HomeMy Public PortalAboutCity of Ferguson3/26/2021 Ferguson, MO Code of Ordinances
1/5
(a)
(b)
ARTICLE XI. - STORMWATER MANAGEMENT
Sec. 7-225. - Stormwater quality—Best management practices.
Purpose and intent. Two (2) consequences of construction and development are increased runoff
created by the changed properties of ground surface and the rate of discharge of this increased
runoff. These are both of great relevance to stormwater. The natural condition of the land before
development is in relative balance with the natural capacity of the receiving creeks. Normally the
undeveloped conditions provide greater permeability and longer times of concentration. By
modification of the ground surface from the irregular, pervious, and vegetation-covered, the
areas are changed to more impervious, more quickly drained and., in some cases, denuded of
vegetation. It is the policy of the city to protect and promote the public, health, safety and general
welfare. The management of stormwater will reduce the erosion on land and creek, channels, will
reduce the possibility of damage to public and private property, and will assist in the attainment
and maintenance of water quality standards, and will preserve the environmental quality of the
watercourses in the city.
Requirements—Creekbank setback. New development along natural watercourses shall have
residential lot lines, commercial or industrial improvements, parking areas and driveways setback
a minimum of twenty-five (25) feet from the top of the existing stream bank. This is not meant to
prevent access across creeks. Except as otherwise provided herein or as allowed by the city, the
section of land between a natural watercourse and lot lines shall be designated as common
ground and drainage easement to be maintained by the trustees or homeowners association of
the subdivision within all types of residential developments. In lieu of the common ground
requirement, the section of land between the natural watercourse and twenty-five (25) feet from
the top of the bank can be (i) private property with an easement dedicated to the trustees or
homeowners association requiring maintenance of the areas as the responsibility of the trustees
or homeowners association, (ii) private property subject to a conservation easement in favor of
an organization or land trust dedicated to environmental protection or land preservation such as
Trailnet, Inc., the Open Space Council for the St. Louis Region or similar organization, (iii) set aside
in a stream bank mitigation program approved by the United States Army Corps of Engineers
under the provisions of the Clean Water Act. All developments shall maintain a setback minimum
of fifty (50) feet from the top of the existing hank to any building structure requiring a
construction permit that necessitates excavation or also requires a foundation. Commercial and
industrial areas shall have creek areas dedicated as drainage easements. Notwithstanding the
foregoing setback requirements, an applicant may obtain a variance to develop within the stream
buffer area from the city provided the applicant is able to demonstrate that the water quality and
stream morphology will not be adversely affected or adequate mitigation is provided to offset
such adverse affects. Mitigation may include, but not be limited to the following: (i) installing
3/26/2021 Ferguson, MO Code of Ordinances
2/5
(c)
(1)
(2)
a.
b.
c.
d.
additional erosion and sediment control; (ii) if the stream has the potential for lateral movement,
installing stream stabilization practices within the stream; (iii) for those sites where vegetation
does not exist, establishing vegetation; and/or (iv) additional tree planting.
Post construction—Water quality. In order to preserve the quality of water in natural streams it is
important to provide a mechanism to remove contaminants on the site prior to water entering
the natural water course. Typically called post construction BMPs (best management practices),
these methods identify a critical water quality volume that will need to receive a treatment to
remove certain contaminants. These improvements whether structural or non-structural will
remain in place after the construction is completed. The concepts introduced in the following
paragraphs are taken from the Georgia Stormwater Management Manual, Volume 2, August,
2001. Nothing in the following paragraphs shall change or replace any of the city's detention
ordinances.
Water quality volume (WQv). The water quality volume (denoted as the WQv) is the storage
needed to capture and treat the runoff from ninety (90) percent of the recorded daily rainfall
events. In numerical terms, it is equivalent to 1.14 inches of rainfall multiplied by the
volumetric runoff coefficient (Rv) and site area. The WQv is directly related to the amount of
impervious cover created at a site. A minimum WQv of 0.2 inches per acre shall be met at all
sites.
Redevelopment projects can appeal to the planning and zoning commission to reduce or
eliminate WQv if it can be shown that there are stormwater enhancements being provided.
As a basis for determining water quality treatment volume the following assumptions may he
made:
The water quality volume WQv for offsite areas is not required. The following equations
are used to determine the storage volume, WQv (in acre-feet of storage):
WQv = [(P)(Rv)(A)]/12
P = 1.14 inches of rainfall
Where: WQv = water quality volume (in acre-feet)
Rv = 0.05 + 0.009(I) where I is percent impervious cover
A = area in acres
Measuring impervious cover: The measured area of a site plan that does not have
vegetative or permeable cover shall be considered total impervious cover.
Multiple drainage areas: When a project contains or is divided by multiple drainage areas,
the WQv volume shall be addressed for each drainage area.
Offsite drainage areas: The WQv shall he based on the impervious cover o the proposed
3/26/2021 Ferguson, MO Code of Ordinances
3/5
e.
f.
g.
(d)
(1)
(2)
a.
b.
(3)
a.
site. Offsite existing impervious areas may be excluded from the calculation of the water
quality volume requirements.
BMP treatment: The final WQv shall be treated by an acceptable BMP(s) from the list
presented in Section 2.
Subtraction for non-structural practices: When non-structural practices arc employed in
the site design, the WQv volume can be reduced in accordance with the conditions
outlined in Section 3.
Extended detention for water quality volume: The water quality requirements can be met
by providing a twenty-four-hour draw down of a portion of the water quality volume
(WQv) in conjunction with a stormwater pond or wetland system.
Acceptable urban BMP options. This section sets forth five (5) acceptable groups of BMPs that can
be used to meet the water quality volume criteria (WQv). The design and selection of these BMPs
should comply with the Georgia Stormwater Management Manual, as prepared by the State of
Georgia.
Where the city's criteria or requirements are more stringent, then they shall govern. Adapting to local
Missouri environment and natural conditions should be expected but shall be as approved by the city or a
higher authority.
The acceptable BMP designs are assigned into six (6) general categories for stormwater
quality control (WQv):
BMP Group 1 - stormwater ponds.
BMP Group 2 - stormwater wetlands.
BMP Group 3 - infiltration practices.
BMP Group 4 - filtering practices.
BMP Group 5 - open channel practices.
See Section 1.3 of the Georgia Stormwater Management Manual for additional BMP options.
Section 3 of the Georgia manual has detailed descriptions of each control.
To be considered an effective BMP for stand-alone treatment of WQv, a design shall he
capable of:
Capturing and treating the required water quality volume (WQv).
Removing eighty (80) percent of the TSS.
A combination of BMPs and/or credits is normally required at most development sites to
meet all three (3) stormwater sizing criteria.
BMP Group 1. Stormwater ponds: Practices that have a combination of permanent pool,
extended detention or shallow wetland equivalent to the entire WQvs include:
3/26/2021 Ferguson, MO Code of Ordinances
4/5
b.
c.
d.
P-1 micropool extended detention pond.
P-2 wet pond.
P-3 wet extended detention pond.
P-4 multiple pond system.
P-5 pocket pond.
BMP Group 2. Stormwater wetlands: Practices that include significant shallow wetland
areas to treat urban stormwater but often may also incorporate small permanent pools
and/or extended detention storage to achieve the full WQv include (Modification of
existing wetland areas will require a Corps 404 permit):
W-1 shallow wetland.
W-2 ED shallow wetland.
W-3 pond/wetland system.
W-4 pocket wetland.
Wetlands shall not he used for control of water quantity (i.e. the flood protection volume).
BMP Group 3. Infiltration practices: Practices that capture and temporarily store the WQv
before allowing it to infiltrate into the soil over a two-day period include:
I-1 infiltration trench.
I-2 infiltration basin.
Infiltration practices will he allowed on sites where it is proven that infiltration will work.
Percolation rates shall be determined for proper use.
BMP Group 4. Filtering practices: Practices that capture and temporarily store the WQv
and pass it through a filter bed of sand, organic matter, soil or other media are
considered to be filtering practices. Filtered runoff may be collected and returned to the
conveyance system. Design variants include:
F-1 surface sand filter.
F-2 underground sand filter.
F-3 perimeter sand filter.
F-4 organic filter.
F-5 pocket sand filter.
3/26/2021 Ferguson, MO Code of Ordinances
5/5
e.
1.
2.
3.
(e)
(1)
(2)
(3)
F-6 bioretention.*
F-7 proprietary filtering system.
* May also be used for infiltration.
A maintenance agreement and maintenance schedule shall be required.
BMP Group 5. Open channel practices: Vegetated open channels that are explicitly
designed to capture and treat the full WQv within the dry or wet cells formed by
creekdams or other means include:
Dry swale.
Wet swab.
Filter strips.
Open channel practices shall he designed with the proper plantings. Wet swales shall be
designed to drain out over time.
When section not applicable. The provisions of this section shall not apply to the extent that any
owner has obtained a variance from such requirements as allowed under subsection (b) of this
section. Additionally, the provisions of this section shall not apply to the extent that the new
construction or development is merely replacement of existing structures which were destroyed
by fire or a natural disaster as long as:
No subdivision of land takes place;
The original structure's footprint, location on the lot and size is not changed; and
No new construction or additions are added beyond mere replacement or rebuilding of the
destroyed structure.
(Ord. No. 2008-3349, § 1, 3-11-08)
Secs. 7-226—7-234. - Reserved.