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ORDINANCE NO. 2022-18 <br />Page 15 <br />runoff will be adequately conveyed through the development site in a <br />manner that does not exacerbate upstream or downstream flooding and <br />erosion. <br />Sheet flow: The site shall be graded in a manner that maintains sheet flow <br />over as large an area as possible. The maximum area of sheet flow shall be <br />determined based on the slope, the uniformity of site grading, and the use <br />of easements or other legally -binding mechanisms that prohibit re -grading <br />and/or the placement of structures within sheet flow areas. The sheet flow <br />length shall not exceed seventy-five (75) feet from impervious area or one <br />hundred and fifty (150) feet from pervious areas. Flow shall be directed <br />into an open channel, storm sewer, or other SCMs from areas too long <br />and/or too large to maintain sheet flow, all as determined by the Village <br />Engineer. <br />4. Open channels: Unless otherwise allowed by the Village Engineer, <br />drainage tributary to SCMs shall be provided by an open channel with <br />vegetated banks and designed to carry the 10 -year, 24-hour stormwater <br />runoff from upstream contributory areas. <br />5. Open drainage systems: Open drainage systems shall be preferred on all <br />new development sites to convey stormwater where feasible. Storm sewer <br />systems shall be allowed only when the site cannot be developed at <br />densities allowed under the Village's zoning or where the use of an open <br />drainage system affects public health or safety, all as determined by the <br />Village Engineer. The following criteria shall be used to design storm <br />sewer systems when necessary: <br />a. Uniform Standards for Sewerage Improvements, Latest Edition <br />shall be followed. <br />b. The minimum inside diameter of pipe to be used in public storm <br />systems is 12" unless smaller is approved by the Village Engineer. <br />Smaller pipe sizes may be used in private systems, subject to the <br />approval of the Village Engineer. <br />C. All storm sewer systems shall be designed taking into <br />consideration the tailwater of the receiving facility or water <br />resource. The tailwater elevation used shall be based on the design <br />storm frequency. The hydraulic grade line for the storm sewer <br />system shall be computed with consideration for the energy losses <br />associated with entrance into and exit from the system, friction <br />through the system, and turbulence in the individual manholes, <br />catch basins, and junctions within the system. <br />C; d. The inverts of all curb inlets, manholes, yard inlets, and other <br />