(a) General Information. These guidelines apply to storm sewers in the public right-of-way and on private property within the Municipality. Storm drainage shall be designed for conveyance in a separate gravity system.
(b) Investigations and Surveys.
(1) Information required. Each project shall be identified by name. A general description of the project shall be included indicating approximate project size, zoning, general description of discharge points, off site tributary area drainage area maps, and any special factors to be considered in the design.
(2) Investigations. Information on all existing conditions shall be listed. This information shall include capacity of receiving sewers or downstream culverts and the ability of receiving waterways to provide an adequate outlet with respect to both depth and capacity in vicinity of storm outlet. Special analysis will be required for known flooding areas.
(c) Design Criteria for Storm Sewers.
(1) Design storm frequency. Storm sewers shall be designed to accommodate the stormwater runoff from and have adequate capacity, flowing full, for the ten (10) year storm frequency.
(2) Rainfall intensity – duration.
5 – Year Storm i = 1.50 Inches/Hr.
10 – Year Storm i = 1.80 Inches/Hr.
25 – Year Storm i = 2.00 Inches/Hr.
50 – Year Storm i = 2.25 Inches/Hr.
100 – Year Storm i = 2.50 Inches/Hr.
(3) Runoff coefficient.
Zoning Lot Area (ft2) c =
Residential 0 – 5,000 0.7
5,000 – 10,000 0.6
10,000 – and over 0.5
Zoning Lot Area (ft2) c =
Multifamily and Schools 0.75
Industrial/Commercial 0.90
Shopping Centers 0.90
Major Urban 0.90
Business Area 0.90
Cover Type c =
Impervious Areas (pavement or building) 0.9
Lawns 0.3
Woods, forest 0.3
Farmland/pasture 0.3
The above runoff coefficients assume typical ground cover and average slope.
(4) Concentration times.
A. Residential areas. The concentration times to the critical inlet varies between 12 and 20 minutes with 15 minutes to be used as the average case based upon full development of the land.
B. Industrial – multifamily – school areas. The concentration time to the critical inlet varies between 10 and 15 minutes with 12.5 minutes to be used as the average case based upon full development of the land.
C. Major urban business areas and shopping centers. The concentration time to the critical inlet varies between 5 and 12 minutes with 10 minutes used as the average case based upon full development of the land.
(5) Standard Rainfall Intensity-Duration Tables. The Standard Rainfall Intensity-Duration Tables shall be used to determine the rainfall intensity occurring at the time of concentration to the inlet under consideration.
STANDARD RAINFALL INTENSITY-DURATION TABLES
Rainfall Intensity in Inches Per Hour
Time of Concentration in Minutes | 5 yr. 1.50"/Hr. | 10 yr. Design 1.80"/Hr. | 25 yr. Storm 2.00"/Hr. | 50 yr. Frequency 2.25"/Hr. | 100 yr. 2.50"/Hr.
|
10 | 4.30 | 4.95 | 5.20 | 5.75 | 6.15 |
11 | 4.14 | 4.78 | 5.04 | 5.58 | 5.98 |
12 | 4.00 | 4.63 | 4.89 | 5.41 | 5.81 |
13 | 3.87 | 4.48 | 4.74 | 5.26 | 5.65 |
Time of Concentration in Minutes | 5 yr. 1.50"/Hr. | 10 yr. Design 1.80"/Hr. | 25 yr. Storm 2.00"/Hr. | 50 yr. Frequency 2.25"/Hr. | 100 yr. 2.50"/Hr.
|
Time of Concentration in Minutes | 5 yr. 1.50"/Hr. | 10 yr. Design 1.80"/Hr. | 25 yr. Storm 2.00"/Hr. | 50 yr. Frequency 2.25"/Hr. | 100 yr. 2.50"/Hr.
|
14 | 3.74 | 4.34 | 4.61 | 5.11 | 5.51 |
15 | 3.62 | 4.21 | 4.48 | 4.98 | 5.37 |
16 | 3.51 | 4.09 | 4.36 | 4.85 | 5.23 |
17 | 3.41 | 3.98 | 4.25 | 4.72 | 5.11 |
18 | 3.31 | 3.87 | 4.14 | 4.60 | 4.99 |
19 | 3.22 | 3.76 | 4.04 | 4.49 | 4.87 |
20 | 3.13 | 3.67 | 3.94 | 4.39 | 4.76 |
21 | 3.05 | 3.57 | 3.85 | 4.28 | 4.65 |
22 | 2.97 | 3.49 | 3.76 | 4.19 | 4.55 |
23 | 2.89 | 3.40 | 3.67 | 4.09 | 4.46 |
24 | 2.82 | 3.32 | 3.59 | 4.01 | 4.37 |
25 | 2.76 | 3.25 | 3.51 | 3.92 | 4.28 |
26 | 2.69 | 3.17 | 3.44 | 3.84 | 4.19 |
27 | 2.63 | 3.10 | 3.37 | 3.76 | 4.11 |
28 | 2.57 | 3.04 | 3.30 | 3.69 | 4.03 |
29 | 2.52 | 2.97 | 3.23 | 3.61 | 3.96 |
30 | 2.46 | 2.91 | 3.17 | 3.54 | 3.88 |
35 | 2.22 | 2.64 | 2.89 | 3.23 | 3.58 |
40 | 2.03 | 2.41 | 2.65 | 2.97 | 3.28 |
45 | 1.86 | 2.22 | 2.45 | 2.75 | 3.04 |
50 | 1.72 | 2.06 | 2.28 | 2.56 | 2.84 |
55 | 1.60 | 1.92 | 2.13 | 2.40 | 2.66 |
60 | 1.50 | 1.80 | 2.00 | 2.25 | 2.50 |
70 | 1.33 | 1.60 | 1.78 | 2.01 | 2.23 |
80 | 1.19 | 1.43 | 1.60 | 1.81 | 2.02 |
90 | 1.08 | 1.30 | 1.46 | 1.65 | 1.84 |
100 | 0.99 | 1.19 | 1.34 | 1.51 | 1.70 |
110 | 0.91 | 1.10 | 1.24 | 1.40 | 1.57 |
120 | 0.84 | 1.02 | 1.15 | 1.30 | 1.46 |
(6) Flow formulas.
A. Quantity of runoff by rational method.
1. Areas up to 25 acres. "Q" = CIA in cubic feet per second where "A" is the area to be drained in acres, "C" is the runoff coefficient for the area under consideration and "I" is the rainfall intensity derived from the Standard Rainfall Intensity-Duration Tables for the concentration time to the inlet under consideration.
2. Areas greater than 25 acres. U.S. Soil Conservation Service procedures in Technical Release No. 55, 1986 edition or latest edition with modifications described in Section 1481.01 (i) shall be used for computing runoff quantities.
B. Manning's Formula.
V = 1.486 (R)2/3 (S)1/2
n
where "S" is slope in feet per foot; "R" is hydraulic radius; and "n" is the roughness coefficient. The roughness coefficient shall be n = 0.015 for sizes up to and including 27 inches; n = 0.013 for sizes including 30 inches through 84 inches and n = 0.011 for 90 inches and larger. Graphs for the Manning Formula are provided in the following table. This table is based on Quantity of flow Q = Av where "A" is the cross-sectional area of the conduit developed by the nominal conduit diameter.
Manning's Formula Flow Table
Q = AV V = 1.486 (R)2/3 (S)1/2
n
Diameter (in.) | CAP. @ 1% (CFS)
| Area (ft.2) | CAP. @ 1% (MGD)
|
Diameter (in.) | CAP. @ 1% (CFS)
| Area (ft.2) | CAP. @ 1% (MGD)
|
n = 0.015 | |||
6 | 0.485 | 0.196 | 0.313 |
8 | 1.061 | 0.349 | 0.686 |
10 | 1.906 | 0.545 | 1.232 |
12 | 3.087 | 0.785 | 1.995 |
15 | 5.567 | 1.227 | 3.598 |
16 | 6.604 | 1.389 | 4.266 |
18 | 9.105 | 1.767 | 5.827 |
21 | 13.730 | 2.405 | 8.870 |
24 | 19.610 | 3.142 | 12.670 |
27 | 26.750 | 3.977 | 17.290 |
n = 0.013 | |||
30 | 40.790 | 4.909 | 26.370 |
33 | 53.030 | 5.940 | 34.280 |
36 | 66.670 | 7.069 | 43.090 |
39 | 82.410 | 8.296 | 53.260 |
42 | 100.200 | 9.621 | 64.760 |
48 | 143.600 | 12.570 | 92.840 |
54 | 196.000 | 15.900 | 126.700 |
60 | 260.400 | 19.640 | 168.300 |
66 | 334.800 | 23.760 | 216.400 |
72 | 423.400 | 28.270 | 273.700 |
78 | 523.100 | 33.180 | 338.100 |
84 | 638.800 | 38.490 | 412.900 |
n = 0.011 | |||
90 | 906.000 | 44.180 | 585.600 |
96 | 1077.700 | 50.270 | 696.500 |
102 | 1264.900 | 56.750 | 817.500 |
108 | 1475.600 | 63.620 | 953.700 |
120 | 1954.400 | 78.540 | 1263.200 |
132 | 2520.200 | 95.030 | 1628.800 |
144 | 3177.900 | 113.100 | 2053.900 |
TO FIND CAPACITY AT ANY SLOPE MULTIPLY; CAPACITY LISTED @ 1% BY (S)1/2 in %
Where other than circular pipe is proposed, the actual cross-sectional area developed may be used.
C. Hydraulic radius. The formula for the hydraulic radius is R = A/p where "p" is wetted perimeter developed by the nominal pipe diameter. Where other than circular pipe is proposed, the actual wetted perimeter developed may be used.
D. Velocities. Storm sewers shall have a minimum flowing full velocity of three feet per second and a maximum velocity of 15 feet per second.
(7) Pavement drainage. Pavement inlets or catch basins shall be spaced to limit the spread of storm water flow on the traveled lane to 6-feet (allowable spread). Design shall be based upon the 2-year storm frequency. Pavement inlet spacing and bypass calculations shall be in accordance with the latest edition of the Ohio Department of Transportation Location and Design Manual, Volume 2 – Drainage Design.
(8) Hydraulic grade line. Starting at the storm sewer system outlet and working upstream, the elevation of the Hydraulic Grade Line (HGL) shall be determined for the 25- and 100-year storm frequencies. The outlet shall be analyzed to determine if it is free draining or if the storm sewer system is operating under a submerged condition. In general, the HGL will be above the top of the pipe, causing the system to operate under pressure.
(9) Layout of sewers.
A. General information. The layout of the storm system shall place the storm and sanitary sewers on opposite sides of roadways and within the tree lawn areas where practical. Where opposite side construction is not practical, every effort shall be made to separate the storm and sanitary sewers by six feet barrel to barrel. Manhole spacing interval shall be a maximum of 400-feet. Catch basins shall be used prior to the connection of inlets into the main storm sewer system. Consideration shall be given to installing traps or other methods to control the release of floatable debris into the sewer system.
B. Minimum size.The minimum size of all storm sewers, excluding connections, shall be 12 inches in diameter.
C. Type of conduits. All storm sewer conduits excluding connections within the public rights-of-way within the Municipality shall be reinforced concrete pipe in accordance with American Society for Testing Materials (ASTM) Designation C-76 or as directed by the City Engineer.
Beyond the public right-of-way limits, other conduit types may be specified provided that proper backfill, pipe cover and bedding is specified and approved by the City Engineer.
Only wye branch fittings will be accepted for service connections for sewers up to and including 21" diameter. For sewers 24 inches and larger, tee connections are permitted.
Deflection test is required on all plastic pipe with a pipe stiffness less than 200 P.S.I. Air testing is not required for storm sewers.
All storm sewer pipes between manholes increments shall be one type and class of pipe. In case of lateral connections, transition connections of different materials may be permitted.
D. Lateral connections. Lateral connections to building sites shall be a minimum of six inches in diameter at a minimum slope of one percent. Building footer drains shall be free draining and outlet above the 100-year storm frequency hydraulic grade line.
E. Storm sewer joints. Storm sewers shall have premium joints conforming to ASTM D-3212 for plastic pipes or ASTM C-443 for concrete pipes or as approved by the City Engineer.
F. Manholes. Storm sewer manholes shall be constructed in accordance with the following specifications or as approved by the City Engineer.
1. All storm sewer manholes shall be constructed of reinforced precast concrete sections in accordance with ASTM Designation C-478.
2. All storm sewer manhole wall joints shall be rubber O-Ring type conforming to ASTM Designation C-443.
3. Adjustment of the storm sewer manhole casting to the final grade shall be accomplished with precast concrete adjusting rings.
4. All storm sewer manholes shall have steps installed internally in accordance to the latest OSHA requirements.
G. Headwalls, inlet basins and catch basins. All headwall, inlet and catch basin structures shall be in accordance with the latest Ohio Department of Transportation (ODOT) Standard Construction Drawings or as approved by the City Engineer. All yard inlet basins shall be installed with a "beehive" type grate.
(10) Culverts. Culverts under all roads within the Municipality shall be designed for a 25-year storm flow with headwater of one foot below the edge of the roadway. Consideration shall be given to the headwater elevation with respect to adjacent buildings.
(Ord. 05-79. Passed 6-7-05.)