2021-093 Ordinance - Laserfiche WebLink

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EXHIBIT A: CHAPTER 928 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 systems: 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 affects public health or safety, all as determined by the City Engineer. The following criteria shall be used to design storm sewer systems when necessary: a. Storm sewers capacity and hydraulic grade line shall be designed in accordance with the current version of UNIFORM STANDARDS FOR SEWARGE IMPROVEMENTS unless otherwise approved by the City Engineer. b. The minimum inside diameter of pipe to be used in public storm sewer systems is 12 inches. Smaller pipe sizes may be used in private systems, subject to the approval of the City Engineer. C. All storm sewer systems shall be designed taking into consideration the tailwater of the receiving facility or water resource. The tailwater elevation used shall be based on the design storm frequency. The hydraulic grade line for the storm sewer system shall be computed with consideration for the energy losses associated with entrance into and exit from the system, friction through the system, and turbulence in the individual manholes, catch basins, and junctions within the system. d. The inverts of all curb inlets, manholes, yard inlets, and other structures shall be formed and channelized to minimize the incidence of quiescent standing water where mosquitoes may breed. e. Headwalls shall be required at all storm sewer inlets or outlets to and from open channels or lakes. 6. Water Resource Crossings: The following criteria shall be used to design structures that cross a water resource in the City of North Olmsted: a. Water resource crossings other than bridges shall be designed to convey the stream's flow for the minimum 25 -year, 24-hour storm. b. Bridges, open bottom arch or spans are the preferred crossing technique and shall be considered in the planning phase of the development. Bridges and open spans should be considered for all State Scenic Rivers, coldwater habitat, exceptional warmwater habitat, seasonal salmonid habitat streams, and Class III headwater streams. The footers or piers for these bridges and open spans shall not be constructed below the ordinary high water mark. C. If a culvert or other closed bottom crossing is used, twenty-five (25) percent of the cross-sectional area or a minimum of I foot of box culverts and pipe arches must be embedded below the channel bed. The conduit or conveyance must to be sized to carry the 25 -year storm under these conditions.