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| For practices with no underdrain: | | For practices with no underdrain: |
| <math>A_{r}=V_{i}/[d_{i}+(f'\times D)]</math> | | <math>A_{r}=V_{i}/[d_{i}+(f'\times D)]</math> |
| + | {{Plainlist|1=Where: |
| + | *V<sub>i</sub> = Infiltration volume target for the design storm event (m<sup>3</sup>), based on average annual water budgets for pre- and post-development scenarios, and the target of maintaining pre-development infiltration volume. |
| + | *d<sub>i</sub> = Infiltration water storage depth of the practice (m), see equations above to calculate for with and without underdrain designs. |
| + | *f' = Design infiltration rate of the underlying native soil (m/h) |
| + | *D= Duration of design storm (h)<br> |
| + | If A<sub>r</sub> is greater than A<sub>p</sub>, calculate the design infiltration water storage depth, d<sub>i</sub>', required to capture the infiltration volume target for the design storm: |
| + | <math> d_{i}' = (V_{i}/A_{p})- (f'\times D)</math> |
| {{Plainlist|1=Where: | | {{Plainlist|1=Where: |
| *V<sub>i</sub> = Infiltration volume target for the design storm event (m<sup>3</sup>) | | *V<sub>i</sub> = Infiltration volume target for the design storm event (m<sup>3</sup>) |
− | *d<sub>i</sub> = Infiltration water storage depth of the practice (m), see equations above to calculate for with and without underdrain designs. | + | *A<sub>p</sub> = Surface area of the practice (m<sup>2</sup>, see equations above to calculate for designs that deliver water to a surface ponding area vs. directly to storage reservoir. |
| *f' = Design infiltration rate of the underlying native soil (m/h) | | *f' = Design infiltration rate of the underlying native soil (m/h) |
− | *D= Duration of design storm (h) | + | *D= Duration of design storm (h)<br> |
| + | <br> |
| + | *Step 13: Calculate practice drainage time, t<sub>p</sub> (h), which is the time required to fully drain d<sub>i</sub> or d<sub>i</sub>' assuming one dimensional drainage from the storage reservoir bottom: |
| + | |
| | | |
| ==Calculate peak flow rates== | | ==Calculate peak flow rates== |