Bioretention: TTT
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| Surface | |
|---|---|
| Berm height (mm) | Sometimes referred to as the bowl depth |
| Surface roughness (Manning’s n) | Lower numbers indicate less surface obstruction and result in faster flow
Suggested ranges:
|
| Surface slope (%) | If the slope > 3% a series of Check dams or weirs should be included in the design. |
| Soil (bioretention filter media) | |
| Thickness (mm) | Depth of filter media |
| Porosity (fraction) | Suggest range 0.3 – 0.35 unless otherwise tested |
| Field capacity (fraction) | Suggested range 0.10 - 0.12 [1] |
| Wilting point (fraction) | Suggested value 0.03 [1] |
| Conductivity (mm/hr) | Suggested range 25 – 250 mm/hr |
| Conductivity slope | Suggested value 45 [1] |
| Suction head (mm) | Suggested range 50 - 60 [1] |
| Storage | |
| Thickness (mm) | Depth of storage aggregates layer |
| Void ratio | Suggest value 0.4 unless otherwise tested |
| Seepage rate (mm/hr) | Infiltration rate of native soil |
| Clogging factor | Maybe up to 0.5 to account for some anticipated maturation. |
| Design drawdown time (hrs) | Also known as 'drainage time' |
| Drain (underdrain) | |
| Flow coefficient | Suggested value 1 |
| Flow exponent | Suggested value 1 |
| Offset height | This is the height from the base of the cell to the height at which the drain discharges. In some designs this may be the height of the perforated pipe within the storage layer; in others this height is adjusted by creating an upturn in the discharge pipe.Bioretention: Partial infiltration |
- ↑ 1.0 1.1 1.2 1.3 1.4 Oregon State Univ., Corvallis. Dept. of Civil, Construction and Environmental Engineering.; Environmental Protection Agency, Cincinnati ONRMRL. Storm Water Management Model Reference Manual Volume I Hydrology (Revised). 2016:233. https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100NYRA.txt Accessed August 23, 2017.