(a) A complete storm sewer system and other drainage improvements shall be constructed in accordance with these standards. Where downstream storm drainage facilities are inadequate, consideration shall be given to detention basins, oversized storm sewers, or other techniques to minimize the amount of runoff developed and to provide a means of controlling the discharge to off-site outlets.
(b) A ten-year storm frequency shall be used in the design of all storm sewers and ditches, and a twenty-five year frequency shall be used in the design of major facilities such as culverts and detention facilities.
(c) Storm sewer pipes shall conform to the following standards:
(1) Minimum size shall be twelve (12) inches.
(2) Minimum cover shall be two (2) feet.
(3) Minimum grade for smooth pipe shall be as per Table 1.
(4) Materials shall consist of reinforced concrete, smooth interior high density polyethylene, corrugated aluminum, aluminized steel or galvanized steel, or PVC.
TABLE 1
MINIMUM GRADES "SMOOTH PIPE"
Using an "n" factor of 0.013, the following grades of pipe line shall be considered MINIMUM:
Pipe Size (Inches) | Minimum Grade (percent) |
12 | 0.33 |
15 | 0.23 |
18 | 0.18 |
21 | 0.14 |
24 | 0.12 |
For sizes larger than 24 inches where an "n" factor other than 0.013 is used, the minimum grade shall be considered as that which produces a full flow velocity of not less than 2-1/2 feet per second.
(d) Storm sewers installed under or within five feet of pavements and sidewalks shall be reinforced concrete or high density polyethylene installed per ODOT 603. One year of natural settlement may be accepted in lieu of granular material compacted in place if soil conditions appear to be suitable (subject to Village approval).
(e) Storm sewer manholes, or inlets serving as manholes, shall be spaced a intervals of 400 feet or less for pipe less than twenty-four (24) inches, and at all grade, alignment and pipe size changes. Manholes shall conform to ODOT Item 604 and be designed per ODOT standards Construction Drawing MH-3. Layed up manholes may be permitted providing they are specified at the time of improvement plan submission, constructed in accordance with ODOT Standard Construction Drawing MH-1 and are plastered with cement mortar both inside and out to ensure water tightness. Manhole castings located in asphalt pavement shall be set in a minimum twelve (12) inch wide concrete collar with a thickness equal to the pavement section and finished one quarter (1/4) inch below the pavement surface. The concrete/asphalt interface shall be sealed with liquid asphalt cement.
(f) Storm sewer inlets shall be designed and constructed in conformance with ODOT Item 604 and ODOT Standard Construction Drawings for CB2-2-A and B; CB 2-3 and 2-4; CB2-5 and 2-6; and CB-3 and 3A. Inlet CB-3 or CB-3A shall be used with curbing wherever possible and shall be fitted with vee type grates. Inlets shall be designed to accept no less than one and one-half (1-1/2) cubic feet of storm water per second. Inlet time shall be computed based upon Table 2. Layed up catch basins may be permitted providing they are specified at the time of improvement plan submission, constructed in accordance with the time appropriate ODOT Standard Construction Drawing and are plastered with cement mortar both inside and out to ensure tightness. When inlets are located in asphalt pavement, the concrete/asphalt interface shall be sealed with liquid asphalt cement.
TABLE 2
MAXIMUM INLET TIMES
Inlet time shall be computed by the design engineer. However, the maximum inlet time shall be as follows:
Distance of Travel to Inlet (Feet) | Inlet Time (Minutes) |
100 | 12 |
200 | 16 |
300 | 30 |
(g) The allowable velocity in open drainage channels shall not exceed the values shown below in Table 3 for the various soil types and flexible linings. If the calculated velocity exceeds the shown, a gabion lining or other satisfactory treatment shall be required.
TABLE 3
ALLOWABLE DITCH VELOCITY (FEET PER SECOND)
Soil Type | Seed Lining ODOT 659 | Sod Lining ODOT 660 | Jute or Excelsior Matting ODOT 667 or 669 |
Sand | 1.5 | 3.5 | 3.0 |
Firm Loan | 2.0 | 4.0 | 4.0 |
Clay | 2.5 | 5.0 | 4.0 |
Gravel | 3.5 | 6.0 | 5.0 |
Weathering Shale | 4.5 | 6.0 | 5.0 |
(h) In designing the storm system, the developer shall use the methods described in Urban Hydrology for Small Watersheds, Technical Release Number 55, by the Natural Resources Conservation Service of the United States of Department of Agriculture and its Ohio Supplement to determine storm water runoff. The rational method shall only be used for very small areas with prior approval of the Village. When determining runoff from upstream areas, the developer shall use the most recent Land Use Development Plan in conjunction with topographic and other available sources of information.
(i) Storm water runoff control involves both peak and total volume of runoff.
(1) The peak rate of runoff from an area after development shall not exceed the peak rate of runoff from the same area before development for all storms up to a 200-year frequency, 24-hour storm. In addition, if it is found a proposed development will increase the volume of runoff from an area, the peak rate of runoff from certain more frequent storms must be controlled further. The permissible peak rate shall be determined as follows:
(A) Determine the total volume of runoff from a 1-year frequency, 24- hour storm occurring over the area to be developed before and after development.
(B) Determine the percent of increase in volume due to development and; using this percentage, pick the critical storm from the following Table 4:
TABLE 4
CRITICAL STORMS
If the percentage of increase in volume of runoff is: | The critical storm for discharge limitation will be: | |
Equal to or greater than: | and less than: | |
-- | 10 | 1 Year |
10 | 20 | 2 Years |
20 | 50 | 5 Years |
50 | 100 | 10 Years |
100 | 250 | 25 Years |
250 | 500 | 50 Years |
500 | -- | 100 Years |
(2) The peak rate of runoff from the critical storm occurring over the development shall not exceed the peak rate of runoff from a one-year frequency storm occurring over the same area under predevelopment conditions. Storms of less frequent occurrence (longer return period) than the critical storm shall have peak rate of runoff not greater than for the same storm under predevelopment conditions.
(3) Storage volume does not have to be provided for off-site upstream areas. Flow from such areas will be routed through the drainage system in the development under consideration at a rate determined in the same manner as the on-site system. Off-site land uses averaged over the last five preceding years before the development shall be considered as the predevelopment condition for the purpose of calculating changes in runoff. The required detention shall be determined using the TR-55 methodology.
(A) The subdivider shall obtain Village approval of his detention facilities and outlot control devices prior to final plat approval.
(B) All detention facilities shall be graded and seeded, and easily maintained.
(C) All open detention facilities designed to hold water for more than twenty-four (24) hours and having side slopes steeper than one (1) to four (4) shall be fenced with a six (6) foot chain link fence set back ten (10) feet from the top of the bank and have a twelve (12) foot wide lockable gate for maintenance access.
(Ord. 75-96. Passed 11-18-96)