(a) General. Each Comprehensive Stormwater Management Plan shall include stormwater management facilities for storage, treatment and control, and conveyance; shall be designed to prevent structure flooding during a 100-year, 24-hour storm event; shall maintain predevelopment flow rates and discharge volumes; and shall meet the following criteria:
(1) Exemption. The site where soil-disturbing activities are conducted shall be exempt from the requirements of Section 961.10 if it can be shown to the satisfaction of the City that the site is part of a larger common plan of development where the stormwater management requirements for the site are provided by an existing stormwater management practice, facility or improvement.
(2) Maintenance. All stormwater management facilities shall be maintained in accordance with the approved Inspection and Maintenance Plans prepared pursuant to Section
961.09. All stormwater management facilities whether mandated by this ordinance or not shall maintain their facility in accordance with standard best practices or may be declared a public nuisance as described in Section 961.08 of these codified ordinances.
(3) Velocity dissipation. Velocity dissipation devices shall be placed at discharge locations and along the length of any outfall to provide non-erosive flow velocity from the structure to a water resource so that the natural physical and biological characteristics and functions of the water resource are maintained and protected.
(b) Stormwater Quality Control.
(1) Criteria applying to all stormwater management facilities. Each facility shall be designed to facilitate sediment removal, vegetation management, debris control, and other maintenance activities defined in the Inspection and Maintenance Plan for the site. Approved practices are listed in the Ohio DNR Rainwater and Land Development Manual (Third Edition, 2006). The City may approve other proposed facilities if the applicant can demonstrate to the City's satisfaction that these facilities meet the objectives of this regulation.
(2) Additional criteria applying to infiltration facilities.
A. All runoff directed into an infiltration basin must first flow through a pretreatment facility as described in the Ohio DNR Rainwater and Land Development Manual, (Third Edition, 2006).
B. Pursuant to Chapter 1153 of these Codified Ordinances, a site owner required to provide off street parking can receive a reduction of required parking spaces for the use of stormwater practices described therein.
C. The City may require a soil engineering report to be prepared for the site to demonstrate that a proposed infiltration facility meets these performance standards.
(3) Additional criteria for above-ground stormwater management facilities.
A. A forebay and micropool, as described in the Ohio DNR Rainwater and Land Development Manual, (Third Edition, 2006) shall be a part of all above ground stormwater management facilities.
B. Above ground stormwater management facilities shall be designed to spread stormwater across its floor and promote infiltration and filtering of pollutants. Low flow concrete channels are strictly prohibited.
(c) Stormwater Quantity Control. The Comprehensive Stormwater Management Plan shall describe how the proposed stormwater management practices are designed to meet the following requirements for stormwater quantity control
for each watershed in the development:
(1) The Critical Storm for each
specific development drainage area shall be determined according to the Ohio Stormwater Control Guidebook (ODNR, 1980).
(2) Critical Storm calculations shall meet the following standards:
A. Calculations shall include the lot coverage assumptions used for full build out as proposed.
(i) Calculations shall be based on the entire contributing watershed to the development area.
(ii) Curve numbers for the pre-development condition may reflect any curve number from 10 years preceding application.
(3) The peak discharge rate of runoff from the Critical Storm and all more frequent storms occurring under post-development conditions shall not exceed the peak discharge rate of runoff from a 1-year, 24-hour storm occurring on the same development drainage area under pre-development conditions.
(4) The peak discharge rate of runoff from storms of less frequent occurrence (longer return periods) than the Critical Storm, up to the 100-year, 24-hour storm shall have peak runoff discharge rates no greater than the peak runoff rates from equivalent size storms under pre-development conditions. The 1-, 2-, 5-, 10-, 25-, 50-, and 100-year storms shall be considered in designing a facility to meet this requirement.
(Ord. 19-289. Passed 12-10-19.)