2021-093 Ordinance - Laserfiche WebLink

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that have been compacted or had the topsoil or duff layer removed should be amended using the soil profile restoration design criteria in Rainwater and Land Development. B. Stormwater Conveyance Design Criteria: All SCMs shall be designed to convey stormwater to allow for the maximum removal of pollutants and reduction in flow velocities. This shall include but not be limited to: Surface water protection: The City Engineer may allow modification to streams, rivers, lakes, wetlands or other surface waters only if the applicant shows proof of compliance with all appropriate permits from the Ohio EPA, the U.S. Army Corps, and other applicable federal, state, and local agencies as required in Section 928.07 of this regulation, and the activity is in compliance with Section 927 Erosion and Sediment Control and Section 926 Riparian Setbacks and Wetland Setbacks, all as determined by the City Engineer. At a minimum, stream relocation designs must show how the project will minimize changes to the vertical stability, floodplain form, channel form and habitat of upstream and downstream channels on and off the property. 2. Off-site stormwater discharges: Off-site stormwater runoff that discharges to or across the applicant's development site shall be conveyed through the stormwater conveyance system planned for the development site at its existing peak flow rates during each design storm. Off-site flows shall be diverted around stormwater quality control facilities or the stormwater quality control facility shall be sized to treat the off-site flow. Comprehensive Stormwater Management Plans will not be approved until it is demonstrated to the satisfaction of the City Engineer that off- site runoff will be adequately conveyed through the development site in a manner that does not exacerbate upstream or downstream flooding and erosion. Sheet flow: The site shall be graded in a manner that maintains sheet flow over as large an area as possible. The maximum area of sheet flow shall be determined based on the slope, the uniformity of site grading, and the use of easements or other legally -binding mechanisms that prohibit re -grading and/or the placement of structures within sheet flow areas. The sheet flow length shall not exceed 75 feet from impervious area or 150 feet from pervious areas. Flow shall be directed into an open channel, storm sewer or other SCMs from areas too long and/or too large to maintain sheet flow, all as determined by the City Engineer. 4. Open channels: Unless otherwise allowed by the City Engineer, drainage tributary to SCMs shall be provided by an open channel with vegetated banks and designed to carry the 10 -year, 24-hour stormwater runoff from upstream contributory areas. Open drainage_s stems: Open drainage systems shall be preferred on all new development sites to convey stormwater where feasible. Storm sewer systems shall be allowed only when the site cannot be developed at densities allowed under City of North Olmsted zoning or where the use of an open drainage system