The periodic flooding of areas within the City of Weatherford results in hazards to life and property, in the disruption of commerce and governmental services, extraordinary expenditures for flood protection and relief, and impairment of the tax base, all of which adversely affect the public health safety and general welfare. Flood and associated losses are caused by the location in flood hazard areas of buildings, structures and uses of land which are inadequately protected from flooding and erosion, and which contribute to flooding by impeding the flow of drainage and by increasing flood heights through displacement of storm water in floodway and flood-fringe areas. (See Article 4, Chapter 4, of this Code).
These regulations and standards are to protect the various portions
of the urban area from flooding, to provide clean and sanitary channels
for runoff, to prevent pollution of watersheds, streams and natural
drainage channels, to prevent the encroachment of buildings and improvements
on natural drainage channels, to equitably apportion the cost of improvements,
to protect natural scenic areas, and to provide for the conservation
of the natural resources of the area.
All subdivisions of land shall comply with the design and improvement
requirements herein established for the protection of flood hazard
areas and the prevention of erosion.
1.
For the purposes of these regulations, drainage shall be classified
as follows:
a.
Surface drainage is runoff of such a limited quantity and/or slow
rate that it does not cause erosion of defined channel.
b.
A minor tributary is any drainage channel having a drainage basin
of 640 acres (one square mile) or less in area.
c.
A major tributary is any channel having a drainage basin of not less
than one square mile or greater than 25 square miles.
d.
A river is any channel having a drainage basin of greater than 25
square miles.
2.
It is intended that responsibility for drainage be allocated as follows,
unless otherwise specifically designated:
a.
The developer of a subdivision is responsible for the following:
(1)
All surface drainage on the subdivision.
(2)
All increase in surface drainage outside the subdivision which
results from the development of the subdivision.
(3)
The improvement of all minor tributaries lying within the subdivision.
(4)
Any significant increase in rate or quantity of runoff in any
minor or major tributary or river which results from the development
of the subdivision.
(5)
Provision for the maintenance of all floodway and flood-fringe
areas of major tributaries and rivers which have not been dedicated
to the public.
1.
Flood Hazard Areas. The designation of flood hazard areas is set
forth on the flood hazard map. The boundaries of all floodway and
flood-fringe areas shall be designated on the preliminary and the
final plat and shall be clearly marked.
2.
Alternative Methods for Determining Stream Flow and Runoff Characteristics.
For all areas not otherwise designated in a floodway or a flood-fringe
area, the developer shall be responsible for having an engineer, registered
in Oklahoma, prepare a drainage assessment of all of the area of the
proposed subdivision, and all area affected by runoff resulting from
development of proposed subdivision in accordance with the following
provisions:
a.
The 100-year maximum flood shall be used as the basis for the sizing
of all drainage channels, bridges and other structures, unless otherwise
specified herein.
b.
The calculation of all runoff shall be based on saturated urbanization
of the drainage basin for minor tributaries and surface drainage,
as reflected in the Comprehensive Plan for the City; and shall be
based on the maximum degree of urbanization, as reflected in the Comprehensive
Plan, for the drainage basin of a major tributary or river.
c.
The calculation of stream flow and runoff characteristics of the
subdivision shall be carried out in consultation with the City Engineer,
and the methodology and formulas used shall result in quantities which
would be not less than those derived from the application of the following
formulas and values:
(1)
Runoff from all drainage areas shall be not less than that determined
by Rational Formula:
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Q = AIR
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Q - Cubic feet per second.
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A - Area to be drained in acres, determined by field
surveys for areas less than 640 acres, and by latest government quadrangle
maps for larger areas.
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I - Percent of imperviousness of the area. This
may vary between 40% and 95% but no value of less than 50% may be
used for saturated urban development.
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R - Rate of rainfall over entire drainage area in
inches per hour, based on time of concentration and latest government
records for area.
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(2)
The size of closed storm sewers, open channels, culverts, and
bridges shall be not less than that determined by using the Manning
Formula:
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1,486 r 2/3 s 1/2 A
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Q
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=
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n
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Q - Discharge in cubic feet per second.
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A - Cross sectional area of water in conduit in square feet.
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r - Hydraulic radius of water in conduit.
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s - Mean slope of hydraulic gradient, in feet of vertical rise
per foot of horizontal distance.
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n - Roughness coefficient, based on condition and type of material
of conduit lining, but not less than 0.013.
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All floodway and flood-fringe areas located within the subdivision
shall be protected and improved by the developer as follows:
1.
All floodways shall be designated as "Flowage Easements" and shall
be maintained as permanent open space for use for private recreation
or agriculture for which no buildings or structures are required,
or dedicated to the public for drainage, recreation and utility use.
2.
All flood-fringe areas shall be planned for uses which are permitted
in the flood-fringe area of the zoning ordinance, and in no case shall
the proposed use or construction cause a displacement of flood water
in the flood-fringe that will increase flooding in other areas of
the floodway or flood-fringe.
3.
When it is determined by the City Engineer that the development of
the subdivision will significantly increase runoff in the flood hazard
area or will otherwise adversely affect storm water runoff, the Planning
Commission may require any or all of the following to the extent needed
to reduce the adverse affects of the development:
a.
The design and installation of storm water detention basins and flow
retardation structures to control the rate of runoff may be required
within or outside the subdivision.
b.
The existing floodway lying within or immediately adjacent to the
subdivision shall be cleaned to provide for the free flow of water,
and the channel shall be straightened, widened, and improved to the
extent required to prevent overflow beyond the limits of the floodway.
c.
Site improvement shall provide for the grading of all building sites
and streets to an elevation where all lots, building areas, and streets
will not be subject to overflow, and in a manner that will provide
for the rapid runoff of all rainfall; however, such improvements shall
be carried out in a manner that will preserve and protect large trees
and attractive physical features of the area.
d.
Whenever channel improvement is carried out, sodding, backsloping,
cribbing, and other bank protecting shall be designed and constructed
to control erosion for all the anticipated conditions of flow for
the segment of channel involved.
e.
A drainage channel shall not be located in a street easement unless
it is placed in an enclosed storm sewer, or unless a paved street
surface is provided on both sides of a paved channel to give access
to abutting properties.
f.
Culverts, bridges, and other drainage structures shall be constructed
in accordance with the specifications of the City at all locations
where drainage channels intersect with continuous streets or alleys.
[Amended 12-29-2004, Ordinance
No. 2004-15; amended 1-30-2018, Ordinance 2018-03]
All minor tributaries and surface drainage located within or
immediately adjacent to and serving the subdivision shall be improved
by the developer, as follows:
1.
All minor tributary channels shall be improved in accordance with
the standards set forth on Figures B, C, D, or E, or other equivalent
standards, as determined by the City Engineer. Sections on Figure
E shall be used only for channels of minor tributaries which drain
less than 80 acres, and which are designed as an integral part of
the landscape of the area so that maintenance of sodded slopes will
be the responsibility of the property owners abutting the channel.
All channels shall be designed to carry a 100-year maximum flood,
shall be designed for self-cleaning and ease of maintenance, shall
have sufficient hard surface along the flow line to prevent ponding
of water, and shall have design characteristics of alignment, materials
of construction and cross-sectioned elements that will be hydraulically
efficient and visually harmonious with the adjacent landscape.
2.
a.
The design and installation of storm water detention basins and flow
retardation structures to control the rate of runoff may be required
within or outside the subdivision. The developer shall furnish to
the City an engineering study determining the amount of water developed
by the proposed subdivision, and to determine whether retention/detention
ponds are necessary to provide for the 100-year flood levels the development
would create.
b.
The areas so provided shall be free from erosion, and shall be properly
sodded all at the expense of the developer.
c.
When the retention/detention pond is completed as required, the developer
shall request and receive an inspection and report by the City Engineer.
d.
Five years after approval; the facility will again be inspected by
the City Engineer, and after any requirements have been met, the property
comprising the retention/detention facility will be conveyed to the
City of Weatherford, which will assume responsibility for maintenance
thereafter.
3.
Enclosed storm sewers may be required by the City Engineer where
special or unusual conditions make open channels hazardous or otherwise
unfeasible.
4.
A drainage channel shall not be located in a street easement unless
it is placed in a closed storm sewer, or unless a paved street surface
is located on both sides of a paved drainage channel to give access
to abutting properties.
5.
Site grading shall be carried out in such a manner that surface water
from each lot shall flow directly to a storm sewer, improved channel
or paved street without crossing more than two adjacent lots.
6.
Surface water collected on streets shall be diverted to storm drains
at satisfactory intervals to prevent overflow of six inch high curbs
during a fifty-year frequency rain for the area and grades involved;
provided; however, that in no case shall the drainage area served
by one street exceed 20 acres, regardless of the amount of flow.
7.
Drainage easements of satisfactory width to provide working room
for construction and maintenance shall be provided for all storm sewers.
In no case shall the total easement be less than 20 feet.
8.
Bridges and Culverts.
9.
Closed Storm Sewers. Closed storm sewers shall be constructed of
precast or prefabricated pipe or built in place of closed box design
to conform with City construction specifications to serve a 100-year
frequency rain for the drainage area involved.
10.
Open Paved Storm Drainage.
a.
Open paved storm drainage channels shall be constructed in accordance
with City specifications.
b.
Side slopes above the paved section shall be shaped and sodded on
a slope of four horizontal to one vertical or flatter.
c.
Fences shall be outside of the 100-year frequency flooding line,
shall not be erected below the shoulder of the sodded section, and
in no case shall fences be closer than six feet (measured horizontally)
to the edge of the paved section, except on Figure C sections.
d.
Hand-laid rip rap may be substituted for sodded shoulders where desired
for landscape purposes.
[1]
Editor's Note: Figures referred to herein may be found as
an attachment to this chapter.
The City reserves the right to require improvements, provisions
of drainage easements, and for provision of agreements beyond the
boundaries of the subdivision to facilitate flow of water through
the addition, to avoid probability of law suits based on damage from
changed runoff in the subdivision, and to provide continuous improvement
of overall storm drainage system.
Requirements outside the addition may include the following:
1.
Improvements may be required in channels or storm sewers flowing
to or from the addition, or in channels or storm sewers located in
adjacent areas that are affected by flow of water from the addition.
2.
The following kinds of improvements may be required:
a.
Enlargement or replacement of undersized drainage structures to provide
free flow.
b.
Removal of obstructions.
c.
Straightening of channel.
d.
Widening or deepening of the channel.
e.
Construction of erosion control structures.
f.
Back sloping, sodding, and/or rip rapping of bank.
g.
Construction of closed or open paved storm sewers for the purposes
of closing gap or continuation of overall storm sewer system.
3.
Property owner agreements, where required, shall be designed to protect
the City from probable law suits for damage caused by changed runoff
condition.
4.
When subdivision development will result in increased runoff beyond
the boundaries of the subdivision which cannot be accommodated through
channel improvements without causing downstream flooding, the City
Planning Commission may require the construction of one or more retention
reservoirs on the subdivision which will temporarily impound and discharge
water from the subdivision site at the rate and volume equivalent
to the discharge from the undeveloped subdivision site. The design
shall be for a 100-year frequency flood. Plans shall be approved by
the City Engineer. The construction and maintenance of retention reservoirs
shall be the responsibility of the developer.
