Sec. 24-68 Stormwater, drainage(a)
(b)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Sec. 24-68. - Stormwater, drainage, storage and treatment requirements.
Topography and grading. All lots and development sites shall be constructed and graded in such a manner
so that the stormwater drains to the adjacent street, an existing natural element used to convey stormwater
(see section 22-303, definitions: Stormwater management system), or a city drainage structure after meeting
onsite storage requirements, as set forth within this section. The city shall be provided with a pre-
construction topographical survey prior to the issuance of a development permit and a post-construction
topographical survey prior to the issuance of a certificate of occupancy. Elevations in all topographic surveys
will be referenced to NAVD 1988. Said surveys shall be signed and sealed by a licensed Florida surveyor.
Except as required to meet coastal construction codes as set forth within a valid permit from the Florida
Department of Environmental Protection; or as required to meet applicable flood zone or stormwater
regulations as set forth herein, the elevation or topography of a development or redevelopment site shall not
be altered.
Onsite storage. Except as provided for herein, an applicant shall be required to provide onsite storage of
stormwater in accordance with this section as follows:
All development and redevelopment projects which result in improvements that exceed fifty (50) percent
of the market value of all improvements, if any, on the subject development parcel before the new
development or redevelopment project is started shall provide onsite storage of stormwater for all
impervious surface on the development parcel.
Projects which do not exceed the fifty (50) percent threshold described in subsection (1) above, but
increase the impervious surface on the development parcel by more than two hundred fifty (250) square
fee shall provide onsite storage of stormwater for the increase in the impervious surface area only.
Projects which do not exceed the fifty (50) percent threshold and increase the impervious surface on the
development parcel by two hundred fifty (250) square feet or less are not required to provide onsite
storage of stormwater; provided, however, as of July 8, 2019, this exemption shall apply one (1) time only
for each development parcel.
Any modification or replacement of driveway and sidewalk areas only on a developed lots shall not be
required onsite storage improvements provided the modification or replacement does not alter the
footprint of the existing driveway or sidewalk area.
Applicants shall provide documentations and calculations to demonstrate compliance with submittal of
applications for construction.
Projects previously permitted by the St. Johns River Water Management District (SJRWMD), which have an
in-compliance existing retention or detention that collects and controls stormwater are exempt for
further onsite storage requirements; provided, however, a copy of the Engineer's Certification of As-Built
Construction to the SJRWMD must be submitted to the city before building permits for individual lot
construction may be issued.
When onsite storage is required, an as-built survey, signed and sealed by a licensed Florida surveyor,
documenting proper construction and required volume of the storage system, must be submitted to and
approved by the director of public works prior to permit closeout or issuance of a certificate of
(8)
(9)
(c)
(d)
(e)
occupancy. For an under-ground system, a notarized letter from the general contractor, along with as-
built plans and construction photographs will be sufficient to document proper construction.
In addition, a declaration of restrictive covenant, in recordable form and approved by the city, identifying
and describing the required on-site storage improvements to be maintained, shall be executed and
recorded in the public records of Duval County, Florida, by the owner of the development parcel and
shall be binding on successors and assigns, prior to permit closeouts or issuance of a certificate of
occupancy.
Volume calculations for any projects that require onsite storage shall be based on the following
calculation:
V = CAR/12, where
V = volume of storage in cubic feet,
A = total impervious area,
R = 25-year and 24-hour rainfall depth (9.3 inches) over the lot area, and ;b21; C = runoff coefficient,
which is 0.92 which is the difference between impervious area (C=1.0) and undeveloped conditions
(C=0.08).
This volume must be stored at least one (1) foot above the wet season water table and below the
overflow point to offsite (in many cases this may be the adjacent road elevation). As an option, and as
approved by the director of public works, an applicant may implement, at the applicant's cost, offsite
storage and necessary conveyance to control existing flood stages offsite, provided documentation
showing appropriate authorization for the off-site use and meeting the requirements of this section is
submitted and approved by the city.
Floodplain storage. There shall be no net loss of storage for areas in a special flood hazard area (100-year
floodplain), where a base flood elevation has been defined by the Federal Emergency Management Agency
(FEMA) on flood insurance rate maps (FIRMs). Site grading shall create storage onsite to mitigate for filling of
volume onsite. This storage is in addition to the storage required for the increase in impervious surface area.
The applicant shall provide signed and sealed engineering plans and calculations documenting that this "no
net loss" requirement is met.
Stormwater treatment. For all new development or redevelopment of existing properties, excluding single-
and two-family uses, where construction meets limits for requiring building code upgrades, stormwater
treatment shall be provided for a volume equivalent to either retention or detention with filtration, of the
runoff from the first one (1) inch of rainfall; or as an option, for facilities with a drainage area of less than one
hundred (100) acres, the first one-half (½) inch of runoff pursuant to Chapter 62-330, Florida Administrative
Code (FAC). No discharge from any stormwater facility shall cause or contribute to a violation of water quality
standards as provided in Section 62-302, FAC. This treatment volume can be included as part of the onsite
storage requirement in item d(2) [subsection (b)] of this section.
NPDES requirements. All construction activities shall be in conformance with the city's National Pollutant
Discharge Elimination Systems (NPDES) permit, in addition to the requirements of the St. Johns River Water
Management District and the Florida Department of Environmental Protection. NPDES requirements include
(f)
(g)
use of best management practices (BMPs) prior to discharge into natural or artificial drainage systems. All
construction projects of one (1) acre or more require a stand-alone NPDES permit. Site clearing, demolition
and construction on any size site may not commence until site inspection and approval of the proper
installation of a required best management practices erosion and sediment control plan is completed.
Enforcement. Subsequent to approval of a property owner's final grading, including onsite and/or floodplain
storage and stormwater treatment and closeout of the applicable permit or issuance of certificates of
occupancy, the improvements shall be maintained by the property owner. In order to ensure compliance
with the provisions of this section and the requirements to maintain onsite stormwater improvements over
time, the city is authorized to conduct inspections of property, upon reasonable notice and at reasonable
times, for the purpose of inspecting said property and/or onsite storage improvements for compliance with
this section and with any applicable conditions of previously issued permits. Failure to maintain the
improvements will require restoration upon notification by the director of public works, within a stipulated
time frame. If restoration is not timely completed, the city shall have the right to complete the restoration,
and the city's actual cost incurred, together with a charge of one hundred (100) percent of said costs to cover
the city's administrative expenses, shall be charged to the then owner of the property.
Variances to impervious surface area limits. Variances to impervious surface limits shall be subject to the
provisions in section 24-65. Impervious surface requirements shall not be eligible for relief via waivers from
the city commission.
(Ord. No. 90-10-212, § 2(Exh. A), 3-8-10; Ord. No. 90-19-240 , § 3(Exh. A), 7-8-19)