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may include minimizing site grading and compaction; protecting and/or restoring water <br />resources, riparian areas, and existing vegetation; and maintaining unconcentrated storm <br />water runoff to and through these areas. <br />B. Storm Water Conveyance Design Criteria: All storm water management practices shall be <br />designed to convey storm water to allow for the maximum removal of pollutants and reduction in <br />flow velocities. This shall include but not be limited to: <br />1. Stream relocation or enclosure: The Mayfield Village. Engineer may allow the enclosure <br />or relocation of water resources only if the applicant shows proof of compliance with all <br />appropriate permits from the Ohio EPA, the U.S. Army Corps, and other applicable <br />federal, state, and local agencies as required in Section 1128.07 of this regulation, and the <br />activity is in compliance with Chapter 1129 Mayfield Village's Erosion. and Sediment <br />Control requirements as determined by the Mayfield Village Engineer. At a minimum, <br />stream relocation designs must show how the project will minimize changes to the vertical <br />stability, floodplain form, channel form, and habitat of upstream and downstream channels <br />on and off the property <br />2. Off-site storm water discharges: Off-site storm water runoff that discharges to or across <br />the applicant's development site shall be conveyed through the storm water conveyance <br />system planned for the development site at .its existing peak flow rates during each design <br />storm. Off-site flows shall be diverted around storm water quality control facilities or, if <br />this in not possible, the storm water quality control facility shall be sized to treat the off- <br />site flow. Comprehensive Storm Water Management Plans will not be approved until it is <br />demonstrated to the satisfaction of the Mayfield Village Engineer that off-site runoff will <br />be adequately conveyed through the development site in a manner that does not exacerbate <br />upstream or downstream flooding and erosion. <br />3. Sheet flow. The site shall be graded in a manner that maintains sheet flow over as large an <br />area as possible. The maximum area of sheet flow shall be determined based on the slope, <br />the uniformity of site grading, and the use of easements or other legally-binding <br />mechanisms that prohibit re-grading and/or the placement of structures within sheet flow <br />areas. In no case shall the sheet flow length be longer than 300 feet, nor shall a sheet flow <br />area exceed 1.5 acres. Flow shall be directed into an open channel, storm sewer, or other <br />storm water management practice from areas too long andlor too large to maintain sheet <br />flow, all as determined by the Mayfield Village Engineer. <br />4. Open channels: Unless otherwise allowed by the Mayfield Village Engineer, drainage <br />tributary to storm water management practices shall be provided by an open channel with <br />landscaped banks and designed to carry the 10-year, 24-hour storm water runoff from <br />upstream contributory areas. <br />Open drainage systems: Open drainage systems shall be preferred on all new development <br />sites to convey storm water where feasible. Storm sewer systems shall be allowed only <br />when the site cannot be developed at densities allowed under Mayfield Village zoning or <br />where the use of an open drainage system affects public health or safety, all as determined <br />by the Mayfield Village Engineer. The following criteria shall be used to design storm <br />sewer systems when necessary: <br />a. Residential storm sewers shall be designed such that they do not surcharge from <br />