HYDRO25403 - Laserfiche WebLink

Home Browse Search

COAL CANYON PERMANENT DIVERSION CERTIFICATION This certification covers the Coal Canyon Permanent Diversion that was reconstructed in 1998 to comply with the approved design and to repair damage caused to the original structures by storm water flows over the yeazs. The diversion design includes four rock structures constructed on approximate equal spacing beginning below the upper dip section crossing and extending downstream toward the lower dip section crossing on Haul Road 4. The rock structures aze to be constructed from large rock, Dso = 30". The bottom and side of the channel are lined with rock and include an approximate ]0' apron on each side of the transition section. The transition section slope length varies with the vertical drop and should have a slope of 4h:1 v. The channel section should have a 40' bottom width and a 62' top of~hannel width. The channel side slopes aze a nominal 2h:1 v. The permanent channel diversion site was inspected on May 19, and June 23, 1998 to determine if the diversion structures comply with the above design description. The diversion transition structures aze numbered from 1 to 4 with No. 1 being the furthest upstream. The diversion structures have been constructed from large rock with 8" cobble rock used to provide infilling of the spaces between the large rock. The structures appear to have the aprons on either side of the transition structwe. The undersigned was not on site during the construction of the diversion structures. Based on conversations with Larry Reschke, the engineer on site during construction, and Bob Blue, one of the Powderhorn Coal Company employees who constructed the structures, the aprons were constructed within the constraints of the field conditions. The undersigned dug down approximately 10 feet from the beginning of the drop on the transition structure on structures No. 1 and 2 and found cobble rock. As the cobble rock was reported to have been used to fill in around the large rock, the undersigned assumes that the aprons have been constructed as reported~.The.third..agd fourth transition sections vary from the ?_ ? design vertical drop of approximately 5'. The hind structure has a vertical drop of appro~iuma~ y w e the fourth struchue has a drop of 8'. These variances from the design aze not expected to adversely affect the performance of the diversion structure. The channel cross section was measured just upstream of the inlet to each transition structure. The channel measurements meet or exceed the design criteria at these locations. The downstream point of the intersection of the Pond 6 emergency spillway overflow and the permanent diversion channel has been lined with large rock to prevent erosion. While not specifically part of the diversion design, this work was added at the request of DMG personnel on the above referenced joint inspection in May. The side slopes of the channel and other disturbed areas associated with the diversion construction require seeding to prevent erosion. This work should be done in the fall with the approved seed mix and procedures.