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Line 313: − Options for [[pretreatment]] include:+ − + − + − + − For further guidance see [[Pretreatment]]+ + + + +
→Pretreatment
===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:
*A [[level spreader]], [[gravel diaphragm]] or [[Vegetated filter strip |vegetated filter strip]] for sheet flow
*[[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.
*A [[Forebays|forebay]] for concentrated surface flow
*[[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.
*An [[Oil and grit separators|oil and grit separator]] for concentrated underground flow
*[[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.
*Catch basin, manhole, or other inlet structure sump: Consider using shield, baffle, trap or filter insert device to increase removal of sediment and debris. Used with overland or underground concentrated inflows.
*[[Forebays |Forebay]]: Constructed with 2:1 length to width ratio and sized to accommodate ponding volume of 25% of the surface ponding storage requirement. Used with concentrated overland flow inlets.
*[[Oil and grit separators |Oil and grit (hydrodynamic) separator]]. Used with concentrated underground flow inlets (inlet pipes).
See [[Pretreatment]] for further guidance.
===Overflow Configuration===
===Overflow Configuration===