20240641 Ver 1_Water runnoff_20240430

March 7, 2014
Page 3 of 3
options for Meeting Diffuse Flow Provisions of the
Stormwater and Riparian Buffer Protection Programs
C
Exempt
Allowable
Allowable
with
Mitigation
Prohibited
rainage ditches, roadside ditches water
outfalls through riparian buffers:
• Existing drainage ditches, roadside ditches, and
stormwater outfalls provided that they are
managed to minimize the sediment, nutrients
and other pollution that convey to waterbodies
New-3rainage s an
x
stormwater outfalls provided that a stormwater
management facility is installed to control
nitrogen and attenuate flow before the
conveyance discharges through the riparian
buffer
N
• New drainage ditches, roadside ditches and
stormwater outfalls that do not provide control
for nitrogen before discharging through the
riparian buffer
X
• Excavation of the streambed in order to bring it
to the same elevation as the invert of a ditch
In the past, the state has interpreted the diffuse flow language in the buffer rules to mean that
designers have two primary options to provide diffuse flow:
Provide a Level Spreader -Vegetated Filter Strip (LS-VFS) in accordance with Chapter 8 of
the BMP Manual. Per the BMP Manual, the LS-VFS may be designed to handle the one
inch/hour storm and larger storms may be discharged non-erosively. (Option 1 above)
• Provide a BMP that removes a minimum of 30% of TN removal outside of the vegetated
or riparian buffer to treat the design storm before it is discharged through the buffer.
(Option 2 above)
The above table provides three additional options. Options 3 and 4 are intended to provide
relatively low-cost approaches to providing treatment in the swale prior to discharge through a
buffer. Option 5 provides an exemption to the diffuse flow provision in the stormwater rules
for very low flows. As stated previously, the current wording in the riparian buffer rules does
not allow the Division of Water Resources to provide an exemption to the diffuse flow
requirements, even for low flows.