HomeMy WebLinkAboutApplication Files_82693_pg0615 O Substituting the water quality volume(WQV), converted to watershed inches,for runoff depth(Q), compute
the water quality.ftow(WQF)from the following equation:
WQF=(qu)(AX 0
where: WI'QV=crater quality flow(cfs)
q, =unit peals discharge(cfs/mi2/inch)
A = drainage area(mi2)
Q =runoff depth (in
watershed inches)
_ �WQV(acre--�eet.�s[7.2(inches/_joot)J
Drainage Area(acres)
Other peals flow calculation methods may be used for determining the WQF, such as those recommended by
manufacturers of proprietary treatment systems, provided that the\VQF calculated by other methods is equal to
or greater than the WQF calculated using the.above NRUS Graphical Peak Discharge Method.
Flow Diversion Structures
Plow diversion structures, also called flow sputters, are designed to deliver flows up to the design water quality
floe,(WQF)or water quality volurne(WQV)to off-fine stormwater treatment practices.Flows in excess of the WQF
or WQV are diverted around the treatment facility with minimal increase in head.at the flow diversion structure
to avoid surcharging the treatment facility under higher flow conditions. Flow diversion structures are typically
manholes or vaults equipped with We.lis, orifices, or pipes to bypass excess runoff. A number of design options
exist. Figures B-2 through.B-3 show common examples of flow diversionn structures for use upstreun of storm-
water treatment practices. Other equivalent designs that achieve the result of diverting flows in. excess of the
WQF or IXTQV around the treatment facility, including.bypasses or overflows located inside the facility, are also
acceptable.
The following general procedures are recommended for design.of flow diversion structures:
O Locate the top of the weir or overflow structure at the maximum water surface elevation associated with the
WQF, or the water surface elevation in the treatment practice when the entire WQV is being held, whichever
is higher.
O Determine the diversion structure dimensions required to divert flows in excess of the WQF using standard
equations for a rectangular sharp-crested weir, uniform flow in pipes or channels, or orifice depending on
the type of diversion structure.
O Provide sufficient freeboard in the stormwater treatment practice and flow splitter to accommodate flow over
the diversion structure.
O Limit the maximum head over the flow diversion structure to avoid surcharging the stormwater treatment
practice under high flow conditions.Flow to the stormwater treatment practice at the 100 year water surface
elevation should not increase the WQF by more tban 10 percent.
O Design diversion structures to withstand the effects of freezing,frost in foundations, erosion, and flotation
due to bigh water conditions. These structures should be designed to minimize clogging potential and to
allow for ease of inspection and maintenance.
2004 Connecticut Storrnwater Quality Manual '