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  • In swales conveying flowing water a freeboard of 300 mm is generally accepted as a good starting point.
  • In bioretention the freeboard is being defined as the depth between the invert of the overflow and the the inlet 150 mm would suffice, so long as the inlet will not become inundated during design storm conditions.
  • In above grade stormwater planters, the equivalent dimension would be the depth between the invert of the overflow and the lip of the planter (150 mm minimum)
  • Where the stormwater planterA vegetated practice that collects and treats stormwater through sedimentation and filtration. Contributions to water cycle/water balance are through evapotranspiration only; no infiltration. is configured more like a lined/non-infiltrating bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. system, the inlet will be the depth to which this is measured, as above (150 mm minimum).