This article shall be known, cited, and referred to as the "Storm
Water Control Ordinance of the Village of Oakwood, Vermilion County,
Illinois."
The purpose of this article is to control the transportation
or movement of stormwater and reduce the damage to property and injury
to persons and hazards to public health and safety occasioned thereby,
and to protect, conserve, and promote the orderly development of land
and water resources. Additionally the purpose of this article is to
control soil erosion on land that is undergoing changes to existing
grades by adding, removing, or relocating dirt on-site for nonagricultural
purposes and to preserve the natural terrain and waterways of land
within the incorporated portions of the Village. Soil erosion scars
the land and creates sediment that clogs storm sewers and road ditches,
chokes streams and creates silt lakes, all of which pose a threat
to public health and safety. The provisions of this article are intended
to provide a natural community environment, to prevent soil erosion
and to reduce costly repairs to gullies, washed out fills, water conveyance
systems, roads and embankments. Application of the regulations in
this article will effectively control soil erosion and sedimentation.
Any person, firm, corporation or business proposing to change existing
grades by adding, removing or relocating any dirt within the Village
of Oakwood shall first apply to the Village Superintendent of Public
Works and the Village Engineer for approval of required erosion control
plans and issuance of any permits as specified in this article.
This article is intended to require the temporary storage of
stormwater runoff and to control the rate of release of stormwater
runoff thereby equitably apportioning the liabilities and benefits
of stormwater runoff between the dominant and servient estates. Further,
it is intended that this article compliment the Village Subdivision
Ordinance (Title 16).
For the purposes of this article, the words and phrases listed
hereunder have the meanings designated herein, except when a particular
context clearly requires a different meaning:
ADMINISTRATOR
Is the Village Engineer and the Village Superintendent of
Public Works, who shall jointly administer and enforce this article.
If only one of them is available, that one person may serve as administrator.
BOARD
The Board of Trustees of the Village of Oakwood, Illinois.
CAPACITY OF A STORMWATER DETENTION FACILITY
The maximum volume that can be stored by a stormwater detention
facility without causing damage to the public or encroachment upon
private property. The capacity of a stormwater detention facility
is generally determined utilizing stormwater flood routing methods.
CAPACITY OF A STORMWATER DRAINAGE FACILITY
The maximum flow at atmospheric pressure that can be conveyed
by the facility without causing damage to the public or encroachment
upon private property. The capacity of a stormwater drainage facility
is determined utilizing "Manning's Equation" or similar formulae.
CHANNEL
A natural or artificial watercourse of perceptible extent
which periodically or continuously contains moving water, or which
forms a connecting link between two bodies of water. It has a definite
bed and banks which serve to confine the water.
CONTROL STRUCTURE
A facility constructed to regulate the volume of stormwater
that is released during a specific length of time.
COUNTY
The County of Vermilion, Illinois.
CULVERT
A closed conduit for the passage of surface drainage water
under a roadway, railroad, canal, or other impediment.
DEBRIS OR SEDIMENT BASIN
A barrier or dam built across a waterway or at other suitable
locations to retain rock, sand, gravel, silt or other materials.
DETENTION STORAGE
The temporary detaining or storage of stormwater in storage
basins, on rooftops, in streets, parking lots, schoolyards, parks,
open space, or other areas under predetermined and controlled conditions,
with the rate of drainage therefrom regulated by appropriately installed
devices.
DEVELOPMENT
Any man-made change to improved or unimproved real estate,
including, but not limited to, construction of or substantial improvements
to buildings or other structures, the placement of mobile homes, mining,
dredging, filling, grading, paving, excavation or drilling operations.
DRAINAGE AREA
The area from which water is carried off by a drainage system;
a watershed or catchment area above a given point.
DRAINAGE EASEMENT
Authorization by a property owner allowing use of a designated
portion of his or her property by others for drainage purposes.
DRY BOTTOM STORMWATER DETENTION BASIN
A facility that is designed to be normally dry and which
accumulates stormwater runoff only during periods when the restricted
stormwater runoff release rate is less than the stormwater inflow
rate.
EROSION
The wearing away of the land surface by the action of wind,
water and gravity.
EXCAVATION or CUT
The removal, stripping or disturbance of soil, earth, sand,
rock, gravel or other similar substances from the ground.
EXCESS STORMWATER PASSAGEWAY
A channel formed on the surface of the soil to carry excess
stormwater runoff through a specific area from dominant to servient
estates.
EXCESS STORMWATER RUNOFF
That portion of stormwater runoff which exceeds the transportation
capacity of storm sewers or natural drainage channels serving a specific
watershed.
FEMA
The Federal Emergency Management Agency.
FILL or FILLING
The placing of any soil, earth, sand, rock, gravel, or other
substance on the ground.
FINISHED GRADE
The final grade or elevation of the ground surface conforming
to the proposed design.
FLOOD ELEVATION
The elevation of all locations delineating the maximum level
of high waters for a flood of given return period.
FLOODPLAIN
The special flood hazard lands adjoining a watercourse, the
surface elevation of which is lower than the flood elevation and which
are subject to periodic inundation during floods.
FLOODWAY
The channel of a watercourse and those portions of the adjoining
floodplain which are reasonably required to carry and discharge the
design flood.
GRADE
The inclination or slope of a channel, canal, conduit, etc.,
or natural ground surface, usually expressed in terms of the percentage
the vertical rise (or fall) bears to the corresponding horizontal
distance.
GRADING
Any excavation, filling, or combination thereof.
IBC
The International Building Code, latest edition.
IEPA
The Illinois Environmental Protection Agency.
IMPERVIOUS
A term applied to material through which water cannot pass,
or through which water passes with great difficulty or at a very slow
rate. For the purposes of this article, any surface which typically
would be assigned a Rational Method "C" value of 0.60 or greater shall
be considered impervious.
INLET
An opening into a storm sewer system for the entrance of
surface storm runoff, more completely described as a storm sewer inlet.
NATURAL DRAINAGE
Water flow by gravity in channels formed by the true surface
topography of the earth prior to changes made by the efforts of man.
NATURAL DRAINAGE CONDITION
The situation whereby water flows by gravity in channels
formed by the true surface topography of the earth prior to changes
made by the efforts of man.
NATURAL SAFE STORM WATER DRAINAGE CAPACITY
The quantity of stormwater runoff that can be transported
by means of a channel, passage, conduit, tube, duct, or combination
thereof, in such a manner that the elevation of the water does not
rise significantly above the level of the adjacent soil surface, and
cause damage or encroachment upon public or private property. For
the purposes of this article, it is presumed that the maximum safe
stormwater drainage capacity for downstream stormwater drainage systems
is the capacity required to carry the rate of stormwater runoff from
a five-year return period storm prior to the date of adoption of the
ordinance codified in this article.
NOI
The notice of intent for a general permit to discharge stormwater associated with construction activities. (See §
144-5)
NPDES
The National Pollutant Discharge Elimination System.
OPEN CHANNEL
A constructed ditch or channel designed for water flow.
OWNER
The record title holder or a beneficiary of a land trust
which is the record title holder, and includes singular or plural;
if the owner is other than an individual, the term includes beneficiaries,
agents, shareholders, officers and directors, partnerships, associations,
firms, trusts, clubs, companies or corporations.
PEAK FLOW
The maximum rate of flow of water at a given point in a channel
or conduit resulting from a pre-determined storm or flood.
PERSON
An individual, public or private corporation, government,
partnership, or unincorporated association.
PLANNED UNIT DEVELOPMENT or PUD
A parcel of land of a minimum contiguous size as specified
by ordinance initially under single ownership or control, which contains
two or more principal buildings and/or more than one principal use;
planned, developed and constructed as a unified development.
POSITIVE GRAVITY OUTLET
A term used to describe the drainage of an area in a manner
that will ensure complete removal of all surface water by means of
gravity.
RECOGNIZED AGENCY
A governmental unit or agency that has statistically and
consistently examined local, climatic, and geologic conditions and
maintained records as they apply to stormwater runoff, e.g., United
States Weather Bureau, University of Illinois Engineering Experiment
Station, and Illinois State Water Survey.
RETURN PERIOD
The average interval of time within which a given rainfall
event will be equaled or exceeded once. A flood having a return period
of 50 years has a 2% probability of being equaled or exceeded in any
one year.
RUNOFF COEFFICIENT
A decimal fraction relating the amount of rain which appears
as runoff and reaches the storm sewer system to the total amount of
rain falling. A coefficient of 0.5 implies that 50% of the rain falling
on a given surface appears as stormwater runoff.
SEDIMENT
Solid material, mineral or organic that has been moved by
erosion and deposited in a location other than the point of origin.
SILT TRAPS OR FILTERS
Staked bales or silt fencing systems that function as a filter
and a velocity check to trap fine-grained sediment while allowing
satisfactory passage of stormwater runoff.
SITE
A lot or parcel of land, or a contiguous combination thereof,
where grading work is performed as a single unified operation.
SITE DEVELOPMENT
Altering terrain and/or vegetation and construction improvements.
STORM SEWER
A closed conduit for conveying collected stormwater.
STORMWATER DRAINAGE SYSTEM
All means, natural or man-made, used for conducting stormwater
to, through or from a drainage area to the point of final outlet,
including but not limited to any of the following: conduits, appurtenant
features, canals, channels, ditches, streams, culverts, streets and
pumping stations.
STORMWATER MANAGEMENT PLAN
No development shall be approved unless the developer submits
and the Village Engineer approves a stormwater management plan that
attenuates the acceleration of runoff due to development. A stormwater
management plan shall mean and shall include those report(s), plans
and other documents which identify the water which naturally flows
to, from and through the development, the means of controlling the
stormwater runoff release from the development, and the storage potential
provisions for the anticipated excess stormwater runoff.
A.
A stormwater management plan is required for all developments
that meet the following criteria:
(1)
Residential developments of five or more acres gross aggregate
land area, including roads, utility rights-of-way, and any other dedicated
lands. Residential developments of less than five acres if the amount
of impervious surface is greater than 50% of the area of development.
(2)
Nonresidential developments of two or more acres gross aggregate
land area including roads, utility rights-of-way, and any other dedicated
lands. Nonresidential developments of less than two acres if the amount
of impervious surface is greater than 50% of the area of development.
B.
The following definitions shall apply to the stormwater management
plan, over and above other definitions provided elsewhere in this
article:
(1)
DETENTION FACILITYAny structure which is designed to collect and store surface water for subsequent gradual discharge.
(3)
PROTECTED CHANNELA channel which receives stormwater discharge and is constructed of pavement, rip-rap or man-made materials to reduce the potential for erosion.
(4)
SAFE STORM DRAINAGE CAPACITYThat capacity of the collection system which keeps the hydraulic gradient below the points of stormwater collection on abutting land served.
(5)
STORMWATER CHANNELA natural or man-made open watercourse with definite bed and banks which periodically or continuously contains moving water, or forms a connecting link between two bodies of water.
(6)
YEAR RAINFALLL — A precipitation event having a 1.0% chance of occurring in any one calendar year.
C.
Preparation of stormwater management plan. All computations,
plans and specifications related to the implementation of this article
must be prepared and sealed by a professional engineer registered
in the State of Illinois.
D.
Plan requirements. Unless the Village Engineer excludes specific
items, the stormwater management plan shall include, but not be limited
to, the following information:
(1)
A topographic map of the project site, and a drainage basin
limits map and other pertinent data necessary to define flows entering
the development from adjacent land. Maps shall be of suitable scale
and contour interval, and include the extent of floodplains, calculated
high water elevations, the shoreline of existing lakes, ponds, swamps
and detention basins as well as their inflow and outflow structures,
if any. Maps shall also include the fifty-year and 100-year floodplain
elevations for any streams for which detailed flood studies have been
prepared by the Illinois Division of Water Resources or federal agencies.
Floodway limits should also be shown as defined by available studies.
(2)
The locations and invert elevation of all existing sanitary
and storm sewers in the developing area or in adjacent areas.
(3)
Detailed calculations of runoff anticipated for the developed
site which indicate design volumes and existing and proposed runoff
rates for each portion of the watershed tributary to the storm drainage
system. The project engineer shall submit the calculations used to
determine said runoff volumes and rates as well as a restatement of
the criteria used throughout the calculations. Calculations shall
be provided for a five-year storm, fifty-year storm and a 100-year
storm event.
(4)
A site plan of the proposed stormwater management system including
the location and size of all drainage structures, storm sewers, channels
and channel sections, detention basins, outlet lines, and analyses
of the effect of said improvement on the receiving outlet pipe, the
associated channel and high water elevations.
(5)
The slope, type, and size of all existing and proposed storm
sewers and other waterways.
(6)
A plot or tabulation of storage volumes with corresponding water
surface elevations and of the basin outflow rates for five-year, fifty-year
and 100-year water surface elevations for all detention basins. If
development work is to be performed in phases, said tabulations should
be performed independently for each phase.
(7)
Design hydrographs of inflow and corresponding outflow for both
the fifty-year and 100-year design runoff events for the site's
projected final state of development and the calculated five-year,
fifty-year, and 100-year peak inflows from the development under natural,
existing conditions and under the projected final state of development
for all detention basins.
(8)
A profile and one or more cross sections of all existing and
proposed channels or other open drainage facilities, showing existing
conditions and the proposed changes thereto. In addition, the project
engineer will provide high water elevations expected from stormwater
runoff under the controlled conditions called for by these regulations
and the relationship of structures, streets, and other utilities to
such channels.
(9)
An engineering cost estimate detailing and explaining all construction
costs associated with the stormwater management plan.
STORMWATER RUNOFF
Water that results from precipitation which is not absorbed
by soil or plant material, which does not evaporate and which flows
over the surface of the ground or is collected in channels, conduits
or ponds.
STREAMBANK, TOP OF EXISTING
The usual boundaries, not the flood boundaries of a stream
channel. The top of the natural incline bordering a stream.
STRUCTURE
Anything that is constructed or erected with a fixed location
on the ground or attached to something having a fixed location on
the ground. Among other things, structures include buildings, fences,
signs, mobile homes, swimming pools, and walls.
SWPPP
The Stormwater Pollution Prevention Plan.
TRADITIONAL AGRICULTURAL USES
Uses commonly classed as agricultural or horticultural, including
forestry, crop farming, truck gardening, wholesale nursery operations,
animal husbandry, the operation of any machinery or vehicles incidental
to such uses, and the construction of single-family dwellings and
other farm structures incidental to and typically associated with
such uses. Agri-business uses are not considered to be traditional
agricultural uses and include but are not limited to commercial grain
elevators, commercial facilities for grain storage, drying, or other
processing; commercial feed, seed, or fertilizer manufacturing, processing,
or sales; commercial farm machinery repair or sales; large scale or
commercial livestock or poultry production facilities; agricultural
research or development offices or laboratories; or any other agriculture-related
use, which substantially increases the size of paved or compacted
areas which may cause significant or measurable increases in stormwater
runoff.
TRIBUTARY WATERSHED
The entire catchment area that contributes stormwater runoff
to a given point.
VILLAGE
The Village of Oakwood, Vermilion County, Illinois.
WATERCOURSE
Any stream, creek, brook, branch, natural or artificial depression,
slough, gulch, reservoir, lake, pond or natural or man-made drainage
way in or into which stormwater runoff and flood waters flow either
regularly or intermittently.
WET BOTTOM STORMWATER STORAGE AREA
A facility that contains a body of water and which accumulates
excess stormwater during periods when the restricted stormwater runoff
release rate is less than the stormwater inflow rate.
The following requirements shall be applicable and shall be
satisfied prior to the construction, improvement or development of
any structure, project or land which is subject to the provisions
of this article:
A. Maximum release rate. The maximum controlled release rate for each
independent watershed area within the owner's land shall be determined
in the following manner:
(1) For that portion of the watershed outside of an owner's land,
the peak rate of runoff which would have occurred for a five-year
return period storm under the state of development existing just prior
to application for development of an owner's land shall be calculated
and determined.
(2) For that portion of the watershed within the lands of an owner, the
peak rate of runoff which would have occurred for a five-year return
period storm under a state of traditional agricultural usage shall
be calculated and determined.
(3) The maximum controlled release rate for each independent watershed area within the owner's land as it exits the owner's land for storms up to and including the fifty-year return period storm shall be the sum of Subsection
A(1) and
(2) of this section.
(4) The peak rate of runoff which would have occurred for a five-year
return period storm shall be determined using the rational method
or other substantial method acceptable to the Village Engineer.
(5) The five-year and fifty-year return period storm shall be determined
utilizing "Bulletin 71 - Rainfall Frequency Atlas for the Midwest"
by Floyd A. Huff and James R. Angel and published in 1992 by the Illinois
State Water Survey, or the most recently available information.
(6) In the event that the downstream stormwater runoff drainage system
is inadequate to accommodate the maximum release rate provided above,
then the Village, at its option, may reduce the allowable release
rate to that rate permitted by the capacity of the receiving stormwater
runoff drainage system and additional storage as determined by the
Village Engineer may be required to store that portion of the runoff
exceeding the capacity of the receiving stormwater runoff drainage
system. When the Village exercises this option, the owner and the
Village shall pay a proportional share of the costs of the storage,
as mutually determined by the Village and the owner.
B. Storm sewer systems.
(1) Capacity. All storm sewer systems shall be designed for the peak
rate of runoff from a minimum of a five-year return period storm.
The five-year return period storm shall be determined utilizing "Bulletin
71 - Rainfall Frequency Atlas for the Midwest" by Floyd A. Huff and
James R. Angel and published in 1992 by the Illinois State Water Survey,
or the most recently available information. The minimum pipe diameter
shall be 10 inches. The system shall have a free outlet. All design
calculations and modeling results, as applicable shall be submitted
to the Village Engineer for approval.
(2) Grade. Sewer grades shall be such that, in general, a minimum of
two feet of cover is maintained over the top of the pipe; however,
the minimum cover shall be three feet for vitrified clay pipe. Pipe
cover less than the minimum may be used upon site-specific approval
by the Village Engineer. Uniform slopes shall be maintained between
inlets, manholes and inlet to manhole. Minimum and maximum allowable
slopes shall be those capable of producing velocities between two
and 10 feet per second, respectively, when the sewer is flowing full.
Velocities lower than the minimum or higher than the maximum may be
used upon site-specific approval by the Village Engineer.
(3) Overland flow. The maximum distance for overland flow of stormwater
runoff to an underground storm sewer system shall be 600 feet.
(4) Alignment. Storm sewers shall be constructed in a straight line between
manholes insofar as possible. Where long radius curves are necessary
to conform to street layout, the minimum radius of curvature shall
be no less than 100 feet. Deflection of pipe sections shall not exceed
the maximum deflection recommended by the pipe manufacturer. The deflection
shall be uniform and the finished installation shall follow a smooth
curve.
(5) Manholes. Manholes shall be installed to provide access to continuous
underground storm sewers for the purpose of inspection and maintenance.
Manholes shall be provided at the following locations:
(a)
Where two or more storm sewers converge;
(b)
At the point of beginning or at the end of a curve, and at the
point of reverse curvature (PC, PT, PRC) of a storm sewer;
(d)
Where an abrupt change in alignment occurs;
(e)
Where a change in pipe slope occurs;
(f)
At suitable intervals in straight sections of sewers;
(g)
The maximum distance between manholes shall be as follows:
For 10-inch diameter storm sewers:
|
300 feet
|
For 12-inch to 24-inch diameter storm sewers:
|
350 feet
|
For storm sewers over 24 inches in diameter:
|
500 feet
|
(h)
All manholes shall be constructed in accordance with the standard
details in Appendix A.
(6) Inlets and catch basins. Inlets and catch basins on drainage structures
shall be utilized to collect surface water through grated openings
and convey it to storm sewers or culverts. All inlets and catch basins
shall be constructed in accordance with the attached standard details
and as approved by the Village Engineer.
(7) Trench backfill. Trench backfill requirements shall conform to the
applicable portions of the Standard Specifications for Road and Bridge
Construction, Illinois Department of Transportation (latest edition)
and shall be compacted coarse aggregate CA-6 or CA-10, or as otherwise
approved by the Village Engineer.
(8) Materials.
(a)
The type of sewer pipe shall be:
[1] Concrete and/or reinforced concrete pipe;
[2] Bituminous coated corrugated steel culvert pipe;
[3] Bituminous coated corrugated aluminum alloy culvert pipe.
(b)
The strength requirements of the sewer pipe shall conform to
the requirements of the Standard Specifications for Road and Bridge
Construction, Illinois Department of Transportation; Engineer to verify
the strength of the pipe used.
(9) Workmanship. The specifications for the construction of storm sewers
shall not be less stringent than those set forth in the Standard Specifications
for Water and Sewer Main Construction in Illinois, latest edition.
Construction of any utility pipe or conduit such as gas, electric
and water through any storm sewer structure shall be prohibited, except
with approved conflict structures.
C. Surface drainage systems. Surface drainage will be permitted for
stormwater, where cost estimates show storm sewers are not economically
feasible (including all life-cycle costs and the value of the land
consumed), where land use conditions indicate this method is feasible,
and where topographic conditions indicate there will be no difficulty
from this method of disposal of stormwater. Such economic and feasibility
studies shall be reviewed and approved by the Village Engineer.
(1) Capacity. All surface drainage systems of stormwater shall be designed
for the peak rate of runoff from a minimum of a five-year return period
storm. The five-year return period storm shall be determined utilizing
"Bulletin 71 - Rainfall Frequency Atlas for the Midwest" by Floyd
A. Huff and James R. Angel and published in 1992 by the Illinois State
Water Survey, or the most recently available information. The system
shall have a free outlet. All design calculations must be submitted
to the Village Engineer for approval.
(2) Grade. Stormwater surface drains shall be constructed with uniform
bottom slopes along the entire length of the drains. Minimum and maximum
allowable grade shall be those capable of producing velocities between
0.5 and 10.0 feet per second, respectively, when the surface drain
is flowing full. In all cases, stormwater velocity shall be controlled
to eliminate problems of soil erosion or other damage which could
detract from the primary use of the area.
(3) Side slopes and bottom widths. Surface drains shall be constructed
having side slopes of not less than three feet horizontal to one foot
vertical, or flatter. Side slopes steeper than three feet horizontal
to one foot vertical shall not be used without site-specific approval
by the Village Engineer. A channel bottom width of not less than one
foot shall be provided.
(4) Erosion. Design of surface drains shall include control of soil erosion.
Temporary seeding or other soil stabilization measures shall be utilized
during construction to control erosion. Permanent erosion control
measures such as mulching, hydro-seeding, nurse crops, conventional
seeding, or other similar measures shall be utilized upon completion
of construction. These measures shall meet or exceed the standards
established by the Vermilion County Soil and Water Conservation District,
if any.
(5) Culverts. Culverts and similar structures shall have a capacity which
meets or exceeds the capacity of the surface drain, but shall be a
minimum of 12 inches in diameter. The flow line of a culvert shall
match the flow line of the surface drain. Culverts shall meet or exceed
the requirements of "An Ordinance to Regulate the Construction, Maintenance,
or Replacement of driveways and driveway culvert pipes within the
right-of-ways under the jurisdiction of the Village of Oakwood" as
amended.
(6) Workmanship. The specifications for the construction of stormwater
surface drains shall equal or exceed those set forth in the Standard
Specifications for Road and Bridge Construction, Illinois Department
of Transportation (latest edition) or shall be as otherwise approved
by the Village Engineer.
(7) Tile drains. All major stormwater surface drains as designated by
the Village Engineer shall also be constructed with a subsurface drainage
title or tubing encased to the surface with Class "X" washed gravel
as shown on the attached standard details.
D. Excess stormwater passageway. An excess stormwater passageway shall
be provided for the floodplains of all natural watercourses and such
man-made watercourses and storm drainage systems as the Village Engineer
may direct, which shall have adequate capacity to convey the excess
stormwater from the tributary watershed. The capacity of this excess
stormwater passageway shall be adequate to transport the peak rate
of runoff from the fifty-year return period storm, assuming all upstream
areas are fully developed for uses specifically permitted by existing
zoning and antecedent rainfall has saturated the tributary watershed.
The increase due to saturation shall be calculated by a ratio of the
amount of runoff of the Antecedent Moisture Condition III to Antecedent
Moisture Condition II of the twenty-four-hour, fifty-year return frequency
storm as outlined by the United States Soil Conservation Service for
the tributary watershed. No structures shall be constructed within
this passageway; however, streets, parking lots, playgrounds, park
areas, pedestrian walkways, open green space, and utility and sewer
easements shall be considered compatible uses. Design of the excess
stormwater passageway shall include control of stormwater velocity
to eliminate problems of soil erosion or other damage which would
detract from the primary use of the area. The entire area of any excess
stormwater passageway within the corporate limits of the Village and
1 1/2 miles thereof shall be placed in a drainage easement or
remain under the jurisdiction of the Village, other governmental unit,
or Village-approved quasi-public agency (i.e., homeowner's association,
etc.) In the event this passageway is reshaped or its capacity to
transport excess stormwater is otherwise restricted, the Village may
cause to have any restrictions removed at the expense of the agency,
party, or parties causing or permitting these restrictions. Should
a natural drain exist, it shall be preserved and used to the extent
possible, as a part of the excess stormwater passageway. Where it
is necessary to reroute a natural drain, the rerouted drain shall
have a capacity equivalent to or greater than that which existed in
the natural drain and as otherwise required by this article.
E. Stormwater storage. When the maximum controlled stormwater runoff
rate would be exceeded upon the development, redevelopment, or new
construction on the owner's land, stormwater storage methods
shall be provided and constructed by the owner. Any one or all of
the stormwater storage methods listed shall be provided and constructed.
(1) General requirements.
(a)
The volume of required stormwater storage shall be calculated
on the basis of the maximum value achieved from the runoff of a fifty-year
return period storm less the volume of water released through the
outlet structure. The fifty-year return period storm shall be determined
utilizing "Bulletin 71 - Rainfall Frequency Atlas for the Midwest"
by Floyd A. Huff and James R. Angel and published in 1992 by the Illinois
State Water Survey, or the most recently available information. The
method utilized for calculation of volume of storage shall be the
Soil Conservation Service (SCS) method or any other substantial method
acceptable to the Village Engineer. The release rate of the outlet
structure when one-half of the storage volume is filled may be used
in lieu of routing techniques in small drainage areas. The control
structure shall be designed to maintain as uniform a flow as possible,
independent of the stormwater storage volume. Where the proposed structure,
project, or land development forms only a portion of a watershed or
contains portions of several watersheds, the storage volume calculations
shall be based upon the area of the entire project, development, or
land use change.
(b)
The storage of excess stormwater runoff from a fifty-year return
period storm having a duration of 24 hours, released at the allowable
rate, shall not result in a storage duration in excess of 24 hours,
but storage duration may be as long as 48 hours upon site-specific
approval by the Village Engineer. All design calculations must be
submitted to the Village Engineer for approval.
(c)
Each stormwater storage area shall be provided with a method of overflow in the event a storm in excess of the design capacity occurs. This overflow facility shall be constructed to function without special attention and can become a part of the excess stormwater passageway described in Subsection
C of this section.
(d)
The entire stormwater storage area shall be designed and constructed
to fully protect the public health, safety, and welfare. If a condition
occurs in the stormwater storage area which is hazardous to the public
health, safety, or welfare, the person responsible for the condition
will be required to provide approved corrective measures. In the event
these corrective measures are not provided, the Village may eliminate
the hazard at the expense of the person responsible.
(2) Dry bottom stormwater storage.
(a)
Dry bottom stormwater storage areas may be designed to serve
a secondary purpose for recreation, open space, or similar type of
uses which will not be adversely affected by occasion intermittent
flooding;
(b)
Minimum grades for turf areas shall be 0.5% (200 units horizontal
to one unit vertical) and maximum side slopes shall be 25% (four units
horizontal to one unit vertical). Storage areas side slopes shall
follow the natural land contours as closely as practicable, and a
minimum of earth excavation shall be used to create the storage facility.
Geometrics of dry bottom stormwater storage areas shall be approved
by the Village Engineer.
(c)
Temporary seeding or other soil stabilization measures shall
be established in the stormwater storage area and excess stormwater
passageway immediately following the construction or reconstruction
of these areas. During the construction of the overall development,
it is recognized that a limited amount of sediment buildup may occur
in the stormwater storage area due to erosion. In no case shall the
volume of the storage area be reduced to less than 90% of the required
volume during the construction phase of the development. Permanent
erosion control measures such as mulching, hydro-seeding, conventional
seeding, nurse crops, fertilizing, or sod installation shall be utilized
to control soil movement and erosion within the storage area and excess
stormwater passageway. These measures shall meet or exceed the standards
established by the Vermilion County Soil and Water Conservation District,
if any. The installation of these permanent measures shall take place
only after the majority of construction and other silt- and sediment-producing
activities have been completed. Prior to the establishment of the
permanent erosion control measures, the required capacity of the stormwater
storage area and the excess stormwater passageway shall be restored.
(d)
The control structure shall be provided with an interceptor
for trash and debris, and it shall be designed and constructed to
prevent soil erosion and not to require manual adjustments for its
proper operation. The control structure shall be designed to operate
properly with little or no maintenance and/or attention. The control
structure shall be provided with safety screens for any pipe or opening
to prevent children or large animals from crawling into structures.
The control structure shall be constructed to allow access to it at
all times, including times of flood flow.
(e)
Adequate impact stilling basins shall be provided to ensure
that downstream soil erosion is mitigated as much as practical and
the regime of the downstream drain facility is not disturbed.
(f)
Low-flow conduits or channels shall be provided in stormwater
storage areas; these conduits or channels shall be so constructed
that they will not interfere with any secondary usage of the storage
area and will reduce the frequency of time that the storage area will
be covered with water. Low-flow conduits shall facilitate complete
interior drainage of the stormwater storage area.
(g)
Pipe outlets of less than six inches in diameter shall not be
allowed. Multiple outlets from a storm storage area shall be avoided
if they are designed to be less than 12 inches in diameter.
(h)
The maximum planned depth of stormwater stored shall not exceed
six feet.
(i)
Tile underdrains shall be provided in dry bottom stormwater
storage areas. These tile underdrains shall be so constructed that
they will not interfere with any secondary usage of the storage area.
Tile underdrains shall be so constructed so that they shall facilitate
dewatering of the soils in the stormwater storage area to avoid marshy
or saturated soil conditions. Tile underdrains systems may be combined
with the low flow conduits or channels system and shall be as approved
by the Village Engineer.
(j)
Danger signs shall be mounted at appropriate locations, as determined
by the Village Engineer, to warn of deep water, possible flood conditions
during storm periods and other dangers that may exist. Fencing shall
be provided whenever side slopes are greater than four horizontal
to one vertical.
(3) Wet bottom stormwater storage. Wet bottom stormwater storage areas
shall be designed in compliance with all the regulations which are
applicable and govern the construction of dry bottom stormwater storage
areas. The following additional regulations shall apply:
(a)
The water surface area of the permanent pool shall not exceed
one-tenth of the area of the tributary watershed, or as approved by
the Village Engineer.
(b)
Protection of the shoreline must be provided to alleviate soil
erosion due to wave action. Provide a protective "safety shelf" that
extends a minimum of eight feet from the edge of the permanent pool
waterward. Safety shelf shall have a slop of 10:1 (horizontal-to-vertical)
or flatter. The maximum depth of the permanent pool of water over
the safety shelf shall be 1.5 feet.
(c)
Except as noted above, the minimum normal water depth shall
be three feet. If fish are to be used to keep the pond clean, at least
one-quarter of the pond area shall be a minimum of 10 feet deep. In
addition to that specified above, an additional two vertical feet
shall be provided for sediment storage.
(d)
Facilities shall be provided to lower the pond elevation by
gravity flow for cleaning purposes and shoreline maintenance.
(e)
The control structure for stormwater release shall be designed
to operate at full design release rate with only a small increase
in water depth in order to minimize the land surface wetted by frequent
minor stormwater runoff conditions.
(f)
Measures shall be included in the design to prevent pond stagnation.
This may be accomplished by aeration or some other method used to
ensure aerobic pond conditions.
(g)
The volume of water permanently stored shall not be considered
to be part of the required excess stormwater storage volume.
(h)
Wet storage basins shall be permanently fenced when so required
by the Village Planning Commission, using six-foot-tall chain link
or PVC fencing.
(4) Paved stormwater storage. Design and construction of the pavement
base must insure that there is no pavement damage due to flooding.
Control structures in paved areas must be readily accessible for maintenance
and cleaning. Vortex control devices will be required.
(5) Rooftop stormwater storage. Rooftop storage of excess stormwater
shall be designed and constructed to provide permanent control inlets
and parapet walls to contain excess stormwater. Adequate structural
roof design must be provided to ensure that roof deflection does not
occur which could cause the roofing material to fail and result in
leakage. Overflow areas must be provided to ensure that the weight
of stored stormwater will never exceed the structural capacity of
the roof.
(6) Automobile parking lot storage areas. Automobile parking lots may
be designed to provide temporary detention storage on a portion of
their surfaces. Automobile parking facilities used to store excess
stormwater must be constructed having a maximum depth of stored stormwater
of 0.5 feet; and these areas shall be located in the most remote,
least used areas of the parking facility. Design and construction
of automobile parking in stormwater areas must insure that there is
no damage to the parking facility due to flooding, including damage
to the subbase. "WARNING" signs shall be mounted at the locations
deemed by the Village Engineer to warn others of possible flood conditions
during storm periods.
(7) Underground stormwater storage. Underground stormwater storage facilities
must be designed for easy access in order to remove accumulated sediment
and debris. These facilities must be provided with a positive gravity
outlet.
(8) Stormwater storage areas which will be filled to capacity by frequent
storms shall be designed in a manner that will protect immediate downstream
properties, and all overflow structures shall be designed to function
properly and effectively without the necessity of making manual adjustments
A larger outlet for a stormwater storage area may be permitted by
the administrator for the orderly management of stormwater runoff
where large tributary areas were developed without detention.
(9) If the orderly management of the stormwater runoff cannot be achieved
by passing the entire tributary area runoff through the stormwater
storage area, then the stormwater storage area may be constructed
to exclude the runoff from the tributary area originating outside
of the area to be developed.
(10)
Where the owner has a large tract of land upon which development
is to occur in several phases, the owner may construct, upon site-specific
approval by the Village Engineer, one stormwater storage facility
which is designed to be enlarged at later dates as additional portions
of the owner's lands are developed and as additional stormwater
storage is required due to that development.
(11)
Where portions of the owner's land are tributary to the
same drain for an outlet, but which are within two or more tributary
areas to that drain, the owner may construct, upon site-specific approval
by the Village Engineer, compensatory stormwater detention facilities
within one tributary area which offset the lack of construction of
stormwater detention facilities in another tributary area. Such compensatory
storage shall be designed and constructed such that the net effect
of these facilities shall be to limit the amount of stormwater runoff
released into the drain to that which would have occurred had stormwater
detention facilities been constructed for all the tributary areas.
(12)
Storm water storage areas may be planned and constructed jointly
by two or more land owners so long as compliance with this article
is maintained.
(13)
Where fringe portions of the owner's land are, in the opinion
of the Village Engineer, difficult or impractical to drain to the
detention facilities to be constructed for the rest of the property,
the owner may apply for a variance of the requirements of this article.
Such a variance may be granted for an area of land equal to up to
2% of the total property involved. In such cases, a variance may be
granted without owner's proof of the avoidance of an unnecessary
hardship and without specifically stating the public's interest
in granting the variation.
(14)
Where detention, retention, or depressed stormwater storage
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
for the development. Any eroded sediment captured in these facilities
shall be removed by the developer before project completion in order
to maintain the design volume of the facilities.
F. Other requirements.
(1) Automobile parking lots and other land uses with significant portions
of paved and roofed areas as determined by the Village Engineer shall
be constructed with internal stormwater runoff drainage systems.
(2) Sump pumps. Sump pumps installed to receive and discharge ground
waters or stormwater runoff shall be connected to the storm sewer
where possible or discharged into a designated stormwater runoff drainage
facility. No discharge of stormwater runoff or ground water by a sump
pump into a sanitary sewer shall be allowed. No discharge of sanitary
sewage into a storm drain shall be allowed.
(3) No sump pump, footing drain, or downspout shall discharge onto a
street surface, paved curb and gutter system, or public sidewalk.
(4) Downspouts. Downspouts and roof drains shall discharge onto the ground
or be connected to a storm drain. No downspouts or roof drains shall
be connected to a sanitary sewer.
(5) Footing drains. Footing drains and drainage tile shall discharge
into a storm sewer or other storm drainage facility. No footing drains
or drainage tile shall be connected to a sanitary sewer.
(6) Sump pump drains. Beginning on the effective date of this article,
any newly constructed or installed structure equipped with a sump
pump and located on property, any part of which is within 100 feet
of a sump drain line or storm sewer outlet, shall be required to connect
to tie-in to such line or outlet.
It is illegal and a violation of this article for any person,
firm or corporation to allow or cause any cross connection between
any storm sewer line within the Village with any sanitary sewer line
within the Village, which violation shall be punishable in accordance
with the general penalty provisions of the Village ordinances, be
subject to injunctive relief, and, to the extent consistent with applicable
law, be subject to the Village's immediate action to block or
sever such illegal cross connection, if the public health is significantly
jeopardized by such illegal connection.
Any party shall have the right to appeal decisions of the Village
Superintendent of Public Works to the Village Board of Trustees. A
request for an appeal shall be filed by the owner with the Village
Superintendent of Public Works who shall refer it, together with his
or her recommendation to the Board for its decision. The request for
an appeal shall be written and shall state specifically what action
is sought and the public's interest in granting the appeal.
The drainage design standards required by this article are considered
reasonable for regulatory purposes and are based upon engineering
and scientific methods of study. Larger rainfalls may occur on rare
occasions, and greater runoff rates or decreased hydraulic capacities
of the structures may occur due to uncontrollable circumstances. This
article does not imply that an area within or outside of the sites
to which the standards of this article have been applied will be totally
free from potential flooding or runoff damages. This article shall
not create liability on the part of the Village or any officer or
employee or agent thereof for any damages that result from reliance
on this article or any administrative decision lawfully made thereunder.
When this article imposes a greater restriction than those imposed
or required by the provisions of existing ordinances or rules and
regulations, this article shall control. When the provisions of existing
ordinances or rules and regulations impose greater restrictions than
those imposed or required by this article, they shall control.