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| :<math>d_{r}=a[e^{\left ( -bD \right )} -1]</math> | | :<math>d_{r}=a[e^{\left ( -bD \right )} -1]</math> |
| Where | | Where |
− | :<math>a=\frac{Ar}{x}-\frac{i Ai}{x f'}</math> | + | :<math>a=\frac{A_{r}}{x}-\frac{i\times A_{i}}{x\times f'}</math> |
| and <br> | | and <br> |
− | :<math>b=\frac{xf'}{nAr}</math> | + | :<math>b=\frac{x\times f'}{n\times A_{r}}</math> |
| | | |
| (The rearrangement to calculate the required footprint area of the facility for a given depth assuming three-dimensional drainage is not available at this time. Elegant submissions are invited.)<br> | | (The rearrangement to calculate the required footprint area of the facility for a given depth assuming three-dimensional drainage is not available at this time. Elegant submissions are invited.)<br> |
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| It is best applied to calculate the maximum duration of ponding on the surface of [[bioretention cells]], and upstream of the [[check dams]] of [[bioswales]] and [[enhanced grass swales]] to ensure all surface ponding drains within 48 hours. | | It is best applied to calculate the maximum duration of ponding on the surface of [[bioretention cells]], and upstream of the [[check dams]] of [[bioswales]] and [[enhanced grass swales]] to ensure all surface ponding drains within 48 hours. |
| To calculate the time (''t'') to fully drain surface ponded water through the filter media or planting soil: | | To calculate the time (''t'') to fully drain surface ponded water through the filter media or planting soil: |
− | <math>t=\frac{dp'}{Kf}</math> | + | <math>t=\frac{d_{p}'}{K_{f}}</math> |
| Where <br> | | Where <br> |
| d<sub>p</sub>' is the effective or mean surface ponding depth (mm).<br> | | d<sub>p</sub>' is the effective or mean surface ponding depth (mm).<br> |
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| <br> | | <br> |
| To calculate the time (''t'') to fully drain the facility assuming three-dimensional drainage: | | To calculate the time (''t'') to fully drain the facility assuming three-dimensional drainage: |
− | <math>t=\frac{nAr}{f'x}ln\left [ \frac{\left (d+ \frac{Ar}{x} \right )}{\left(\frac{Ar}{x}\right)}\right]</math> | + | <math>t=\frac{n\times A_{r}}{f'\times x}ln\left [ \frac{\left (d_{r} \frac{A_{r}}{x} \right )}{\left(\frac{A_{r}}{x}\right)}\right]</math> |
| Where "ln" means natural logarithm of the term in square brackets <br> | | Where "ln" means natural logarithm of the term in square brackets <br> |
| Adapted from CIRIA, The SUDS Manual C753 (2015). | | Adapted from CIRIA, The SUDS Manual C753 (2015). |