Stormwater drainage improvements shall be provided for the subdivision
or addition. Stormwater impacts resulting from new development must
not adversely affect any properties, including those abutting, downstream,
and in upstream areas. Stormwater drainage facilities shall be designed
by an engineer licensed to practice in State and in compliance and
in accordance with this chapter, the design and construction standards,
and generally recognized and accepted engineering practices. Privately
maintained stormwater drainage facilities including channels and swales
located outside a public easement shall follow all requirements of
the drainage design and construction standards, with exceptions for
the following components: pipe material, pipe size, junction structures,
inlets, roof drains, and minimum depth requirements. Variations to
the aforementioned components shall not violate the International
Plumbing Code, with local amendments, and must be approved by the
city engineer variations are not permitted for any residential use.
(1)
The ultimate 4% and ultimate 1% annual chance floodplains shall
be determined for watercourses draining 50 or more acres. Calculations
for floodplains shall utilize generally recognized backwater computational
methods and actual field channel and overbank configuration.
(2)
At a minimum, all stormwater drainage facilities shall be engineer-designed
to intercept and transport the projected runoff from a 4% annual chance
event. In addition, those flows greater than a 4% annual chance event
up to and including a 1% annual chance event shall be contained within
private streets, public streets, drainage easements, or a combination
thereof.
(3)
All stormwater drainage facilities shall be designed to prevent
the erosion of existing and proposed on-site and off-site facilities.
(4)
Projected runoff rates for the design and analysis of stormwater
drainage facilities shall be based on the expected ultimate developed
state of the upstream contributing area and shall apply to any and
all references to floodplain, flows, design frequencies or any other
hydrologic and hydraulic reference found in this article.
(5)
The requirements provided in this article shall not relieve
the owner of responsibility under state law to adjacent, upstream,
and downstream property owners.
(6)
The requirements provided in this article are in addition to
Unified Development Code Stormwater and Drainage Standards, in the
event that there are conflicting requirements, the more stringent
requirements shall apply.
(Ordinance O-2023-052 adopted 8/3/2023)
(a)
On-site detention facilities.
Except as stated
herein, all development establishing impervious cover or otherwise
modifying an existing site shall incorporate on-site drainage facilities
to prevent any increase in the peak rate of runoff from storm events
having a 50%, 10%, 4%, 2%, and 1% chance of occurring each year. The
city engineer may modify this requirement under either of the following
circumstances:
(b)
Regional stormwater management program.
(1)
Participation.
In lieu of required on-site or
off-site detention facilities, a developer may request to participate
in the regional stormwater management program. The city engineer may
accept a tract of land in the regional stormwater management program
if the proposed development, including any off-site improvements will
not result in additional identifiable adverse flooding of other property.
A comprehensive engineering report providing engineering data and
calculations which fully describe and justify participation in the
program shall accompany all participation requests.
(2)
Fees.
Regional stormwater management program fees
are indicated in the city's fee schedule.
(A)
Adjustment of these fees may be allowed by the
city engineer, in consultation with the utilities director, if it
is determined that certain impervious coverage restrictions, (e.g.,
special watershed ordinances), reduce the actual land use. However,
the minimum fee shall not be less than $800.00/acre.
(B)
Upon approval of participation, the full fee will
be due prior to approval of construction plans for single-family projects
and upon building permit approval for multifamily, commercial, and
industrial projects.
(Ordinance O-2023-052 adopted 8/3/2023)
(a)
Sealed engineered plans for proposed drainage facilities shall
be submitted to the city engineer for acceptance prior to construction.
(b)
Computations for all drainage-related design shall be submitted
with the application for either a site development permit or subdivision
improvement permit. Data submitted shall include a drainage area map,
a summary of methodology employed and resulting data, land use and
runoff coefficient assumptions and other pertinent hydrologic and
hydraulic data. Additional data may be required by the city engineer.
(c)
Certification shall be submitted by an engineer licensed in
the state that the plans and computations are in compliance with the
requirements of this article.
(d)
Following construction, but prior to acceptance of improvements
by the city, the design engineer shall furnish certification that
based upon his or her periodic inspection of the work all improvements,
including those covered by this section, have been constructed in
compliance with the city's requirements.
(Ordinance O-2023-052 adopted 8/3/2023)
(a)
Preliminary and final plats for additions or subdivisions shall
show the limits of the ultimate 1% annual chance floodplain for all
waterways draining 50 or more acres by hatch marking said floodplain
on the plat. In addition, all preliminary and final plats shall show
the limits of zones A and AE as depicted on the Federal Emergency
Management Agency (FEMA) flood insurance rate map (FIRM), if such
zones fall within the boundaries of the plat.
(b)
The final plat of any proposed addition or subdivision showing
the limits of the ultimate 1% annual chance floodplain shall contain
the following plat note:
"No fences, structures, storage or fill shall be placed within
the limits of the ultimate 1% annual chance floodplain unless approved
in accordance with city ordinances."
(c)
The final plat of any proposed addition or subdivision containing
any property within SF-R, SF-1, SF-2, SF-3, SF-D, TF or TH zoning
districts, or single-family condominiums or detached townhomes contained
within a planned unit development, shall provide public right-of-way,
drainage easements or separate lots dedicated for such purposes, as
approved by the city, to cover at a minimum the ultimate 1% annual
chance floodplain areas, drainage channels, pipe systems, and any
other related drainage facilities. All other final plats shall provide
drainage easements or separate lots dedicated for such purposes, as
approved by the city, to cover at a minimum the ultimate 4% annual
chance floodplain areas, drainage channels, pipe systems and any other
related drainage facilities.
(d)
If any lot is adjacent to the ultimate 1% annual chance floodplain,
the final plat shall establish minimum finished floor elevations (MFFE)
for all such lots at two feet above the ultimate 1% annual chance
floodplain elevation.
(1)
For single-lot plats containing multiple foundations, a separate
exhibit shall be provided prior to recordation indicating the MFFE
for each proposed slab adjacent to the ultimate 1% annual chance floodplain.
(e)
The final plat shall contain a statement by an engineer certifying
the easements, slab elevations and any other drainage related notes
are in compliance with this article.
(f)
No portion of any land located in the ultimate 1% annual chance
floodplain shall be counted toward the minimum lot area requirement.
(g)
For final plats that have been approved by the planning and
zoning commission (P&Z) prior to October 1, 2020, re-delineation
of floodplain limits and MFFE on the approved final plat, due to adoption
of Atlas 14 rainfall data, shall not be required as long as the final
plat does not expire prior to recordation with the county. P&Z
approval of a preliminary plat shall not vest floodplain or MFFE delineation
for a subsequent final plat application.
(Ordinance O-2023-052 adopted 8/3/2023)
(a)
No channel modifications shall be undertaken within the area
of the ultimate 1% annual chance floodplain without permission of
the city engineer. Such permission shall be based upon certified engineering
data and calculations furnished by the proposing permittee.
(b)
All constructed or modified earthen channels shall be designed
utilizing a side slope of 4:1, or flatter, to allow for future maintenance
and promote adequate slope stability.
(Ordinance O-2023-052 adopted 8/3/2023)
(a)
All street sections shall be in accordance with city standards
with an allowable design drainage capacity for gutter flow no deeper
than the top of the curb.
(b)
Depth of flow in streets is to be controlled to allowable levels
by modification of crossfall, gradient changes, or the use of curb
inlets and storm sewers.
(c)
Curb inlets shall be spaced as required to control flow in streets
to allowable levels and placed to minimize interference of runoff
to traffic flow, particularly at intersections.
(d)
All storm sewer pipe shall be reinforced concrete, minimum size
18 inches diameter, and installed in compliance with the city's standard
specifications for public works construction for the city.
(Ordinance O-2023-052 adopted 8/3/2023)
(a)
All bridge or culvert structures shall be designed to carry
and/or store the upstream runoff from a 4% annual chance event.
(b)
Runoff from the 1% annual chance event may overtop the road
surface at bridge or culvert crossings a maximum of six (6) inches
for a major or collector street crossing, and a maximum of 17 inches
on a minor or residential street crossing.
(Ordinance O-2023-052 adopted 8/3/2023)
(a)
Plans submitted for building permits other than single-family
residential or duplex construction shall include the necessary drainage-related
facilities designed and provided for in compliance with this article
and the drainage criteria manual.
(b)
Plans and design calculations for all drainage facilities shall
be submitted to the city Engineer for review and approval prior to
issuance of the building permit.
(c)
The design engineer shall certify that the plans and calculations
for all drainage facilities are in compliance with the ordinances
of the city.
(d)
Following construction, but prior to issuance of a certificate
of occupancy, the design engineer shall certify that the public works
improvements, including those covered by this section, have been constructed
in compliance with the city's requirements based on his/her inspection
of the completed work.
(Ordinance O-2023-052 adopted 8/3/2023)
