Changes

*For optimal performance recommended ratios of impervious drainage area to pervious facility footprint area (I:P area ratio) range from 5:1 on low permeability soils (HSG C and D) to 20:1 on high permeability soils (HSG A and B).

*For optimal performance recommended ratios of impervious drainage area to pervious facility footprint area (I:P area ratio) range from 5:1 on low permeability soils (HSG C and D) to 20:1 on high permeability soils (HSG A and B).

*Minimum bioretention facility footprint area (i.e., filter bed area) is based on the design storm runoff volume and effective surface ponding depth.

*Minimum bioretention facility footprint area (i.e., filter bed area) is based on the design storm runoff volume and effective surface ponding depth.

*Bioretention cells work best when distributed, so that no one facility receives runoff from more than 0.8 Ha, although there is a trade off to be considered regarding distributed collection and treatment versus ease of maintenance.  

*Bioretention cells work best when distributed, so that no one facility receives runoff from more than 0.8 Ha, although there is a trade-off to be considered regarding distributed collection and treatment versus ease of maintenance.  

*Bioretention can be almost any shape, from having very curvilinear, soft edges with variable depth, to angular, hard-edged and uniform depth.

*Bioretention can be almost any shape, from having very curvilinear, soft edges with variable depth, to angular, hard-edged and uniform depth.

*Linear trench or swale geometries will drain faster than round or square shapes because they have larger perimeters.

*Linear trench or swale geometries will drain faster than round or square shapes because they have larger perimeters.