Volume 2-05, Chapter 3 - City of Wichita

Section 3.2.9 - Bioretention Areas
Step 4
Step 5
Size flow diversion structure, if needed.
A flow regulator (or flow splitter diversion structure) should be supplied to divert the
WQ v to the bioretention area.
Size low flow orifice, weir, or other device to pass Q wq (Chapter 5, Section 6).
Determine size of bioretention ponding/filter area.
The required planting soil filter bed area is computed using the following equation
(based on Darcy’s Law): (Claytor & Schueler, 1996).
Equation 3-7 (
f f
)
f
A
f
WQv
* df
=
k * h + d * t
where:
A f = surface area of ponding area (ft 2 )
WQ v = water quality protection volume (or total volume to be captured)
d f = filter bed depth (2.5 feet minimum)
k = coefficient of permeability of filter media (ft/day) (use 0.5 ft/day for siltloam)
h f = average height of water above filter bed (ft) (typically 3 in, half of the 6 in
ponding depth)
t f = design filter bed drain time (days) (2.0 days or 48 hours is recommended
maximum)
Step 6
Set design elevations and dimensions of facility.
Step 7 Design conveyances to facility (off-line systems) (Chapter 3, Section 1).
See the example Figure 3-37 to determine the type of conveyances needed for the
site.
Step 8 Design pretreatment (Chapter 2, Section 3).
Pretreat with a grass filter strip (on-line configuration) or grass channel (off-line),
and stone diaphragm.
Step 9
Step 10
Step 11
Size underdrain system
See Section 3.2.9.5.
Design emergency overflow
See Section 3.2.10.5.
An overflow must be provided to bypass and/or convey larger flows to the
downstream drainage system or stabilized watercourse. Nonerosive velocities
need to be ensured at the outlet point.
Prepare vegetation and landscaping plan.
A landscaping plan for the bioretention area should be prepared to indicate how it
will be established with vegetation.
Volume 2, Technical Guidance Page 3 - 121