Changes

===Pretreatment===  

===Pretreatment===  

Pretreatment prevents clogging by capturing sediment before it reaches the filter bed. It is typically necessary unless runoff sediment loads are very low (e.g. roof drainage). Pretreatment options include:

Pretreatment prevents clogging by capturing sediment before it reaches the filter bed. It is typically necessary unless runoff sediment loads are very low (e.g. roof drainage). Pretreatment options include:

*[[Level spreader]]: A shallow trench structure (with concrete, metal or wood lip), graded to be level and installed parallel to the pavement edge or flush curb. Recommended sizing: (i) 1.4 m of length for every 0.01 m³/s of inflow during the design storm event, (ii) width of 300 mm or 3 times inflow pipe diameter, (iii) depth of 200 mm or half the inflow pipe diameter. Used with any overland flow inlets.

*[[Level spreaders |Level spreader]]: A shallow trench structure (with concrete, metal or wood lip), graded to be level and installed parallel to the pavement edge or flush curb. Recommended sizing: (i) 1.4 m of length for every 0.01 m³/s of inflow during the design storm event, (ii) width of 300 mm or 3 times inflow pipe diameter, (iii) depth of 200 mm or half the inflow pipe diameter. Used with any overland flow inlets.

*[[Gravel diaphragms |Gravel diaphragm]]: A shallow, geotextile-lined depression, filled with clean aggregate, graded level and installed parallel to pavement edge (for sheet inflows) or perpendicular to concentrated inflows. Elevation change of 75 to 100 mm from pavement to top of diaphragm. Typically 600 mm wide by 300 mm deep. Stone: 5 to 20 mm (sheet flow inlets) or rip rap for concentrated inflows. Used with overland flow inlets.

*[[Gravel diaphragms |Gravel diaphragm]]: A shallow, geotextile-lined depression, filled with clean aggregate, graded level and installed parallel to pavement edge (for sheet inflows) or perpendicular to concentrated inflows. Elevation change of 75 to 100 mm from pavement to top of diaphragm. Typically 600 mm wide by 300 mm deep. Stone: 5 to 20 mm (sheet flow inlets) or rip rap for concentrated inflows. Used with overland flow inlets.

*[[Vegetated filter strip]]: Receive runoff as overland sheet flow via pavement edge or flush curb. Use where drainage area flow path length is ≤ 25 m and slopes are <3%. Min. flow path length of 3 m, with 5 m preferred, and slope between 1 and 3%. Must be graded to provide a 75 to 150 mm elevation drop between the pavement and the filter strip surface.

*[[Vegetated filter strip]]: Receive runoff as overland sheet flow via pavement edge or flush curb. Use where drainage area flow path length is ≤ 25 m and slopes are <3%. Min. flow path length of 3 m, with 5 m preferred, and slope between 1 and 3%. Must be graded to provide a 75 to 150 mm elevation drop between the pavement and the filter strip surface.