[Ord. No. 2994 §1, 3-15-2005]
A. Stormwater
management plans shall be submitted to the City Engineer or his/her
designated representative by the owner of any proposed residential,
commercial or industrial development within the City unless the City
Engineer waives such requirement in writing for one (1) of the following
reasons:
1. Off-site facility, two (2) or more developments. If two (2) or more developments, including that of the applicant,
have provided for a common system.
2. Off-site facility by City. If an off-site stormwater management system has been either constructed or programmed or identified for construction by the City or if, as a result of the topographical conditions present at the development site, there exists in the opinion of the City Engineer a suitable natural retention area and the applicant has agreed to either contribute to a stormwater management fund or participate in the construction of an off-site system as part of a City project. The applicant must agree in writing to contribute to the City fund in accordance with Subsection
(4) hereof.
3. Other management techniques. Management techniques
other than detention facilities may be utilized by the development
provided the techniques proposed meet the intent of this Chapter and
provide a benefit to the watershed that equals or exceeds the benefit
that a detention facility would provide.
4. Stormwater Management Fund. A Stormwater Management
Fund is hereby created and established by City. Said fund shall be
used exclusively by City for programs and projects designed to help
control the effects of stormwater within the City limits. Any contribution
made by an applicant in lieu of constructing an on-site facility shall
be deposited into said fund with any interest income on such funds
to remain a part of such fund. In order to participate in such find,
the following shall apply:
a. Eligibility. It is determined that no adverse effects
will result to adjacent property, and a contribution is made to the
Stormwater Management Improvements Fund. Residential development of
four (4) acres or less and commercial/industrial developments of two
(2) acres or less will be considered as prime candidates for a contribution
in lieu of on-site detention. It is the City's desire that regional
detention storage be utilized to accommodate these smaller developments.
b. Contribution. The contribution shall be an amount
equal to a cost estimate prepared by a professional engineer for site
specific improvements necessary to provide detention as provided herein.
All cost estimates for site specific detention facilities shall be
subject to review and approval by the City Engineer. The cost estimate
must include the value of the land which otherwise would have been
used as part of the system with the value of the subject land determined
by an independent appraiser paid for by the developer. Alternatively,
the procedure detailed in Appendix "A", a copy of which is on file
in the City offices, can be used to determine contribution.
[Ord. No. 2994 §1, 3-15-2005]
A. Sediment
and erosion control on any new development in the City shall be accomplished
by applying conservation practices that will reduce the potential
for damage from these hazards. Control practices use trapping, filtering
or diversion techniques to protect adjacent properties from land disturbance
activities.
1. When controls are required. Standard vegetative
and structural practices, as specified below, that filter, divert
or promote the settlement of sediment particles from storm runoff
shall be provided in the following situations:
a. To prevent sediment-laden runoff from leaving disturbed areas.
b. To isolate disturbed areas from erosive surface runoff associated
with significant undisturbed areas.
c. To protect storm drainage conveyance systems at operable inlets.
2. Types of controls. Acceptable sediment and erosion
controls shall be either vegetative or structural as described below.
a. Vegetative practices.
(1)
Topsoiling. Stockpiling of topsoil to enhance
final site stabilization with vegetation shall be done in such a manner
that natural drainage is not obstructed, and no off-site sediment
damage results.
(2)
Seeding. Of the rate and type to produce a
dense vegetation.
(4)
Mulching. The application of grass, hay, wood
chips, wood fibers, straw, gravel or other suitable material to the
soil surface. Seeded and planted areas where slopes are steeper than
4:1 (four (4) feet horizontal for every one (1) foot vertical) shall
be stabilized with mulch.
b. Structural practices.
(1)
Construction entrance. A rock stabilized pad
located at points of vehicular ingress and egress on a construction
site.
(2)
Straw bale barrier. Shall be placed on downslope
areas to intercept sediment or to reduce flow velocity. Straw bale
barriers shall not be constructed in streams or swales where there
is the possibility of washout.
(3)
Silt fence. Sediment shall be removed when
it reaches one-third () to one-half (½) the height of
the filter fence.
(4)
Storm drain inlet protection. May consist of
filter fabric, sand bags, excavated gravel, straw bale, block and
gravel, and any combination of the above.
(5)
Diversion swale or dike. These may be used
to intercept runoff and divert to a sediment control device around
a disturbed area, or to an area where it can be safely released.
(6)
Sediment trap. Is a small storage or detention
area used to detain construction runoff long enough to allow the larger-sized
sediment particles to settle out before the runoff is released to
downstream areas.
(7)
Temporary sediment basin. Performs the same
function as a sediment trap, although it has a greater volume and
is located below disturbed areas generally greater than five (5) acres.
They shall be sized to provide a minimum volume of three thousand
six hundred (3,600) cubic feet per disturbed acre draining to the
facility.
(8)
Temporary slope drain. May be plastic sheets,
metal or flexible pipe, stone, gutter, fiber mats, concrete or asphalt
ditches, or half round pipe to carry runoff from one elevation to
a lower elevation without excessive erosion of the slope.
(9)
Check dam. May be constructed of logs or stone
across a swale or drainage ditch to reduce the water's velocity and
to trap small amounts of sediment.
(10)
Level spreader. An excavated depression to
convert a concentrated flow to a sheet flow, allowing water to be
released at less erosive levels.
3. Construction plans. A contoured development map
must be submitted with all preliminary plans which clearly indicates
the pattern of surface water runoff, both upstream and downstream
of the development. The type of sediment and erosion control to be
utilized shall be clearly indicated. The City Engineer or his/her
designated representative shall have authority to require proper controls
as specified herein.
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All required plans and maps are submitted by the owner or applicant
to the City Engineer or other qualified professional in order to determine
that all technical requirements of this Chapter have been met.
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[Ord. No. 2994 §1, 3-15-2005]
A. Purpose. A development's stormwater drainage system shall
be designed to:
1. Protect natural waterways.
2. Convey upstream and on-site stormwater runoff to a natural watercourse
or to a storm drainage facility.
3. Provide protection from the design storm event and address the major
storm so as to prevent major property damage and loss of life.
B. All
systems shall conform to the Storm Water Master Plan. All structures
and systems that are to be constructed that share common elements
with the Storm Water Master Plan must be designed to accommodate the
requirements stated or suggested by the Storm Water Master Plan.
C. Rainfall Frequency. All facilities shall be designed to
carry a 25-year storm of a duration which produces the maximum peak
flow rate of stormwater runoff, without inundation or surcharging
for drainage basins of four hundred (400) acres of loss. For larger
drainage basins, the design storm shall be the 100-year storm of a
duration which produces the maximum peak flow rate. The City Engineer
may require a different design storm if, in the opinion of the City
Engineer, a public health or safety issue would exist otherwise. All
systems shall be designed to allow for a 100-year storm to pass through
the development without destroying or damaging property or inundating
dwellings. Design information which substantiates both conditions
shall be provided.
D. Calculation Of Runoff.
1. The method of calculating and routing stormwater runoff shall be
a generally accepted stormwater management practice. The drainage
area shall consider all on- and off-site lands contributing to the
proposed development's drainage system. Capacity for such facilities
shall be based on the maximum potential water shed development permitted
by this Chapter.
2. The rational method for calculating stormwater runoff may be used
for developments up to one hundred fifty (150) acres. Other common
rainfall runoff calculation methods that may be utilized include graphical
peak discharge, tabular, and the synthetic unit hydrograph. For development
greater than one hundred fifty (150) acres, the method must be approved
by the City Engineer.
3. Runoff coefficient. The runoff coefficient "C" is
the variable in the Rational Formula least susceptible to precise
determination and the one, which requires the greatest exercise of
engineering judgment because of the many area characteristics, which
affect the coefficient.
Among the factors to be considered in influencing the runoff
coefficients are the following: present and future zoning; terrain;
local ponding or depressions; the amount of pavement; roofs, turf,
and other areas having different degrees of imperviousness.
The selection of coefficient should take into consideration
the probable ultimate development of presently underdeveloped areas.
Suggested values of runoff coefficients are included in the following
table:
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SUGGESTED RUNOFF COEFFICIENTS "C"
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"C" Value
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Surface Conditions
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.10 — .15
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Tall grass, brush
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.15 — .20
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Parks, golf courses, farms and on-acre, single-family residences
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.35
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Single-family residences on lots of not less than 15,000 square
feet
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.45
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Single-family residences on lots of not less than 10,000 square
feet
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.47
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Single-family residences on lots of not less than 7,500 square
feet
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.51
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Single-family residences on lots of not less than 6,000 square
feet
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.90
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Gravel surfaces
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.95
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Asphalt and concrete surfaces
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1.00
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Buildings and other structures.
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4. Rainfall intensity. The average frequency of rainfall
occurrence used for design determines the degree of protection afforded
by a drainage system.
Maximum intensity of rainfall of a given expectancy is greater
for a short period of time than for longer periods. Therefore, it
is assumed that the maximum runoff will occur as soon as all parts
of the drainage area under consideration are contributing. The length
of time from the beginning of rainfall until runoff from the most
remote point in the drainage area reaches the point under consideration
is called the time of concentration. This may include overland flow
time and channel or gutter flow time. Once the time of concentration
is known, the design intensity rainfall may be determined from the
rainfall intensity curves developed from the Weather Bureau data.
5. Special uses, such as schools, churches, etc., shall have the differential
runoff computed and approved by the City Engineer.
6. Special circumstance may dictate that the developed impervious area
may differ from that shown in the above table. An example may be single-family
lots of larger than fifteen thousand (15,000) square feet. Calculations
prepared by a licensed professional engineer may be submitted to the
City Engineer or his/her designated representative for his/her evaluation
to determine if a minimum impervious area which differs from that
shown in the above table may be utilized. Likewise, the City Engineer
or his/her designated representative may determine that the percent
of impervious area for a particular development differs from that
shown in the above table.
E. Open Channels. Open channels consist of swales, ditches
or depressions, both natural and manmade, that convey water. Channels
shall be protected from scour and erosion by providing a channel lining
adequate to sustain the velocity of the design storm. If velocities
in channels exceed three and one-half (3.5) feet per second during
the design storms, then erosion control other than vegetation shall
be provided in channel construction. Channels shall have the hydraulic
capacity to carry the design storm runoff within the channel bed and
banks with one (1) foot of freeboard. Out of bank flow may be permitted
on land slopes parallel to the channel where it can be shown that
no erosion damage or property damage will result. Channels that function
as part of the major drainage system shall be evaluated for the 100-year
design storm to determine the impacts of runoff on adjacent property.
The channel's hydraulic capacity shall be increased where adjustments
to channel geometry provide significant protection to adjacent properties
during the 100-year event.
F. Closed Conduit Storm Sewers.
1. Pipe sizes for closed conduit flow shall be based on the design storm
runoff and minimum allowable velocities. The system shall provide
for the clearing of sediment and other deposits by maintaining a minimum
velocity of two (2) feet per second during the 2-year storm.
2. Manning's Equation is the most common method of estimating the capacity
and flow resistance in closed conduits, although the Kutter, Hazen-Williams,
and Darcy Weisbach formulas are also acceptable.
3. All drainage and storm sewer systems shall be designed and constructed
in accordance with standards and specifications of the City. All facilities
shall be designed to carry a 25-year storm while maintaining a minimum
of one (1) foot of freeboard between the hydraulic grade line and
the gutter. The developer's engineer shall verify that the 100-year
storm may be contained in the road right-of-way and/or in a dedicated
drainage easement. The engineer shall provide a storm water report
to document meeting those requirements.
4. Generally, pressure flow occurs where the capacity of pipe run exceeds
the design flow and the outfall point does not control discharge.
Storm sewer systems may be designed for pressure flow when the hydraulic
grade line is above the crown of the pipe. The decision to design
a pressure flow system may be based on aesthetics, the need to submerge
outfalls, economics, limitations associated with reduced pipe sizes,
or grade constraints in outfalling the system.
G. Inlets. Calculations shall be submitted to demonstrate the
capacity of all inlets, such calculations must consider the cross-slope
of the pavement, depth of water at the curb face, size of opening,
and the longitudinal grade of street. Street inlets and inlets in
parking areas shall reduce the spread and depth of flow to acceptable
levels during the 25-year design storm. Inlets located on continuous
grades may be designed to permit a portion of flow to bypass the structure;
however, calculations for the downstream structure must consider the
bypass. Street flow shall be limited by pavement encroachment and
depth of flow as follows:
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Street Classification
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* Maximum Encroachment of a 2-year Storm
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Local
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No curb overtopping. Flow may spread to crown of street.
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Collector
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No curb overstopping. Flow may leave the equivalent of one (1)
10-foot driving lane clear of water.
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Arterials
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No curb overtopping. Flow spread must leave the equivalent of
two (2) 10-foot driving lanes clear of water. One (1) lane in each
direction.
* Where no curbing exists, encroachment shall not extend past
property lanes.
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The storm sewer system shall commence at the point where the
volume of flow equals five (5) cfs.
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Street Classification
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Allowable Depth and Inundated Areas 100-year Storm
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Local and Collector
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Residential dwellings, public, commercial and industrial buildings
shall not be inundated at the ground line. The depth of water over
the gutter flowline shall not exceed eighteen (18) inches.
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Arterials
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Residential dwellings, public, commercial and industrial buildings
shall not be inundated at the ground line. Depth of water at the street
crown shall not exceed six (6) inches to allow operation of emergency
vehicles. The depth of water over the gutter flowline shall not exceed
eighteen (18) inches.
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H. Plans And Calculations.
1. A drainage map shall be developed from a base reproduction of the
site plan or grading plan. The existing and proposed contours shall
be shown, of suitable scale and two (2) foot contour interval for
the subject property, extending off-site one hundred (100) feet or
less as determined by the City for proper design of the proposed improvements.
Contour intervals other than the above shall be used as determined
by the site topography.
2. The location of existing and proposed property lines, streets, sinkholes,
railroads, areas within the tract subject to inundation by stormwater
and other significant natural features, such as wooded areas and rock
formations, etc., shall be included on the map. All existing and proposed
stormwater facilities, such as inlets, manholes, pipes, culverts,
bridges, channels, etc., and all existing and proposed improvements
required for property design review, such as pavement, buildings,
etc., shall be included on the map.
3. The location of streams and other floodwater runoff channels, calculations
supporting the method and capacity needed for the safe and temporary
storage of increased runoff resulting from the proposed development.
4. Basic information regarding the receiving watercourse into which
the proposed stormwater system will discharge. This information should
include a general cross section and existing downstream culverts,
bridges, and other waterway openings.
5. The runoff details shall be required, showing individual flows for
each existing and proposed structure and cumulative flows in pipes
and gutters, including "Q" and area. The map shall show all bodies
of water, such as ponds or lakes (including surface area and elevation),
and all waterways (including their names or the names of creeks or
rivers they flow into).
6. Lots shall be laid out so as to provide positive drainage away from
all buildings. Individual lot drainage shall be shown and coordinated
with the drainage pattern for the area and designed so that runoff
from one (1) lot will not adversely affect an adjoining lot. All necessary
grading to direct stormwater runoff shall be located within a drainage
easement. A layout of the proposed stormwater management system including
the location and size of all drainage structures, storm sewers, channels,
channel sections, detention basins, and analysis regarding the effect
said improvements will have upon the receiving channel and its high
water elevation.
7. All computations, plans and specifications related to the implementation
of this Chapter must be prepared and sealed by a professional engineer
registered in the State.
[Ord. No. 2994 §1, 3-15-2005; Ord. No. 3362 §1, 9-15-2009]
A. The
rates (pre-developed and post-developed) of runoff shall be determined
for the 2-, 10-, 25- and 100-year rainfall frequencies. The minimum
storm duration shall be twenty (20) minutes.
B. Stormwater
shall be detained on site or on adjacent property under agreement
and metered out at the rate of an undeveloped site for the above frequencies
and minimum duration to prevent possible flooding and erosion downstream.
C. In
the event the natural downstream channel or storm sewer system is
inadequate to accommodate the release rate provided above, then the
allowable release rate shall be reduced to that rate permitted by
the capacity of the downstream channel or storm sewer system.
D. Detention
basin volume will be based on routing all post-developed runoff through
the detention facility while satisfying the appropriate allowable
release rate.
E. No
credit will be given for existing impervious area, regardless of age
or character or reuse of any existing improvements.
1. Exception for existing structures. Additions to
existing structures that were constructed prior to detention requirements,
that increase the gross area of the existing structure by fifty percent
(50%) or less will only require detention for the addition and any
additional impervious surface added for the addition such as parking.
This exception shall also apply when redeveloping a parcel. If fifty
percent (50%) or less of the existing building is razed and rebuilt,
then only that portion and required impervious area such as parking,
will require detention. If more than fifty percent (50%) of the building
is razed or if more than a fifty percent (50%) addition is added,
then detention will be required for the entire site calculated as
if the site was undeveloped. This analysis shall be presented by the
developer for acceptance by the City Engineer. This shall apply to
detention, retention or payment in lieu of construction of detention.
[Ord. No. 2994 §1, 3-15-2005]
A. Dry Bottom Basins. Dry bottom basins may be constructed
to temporarily detain the stormwater runoff so that the rate at which
it is released is the same rate as before development. The following
features shall be incorporated into the design of any detention basin:
1. Freeboard. Detention storage areas shall have adequate
capacity to contain the storage volume of tributary stormwater runoff
with at least one (1) foot of freeboard above the water surface for
a 100-year storm event.
2. Outlet control works. Outlet works shall be designed
to limit peak outflow rates from detention storage areas to below
peak flow rates that would have occurred prior to the proposed development.
Outlet works shall not include any mechanical components or devices
and shall function without requiring attendance or control during
operation, unless specifically approved by the City Engineer or his/her
designated representative.
3. Emergency overflow/spillway. Emergency structures
shall be provided to permit the safe passage of runoff generated in
excess of the design storm event. Antivortex measures shall be provided
along with the design plan.
4. Maximum depth. The maximum planned depth of stormwaters
stored shall not normally exceed five (5) feet.
5. Side slopes. The maximum side slopes for grassed
basins shall not normally exceed one (1) foot vertical for three (3)
feet horizontal.
6. Limits of ponding. In no case shall the limits of
maximum ponding be closer than thirty (30) feet horizontally from
any building and less than two (2) feet vertically below the lowest
sill elevation.
7. Interior drainage. The basin bottom should be designed
to drain expeditiously. Flows through the detention basin should be
handled by paved ditch from inflow structure to outflow structure
to minimize erosion.
8. Multipurpose basins. If the detention basin is to
have other uses, the design of the basin bottom should include underdrains
to expedite drying of the bottom between runoff events.
9. Aesthetics. Designs should result in aesthetically
pleasing configurations which will enhance public acceptability.
B. Retention Basins. All such privately owned and maintained
systems shall be subject to periodic inspection by the City Engineer
or his/her designated representative. Wet bottom basins may also be
used to temporarily detain the differential runoff from the development.
In addition to the general design features enumerated above for dry
bottom basins, the following features should also be incorporated
into the design of any wet bottom basin:
1. Normal pool depth. In order to manage weed growth,
the normal pool depth should be four (4) feet minimum.
2. Depth for fish. If fish are to be kept in the pond,
at least one-quarter (¼) of the area of the permanent pool
should have a minimum depth of ten (10) feet.
3. Facilities for emptying. In order to ease cleaning
of the pond or shoreline maintenance, the pond design should include
provisions for emptying the pond.
4. Low flow bypass. The design of any pond may include
a low flow bypass channel or pipeline to divert runoff that can be
accommodated by downstream drainageways.
5. Side slopes below normal pool. The side slopes below
the normal pool elevation may exceed the maximum side slope permitted
above normal pool (3:1 slope). The design shall, however, include
provisions for a safety ledge having a depth of water not greater
than three (3) feet immediately adjacent to the shoreline.
6. Permanent pool volume. The permanent pool volume
in a wet basin at normal depth should be equal to the runoff volume
from its watershed for the 2-year event.
C. Detention In Flood Fringe Areas. The placement of a detention basin in a flood fringe area shall require compensatory storage for one and one-half (1.5) times the volume below the base flood elevation occupied by the detention basin including any berms. The release rate from the detention storage provided shall still be controlled consistent with the requirements of Section
410.080. The applicant shall demonstrate its operation for all streamflow and floodplain backwater conditions. Excavations for compensatory storage along streams and watercourses shall be opposite or adjacent to the area occupied by detention. All floodplain storage lost below the 25-year flood elevation shall be replaced below the 25-year flood elevation. All floodplain storage lost above the existing 25-year flood elevation shall be replaced above the proposed 25-year flood elevation. All compensatory storage excavations shall be constructed to drain freely and openly to the watercourse.
D. Rooftop Storage. Detention storage may be met in total or
in part by detention on roofs. Details of such design, which shall
be included in the building permit application, shall include the
depth and volume of storage, details of outlet devices and downdrains
and elevations of overflow provisions. Direct connection of roof drains
to sanitary sewers is prohibited.
E. Parking Lot Storage. Paved parking lots may be designed
to provide temporary detention storage of stormwater on all or a portion
of their surfaces. Outlets will be designed so as to slowly empty
the stored waters and depths of storage must be limited so as to prevent
damage to parked vehicles.
F. Other Detention Methods. All or a portion of the detention
storage may also be provided in underground or surface detention facilities
to include basins, tanks or swales, etc. Emergency overflow conditions
shall be considered in all methods.
G. Detention Basins In Floodways. Detention basins shall not
be placed in the floodway.
[Ord. No. 2994 §1, 3-15-2005]
A. Storm
pipes shall be protected from excessive bearing pressures by placing
them outside the forty-five degree (45°) influence zone of building
structures unless an engineer's calculations show the pipe material
or soil condition to be adequate for the subjected load.
B. Pipes
on twenty percent (20%) slopes or greater shall be anchored securely
with concrete anchors or their equal to prevent the pipe from creeping
downhill.
C. Pipes
or structures constructed on fill shall be stable and protected against
settlement by compacting fill material to ninety-five percent (95%)
of the modified proctor maximum dry density.
D. Pipes
thirty-six (36) inches or larger may be placed on a curved alignment
utilizing alignment radii established by the pipe manufacturer.
E. The
receiving surface where pipes discharge shall be protected from erosion
by evaluating the discharge velocity for the 25-year design storm.
The use of energy-dissipating devices may be necessary to reduce the
velocity to acceptable levels for the receiving surface. The energy-dissipating
device used shall be a minimum length of ten (10) times the diameter
of the discharge pipe.
F. A manhole,
inlet or junction box shall be located at changes in pipe size, grade,
alignment or material.
G. The
angle between influent and effluent pipes shall be not less than ninety
degrees (90°), and the drop between inverts shall be not less
than one-tenth (0.1) foot.
H. Manhole
and inlet castings located in travelways shall be capable of withstanding
traffic loads and shall be constructed flush with the finished surface.
I. All
materials and appurtenances for stormwater management systems shall
conform to current standards of the American Society for Testing and
Materials (ASTM).
J. Manholes
shall be pre-cast or cast-in-place concrete with concrete risers and
approved manhole covers.
K. A new
drainage channel or pipe shall intersect an existing drainage channel
at a maximum angle of sixty degrees (60°).
L. All
trenches under roadway pavement shall be backfilled with MHTD Type
I aggregate in six (6) inch layers and compacted to ninety-five percent
(95%) of the modified proctor maximum dry density.
M. All
piping shall be bedded per the manufacturer's requirements.
N. Grated
inlets will not be allowed without special approval by the City Engineer.
O. All
materials used in the construction of storm sewers shall be subject
to inspection and approval of the City Engineer or his/her designated
representative.
P. Acceptable
pipe material shall be reinforced concrete pipe, corrugated metal
pipe and corrugated polyethylene pipe. Reinforced concrete pipe shall
conform to the requirements of the Specifications for Reinforced Concrete
Culvert, Storm Drain and Sewer Pipe, ASTM C76. Strength class or classes
shall be as required per design specifications of the latest edition
of the Concrete Pipe Handbook as published by the American Pipe Association.
Q. Corrugated
aluminized metal pipe shall conform to the appropriate requirements
of AASHTO or Missouri Department of Transportation. Structural design
requirements shall be per the latest edition of the Handbook of Steel
Drainage and Highway Construction Products as published by the American
Iron and Steel Institute. Use of corrugated metal pipe greater than
forty-eight (48) inches in diameter shall only be allowed after approval
by the City Engineer.
R. The
City Engineer may consider for approval a written request to use other
types of pipe. Corrugated polyethylene pipe shall conform to the requirements
of AASHTO M294, "Standard Specifications for Corrugated Polyethylene
Pipe". All polyethylene pipe should be installed according to ASTM
D 2321, "Standard Practice for Underground Installation of Thermoplastic
Pipe for Sewers and Other Gravity-Flow Applications". Use of thermoplastic
pipe in all locations shall be allowed only after approval by the
City Engineer.
S. Reinforced
concrete pipe shall be required under road pavement, unless other
material is approved by the City Engineer.
T. All
construction details pertaining to stormwater drainage shall be in
accordance with the City and State requirements, unless otherwise
noted herein.
[Ord. No. 2994 §1, 3-15-2005]
A. Whenever
the stormwater analysis presented by the developer and accepted by
the City Engineer shows that detention provides no significant benefit,
the developer may apply for a buyout of the required detention volume.
The cost is shown in the application in Appendix "A", a copy of which
is on file in the City offices. Whenever the stormwater analysis shows
that detention will increase downstream flooding, the developer shall
be required to pay to the City the above rate for the equivalent volume
of detention required due to the increase in impervious area.
B. Buyout
funds shall be used by the City to construct and maintain regional
detention and conveyance systems within the drainage basin where the
stormwater facilities would have been constructed.
C. Detention
buyouts are not automatic and must be considered on a case-by-case
basis by submission of the completed application in Appendix "A",
a copy of which is on file in the City offices. Initial determination
of approval will be made by the City Engineer. That decision may be
appealed in writing to the City Administrator for a final determination.
D. When
a buyout is approved, it is the responsibility of the developer to
convey the stormwater runoff from the development to the existing
storm sewer system by making whatever modifications are necessary
to the existing system.
E. When
the detention volume is less than five thousand (5,000) cubic feet,
the table shown in Appendix "A", a copy of which is on file in the
City offices, may be used to determine the buyout amount.
[Ord. No. 2994 §1, 3-15-2005]
A. Easements
shall be provided for stormwater detention facilities on forms approved
by the City Engineer. These easements shall include an access easement.
B. All
detention reservoirs, with the exception of parking lots and roof
detentions, shall be enclosed by an easement. The limits of the easement
shall extend a minimum of ten (10) feet beyond the total area required
for maintenance. The limits of the ponding area and legal description
with the designation of the detention facilities shall be shown on
the improvement plans and the final plat. This easement shall also
be continuous with or to a public access area to allow the City to
maintain the easement if necessary. If it is required that the City
maintain the easement, the City shall have the right to charge the
party primarily responsible for maintenance as stated on the easement
document.
C. A minimum
twenty (20) foot wide easement shall be provided within the reservoir
area connecting the tributary pipes and the discharge system for possible
future elimination of the detention basin. The 100-year peak flow
shall be contained within the limits of the drainage easement shown
on the improvement plans and the final plat.
D. Easements
not included as part of the final plat will have to be recorded on
an easement form suitable for the type of development being proposed.
[Ord. No. 2994 §1, 3-15-2005]
It may be advantageous in some situations to delay the building
of the permanent detention facilities until after the completion of
the other improvements. In these situations, temporary detention facilities
must be provided. The permanent or temporary detention facilities
shall be constructed and be functional before proceeding with any
other construction.
[Ord. No. 2994 §1, 3-15-2005]
A. Off-Site Detention. Stormwater detention facilities designed
and constructed off-site or outside the limits of the proposed development
will be considered for approval. This approval is contingent upon
documentation being furnished to verify that drainage easements have
been obtained from the proposed development to the detention facility
in addition to easements for the detention area. The drainage easements
must clearly set out provisions for maintenance.
B. Detention
facilities designed and located to provide for detention on major
drainage channels will be considered for a regional detention facility.
The drainage area considered for a regional detention facility is
generally several hundred acres. The regional basin must provide a
detention volume for a 100-year storm for the entire drainage area.
The regional detention facility must be designed with a low-flow,
concrete channel through the limits of the basin. Upon conceptual
approval of the location and final approval of the design and construction,
the City may accept the responsibility for the maintenance of a regional
facility. Drainage and access easements will be required giving the
City the authority to gain vehicular access to the facility from a
public street.
C. As
additional development occurs upstream of the regional facility, on-site
detention requirements may be bought out, provided the regional detention
basin has been designed for full development of the basin, or if modifications
are made to the regional facility by the developer to provide for
the additional volume of detention required for the new development.
Easements must be provided along the drainage channel from the new
development to the regional facility, and the channel must be able
to carry the peak rate of runoff from the 100-year storm from the
entire basin upstream of the regional facility.
[Ord. No. 2994 §1, 3-15-2005]
Where detention, retention, or depressional storage areas are
to be used as part of the drainage system for a property, they shall
be completed before general property grading begins. This is to ensure
that if soil erosion and sediment control practices are not adequately
implemented, the eroded sediment will be captured in these areas and
will have to be removed by the applicant before project completion.