(a) Calculations. Stormwater runoff calculations and drainage calculations shall be in accordance with the Ohio Department of Transportation Location and Design Manual, current edition. All such calculations shall be prepared by or under the supervision of a registered professional engineer and shall be sealed by such engineer and shall include detailed hydrologic and hydraulic data to support all calculations.
(b) Criteria. Subdivisions shall not increase the rate of stormwater runoff to other lands, lots, etc. This shall be accomplished by controlling the stormwater runoff so that:
(1) The peak rate of stormwater runoff for the critical storm and all more frequent storms from the subdivision area after development do not exceed the peak rate of stormwater runoff for a two (2) year frequency storm from the subdivision area before development.
(2) The peak rate of runoff for storms of less frequent occurrence than the critical storm up to the one hundred (100) year storm do not exceed the peak rate of stormwater runoff for the same frequency storms from the subdivision area after development.
Stormwater runoff from areas upgrade and outside the subdivision may be conveyed through the subdivision at the same rates as prior to development.
(c) Critical Storm. The critical storm for a subdivision (or portion thereof) shall be determined by comparing the total volumes of stormwater runoff for a two (2) year twenty-four (24) hour storm from the subdivision (or portion thereof) before development and after development. The percent increase in volume of stormwater runoff shall be calculated and used to determine the critical storm based upon the following table:
Percent Increase (%) Critical Storm Less than 20 Two (2) year 20 to less than 50 Five (5) year 50 to less than 100 Ten (10) year 100 to less than 250 Twenty-five (25) year 250 to less than 500 Fifty (50) year 500 and up One Hundred (100) year |
(d) Control Methods. Stormwater runoff control shall be a accomplished by
stormwater detention and/or retention. Such detention and/or retention may be accomplished in basins, ponds, oversized pipes or other methods acceptable to the Service Director and easements shall be provided for such improvements. After the final acceptance of such improvements and the release of the maintenance guarantee, the City shall assume maintenance responsibilities for such improvements.
All detention/retention improvements shall include controlled discharge structures (including staged discharges, if required) to comply with the criteria herein and shall also include emergency overflow structures designed to handle the fifty (50) year storm for residential subdivisions and the one hundred year storm for commercial and industrial subdivisions.
(Ord. 0-37-95. Passed 5-15-95.)
(Ord. 0-37-95. Passed 5-15-95.)