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 Checkdams or weirs should be included in the design. |
| Soil (bioretention filter media) | |
| Thickness (mm) | Depth of filter media |
| Porosity (fraction) | Suggest range 0.35 – 0.4 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 range 0.35 – 0.4 unless otherwise tested |
| Seepage rate (mm/hr) | Infiltration rate of native soil |
| Clogging factor | ? |
| Design drawdown time (hrs) | Recommend 48 hours? |
| 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 Bioretention: Partial infiltration. In other designs this height is adjusted by creating an upturn in the discharge pipe. Bioretention: Internal storage |
- ↑ 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.