A. 
The design of all storm water improvements within the development shall be such that all surface waters occurring within the development, as well as all surface waters flowing onto and/or through the development from proposed future additional developments upstream, shall be conveyed through the development without damage to any improvement, building site, or dwelling which may be constructed within the development. All storm drainage facilities within the development shall be designed to adequately convey the storm water runoff from the ultimate development of the drainage basin or watershed.
B. 
Also, all storm drainage facilities to be constructed outside of the subdivision shall be designed to adequately convey the storm water runoff from the ultimate development of the drainage basin or watershed lying within and above the development to a natural watercourse having capacity to handle the generated present and future runoff. These waters shall be conveyed without damage to any improvement, building, or dwelling to the anticipated natural watercourse having capacity to carry the water or to a point designated by the City.
C. 
The general capacity of the drainage facilities shall be determined by use of the Manning equation as stated below:
Q
=
A(1.486)
R0.667
S 0.5
      n
Where:
Q
=
flow rate in cubic feet per second
n
=
Manning roughness coefficient (see Table IV)
A
=
cross-sectional area in square feet
R
=
hydraulic radius in feet
S
=
slope in ft./ft.
D. 
The minimum velocity at design flow shall be two feet per second using the Manning equation above.
E. 
Predicted surcharging and flooding due to a one-hundred-year design storm imposed upon the proposed facilities will also be calculated.
F. 
The design of drainage facilities shall allow for a minimum freeboard of 0.75 feet between the top of the inlet grade or manhole cover and the design surface water elevation.
G. 
Proper allowance for head losses through junction structures, inlets, and manholes shall be made in determining the hydraulic grade line or water surface elevations.
Table IV.
Manning n Values
Type of Conduit
or Channel
Roughness
Coefficient n
Concrete gutters
.015
Corrugated metal pipe
.024
Reinforced concrete pipe — 12" to 21"
.015
Reinforced concrete pipe — 24" or larger
.013
Asbestos cement pipe
.012
Lined channels:
Concrete
.014
Air blown mortar
.016
Bituminous
.018
Sacked concrete
.025
Loose riprap
.035
Grassed
.035
Concrete—Steel troweled or smooth-form finish
.013
Concrete—Wood float or broomed finish
.015
Asphaltic concrete
.017
PVC
.012
A. 
General pipe system.
(1) 
Minimum inside pipe diameter shall be twelve inches.
(2) 
The maximum spacing of manholes or junction boxes shall not be more than four hundred feet.
(3) 
Manholes or junction boxes shall be provided at all horizontal angle points and at all changes in pipe grade.
(4) 
Curves in pipe systems will only be allowed when the pipe diameter is thirty-six inches or larger.
(5) 
The maximum spacing of catch basins shall not be more than one thousand feet.
B. 
Minimum cover. The minimum cover over pipes installed within the road right-of-way shall be as required for pipe strength, loading conditions, and hydraulic requirements, but in no case shall the minimum cover over storm sewer lines be less than one and one-half feet, and in no case shall the minimum depth to the flow line be less than four and one-half feet.
C. 
Pipe diameter changes. A smaller pipe at a steeper grade downstream will only be allowed if an adequate approvable junction structure is provided at the intersection of the two pipes such that a surcharge condition above the top of the larger pipe will not occur due to entrance losses in the smaller pipe. In all other cases, the reduction in pipe size downstream will not be allowed.
D. 
Surcharging within closed conduit systems. Surcharging or backup of storm waters into catchbasins and manholes will not be allowed under a ten-year design storm.
E. 
Culverts. Drainage culverts under roads shall have a minimum diameter of eighteen inches and under driveways a minimum diameter of twelve inches and shall be placed at a depth as required by section 7-106B unless otherwise approved by the City engineer.
F. 
Loading criteria. All pipe shall be designed to handle earth loading and axle loadings of thirty-eight-thousand pounds in accordance with standard, accepted engineering practices with a maximum deflection of five percent.
G. 
Catch basins. Catch basin types I, II, III, IV, and V shall be used as required by the hydraulic and slope conditions or as directed by the City engineer.
(1) 
Catch basin type I. A type I catch basin shall be used on slopes less than two percent grade where a one to two block area is to be collected into the storm sewer facilities.
(2) 
Catch basin type II. Catch basin type II shall be used on slopes less than two percent grade where a drainage area of four to five blocks or less is to be collected into the storm sewer facilities.
(3) 
Catch basin type III. A type III catch basin shall be used on slopes less than two percent grade where a one to two block area is to be collected and where a standard manhole is to be used as the catch basin.
(4) 
Catch basin type IV. A type IV catch basin shall be used in areas where steep grades and small drainage basins are to be collected into the storm sewer facilities. On grades over two percent and where areas of one or two blocks are to be collected into the storm drainage facilities, a type IV catch basin shall be used.
(5) 
Catch basin type V. A type V catch basin is to be used in areas where steep grades and large drainage basins are to be collected into the storm sewer facilities. On grades over two percent and where areas of several blocks are to be collected, the type IV catch basin should be used to assure that all water is collected into the storm drainage facilities.
H. 
Cleanout structures. A type I, II or III cleanout structure shall be provided in the storm drainage facilities to facilitate the collection of debris and gravel from the streets and from surrounding erosion, or as directed by the City engineer.
(1) 
Type I cleanout structure. A type I cleanout structure shall be used where minor waterways have a significant grade change from steep slope to a fairly flat slope, or from a grade change of steeper than three to four percent to a grade flatter than one to two percent.
(2) 
Type II cleanout structure. A type II cleanout structure shall be used at the bottom end of a complete minor waterway and at significant grade changes from steep to flat slopes.
(3) 
Type III cleanout structure. A type III cleanout structure shall be provided at the entrance to all major retention facilities and at the bottom end of a complete minor or major waterway and prior to discharge into the City's major storm drain facilities or into a receiving stream. The placement of a type III cleanout structure may be waived at the discretion of the City engineer.
A. 
Curbs and gutters. Curbs and gutters shall be designed to carry the ten-year design flow. Breaking of back of curbs for curb cuts shall not be allowed.
B. 
Concrete valley gutters. Concrete valley gutters will not be permitted across collector streets. Concrete valley gutters shall be designed to carry the ten-year design storm at a depth not to exceed eighty percent of the maximum carrying capacity. All valley gutters shall be built as per the City standard storm water details.
C. 
Energy dissipators. Energy dissipators and/or adequate slope protection shall be required for outlets which discharge at velocities greater than ten feet per second or when required by the City engineer.
A. 
Channels or open ditches may be used in place of pipe when the required pipe size would be larger than sixty inches in diameter and approval is received from the City engineer. Existing natural channels and creeks may be retained unimproved in buildup areas if the flow of water is continuous throughout the year and if the channel or creek is adequate to carry a one-hundred-year design storm with one foot of freeboard or more. Existing inadequate creeks or channels shall be enlarged and grassed or otherwise improved as required to obtain the capacity to carry a one-hundred-year storm with one foot of freeboard within the boundaries of the area to be developed.
B. 
In general, open channels and ditches shall be lined or riprapped if the ten-year design storm velocity exceeds three feet per second.
Bridges shall be designed to pass a one-hundred-year design storm with a minimum of two-foot freeboard. Abutments and piers shall be protected from erosion damage which may require the use of riprap or other suitable material and methods. All bridges shall be constructed without significant encroachment to the existing channel.