Changes

==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 components 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, d_T):

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):

<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_T = Total depth of the practice, including surface ponding}}<br>

*d_p' = Design surface ponding depth (m)

*d_m = Depth of mulch (m)

d_a= Depth of storage reservoir below the invert elevation of the underdrain perforated pipe.<br>

*n_m = Porosity of mulch

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):<br>

*d_f = Depth of filter media (m)

d_a= Difference between invert elevations of the reservoir bottom and riser outlet (i.e invert elevation of the 90 degree coupling).<br>

*n_f = Porosity of filter media}}<br>

* Step 5: Calculate the active storage depth of the storage reservoir (''d<sub>a'', mm):<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 no underdrain, this includes the combined surface ponding and storage reservoir depth that will reliably drain within the specified drainage time. <br>

<math>d_{a}= f'/times t</math>

 

For practices with an underdrain, this includes only the storage reservoir depth below the invert of the underdrain perforated pipe that will reliably drain within the specified drainage time:

<math>d_{a}=(f'\times t \times 1/n)</math>

{{Plainlist|1=Where:

{{Plainlist|1=Where:

*''f''' = Design infiltration rate (mm/hr),

*f' = Design infiltration rate of underlying native soil (m/h)

*''t'' = [[Drainage time]] (hrs). Check local regulations for drainage time requirements; and

*t = [[Drainage time]] (h). Check provincial or local criteria for drainage time requirements}}<br>

*''n'' = Porosity of the reservoir aggregate}}<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>

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.