Slide 48 of 52
Notes:
For applications where concentrated (or channelized) runoff enters the bioretention system, such as through a slotted curb opening, a grassed channel with a pea gravel diaphragm is the preferred pretreatment method. The length of the grass channel depends on the drainage area, land use, and channel slope. This slide gives sizing for grass channels leading into a bioretention facility for a one acre drainage area. The minimum grassed channel length should be 20 feet.
The pea gravel diaphragm is designed to slow the velocity and help spread the flow entering the practice. In addition, this component captures the coarser- grained sediments. It is anticipated that the pea gravel diaphragm will exhibit clogging within the first three to four years after installation and may require periodic flushing and/or replacement.