[HISTORY: Adopted by the Mayor and City Council of the City
of Maroa 1-23-2006 by Ord. No.
01/23/2006-1 (Ch. 34, Art. VII, of the 2001 Code).
Amendments noted where applicable.]
A.
It is the policy of the City to protect and promote the public health,
safety and general welfare. The criteria for stormwater management
will reduce the possibility of damage to public and private property,
will help to minimize erosion, will assist in the attainment and maintenance
of water quality standards and will preserve and enhance the environmental
quality of the watercourses in the City. These criteria provide uniform
procedures for designing and evaluating the design of stormwater management
systems.
B.
The Planning and Zoning Board shall not recommend the approval of
any plat unless, after consultation with the City Engineer, it determines
that the proposed provisions for stormwater management are adequate.
Drainage improvements shall be coordinated with existing and planned
improvements elsewhere so as to form an integrated municipal system.
The stormwater drainage system shall be separate and independent of
the sanitary sewer system.
[Amended at time of adoption of Code (see Ch. 1, General
Provisions, Art. I)]
The following definitions shall apply to the Stormwater Management
Plan:
A precipitation event having a 1.0% chance of occurring in
any one calendar year.
The flood generated by the 100-year storm.
The 100-year storm.
See § 223-10.
In a detention/retention pond, a device or devices having
at least the capacity for carrying the peak inflow generated by the
design storm. Activation of the emergency overflow/spillway occurs
only when the excess stormwater run-off exceeds the design storage
capacity.
The difference between the stormwater run-off from the design
storm for the proposed site conditions and the stormwater run-off
from a five-year storm for the undeveloped or existing site.
A precipitation event having a 20.0% chance of occurring
in any one calendar year.
That land area susceptible to being temporarily inundated
by floodwater from an adjacent watercourse.
The channel of a river or other watercourse that must be
reserved for passage of the base flood.
In a detention/retention pond, the vertical distance from
the calculated maximum height of the water surface for the design
storm to the lowest point of the top of the berm or containment wall.
An area that will not appreciably absorb water, such as a
parking lot, driveway, roof area, sidewalk, etc.
The use of parking lots for stormwater detention.
[Amended at time of adoption of Code (see Ch. 1, General
Provisions, Art. I)]
See § 223-12.
A natural or man-made open watercourse with definite bed
and banks, and which periodically or continuously contains moving
water or forms a connecting link between two bodies of water.
That fraction of the water resulting from precipitation that
flows from a given area of land during and immediately after a rainfall.
The rate at which stormwater run-off is released from dominant
to servient land, the discharge rate from detention/retention facilities
or the sum of both types of discharges where applicable.
A.
A combination of storage and controlled release of stormwater run-off
shall be required to be constructed and maintained in the following:
B.
Developments less than two acres with a proposed impervious area
of less than 30.0%, and developments generating less than one cubic
foot per second (cfs) per acre of excess stormwater run-off shall
not be required to provide detention/retention storage unless such
flows will cause damage or exceed the capacity of any downstream drainage
facilities within the City of Maroa.
A.
A drainage plan shall be filed with the preliminary plat for residential
subdivisions and planned unit developments and shall be filed and
approved prior to the issuance of a building permit for commercial,
business, office and research developments.
B.
The drainage plan shall include engineering drawings and supporting
calculations describing the stormwater drainage systems and environmental
features for existing and proposed conditions.
C.
The drainage plan shall show or contain the following:
(1)
Topographic survey of the property, with contours at a minimum interval
of two feet.
(2)
Banks and center lines of streams and channels.
(3)
Shorelines of lakes, ponds and detention/retention basins.
(4)
Locations, sizes and slopes of farm drains and tiles.
(5)
Subwatershed boundaries within the property and the property's location
within the larger watershed.
(6)
Location, size and slope of stormwater conduits and drainage of water.
(7)
Locations, sizes and slopes of sanitary sewers.
(8)
Delineation of upstream and downstream drainage features and watersheds
which might be affected by the development.
(9)
Detention/Retention areas and facilities.
(10)
Roads, streets, inlets and storm sewers.
(11)
Detail of how stormwater run-off from the design storm that
exceeds the capacity of the storm sewer system will be conveyed to
detention/retention areas.
(12)
Site plan showing lots, public improvements, drainage easements
and building outlines.
(13)
Base flood elevation and regulatory floodway where identified
for the property.
(14)
Drainage certificate signed by an Illinois licensed professional
engineer and the owner of the development. The certificate must include
language to the effect that the drainage of surface waters will not
be adversely affected by this development, or that if change does
occur, adequate provision has been made to protect adjoining property
owners from damages which might result from such change in drainage.
D.
All computations, plans and specifications related to the implementation
of the drainage plan must be prepared and sealed by an Illinois licensed
professional engineer.
A.
The maximum allowable run-off shall be limited to:
(1)
The flow that would occur during a five-year storm under existing
conditions for undeveloped sites.
(2)
For developed sites undergoing redevelopment or expansion:
(a)
If 30% or more of the impervious area is increased or modified,
detention/retention must be provided for the entire site and outflow
is not to exceed what would occur for a five-year storm under predeveloped
(natural) conditions. For example, if more than 30% of an area that
will not appreciably absorb stormwater, such as a parking lot or roof
area, is increased, then a stormwater detention/retention facility
must be provided for the entire site to control and detain the excess
stormwater run-off so that it will not exceed that of a five-year
storm.
(b)
If less than 30% of the impervious area is increased or modified,
the outflow shall not exceed what would occur for a five-year storm
under existing (current) conditions, and detention/retention shall
be required only for the area that is to be expanded or modified.
B.
Under all circumstances, the stormwater run-off release rate from
a site shall be limited to such flows as will not cause damage or
exceed the capacity of any downstream drainage facilities within the
City of Maroa.
All flows shall be collected on-site using closed conduits,
open channels, or both. Closed conduits shall be a minimum twelve-inch-diameter
pipe where access to a storm sewer is available.
The Modified Rational Method will be used to compute stormwater
run-off unless the City Council approves the use of another methodology.
Where a single pipe outlet or orifice plate is to be used to
control excess stormwater run-off, it shall have a minimum diameter
of six inches. If the minimum size permits release rates greater than
those specified, alternative outlet designs incorporating self-cleaning
flow restrictors shall be used.
A.
The design maximum storage to be provided in a detention/retention basin shall be based on the run-off generated by the design storm. Detention storage shall be computed using the Modified Rational Method as outlined in Chapter 12 of the Illinois Department of Transportation's Drainage Manual.
B.
The applicable regulations of the Illinois Department of Natural
Resources and the Federal Emergency Management Agency shall apply
to all storage areas located in floodplains.
[Added at time of adoption of Code (see Ch. 1, General Provisions,
Art. I)]
The following restrictions shall apply to parking lots:
A detention pond is an area designated to temporarily store
excess run-off with no permanent pool. Detention ponds shall incorporate
the following design criteria:
A.
A minimum 2% bottom slope or implementation of a low-flow system
or underdrain.
B.
A low-flow bypass system wherever feasible.
C.
Location shall be at least one foot from the property line.
D.
Inner and outer embankment slopes shall have maximum grades of 3:1.
E.
Freeboard shall be a minimum of two feet or 50% of the maximum pond
depth, whichever is less.
F.
Energy dissipation and/or erosion control for areas where velocities
meet or exceed six feet per second.
G.
An emergency overflow/spillway.
H.
Landscaping and multiple use shall be considered in all pond designs.
I.
Subdivision detention ponds shall be incorporated into multiple properties
to encourage maintenance or shall incorporate recreational use and
be the responsibility of the homeowners' association.
J.
Discharges shall be deposited directly into an approved storm sewer
system where available.
K.
Outfalls to ditches and open channels shall be designed to prevent
erosion. If necessary, energy dissipation strategies shall be used
to reduce outfall velocities to acceptable levels.
L.
Detention facilities adjacent to a state highway may use IDOT design
standards for stormwater run-off release rates for all discharges
to the highway drainage system. The developer shall obtain IDOT approval
for such discharges, in addition to any approvals required from the
City of Maroa.
M.
Flows and stormwater run-off from upstream areas outside the site
should be based on the assumption that such areas are fully developed
according to the latest available forecast land use patterns.
A retention pond shall be defined as an area with a permanent
pool having sufficient capacity to store excess run-off and shall
incorporate the following design criteria:
A.
Outer embankment slopes shall have maximum grades of 3:1, and inner
embankment slopes to the pool area shall have maximum grades of 5:1.
B.
Freeboard shall be a minimum of two feet or 50% of the height from
the permanent pool to the maximum water surface for the design storm,
whichever is less.
C.
The inner embankment shall have a shelf area along the sides of a
minimum width of three feet.
D.
The permanent pool area shall have a minimum depth of three feet
with a maximum depth of one foot above the shelf area.
E.
An emergency overflow/spillway.
F.
Shall be designed so that as much flow as possible shall enter the
pond through grass swales or sheet flow across grass areas.
G.
The developer shall submit a maintenance plan for sediment removal
and water quality control.
H.
A structure capable of dewatering the pond within 48 hours.
I.
Discharges shall be deposited directly into an approved storm sewer
system where available.
J.
Outfalls to ditches and open channels shall be designed to prevent
erosion. If necessary, energy dissipation strategies shall be used
to reduce outfall velocities to acceptable levels.
K.
Retention facilities adjacent to a state highway may use IDOT design
standards for stormwater run-off release rates for all discharges
to the highway drainage system. The developer shall obtain IDOT approval
for such discharges, in addition to any approvals required from the
City of Maroa.
L.
Flows and stormwater run-off from upstream areas outside the site
should be based on the assumption that such areas are fully developed
according to the latest available forecast land use patterns.
A.
Commercial development. Maintenance of all structures, conduits and
pooling areas required to convey flow or provide detention/retention
for the development shall be the responsibility of the owner to the
point of its connection to the City's drainage system or its release
onto a right-of-way. A signed drainage covenant as provided by the
City of Maroa shall be required prior to site plan approval.
B.
Residential development.
(1)
Detention/Retention pond areas shall be a part of buildable lots
and shall be maintained by adjacent residents. All conduits and structures
shall be placed in easements and shall be the responsibility of the
City.
(2)
Detention/Retention pond areas not incorporated into buildable lots
shall be designated as recreation areas and shall be the responsibility
of a homeowners' association. Proof of homeowners' association requirements
and responsibilities shall be submitted with the preliminary plat.
(3)
Regional detention/retention areas not incorporated into buildable
lots and owned by the City shall be designated as public recreation
areas and shall be the responsibility of the City of Maroa.
C.
All privately maintained stormwater systems shall be subject to periodic
inspection by the City or its representative to evaluate the condition
and functioning of such systems. The cost of any corrective actions
as determined by the City shall be the sole responsibility of the
owner(s) of the system. Should the City be required to correct deficiencies
in a privately maintained stormwater system, any costs incurred shall
accrue to the owner(s).
A.
Violation of the provisions of this chapter, or failure to comply
with any of its requirements, including conditions and safeguards
established, shall constitute a misdemeanor.
B.
Each day such a violation continues shall be considered a separate
offense. Nothing contained herein shall prevent the City from taking
such other lawful action as is necessary to forbid or remedy any violations.
All such costs connected therewith shall accrue to the person or persons
responsible.
[Amended at time of adoption of Code (see Ch. 1, General
Provisions, Art. I)]
