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Line 125: − ===Additional step for system without underdrain===+ − * Step 4: Determine maximum permissible ponding depth (''d<sub>p, max</sub>''): − <math>d_{p, max}=f'\times48</math> − {{Plainlist|1=Where: − *''f''' = Design infiltration rate (mm/hr), and − *48 = Maximum permissible drainage time for ponded water (hrs) − *Note that in designs without underdrains, conceptually the drainage of ponded water is limited by exfiltration at the base of the practice.}}
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<math>d_{p}'=d_{p, max}</math>
<math>d_{p}'=d_{p, max}</math>
==Determine the active storage depth, d<sub>a</sub> of the practice==
* Step 4: Determine the active storage depth, d<sub>a</sub> of the practice<br>
* Step 4: Determine the active storage depth, d<sub>a</sub> of the practice<br>
For practices without an underdrain, the active storage depth equals the total depth of the practice, including surface ponding depth; <br>
For practices without an underdrain, the active storage depth equals the total depth of the practice, including surface ponding; <br>
<math>d_{a}=d_{T}</math>
<math>d_{a}=d_{T}</math>
For practices with the underdrain perforated pipe elevated off the bottom of the storage reservoir:
For practices with the underdrain perforated pipe elevated off the bottom of the storage reservoir:
d<sub>p, max</sub>= depth of storage reservoir below the invert of the underdrain perforated pipe.<br>
d<sub>a</sub>= depth of storage reservoir below the invert of the underdrain perforated pipe.<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):
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):
d<sub>p, max</sub>= Difference between invert elevation of reservoir bottom and invert of the riser (i.e 90 degree coupling).<br>
d<sub>a</sub>= Difference between invert elevation of reservoir bottom and outlet of the riser (i.e invert elevation of the 90 degree coupling).<br>
* Step 5: Calculate the active storage depth of the practice (''d<sub>a'', mm):<br>
For practices with no underdrain:<br>
<math>d_{a}=(f'\times t \times 1/n) + d_{p}'</math>
{{Plainlist|1=Where:
*''f''' = Design infiltration rate (mm/hr),
*''t'' = [[Drainage time]] (hrs). Check local regulations for drainage time requirements; and
*''n'' = Porosity of the reservoir aggregate
*''d<sub>p</sub>''= design surface ponding depth}}<br>
For practices with an underdrain:<br>
<math>d_{a}=f'\times t \times 1/n</math>
{{Plainlist|1=Where:
*''f''' = Design infiltration rate (mm/hr),
*''t'' = [[Drainage time]] (hrs). Check local regulations for drainage time requirements; and
*''n'' = Porosity of the reservoir aggregate}}
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.
==Calculate the total depth of the practice, d<sub>T</sub>==
==Calculate the total depth of the practice, d<sub>T</sub>==
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.
* Step 2: Determine what the planting needs are and assign an appropriate depth of filter media, using the table above.
* Step 2: Determine what the planting needs are and assign an appropriate depth of filter media, using the table above.
* Step 3: Select an underdrain perforated pipe diameter (typically 100 - 200 mm), assign this as an 'embedded' depth equal to the pipe diameter. *Note that this component does not apply if a downstream riser is being used to create the storage reservoir.
* Step 3: Select an underdrain perforated pipe diameter (typically 100 - 200 mm), assign this as an 'embedded' depth equal to the pipe diameter. *Note that this component does not apply if a downstream riser is being used to create the storage reservoir.