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<br /> <br />Mr. Thomas Ehmett, Acting Director -2- April 21, 1995 <br />Office of Surface Mining Reclamation <br />and Enforcement <br />pattern, and the reconstructed channels remain in dynamic equilibrium with the overall <br />drainage basin without use of structural controls. <br />In the Division's Phase I Bond Release Findings dated April 7, 1995, the Division found <br />the 2275-foot Starkville Gulch permanent stream channel diversion, which includes the 8- <br />foot diameter culvert, in compliance with Rule 4.05.4(4), The mine site area has been <br />mined since the late 1800's; as such, no pre-disturbance maps or photographs exist to <br />illustrate the native land contours. Reference to a topographic map of the surrounding <br />land areas indicates the overall topography of the Starkville Gulch canyon ranges from a <br />maximum elevation of 6800 feet at the ridge top to a valley bottom elevation of 6415 feet. <br />This is an overall elevation change of 385 feet. The 675-foot-long culvert portion of the <br />2275-foot diversion creates an elevation difference of only 12 feet: the eight feet of <br />culvert diameter plus four feet of overlying fill. This accounts for only a three percent <br />rise in the overall elevation drop in the valley. The length of the watershed is <br />approximately 7900 feet long. The 675-foot-long culvert comprises only 8.5 percent of the <br />overall valley length. <br />The 675-foot-long culvert was designed to lay at the channel bottom elevation of the <br />Starkville Gulch, and has been constructed as designed. Since the bottom of the culvert <br />has been installed at the same level of the natural drainage bottom, the culvert does not <br />significantly alter the natural stream channel gradient. The inlet elevation of the culvert <br />is 6420.5 feet and the outlet elevation is 6400.8 feet. This provides for an average <br />channel gradient of 2.9 percent. The overall channel gradient of the permanent stream <br />channel diversion is 3.4 percent. The section serviced by the culvert is thus at a grade <br />within 0.5 percent of the overall permanent diversion gradient. This represents a stable <br />longitudinal profile. <br />The natural channel gradient of Starkville Gulch creates a natural meander pattern that <br />is, for the most part, devoid of convolutions or oxbows. As the permanent stream <br />channel diversion has one small "S" meander where it passes under the access road, and <br />one larger gradual meander near the west end of the permit boundary, the diversion <br />approximates the pre-mining configuration of the natural meander pattern, and blends <br />with the undisturbed drainage above and below the diversion. <br />The permanent diversion does not compromise the dynamic equilibrium of the drainage <br />basin system, nor does it diminish any downstream water rights. The entire diversion, <br />including the culvert, is designed to adequately pass 465 cubic feet of water per second, <br />