[R.O. 1993 § 545.090; Ord. No.
99-2407, 12-14-1999; Ord. No. 2006-2722 § 1, 5-9-2006]
A.
Drainage Area Plan. A plan of the drainage area at a scale of one
(1) inch equals one hundred (100) feet with two-foot contour intervals
using USGS datum for areas less than one hundred (100) acres or a
plan of the drainage area at a scale of one (1) inch equals three
hundred (300) feet with five (5) feet contour intervals for larger
areas. This plan shall include all proposed streets, drainage and
grading improvements with flow quantities and direction of flow at
all critical points. All areas and subareas for drainage calculations
shall be clearly distinguished.
B.
Hydraulic Data. Complete hydraulic data showing all calculations
shall be submitted. A copy of all nomographs and charts used in the
calculations shall be submitted if other than those included herein
are utilized.
C.
Plan And Profile. A plan and profile of all proposed improvements
at a scale of one (1) inch equals forty (40) feet horizontal and one
(1) inch equals four (4) feet vertical shall be submitted this plan
shall include the following:
1.
Locations, size, flow line elevations and grades, type of pipe,
channels, boxes, manholes and other structures drawn on standard plan-profile
sheets;
2.
Existing and proposed ground line profiles along the center
line of the drainage improvement;
3.
A list of the kind and quantity of material;
4.
Typical sections and reinforcement of all boxes and channels;
5.
Location of property lines, street paving, sanitary sewers and
other utilities, both public and private.
D.
Field Study. A field study of the downstream capacity of all drainage
facilities and the effect of additional flow from the area to be improved
shall be submitted. If the effect is to endanger property of life,
the problems must be solved before the plan will be given approval.
E.
Stormwater Flow Quantities. Stormwater flow quantities in the street shall be shown at all street intersections, all inlet openings, and at locations where flow is removed from the streets. This shall include the hydraulic calculations for all inlet openings and street capacities. Street flow shall be limited according to Table 1 at the end of Article II.
F.
Sinkholes Or Karst Areas. Sinkhole or karst areas shall be clearly
defined. If any portion of the stormwater from an area is to be drained
into a sinkhole, all information available shall be obtained, and
the capacity of the sinkhole shall be studied, and this study shall
be submitted to determine the effect of the drainage and pollution
on groundwater and streams.
G.
Additional Information. Any additional information deemed necessary
by the Building Official and/or Wastewater Superintendent for an adequate
consideration of the storm drainage effect on the City of Aurora and
surrounding areas must be submitted.
[R.O. 1993 § 545.100; Ord. No.
99-2407, 12-14-1999; Ord. No. 2006-2722 § 1, 5-9-2006; Ord. No. 2010-2871 § 1, 4-27-2010]
A.
General Design Requirements.
1.
All bridges shall be designed to accommodate a one-hundred-year
frequency rain. Box culverts, pipe culverts, channels and ditches
shall be designed to accommodate a one-hundred-year frequency rain
at all locations having a drainage area in excess of one (1.0) square
mile. Locations having a drainage area of less than or equal to one
(1.0) square mile shall be designed to accommodate a twenty-five-year
frequency rain.
2.
Channel improvements types shall be as follows:
a.
Improvements with a capacity of up to and including 100 CFS
shall be (a) open with a channel lining that is shown to be capable
of resisting erosive forces; or (b) closed conduit;
b.
Improvements with a capacity above the 100 CFS up to and including
250 CFS may be open and (1) concrete paved invert; or (2) concrete
lined; or (3) closed conduit;
c.
Improvements with a capacity above the 250 CFS shall be open
and (1) concrete lined; or (2) have a 100 CFS low-flow paved invert.
B.
Specific Requirements For Various Improvements.
1.
Bridges And Culverts. Bridges, box culverts or concrete pipe
culverts shall be provided where continuous streets or alleys cross
watercourses. The structure shall be designed in accordance with City
specifications for material and to carry HS-20 loadings in all cases.
2.
Closed Storm Sewers. Closed storm sewers shall either be reinforced
concrete box or pipe of approved type designed for HS-20 loadings.
Reinforced concrete pipe or reinforced concrete boxes must be used
within two (2) feet of the back of the street curb and under paved
areas. All storm sewers having trench walls within two (2) feet of
the back of the street curb shall be backfilled with granular material.
The use of corrugated steel, zinc-coated pipe and extra strength clay
pipe will not be permitted within two (2) feet of the curb or under
pavement areas. All pipe material shall meet the requirements of the
latest revision of the City of Aurora standard general conditions
and technical specifications for public works construction.
Grades for closed storm sewers shall be designed so that the
velocity shall not be less than three (3) feet per second nor exceed
twelve (12) feet per second. All other structures such as junction
boxes or inlets shall be in accordance with the standard drawings
adopted by the City of Aurora.
Closed storm sewers shall extend to the furthest downstream
point of the development with consideration given to velocities and
to providing discharge energy dissipaters to prevent erosion and scouring
along downstream properties.
3.
Open Paved Concrete Channels. Grades for open paved channels
shall be designed so that the velocity shall not be less than three
(3) feet per second nor exceed twelve (12) feet per second. Such concrete
channels may be of different shapes according to existing conditions;
however, a channel with a flat bottom and 4:1 to 5:1 side slopes is
the most desirable type and shall be used whenever possible. The thickness
of channel paving shall depend on conditions at site and size of channel;
however, a minimum thickness of six (6) inches is required. A six-inch
freeboard must be provided. An eighteen-inch toe wall is required
at both the outlet and inlet ends of the channel.
4.
Open Ditches (Earth Channels). Ditches shall have a gradient
that limits the velocity within one and one-half (1.5) to five (5)
feet per second depending on existing soil conditions. Such ditches
shall have a minimum side slope ratio of 3:1. The designer's
attention is directed to the fact that the subdivision ordinance[1] prohibits encroachment of buildings and improvements on
natural or designated drainage channels or the channel's floodplains.
Such floodplains are areas of land adjacent to an open paved channel
or an open sodded ditch that may receive a flood condition from a
one-hundred-year frequency rain. The limits of such floodplains shall
be indicated on drainage improvements plans.
[R.O. 1993 § 545.110; Ord. No.
99-2407, 12-14-1999; Ord. No. 2006-2722 § 1, 5-9-2006]
The rate of runoff concentrated at any point shall be determined
by the Rational Formula:
|
Q
|
=
|
CIA, in which
| |
|
Q
|
=
|
Runoff in cubic feet per second
| |
|
C
|
=
|
The runoff coefficient for the area
| |
|
I
|
=
|
Design rainfall intensity in inches per hour over the area based
on the time of concentration and rainfall
| |
|
Intensity curves included as a part of this Article II.
| |||
|
A five-minute time of concentration is the minimum permitted.
| |||
|
A
|
=
|
Drainage area, in acres.
| |
A.
Runoff Coefficient. The runoff coefficient "C" is the variable in
the rational formula least susceptible to precise determination and
the one (1) that requires the greatest exercise of engineering judgment
because of the many area characteristics which affect the coefficient.
Among the factors to be considered in influencing the runoff coefficients
are the following: present and future zoning; terrain; local ponding
or depressions; the amount of pavement; roofs, turf, and other areas
having different degrees of imperviousness.
The selection of a coefficient should take into consideration
the probable ultimate development of presently undeveloped areas.
Suggested values of runoff coefficients are included in the following
table:
|
Suggested Runoff Coefficients "C"
| |
|---|---|
|
Surface Conditions
| |
|
"C" Value
| |
|
0.10 — 0.15
|
Tall grass, brush
|
|
0.15 — 0.20
|
Parks, golf courses, farms and 1-acre single-family residences
|
|
0.35
|
Single-family residences on lots of not less than 15,000 square
feet
|
|
0.45
|
Single-family residences on lots of not less than 10,000 square
feet
|
|
0.47
|
Single-family residences on lots of not less than 7,500 square
feet
|
|
0.51
|
Single-family residences on lots of not less than 6,000 square
feet
|
|
0.90
|
Gravel surfaces
|
|
0.95
|
Asphalt and concrete surfaces
|
|
1.00
|
Buildings and other structures
|
B.
Rainfall Intensity. The average frequency of rainfall occurrence
used for design determines the degree of protection afforded by a
drainage system. Maximum intensity of rainfall of a given expectancy
is grater for a short period of the time than for longer periods.
Therefore, it is assumed that the maximum runoff will occur as soon
as all parts of the drainage area under consideration are contributing.
The length of time from the beginning of rainfall until runoff from
the most remote point in the drainage area reaches the point under
consideration is a channel or gutter flow time. Nomographs which may
be used for determining time of concentration are reproduced at the
end of this Chapter. Once the time of concentration is known, the
design intensity rainfall may be determined from the rainfall intensity
curves developed from United States Weather Bureau data.
[R.O. 1993 § 545.120; Ord. No.
99-2407, 12-14-1999; Ord. No. 2006-2722 § 1, 5-9-2006]
The size of closed storm sewers, open channels, culverts and
bridges shall be designed so that their capacity will not be less
than the runoff computed by using the Manning Formula:
|
Q
|
=
|
1.486/n ar 2/3 s 1/2
|
|
Q
|
=
|
Capacity = Discharge in cubic feet/sec.
|
|
a
|
=
|
Cross sectional area of water in conduit or channel in square
feet
|
|
r
|
=
|
Hydraulic radius of water in conduit or channel = area/wetted
perimeter
|
|
s
|
=
|
Mean slope of hydraulic gradient in feet per foot
|
|
n
|
=
|
Roughness coefficient based on condition and type of material
of conduit or channel lining
|
|
Values of "n" for various kinds of pipe for use in Manning Formula:
| |
|
Concrete pipe — 0.013
| |
|
Corrugated metal pipe — 0.024
| |
|
Concrete-lined channel — 0.015
| |
|
Earth channels — 0.030 to 0.050
| |
|
Design Tabulations. For systems of storm sewers with inlets
in various locations, the time of concentration at any point will
be time of concentration at the most remote inlet upstream, plus the
flow time in the storm sewer to the point under consideration. Computations
for systems lend themselves readily to tabulation showing the drainage
area, time of concentration runoff, and capacity of each inlet and
section of sewer under consideration. This data is to accompany the
improvement plans.
|
|
Table 1 - Street Flow
| ||
|---|---|---|
|
Street flow shall be limited by pavement encroachment and depth
of flow as follows:
| ||
|
Street Classification (Minor)
|
Maximum encroachment of a 2-year storm no curb overtopping.
Flow may spread to crown of street
| |
|
Collector
|
No curb overtopping. Flow spread must leave the equivalency
of one (1) ten-foot driving lane clear of water
| |
|
Arterials (Throughfares)
|
No curb overtopping. Flow spread must leave the equivalent of
two (2) ten-foot driving lanes clear of water. One (1) lane in each
direction. Where no curbing exists, encroachment shall not extend
past property lines
| |
|
The storm sewer system shall commence at the point where the
volume of flow equals five (5) cfs.
| ||
