The bioretention cell  is a depression or shallow basin, which the soils were excavated to a calculated width, length, and depth and replaced with engineered soils and possibly multiple sizes of media (designed for high infiltration rate and storage). This type of facility is also known as a “bio-filter” because it is designed to address both water quantity and water quality. The difference between this facility and a rain garden is that this facility utilizes engineered soils in combination of a rock chamber that usually extends to a depth between 12-18 inches. Like rain gardens, they are usually decorative with native plants and grasses. However, urban grass has been sowed throughout these practices to provide a more uniform landscape. 

Bio-Retention Swale

This type of facility is another type of bio-filter.  An Infiltration Swale is a modified storm water linear conveyance drainage swale/ditch that has been designed for increased infiltration.  The infiltration component of this practice is identical to that of an Infiltration Basin / Bio-Cell (the lowest portion of the swale is excavated to a calculated width, length, and depth and replaced with engineered soils and/or several multiple sized granule layers that promote a higher water quality treatment process through infiltration). This particular design can be incorporated over multiple properties, which each property owner can apply for the reimbursement program.

To further examine this practice, please visit the Iowa Stormwater Management Manual (ISWMM) Ch.5 Sec 4 “Bioretention Systems”. It contains detailed information about the practice’s typical uses, its advantages and disadvantages, maintenance, cross-cut example, planning criteria, design methods, etc.

Iowa Stormwater Management Manual (ISWMM) Ch.5 Sec 4