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<br />dam. Otherwise, the existing spillway capacity shall be enlarged or overtopping <br />protection shall be provided in a manner approved by the State Engineer. <br /> <br />6.1.4.3 Additional reductions of the probable maximum precipitation values for <br />dams at higher elevations can be taken in accordance with Rule 6.1.4.1. <br /> <br />6.1.4.4 The minimum size spillway for all existing High Hazard dams and Large <br />and Small Significant Hazard dams, for which an incremental damage analysis <br />shows a smaHer spillway is justifiable under Rule 5.6, is the spillway size required <br />to safely accommodate the flood generated by a 24-hour, 50-year rainstorm event. <br /> <br />6.1.5 Freeboard - The minimum freeboard requirements for an existing dam shall be the <br />maximum required to either prevent overtopping by wave action or to pass the IDF without <br />overtopping, but not less than three feet. <br /> <br />6.2 Approval Limitation - If construction, alteration, or repair of a reservoir dam is not <br />commenced within five years of approval of the application, the State Engineer's approval shall be <br />void. The owner must resubmit the application and receive approval before commencing <br />construction, and shall meet the requirements ofthe current Rules and Regulations. <br /> <br />Rule 7. Requirements for Removinl! or Breacbinl! an Existinl! Dam: <br /> <br />7.1. Breach Plan and Application - An owner proposing to permanently remove or breach a dam <br />shall submit an application package in a form acceptable to the State Engineer prior to commencing <br />work. Plans for Removal or Breach of a dam shall meet the following requirements: <br /> <br />7.1.1 Application - A completed application shall be submitted on a form provided by the <br />State Engineer. <br /> <br />7.1.2 High Hazard and Significant Hazard Dams - For High Hazard and Significant <br />Hazard dams, a breach plan shall be prepared by an engineer. <br /> <br />7.1.2.1 The dam shall be excavated down to the level of the natural ground, or as <br />necessary in accordance with Rule 7.1.2.3, at the maximum section; and shall be of <br />sufficient width to pass the 24-hour, 100-year flood with a maximum increase in <br />reservoir depth of five feet. However, the maximum breach width shall not exceed <br />the width of the original natural channel before the dam was constructed, regardless <br />ofthe 100-year flood magnitude. <br /> <br />7.1.2.2 The sides of the breach shall be excavated to a slope that is stable, but not <br />steeper than 2: 1 (two horizontal to one vertical). Slope stability analysis that <br />provides an adequate factor of safety for steeper slopes may be accepted by the State <br />Engineer, but in no case shall the slopes be steeper than I: 1. <br /> <br />28 <br />