The purpose of this Article 6 is to diminish threats to public
health, safety and welfare caused by runoff of excessive stormwater
from new development and redevelopment. This excessive stormwater
could result in inundation from surface water, damage to adjacent
properties, overloading of the sewer system, diminished sewer capacity,
and backup into homes. The cause of increases in stormwater runoff
quantity is the development and improvement of land and as such this
Article 6 regulates these activities to prevent adverse impacts.
This Article 6 is adopted to accomplish the following objectives:
(A)
To promote the reduction of drainage or flood hazards from new and
current development.
(B)
To lessen the burden on the taxpayer for flood control projects,
repairs to flood damaged public facilities and utilities, and flood
rescue and relief operations caused by increased stormwater runoff
quantities from new development.
(C)
To protect, conserve, and promote the orderly development of land
and water resources.
The following definitions shall apply in the interpretation
and enforcement of this Article 6.
Refers to any changes to a property which add to either the
total impervious area or total building (superstructure) area or any
combination thereof, to the extent of 2,000 square feet or greater.
The maximum permitted rate of stormwater discharge from a
site during a one-hundred-year design storm.
A physical means or method by which water flow is passed
from an upstream watershed through a site, whether through or around
a detention system.
Sewers intended for the combined collection and conveyance
of stormwater runoff and wastewater flows.
[Added 2-21-2017 by Ord.
No. 2017-3252]
The temporary ponding of runoff achieved by restricting its
release from a basin to a limited flow rate (but not 0).
A facility constructed or modified to provide for the temporary
storage of stormwater runoff and the controlled release by gravity
or pumping of this runoff at a prescribed rate during and after a
flood or storm.
The following changes to real estate, including:
With respect to any industrial or commercial property, development
shall include any new construction on a vacant lot, redevelopment,
or reconstruction of any industrial or commercial building, or any
addition to an existing industrial or commercial building, adjacent
parking lot or accessory structure;
Any residential construction with a lot size of one acre or
larger;
Construction of new roads, new parking lots or similar paving
projects. Pavement maintenance is not considered new construction;
Filling, dredging, grading, clearing, excavating, paving, or
other nonagricultural alterations to the ground surface;
Any other activity that alters the magnitude, frequency, direction,
or velocity of stormwater flows from a property.
A plan, including engineering drawings and supporting calculations,
which describes the existing stormwater drainage system and topographic
features, as well as the drainage system and topographic features
which are proposed after development of a property.
A release elevation above which stored water is allowed to
flow out of a property, primarily to protect buildings from damage
due to malfunctioning or overtaxed stormwater management facilities.
The vertical elevation difference between high water level
or the emergency stormwater release level, whichever is higher (overflow),
and the top of a bank.
A surface that does not readily allow for the infiltration
of stormwater runoff into the ground. Impervious areas include, but
are not limited to, rooftops, asphalt or concrete pavement, compacted
gravel, and ponded water at its normal water level. Volume control
practices, green infrastructure, or other areas which include, but
are not limited to, noncompacted gravel, porous/permeable pavement,
and bioretention (rain gardens and bioswales, composed of an engineered
soil mix) that are designed to promote infiltration of stormwater
runoff into the ground, are not considered to be impervious areas.
[Amended 4-24-2023 by Ord. No. 2023-3684]
A single parcel of land located within a single block which
is under unified ownership or control, and which is designated by
the owner or developer as a tract to be used, developed or built upon
as a unit. A "lot" as used herein may be a single parcel legally described
as such or may consist of one or more lots or parts of lots of a recorded
subdivision.
Metropolitan Water Reclamation District of Greater Chicago.
Conditions resulting from physical, chemical, or biological
processes without intervention by man.
A design storm having an intensity-duration that has a one-percent
probability of being equaled or exceeded on a yearly basis, as defined
by the Illinois State Water Survey.
[Amended 2-21-2017 by Ord. No. 2017-3252]
A designated route over and through which emergency overflows
are directed.
Pavement maintenance items include the following: seal coating,
bituminous concrete overlays of existing impervious areas, pavement
patching of less than 50% of the total parking lot area, milling,
pulverizing, and resurfacing of existing impervious areas, or reconstruction
of existing impervious areas with less than 50% subbase repairs.
Stormwater detention system utilizing underground pipes as
part or all of the detention system.
The empirical method that relates stormwater runoff to rainfall
intensity by the formula Q = CIA where "Q" is the peak runoff rate
in cubic feet per second (cfs), "C" is the runoff coefficient, "I"
is the average rainfall intensity in inches per hour (in./hr.) and
"A" is the area of the site in acres (ac.).
Rebuilding, rehabilitating, renovating or remodeling of the
structures on a property to the extent where the impervious area of
a property is increased by 50% or more from its present size or where
50% or more of the total building area is removed and replaced with
a building, structure or other impervious areas.
Involves a total change in the physical configuration and
content of a property or the removal and replacement of major physical
improvements. Usually will involve the total razing of buildings and
replacement with upgrades.
The rate of discharge in cubic feet per second from a detention
or retention facility.
The physical mechanism or means for controlling the rate
of stormwater discharge from a detention or retention basin. Most
restrictors are in the form of pipes, orifice plates, short tubes,
or weirs, although other forms are possible.
A basin for stormwater storage that functions in the same
manner as a detention basin except that a retention basin has a permanent/inactive
water surface, with active storage above that surface.
The percentage of precipitation that appears as stormwater
runoff.
The minor portion of the overall stormwater transmission
system which carries stormwater and surface water, including round
or elliptical pipes, box sections and other enclosed systems.
All means, natural or man-made, for conducting stormwater
from or through any property to a point of final outlet from that
property. The stormwater drainage system includes, but is not limited
to, any of the following: conduits and appurtenant features, canals,
channels, ditches, streams, culverts, streets, storm sewers, detention
basins, swales and pumping stations.
The waters derived from melting snow or rain falling within
a tributary drainage basin which are in excess of the infiltration
capacity of the soils of that basin, and which flow over the surface
of the ground or are collected in channels or conduits.
A design storm having an intensity-duration that has a fifty-percent
probability of being equaled or exceeded on a yearly basis, as defined
by the Illinois State Water Survey.
[Amended 2-21-2017 by Ord. No. 2017-3252]
This Article 6 shall apply to all development in the Village.
(A)
Each applicant for a building permit for any development, as defined
herein, shall submit a proposed drainage plan in accordance with provisions
of this Article 6. The submittal shall include sufficient information
to enable the Village Engineer to evaluate the effectiveness of the
proposed drainage plan in managing stormwater runoff. The applicant
shall certify on the drawings that all clearing, grading, drainage,
and construction shall be accomplished in strict conformance with
the drainage plan. The information shall be submitted for both existing
and proposed property conditions. A building permit shall not be issued
unless a satisfactory drainage plan has been approved by the Village
Engineer. In cases where no other alterations are made to a property
other than those due to stormwater management, a permit for this specific
purpose will be required.
(B)
Nothing herein shall be deemed to exempt any development from complying
with the water management requirements of any other governmental agency
having jurisdiction with respect thereto. The corporate authorities
may, in their discretion, require evidence of water management plan
approval from other governmental authorities before issuing a building
permit hereunder.
Drainage plans shall consist of and contain the following information.
(A)
Topographic map. A topographic survey of the property at one-foot
contours for existing and proposed conditions, and areas upstream
and downstream necessary to determine off-site impacts of the proposed
drainage plan. The map shall use USGS elevations.
(B)
Drainage system. Mapping and descriptions of existing and proposed
drainage system features of the property and immediate vicinity including,
but not limited to:
(1)
Watershed soils classifications;
(2)
Location, size and slope of stormwater conduits and drainage
swales;
(3)
Sanitary or combined sewers;
(4)
Depressional storage areas;
(5)
Delineation of upstream and downstream drainage features and
watersheds affected by the development;
(6)
Detention facilities;
(7)
Roads and streets and associated stormwater inlets.
Unless some other method is approved by the Village Engineer,
runoff shall be determined by the rational method, as expressed by
the design formula Q = CIA, in which:
|
A
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=
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Total tributary drainage area in acres;
|
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I
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=
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Average rainfall intensity, in inches per hour;
|
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C
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=
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Coefficient of runoff; and
|
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Q
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=
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Runoff, in cubic feet per second.
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(A)
The area in acres used in the design formula shall be the watershed
area tributary to the point in the system under consideration, but
shall not necessarily include any tributary areas that may lie outside
the development which are not now provided with stormwater holding
facilities. Also, that portion of a property not altered by development
need not necessarily be included in the area used for storage calculations.
Storm sewers should, however, be designed for the full tributary area
that lies outside of the property.
(B)
When necessary, design details should be shown for bypass flow
through the site.
[Amended 11-19-2019 by Ord. No. 2019-3430; 4-24-2023 by Ord. No. 2023-3684]
The average rainfall intensity used in the design formula shall
be based on rainfall frequencies set forth in Bulletin 75 (northeast
section), Frequency Distributions and Hydroclimatic Characteristics
of Heavy Rainstorms In Illinois, prepared by the Illinois State Water
Survey, 2020. Rainfall intensity should be calculated using the average
of Chicago and Waukegan data.
The runoff coefficient C is the ratio of runoff to rainfall
and shall be as follows:
(A)
For all impervious areas (paved or hard surfaced areas of all
types and buildings), C shall equal 0.95 (water surface C = 1.0).
(B)
For all pervious areas such as lawn areas (all areas not classified
as impervious), C shall equal 0.45.
|
The runoff coefficient used in design shall be the weighted average composited of Sections 12-6-6-4(A) and (B) of this Code.
| |
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Within a development, the composite runoff coefficient shall
be computed assuming complete development.
|
The drainage system for a property shall be designed to control
the discharge from the property for the two-year and one-hundred-year
frequency storms. The discharge from events less than or equal to
the two-year frequency storm shall not be greater than 0.04 cfs per
acre of property drained and the one-hundred-year storm discharge
shall not be greater than 0.15 cfs per acre of property drained, except
that parking lot type detention may be exempt from strict adherence
to the two-year allowable release rate requirement. The Village Engineer
shall make a determination on the exemption based on the design features
of the project. Two stage restrictors are encouraged.
[Amended 2-21-2017 by Ord. No. 2017-3252; 10-3-2017 by Ord. No. 2017-3301; 4-24-2023 by Ord. No. 2023-3684]
Stormwater detention sized in accordance with MWRD requirements must be provided for all developments tributary to a storm sewer, if the area of disturbance is greater than or equal to 0.50 acre, using the parameters noted in Section 12-6-6-5 of this Code, except that the one-hundred-year release rate shall be as found in the effective MWRD Watershed Management Ordinance. Stormwater detention sized in accordance with the MWRD requirements must be provided for all developments tributary to a combined sewer, regardless of area of disturbance, using the parameters noted in Section 12-6-6-5 of this Code. The size of the required detention for proiects with a disturbed area up to three acres shall be based on the parameters set forth in Section 12-6-6-5 of this Code, less the total cubic feet of stormwater retention constructed in the area of disturbance.
[Amended 2-21-2017 by Ord. No. 2017-3252]
Discharge shall be controlled by means of a restrictor, either
single pipe projecting trap outlet or orifice plate. The pipe restrictor
shall consist of a minimum two-foot long pipe properly sized, projecting
into a pond or a catch basin which shall include a trap. A cleanout
shall be placed immediately adjacent to this restrictor. Methods of
acceptable detention are wet retention ponds, dry bottom detention
basins, pipe storage, and parking lot detention. Rooftop detention
is not allowed.
[1]
Editor’s Note: Former Section 12-6-6-8, Excessive release
rate; fee, was repealed 2-21-2017 by Ord. No. 2017-3252.
[Amended 2-21-2017 by Ord. No. 2017-3252; 4-24-2023 by Ord. No. 2023-3684]
The maximum stormwater ponding depth in any parking area shall
not exceed 12 inches. All parking area detention shall be provided
with an emergency overland flow route.
Design details should be provided showing an emergency overflow
elevation and routing to protect against flooding damage to buildings.
Emergency overland flow routes shall be provided across every site
having an upstream watershed draining across it, and shall be located
in maintenance easements not less than 20 feet in width on terms acceptable
to the Village, granting the Village the right to undertake maintenance,
and lien rights for the cost of such maintenance, in the event the
owner fails to maintain said routes. All such flow routes shall be
designed to meet the one-hundred-year frequency storm, without consideration
for the detention available. Design of such systems including all
appurtenances shall be subject to final review and approval of the
Village Engineer.
All detention and retention basins shall be maintained in their final constructed and approved condition as shown on the as-constructed plans described in Section 12-6-10 of this Code. No alterations of any kind will be allowed to the approved conditions without written approval of the Village Engineer.
(A)
Restrictors/release structures. All restrictors shall be sized at or below the allowable release rate permitted for the subject site, except as noted in Section 12-6-6-9 of this Code.
|
Detention basin release rates shall be computed based on both
the capacity of the restrictor as an orifice Q = Cd*(A)*(2G*H)0.5
and the capacity of the restrictor as a pipe using Manning's formula:
| |
|
Q = 3.14*R2*(1.49/.013)*(Dia/4)0.67*(S)0.5.
| |
|
The more restrictive release rate above shall be used in the
design of the restrictor.
| |
|
Slope shall be hydraulic slope and calculated using the high
water level to 80% of the depth of the release pipe at the point of
discharge.
| |
|
Every restrictor shall be located in a catch basin at least
48 inches in diameter.
| |
|
The upstream end of all restrictors shall be equipped with traps
and cleanouts.
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(B)
Detention basin, vegetative cover.
(1)
Detention basins with vegetative cover shall have a side slope
ratio not steeper than 3:1, except in those areas protected by retaining
walls.
(2)
The design of retaining walls and detention basins shall be
subject to review by the Village Plan Commission. Except as otherwise
authorized by the Village, in order to maximize the size of the release
and minimize the number of restrictors, only one detention basin and
one restrictor shall be provided per watershed within any property
requesting a permit under this Article 6.
(3)
In situations with multiple release directions, the detained
release shall be to the receiving system with the largest remaining
capacity, subject to the approval of the Village Engineer.
(4)
In the above situation, the emergency overflows shall reflect
predevelopment conditions to the extent practical.
(5)
All detention and compensatory storage basins shall have a minimum
surface slope of 2% and an underdrain system used to dry the surface.
(6)
Freeboard is required to be a minimum of 12 inches when earth
banks are utilized for a detention basin. If a concrete curb or solid
concrete retaining wall is utilized, freeboard of two inches above
the stormwater release level (emergency overflow) is required.
(C)
Basin design, retention.
(1)
All retention ponds shall be provided with a minimum slope ratio,
near the water level entrance area, of 3:1. At a depth of approximately
three feet below normal water level, a safety shelf shall be provided
which is approximately three feet in width. Below the safety shelf,
a slope ratio of 2:1 may be used.
(2)
Shore stabilization shall be provided, at a minimum slope ratio
of 3:1, from a point at least one foot below normal water level to
high water level. Said stabilization shall take the form of riprap,
retaining walls, turf-stone, or other permanent methods of stabilization.
NAG P300 or Enkamat-type of vegetation stabilization systems may also
be considered.
(3)
All retention basins shall have at least 12 inches freeboard,
except at the location of the emergency overflow.
(4)
Aeration systems shall be provided, which may be either surface
aerators or diffused air systems when deemed reasonably necessary
by the Village in the interest of public health and safety and to
maintain proper oxygen levels.
(D)
Detention basin capacity. The Illinois State Water Survey Intensity
Chart for a one-hundred-year frequency storm for the region, including
the Village, shall be used, in combination with the allowable release
rate, to determine minimum basin capacity. The Metropolitan District
of Greater Chicago rational method shall be used for computation of
storage.
(E)
Detention basin, parking lot.
(1)
All pavement designs shall incorporate provisions for subbase
drainage, have a surface slope between 1% and 3% and be constructed
pursuant to Illinois Department of Transportation standards.
(2)
All parking lots used for detention shall be surrounded by a
minimum six-inch high curb.
(3)
Provision shall be made for emergency overflow at any point
in a parking lot where water attains a depth of 12 inches or more.
[Added 2-21-2017 by Ord.
No. 2017-3252; amended 4-24-2023 by Ord. No. 2023-3684]
Except for properties within residential zoning districts on which the impervious surface ratio remains below 50%, no person may fill, store, or dispose of earth materials; alter an existing land grade, contour or drainage pattern; or perform any other land-disturbing activity, without first obtaining a grading permit pursuant to this Section 12-6-6-13. Projects that require a grading permit pursuant to this Section 12-6-6-13 include, without limitation:
(A)
Construction of new garages or accessory structures of 500 square
feet or more in floor area;
(B)
Installation of in-ground swimming pools;
(C)
Construction of an addition with a floor area of 500 square
feet or more to an existing structure;
(D)
The addition of greater than 500 square feet of flatwork (driveway,
patio, sidewalk, or similar improvements) on a property within a residential
zoning district;
(E)
Landscaping that changes the grade of the site such that existing
drainage flows will be altered;
(F)
Any project that requires the construction of a foundation;
(G)
Any land-disturbing activity proposed in a floodplain as established
by the Federal Emergency Management Agency;
(H)
Any land-disturbing activity affecting an area of one acre or
more;
(I)
The demolition of any building or structure; and
(J)
Earthmoving by creating any excavations, cuts, filling, or otherwise.
which singly or in combination: (1) alters the existing natural grade
at any point that is five feet or less from a lot line; (2) alters
any stormwater conveyance system or existing drainage flow; or (3)
covers more than 50 square feet in area.
The drainage system components, especially all retention and
detention basins, shall be designed to protect the safety of any person
coming in contact with the system during runoff events. The safety
provisions may include, but will not be limited to, safety shelves,
walls or fencing. Generally accepted design safety criteria shall
be used and specific reviews for safety provisions shall be part of
the overall approval process.
Where detention areas are to be used as part of the drainage
system for a property, they shall be constructed as the first element
of the initial earthwork program. Any eroded sediment captured in
these facilities shall be removed by the applicant before project
completion in order to maintain the design volume of the facilities.
[Amended 10-3-2017 by Ord. No. 2017-3301]
The developer or owner shall pay to the Village a fee per cubic
foot of required stormwater detention not provided, in the amount
set forth in the Annual Fee Resolution,[1] when:
(A)
In the judgment of the Village Engineer, the proposed development
will not cause an increase in the existing rate of runoff from the
property;
(B)
In the judgment of the Village Engineer, the proposed development
will not cause an increase in subsequent detrimental effects to downstream
properties; and
(C)
The proposed development is a reconstruction of an existing property
having an existing impervious lot coverage of 75% or greater, and
the impervious lot coverage on the property will be reduced by the
proposed development.
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Such fee shall not exceed 10% of the construction cost of the
proposed development, as determined by the Director of Community Development,
and may be used by the Village for the purpose of constructing stormwater
management improvements for the Village which provide for other local
or regional relief from sewer system deficiencies which may or may
not be directly related to the subject site.
|
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The election to use a fee in lieu of detention is not an option
of the developer but a provision to be enacted upon the review and
approval of the Village Engineer.
|
(A)
In the opinion of the Village Engineer, in areas where upstream development
has the potential to significantly impact existing downstream development,
the Village may require that owners of the upstream development property
participate in the construction of a stormwater transmission system
downstream of the site. Such participation may be implemented through
a recapture ordinance when appropriate.
(B)
As-constructed plans shall be submitted to the Village Engineer upon
completion of all development projects within the Village. Plans shall
be submitted as electronic portable document format (PDF) files. Reproducible
plans in hard copy format may be requested at the discretion of the
Village Engineer. As-constructed plans shall identify utility locations
and elevations, high water level, normal water level, grading, and
deviations from the design plans. Said plans shall be signed and sealed
by the design engineer and shall be accepted by the Village Engineer
prior to the issuance of a certificate of occupancy or acceptance
or approval of the project by the Village.
[Amended 11-19-2019 by Ord. No. 2019-3430]
(C)
On the face of all construction plans, there shall be inscribed a
notice to the contractor to request inspections at specified stages.
The Village Engineer shall advise the design engineer concerning the
timing of and procedures for such inspections.
(A)
The owner or subsequent owners of any detention, retention or compensatory
storage basin shall maintain that basin in its original design cross
section, surface conditions, and hydraulic system as noted on the
original accepted plans.
(B)
If, in the reasonable opinion of the Village, the owner has failed
to maintain the basin properly, the Village may perform any required
maintenance upon said basin and charge the cost thereof to the current
owners of the basin, which costs shall be a lien on the entire property
served by said basin.
(A)
Detention/retention facility size calculations are not required to include that area of a property not altered by development as defined herein. Only the addition need be included. "Area" shall be as described in Section 12-6-6-2 of this Code.
(B)
For good cause, the Village Manager, upon written recommendation
of the Village Engineer, may grant exceptions or variations to the
requirements of this Article 6 where such exceptions will not adversely
affect stormwater management in the Village and where the following
standards are met:
(C)
Upon recommendation of the Village Engineer, such modifications may
be made by the Village Manager in cases where less than 5,000 cubic
feet of stormwater detention is required hereunder and no subdivision
of land is involved.
(D)
As a condition of any exception or variation, in lieu of constructing
a stormwater detention basin, the owner or developer may be required
to contribute to the Village an amount of money equal to the Village
Engineer's estimate of the cost of constructing such detention basin.
Funds so deposited may be utilized by the Village for the purpose
of constructing stormwater management improvements within the Village.
(E)
Notwithstanding any other criteria, a development shall be subject
to the Stormwater Management Ordinance if so provided in an ordinance
enacting a variation or granting a special use.
(F)
For good cause, the Village Manager, upon written recommendation
of the Village Engineer, may impose additional or increased stormwater
management requirements.
[Added 4-24-2023 by Ord. No. 2023-3684]
(A)
Except
for properties on which the impervious surface ratio remains below
50%, upon the addition or construction of 500 square feet or more
of impervious surface to any residential property, at least one of
the following stormwater management practices must be implemented:
(1)
Installation of a swale, french drain, or other Village-approved
stormwater conveyance system, designed to carry stormwater to the
street-facing side of the subject property, but not closer than five
feet from the front property line; or
(2)
Installation of stormwater detention improvements, such as rain barrels,
rain gardens, dry wells, or permeable pavers, located not less than
five feet from all property lines, capable of detaining the following
minimum volumes of stormwater:
(B)
All stormwater management practices implemented pursuant to this Section 12-6-13 must be designed so as to avoid unauthorized drainage or other adverse impacts on neighboring properties. Specifically, and without limitation, the discharge points for any stormwater conveyance system or detention improvement must be directed away from neighboring properties. The owner of a property subject to this Section 12-6-13 must mitigate any unauthorized drainage or other adverse impacts on neighboring properties, post-construction, to the satisfaction of the Village.
(C)
Residential
stormwater discharge may not be directly connected to the public sewer
system.
