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~ ~ III IIIIIIIIIIIIIIII r it DATE: November 4, 1992 T0: Steve Renner and Dan Hernandez FROM: Cathy Begej C L(J~ RE: Corley Company's Proposed Diversion I have quickly reviewed Dr. Corley's plan to divert water into the Magpie Creek Diversion east of the pond. This plan calls for the construction of a 6' deep triangular ditch with 1:1 side slopes running from the unnamed creek east, along the south side of the pond, discharging approximately 375' east of the pond at a point 18 feet above the Magpie Channel. Dr. Corley proposes to have this ditch run over the 30" culvert which would collect water from the West Pit and direct it to the pond. The profile suggests that fill will be installed on the west end and that a cut will be dug on the east end. I looked at the sizing of the diversion, its location and the general mass balance of the cut and fill. 11 There does not appear to be adequate depth fora 6' deep ditch and a 2 1 /2' deep culvert if the proposed profile is the land surface at the top of the ditch. The profile of the ditch alignment shows a node for the 30" CMP at 150.75' and the proposed topography map shows the culvert inlet at 151' and the outlet at 149' (presumably, the node marks the culvert invert elevation, but it wouldn't hurt to confirm thisl• That puts the top of the culvert at 153.5 ' at the inlet and 151.5' at the outlet. 21 The ditch i~ersized ate r event. T argest calculated~~e 10 year 5~~ /O"c° °'~ flow,the Unn d Cre icfs, ch wou resa dept ofF 3.6'. ~n'^'"P'~~"5 ~ .s rcLt s /cry 31 The ditch probably should be rip-rapped for protection from erosion; the design velocities u,J3 range from 5.1 - 5.7 fps. I would recommend rip-rap with a D60 of 6" - 9". , ~ ~ 4) I have great difficulty with a ditch of a 1 °k grade. It is difficult to accurately construct and I would like a commitment for certification of its installation. 51 The ouffall of the ditch needs to be protected. There is an 18' elevated drop in the 36°h slope between the end of the ditch and the bottom of Magpie Creek. The 10 year - 24 hour storm event will erode this slope severely. In addition the water will enter the Energy Fuels lease area. 61 What type of ditch stabilization work is anticipated following construction, i.e., is the ditch going to be seeded and will matting be put down to protect the steep side slopes? 71 Establishment of a fill upon which to install a ditch is generally unwise, but as such will require heavily compacted fill for construction. In addition, this fill should be considerably wider than the ditch. An engineer should design the fill and verify its stability in a saturated state.