration rate at the base of the practice. See [[Low permeability soils]] for more information.
To boost drainage performance on fine-textured, low permeability soils, consider designing storage reservoirs even deeper than those calculated using the above approach, that many not fully drain between storm events, which increases hydraulic head and infiltration rate at the base of the practice. See [[Low permeability soils]] for more information.