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| *48 = Maximum permissible drainage time for ponded water (h) | | *48 = Maximum permissible drainage time for ponded water (h) |
| *Note that in designs without underdrains, conceptually the drainage of ponded water is limited by infiltration through the base of the practice.}}<br> | | *Note that in designs without underdrains, conceptually the drainage of ponded water is limited by infiltration through the base of the practice.}}<br> |
− | For practices with underdrains elevated in the storage reservoir profile: | + | For practices with underdrains elevated off the bottom of the storage reservoir profile: |
− | <math>d_{p, max}= depth of storage reservoir below invert of the underdrain perforated pipe.<br> | + | d<sub>p, max</sub>= depth of storage reservoir below invert of the underdrain perforated pipe.<br> |
| For practices with underdrain on base of the storage reservoir and connected to a riser (e.g., standpipe and 90 degree coupling): | | For practices with underdrain on base of the storage reservoir and connected to a riser (e.g., standpipe and 90 degree coupling): |
| d<sub>p, max</sub>= Difference between elevation of reservoir bottom and invert of the riser (i.e 90 degree coupling).<br> | | d<sub>p, max</sub>= Difference between elevation of reservoir bottom and invert of the riser (i.e 90 degree coupling).<br> |
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| For practices with soft (i.e. landscaped) edges and bowl-shaped ponding areas calculate the mean ponding depth: | | For practices with soft (i.e. landscaped) edges and bowl-shaped ponding areas calculate the mean ponding depth: |
| <math>d_{p}'=d_{p, max}\divide 2 | | <math>d_{p}'=d_{p, max}\divide 2 |
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| ==Calculate the total depth of the practice, d<sub>T</sub>== | | ==Calculate the total depth of the practice, d<sub>T</sub>== |