HomeMy WebLinkAboutORDINANCE - 1054 - 4/13/1976 - STORM WATER DETENSION AMENDEDORDINANCE NO. 1054
AN ORDINANCE AMENDING CHAPTER 8, SUBDIVISIONS, SECTION 8.005 OF THE
MUNICIPAL CODE OF THE VILLAGE OF ELK GROVE VILLAGE RELATING TO STO tK
DRAINS AND ADDING THERETO STO&`1 WATER DETENTION
NOW, THEREFORE, BE IT ORDAINED by the President and Board of Trustees
of the Village of Elk Grove Village, Counties of Cook and DuPage, Illinois:
Section 1: That Section 8.005 Required Improvements) of Chapter 8,
Subdivisions, is hereby amended to read as follows:
8.005 Required Improvements) Storm Drains. An adequate system of
storm water drainage designed for a one hundred year return frequency
rain*shall be constructed and installed, consisting of pipes, tiles,
manholes, inlets and other necessary facilities that will adequately
drain the subdivision and protect roadway pavements and will prevent
the accumulation of storm water at any place under normal conditions.
Open ditches shall be prohibited in all residential areas. Backyard
swales are permitted in residential areas subject to the following
regulations:
a) Maximum and minimum slopes and general design criteria
of the Federal Housing Administration's "Minimum Property Requirements"
will be acceptable except as herein modified.
b) No continuous swale shall have a length exceeding
six hundred feet.
c) Minimum grade of the flowline shall be four -tenths percent.
d) At no point in the swale shall the flowline be more than
three feet below the finished grade of the top soil at the foundation
of the house opposite the Swale.
*(See attached charts for Rainfall Intensity and Time of Concentration Data)
e) No change in alignment of a backyard swale shall exceed
forty-five degrees.
Open ditches are allowed for rear yard drainage in the industrial
and commercial areas if they conform to the following regulations:
1) The bottom of the ditch shall be lined with a five (5)
inch thick concrete invert minimum of 3'-0" wide. Two.Number 6
Reinforcing Rods are to be equally spaced for the entire length of
the invert.
2) The grade of the invert shall be designed to provide
a velocity of flow between ? and 5 feet per second.
slope.
3) The sides of the ditch shall not exceed a 2 to 1
4) All side slopes shall be sodded from the invert to
the top of the slope.
5) Any alignment change shall require concrete slope
protection on the side slopes of the ditch.
Storm Water Detention General: The following shall govern the design
of any improvement with respect to the drainage and detention of
storm water runoff.
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1) Streets, ckn, depths of lots, parks ni ner public
grounds s..,ll he located and laid out in such a manner a4
to preserve and uttlize natural streams, chann as and
detention basLus, lnc.luding wherever possible the larger
streams and flood plains within parks or other public grounds.
2) Storm water from a ]On year return frequency storm must be
stored and/or transporecd from any drveLopment in such a
manner that no damage results from flooding.
3) A combination of storage and controlled release of storm water run-
off is required for all nonresidential developments, regardless of
size, and for residential developments exceeding 5 acres in are:.
4) The release rate of storm water from all developments requir-
ing detention shall not exceed the storm water runoff rate
from the arca in its natural undeveloped state.
Because of the flat conditions of the land in this area, channel
configurations cut by nature are generally unable to handle
the runoff from high intensity rainfalls and results in flood
plain storage or spreading of runoff over the land areas
during the larger storm periods. In order not to increase the
runoff from such areas after development, the release rate must
be limited to the carrying capacity of these natural channels.
A release rate of not greater than that calculated from a
storm of three (3) year-requency with a runoff rate coefficient
of 0.15 shall be used, unless the applicant can show by detailed
calculations, which are acceptable to the Village Engineer, that
the discharge rate of the natural outlet channel serving the
area is greater.
5) Drainage systems shall have adequate capacity to bypass
through the development the flow from all upstream areas
for a storm of design frequency assuming that the land
is in a fully developed state under present zoning or
zoning proposed under a Comprehensive Plan. The bypass
flow rate shall be computed utilizing a runoff coefficient
of not less than 0.35. An allowance will be made for up-
stream detention when such upstream detention and release
rate has previously been approved by the Village Engineer
and that evidence of its construction can be shown.
6) The live detention storage to be provided will be calculated
on the basis of the 100 -year frequency rainfall as published
by the U. S. Weather Bureau for this area. The detention
volume required will be that necessary to handle the run-
off of a 100 -year rainfall, for any and all durations, from
the fully developed drainage area tributary to the reservoir,
less that volume discharged during the same duration at the
approved release rate.
7) Sharply meandering streams or channels may be partly straightened
and minor changes made in other channels, subject to approval
of the Village Engineer, provided (1) the floodway dimensions
of the stream or channel are maintained, (2) the volume of flood-
water storage outside the floodway is not reduced, and (3) the
changes and channels comply with the provisions of Section A.
8) The smaller uppermost reaches of drainage channels and swal.es
forming the natural drainage system near the watershed divide
may be relocated or eliminated and incorporated into the
planned system of storm sewers upon a showing that the system
is adequate and can safely handle the flood crater runoff
following the heavier rainstorms.
9) Sturm sc%:cr outfalls shall he so designed, by reason of eleva-
tion of the invert, pumping, or othcrwJse., that when the re-
ceiving stream is In full [.loud the :;form se\r(er will continnc
to drain. the arra it is drs:t.;;uoc{ to serve at a uniform rate.
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10) Cross :,e ns and grades of streets des as channels shall
be deulgncn to temporarily store and convey the overflow from
storm sewers and over -the -curb runoff and be provided with
adequate outlets for safe disposal of such overflow. The
street cross-section shall provide a lot grade for the finished
floor of each adjoining building at' lutist 2-Pe(,t higher than
the crown of the pavement, and the minimum sill elevation of
openings in the outer walls of such buildings shill be at
least 2.5 feet above the crown elevation.
11) The crown of street pavements hereafter built adjoining or
near stream, floodwater runoff channels or detention basins
shall be not lower than the established high-water elevation
plus 2 -feet, in the case of major streets, and plus 1 -Foot,
in the case of other streets.
12) Waterway openings of bridges and culverts hereafter built
over streams or floodwater runoff channels shall be designed
with a waterway opening large enough to handle the flow from
a 100 -year frequency storm.
13) Construction, filling, or other similar physical occupation
of the flood plain as defined by the Department of the Interior
United States Geological Survey, which is otherwise prohibited by
this ordinance, may be permitted if adequate compensatory storage
volume is provided. This shall be accomplished by developing
in the existing flood plain excavated spice below the high-
water elevation in an amount equal to the flood storage
capacity preempted by tte proposea construction. in the case
of streams and channels, such excavation shall be made opposite
or immediately upstream from the area to be filled. It shall
be the duty of the property owner to conduct such excavation
in a manner consistent with the other provisions of this
ordinance and may be done only after the approval by the
Village Engineer has been granted. Approval of the Village
Engineer will be contingent upon the property owner's ability
to demonstrate that the compensatory storage will be adequate
and satisfactory for its intended purpose.
B. DRAINAGE PLAN: A comprehensive drainage plan must be submitted to the
Village Engineer vhich incorporates the forementioned
rules and shall provide or be accompanied by maps or
other descriptive material showing the following:
1) The extent and area of each watershed tributary to the drainage
channels in the subdivision.
2) The street storm sewers and other storm drains to be built, the
basis of their design, the outfall and outlet locations and
elevations, receiving stream or channel and its high-water
elevation, and the functioning of the drains during high-water
conditions.
3) The parts of the proposed street system where pavements
are planned to be depressed sufficiently to convey or
temporarily store overflow from strom sewers and over -the -curb
runoff resulting from the heavier rainstorms and the outlets
for such overflow.
k) Existing streams and floodwater runoff channels to be main-
tained, enlarged, altered otherwise, and eliminated; and new
channels to be constructed, their locations, cross sections
and profiles.
5) Existing culverts and bridges, drainage areas, elevation,
and adequacy of waterway openings; and new culverts and .
bridges to be built, their materials, elevations, waterway
openings and basis of design.
G) Existing detention ponds and basins to he maintained, enlarged,
altered otherwir:c and net! ponds or hneinti to he built- with
duns, and their dexiP,n.
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C. CONSTMICTION REQUIREMENTS FOR DETENTION PONDS:
1) Detention Ponds Containing Permanent Water
a - Detention reservoirs containing permanont lakes nust
have a water area of at least one-half acre and a minimum
depth of approximately 10 feat over at least 25 percent of the
total area. The remaining lake area must have an avera,;t
depth of at least 5 feet and should havo no extensive shallow
areas.
b - In excavated lakes the underwater side slopes in the
lakes must be stable. In the case of valley storage,
natural slopes may be considered to be stable.
c - A safety ledge four to six feet in width is required
and must be installed in all lakes approximately 30" to
36" below the permanent water level. In addition a
ledge 12" to 18" above the permanent water line must be
provided. The slope between the two ledges must be
stable and of a material which will prevent erosion due
to wave action such as stone or rip -rap.
d - A safety ramp exit from the lake is required in all cases
and should have a minimum width of 20' and exit slope of
6 horizontal to 1 vertical. The ramp must be of a
material that will prevent its deterioration due to
vehicle use and/or wave action.
e - Periodic maintenance is required in lakes to control week
and larval growth. The reservoir must also be designed
to provide for the easy removal of sediment c:hich will
accumulate in the lake during periods of reservoir opera-
tion. A means of maintaining the designed water level of
the lake during prolonged periods of dry weather is also
required. One suggested method is to have a water hydrant
near the pond site.
2) Detention Ponds Containing Permanent Water and Dry Detention
Ponds:
a - All excavated spoils must be spread so as to provide for
aesthetic and recreational features such as sledding hills,
sport fields etc. Slopes of 6 horizontal ,to 1 vertical
are required except where recreation uses call for steeper
slopes. Even these features must have a slope no greater
than 3 horizontal to 1 vertical for safety, minimal erosion,
stability, and ease of maintenance.
b - Safety screens must be provided for any pipe or opening
to prevent children or large animals from crawling
into the structures. A maximum opening of 6 -inches is
required.
c - Danger signs must be mounted at appropriate locations to
warn of deep water, possible flood conditions during
storm periods and other dangers that exist. Life preservers
must also be placed at appropriate locations. Fencing
must be provided if deemed necessary by the Village Engineer.
d - In valley storage reservoirs, an emergency spillway or
other provision must be provided to allow for by-passing
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flood flows during periods when the design capacity of the
reservoir and outlet has been exceeded. This spillway must
be of such a design that its operation is automatic and does
not require manual attention.
e - Sod or other suitable vegetative cover as approved by the
Village Engineer must be provided throughout the entire
reservoir area.
f - Debris and trash removal and other necessary maintenance
must be performed after each storm to assure continued
operation in conformance to the design.
3) Dry Detention Ponds:
a - Dry detention ponds must have an underdrain system to minimize
the wetness of the bottom so that water does not remain stand-
ing in the bottom thereby harboring insects and limiting the
potential use of the reservoir. The underdrain system could
empty by gravity into the wet well of a pump station or to the
receiving stream directly.
b - The dry detention pond must be designed to serve multi-purpose
functions. Recreational facilities, aesthetic qualities, etc.
as well as flood water storage must be considered in planning
the reservoir.
D. RESPONSIBILITY FOR MAINTENANCE OF DETENTION PONDS:
1. The responsibility for maintenance during construction, and there-
after, shall be the responsibility of the land developer/owner.
2. Storm water detention and retention basins may be donated to the
Village or other unit of government designated by the Village,
for ownership and permanent maintenance, providing:
a - The facility has been designed and constructed according to
Village requirements enumerated above;
b - All improvements have been constructed, approved and accepted
by the Village for the land area served by the drainage basin;
c - Detention ponds containing permanent water are located within
a tract of land consisting of fifteen (15) acres or more, of
which 30% of the area is above the high water line; and in-
cludes a body of water of ten (10) surface acres or more, of
which 50 percent is to have a minimum depth of ten (10) feet:
4 inch size rip rap to be provided 3 feet below and 3 feet
above normal water line; all slopes between the rip rap and
high water line are to be sodded and the remaining land area
is to be hydroseeded; are equipped with electrically driven
aeration devices to maintain proper aerobic conditions to
sustain acquatic life; have a four (4) foot wide crushed
limestone walkway at the high water line entirely around the
body of water; are situated to permit public access 200 feet
wide and not less than 200 feet to the high water line, and
providing further that the high water line is not closer than
thirty-five (35) feet to any property line.
d - Dry detention ponds are located on a tract of land consisting
of two (2) acres or more of land, including a minimum bottom
area 275x275 feet or 200x375 feet; maximum side slopes of 5:1;
all slopes are to be sodded to the high water line; the bottom
of the basin and areas above the high water line are to be
hydroseeded; and providing further that the high water line
is not closer than thirty-five (35) feet to any property line.
Section 2: The Village Clerk is hereby authorized to publish
this ordinance in pamphlet form.
Section 3: This ordinance shall be in full force and effect
from and after its passage, approval and publication according to law.
PASSED this
13th
day
of April
APPROVED this
13th
day
of April ,
VOTE: AYES:
6 NAY:
0
ABSENT: 0
ATTEST:
Village Cle
1976.
1976.
Published in pamplet form this 21st day of April, 1976, in the
Elk Grove Herald.
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L 13.711.. wa
SOURCE: t jTMENT OF THE ARMY. TECHNICAL MANU, '5-820-1.
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—EXAMPLE
0 100
200 300
400
500 600.
LENGTH
STANDARDIZED
TO
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0 10 20 30 40 50
MINUTES
TIME OF CONCENTRATION EASED ON S=1.0%
LENGTH OF OVERLAND FLOW (FEET)
STANDARDIZED TO S=1.0%
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MINUTES
RAINFALL INTENSITY DATA
DATA SOURCE: U.S. WEATHER BUREAU TECHNICAL PAPER \'O. 40
Storm
Duration
minutes or hours)
Rainfall Intensity
(inches per hour)
3 -Year 100 -Year
Storm
Duration
(minutes or hours)
Rainfall Intensity
(inches per hour)
3 -Year 100 -Year
0. 17 hrs. 10 min.
4.3
7.6
10 hrs.
0.27
0.49
0.33 " 20 "
3.0
5.5
11 it
0.25
0.46
0.50 " 30 "
•2.45
4.40
12 "
0.23
0.43
0.67 " 40 "
2.15
3.70
13 "
0.22
0.40
0.83 " 50 "
1.85
3.20
14 "
0.20
0.38
1 hr.
1.67
2.80
15
0.19
0. 36
1.5 "
1.27
2.10
16 "
0.18
0.34
2 "
1.00
1.70
17 "
0.17
0.33
3 "
0.73
1.20
18 "
0.16
0.31
4 "
0.58
1.00
19 "
0.16
0.30
5 "
0.48
0.84
20 "
0.15
0.29
6 "
0.42
0.73
21 "
0.15
0.28
7 "
0.37
0.65
22 "
0.14
0.27
8 "
0.33
0.58
23 "
0.14
0.26
9 "
0.30
0.53
24"
0.13
0.25