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→Determine the active water storage depth of the practice
==Determine the active water storage depth of the practice==
==Determine the active water storage depth of the practice==
* Step 4: Identify the active water storage components of the practice<br>
* Step 4: Identify the active water storage of the practice<br>
For practices without an underdrain, the active storage components include the surface ponding, mulch and filter media depths (i.e. total depth of the practice):
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 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_{a}=d_{p}'+ (d_{m}\times n_{m}) + (d_{f}\times n_{f})</math>
{{Plainlist|1=Where:
{{Plainlist|1=Where:
*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 water in the storage reservoir below the invert of the underdrain perforated pipe that can reliably drained within the specified drainage time:<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 drained within the specified drainage time. The active water storage of the practice can be calculated as :<br>
<math>d_{a}= f' t </math>
<math>d_{a}= 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 depth of water that can be stored in the space between the invert elevations 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 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>
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.