Filter strips: TTT

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Vegetated filter strips are found within the LID toolbox
Berm height (mm) This is the height of the curb which constrains the overland sheet flow of water. Where the bottom of the slope discharges directly into another LID facility without impedance, the value is 0.
Surface roughness (Manning’s n) Lower numbers indicate less surface obstruction and result in faster flow. See Turf for ideas of a good number according to mowing practices.
Surface slope (%) If the slope > 3%, consider using level spreaders to reduce erosion of the surface under high flow velocities.
Soil (native underlying soil, or amended topsoil)
Thickness (mm) If topsoil has been amended Absorbent landscapes
Porosity (fraction) Suggest around 0.4, unless otherwise tested.
Field capacity (fraction) Will vary according to native or amended topsoil[1]
Wilting point (fraction)
Conductivity (mm/hr)
Conductivity slope
Suction head (mm)
Design drawdown time (hrs) Will be determined by regulatory authority, often 48 - 72 hours to reduce nuisance from mosquitoes
  1. 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. Accessed August 23, 2017.