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<br />Summary of Analysis Forming the Basis of a Recommendation for Approval of the Line <br />Camp Pit Construction Materials Permit Application, File No. M-2001-001 <br />This Recommendation was made Over Objections by Concerned Citizens that the <br />Eacavation of the Pits would Create Adverse Offsite Impacts during Flooding <br />Recommendation made by Depart. of Natural Resources, Division of Minerals and Geology <br />During the public comment period for the Line Camp Pit application, concerned parties stated that <br />the excavation of the pits created the potential for loss of life and property during a flood. The basis <br />for this concern was that over bank flood flows would cause down cutting and erosion of riverbanks <br />adjacent to the pits and of the strip of land that separates the pits from the river, and that the erosion <br />could lead to a redirection of the main channel through the excavated pits. The parties to the <br />application review further expressed concern that temporary pit perimeter berms would redirect flood <br />flows causing additional adverse offsite impact. <br />Gravel mining in floodplains is a common practice in Colorado and elsewhere. The Division of <br />Minerals and Geology routinely evaluates the potential for mining activities to alter the nature of the <br />floodplain and cause offsite impacts. The basis for the Division's finding that the potential for offsite <br />impacts is negligible for the Line Camp Pit proposal is documented in the "Rationale for Approval <br />Recommendation" (DMG, 2001) and in the minutes of testimony on the Lined Camp Pit proposal <br />before the Mined Land Reclamation Board. The basis for the Division's finding is that the mining <br />setbacks from the riverbank proposed in the permit application are sufficient to prevent redirection <br />of the river channel or tangible changes in the nature of flood flows during the 100-year event. <br />The concerned parties to the application have expressed that they are not satisfied with the Division's <br />rationale for approval recommendation and are distressed with the Board's decision to approve the <br />application. Certain parties have expressed a belief that loss of life and property during a flood will <br />be a direct result of the excavation of the Line Camp Pit. Due to the magnitude of the concerns <br />expressed for potential mining related impacts, this document provides additional quantitative <br />information in support of the Division's rationale for approval. This level of data analysis is <br />considered during the Division's review of applications for mining in the floodplain, but is typically <br />considered to be too detailed for inclusion in a recommendation rationale document. It is hoped that <br />by providing this analysis, the concerns with flooding impacts related to the Line Camp Pit will be <br />assuaged. <br />Buffer zones in the form of mining setbacks from rivers are a common practice used to minimize <br />impacts on the prevailing hydrologic balance. Two agencies in the State of Colorado with primary <br />responsibility to prevent problems that may be caused by floodplain gravel pits have adopted mining <br />setbacks as an acceptable mitigation measure (DMG, 1998; UDFCD, 1987). The width of the <br />setbacks must be sufficient to prevent down cutting failure of the strip of land between the pit and <br />the river during a 100-year flood. The width of a setback, to be required on asite-specific basis, may <br />be determined by evaluating the depth and velocity of water moving over the ground comprising the <br />setback during a flood. For large rivers in Colorado, a 400-foot setback is recommended, if no <br />1 <br />