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storm event would result in similar erosive velocities . Therefore , <br /> control measures such as riprapping the entire diverted channel <br /> segments to preclude erosion during the 100-year storm event would <br /> not be appropriate for this drainage system. <br /> As an alternative, the permittee will construct the diversions such <br /> that the two channel segments will have non-erosive velocities <br /> while passing the 10-year, 24-hour precipitation event. This will <br /> be accomplished by stair-stepping the diverted channel portions <br /> utilizing riprap "footers" on 90-foot centers which are keyed into <br /> the channel sides and bottom. <br /> 1 . The Division approved two permanent diversions of Coal Creek. <br /> These diversions are consistent with applicable state law, will <br /> not diminish downstream water rights, and will meet the <br /> requirements of Rules 4.05.4 and 4.05. 18 (4.05.4(4) ) . <br /> 2. The permanent diversions shall make use of artificial <br /> structural controls in order to allow them to remain in dynamic <br /> equilibrium with the drainage basin system. The Division <br /> approved the use of riprap "footers" in the channel bottom <br /> (4.05.4(4)(b) ) . <br /> 3. Channel lining structures , retention basins , and artificial <br /> channel roughness structures are proposed for use to control <br /> erosion. These means were approved by the Division since they <br /> are necessary to control erosion , they are stable and will <br /> require infrequent maintenance (4.05.4(2)(a) ) . <br /> In addition to the two permanent diversions of Coal Creek <br /> mentioned above , a temporary diversion is proposed for an <br /> unnamed ephemeral tributary to the Colorado River located <br /> within the 2 West Portal Disturbance Area. The outside bank <br /> closest to the North Portal will be built up to prevent the <br /> diverted stream from entering the portal . Bedrock lies close <br /> to the bottom of the diverted channel and the channel does not <br /> require armoring. The channel will be returned to its natural <br /> configuration upon final reclamation. <br /> 4. The Division approved the temporary diversion of an ephemeral <br /> stream draining less than one square mile located at the 2 West <br /> Portal . This decision is based on a finding that the proposed <br /> diversion meets the requirements of 4.05. 18 and 4.05.4, <br /> applicable local , State , and Federal statutes and regulations <br /> and that the diversion is designed to safeguard public safety <br /> and to minimize adverse impacts to the hydrologic balance <br /> (4.05.4( 1 ) and (4)) . <br /> D. Sedimentation Ponds <br /> Nine sediment ponds are in place , and another pending , as <br /> previously approved by the Division and have been treating <br /> disturbed-area surface water runoff under the existing permit for <br /> the Roadside and Cameo Mines . All ponds have performed well over <br /> -20- <br />