APPCOR10484 - Laserfiche WebLink

Home Browse Search

STATE OF COl0RA00 RiC n=~RU O. LAMM. Govcmm DEPARTMENT OF NATURAL RESOURCES D. Monte Pascoe, Ezecu rive Director MINED LAND RECLAMATION 423 Centennial Building, 1313 Sherman Sireel Denver, Colorado 80203 Tel. (303) 866-3567 April 28, 1982 iiiiiiiiiiiiiiihi David C. Shelton Director TO: Carol Russell and Ed Bischoff FROPf: Jerry Zimpfer :~~__ RE: Magpie Creek Diversion, Dorchester's Portion I have completed my review of the 19agpie Creek diversion contained in the Dorchester permit application. This segment of the diversion was approved and constructed by Dorchester under the interim program as a temporary diversion. The applicant now indicates a desire to have the diversion approved as a permanent diversion. Rule 4.05.4(3) provides that permanent stream channel diversions may be constructed with the approval of the Division if such diversions are consistent with applicable State law, would not diminish downstream water rights and meet the requirements of Rule 4.05.4. In deterrdning whether to approve the diversion as a temporary diversion or a permanent diversion, there are several questions that should be considered. 1) What are the probable hydrologic consequences of the diversion? The most likely effect is increased erosion in the unnamed tributary to 1?agpie Creek which receives the flow. This erosion could effect the stability of the GEC 1•fineral's segment of the diversion. This effect could be avoided by enlarging the natural channel. 2) Is the diversion capable of transporting the sediment load supplied from the watershed above? The t?agpie Creek diversion is constructed at gradients lower than those in the original channel, and may be subject to siltation. As a practical matter, siltation must be avoided if channel capacity is to be maintained. In addition, Rule 4.05,4(6) would require that the diversion be capable of transporting natural sediment loads. 3) Is the location of the permanent diversion appropriate? The diversion is cut into the base of a steep hillslope and the stability of the hillslope may be affected. Landslides would reduce channel capacity. In a temporary diversion, any problem could be handled through maintenance. If, however, the diversion is going to be left permanently, a geotechnical assessment should be performed to assure the Division that the channel may be expected to function over the long term. Talk to Jim Pendleton about what might be appropriate for a technical demonstration of stability.