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APPENDIX-D The estimate of riprap size needed to protect the diversion berms from erosion has been determined. This was done using methods described in NUREG-1623, Sept. 2002, Design of Erosion Protection for Long Term Stabilization, Appendix D and NUREG/CR-4651, May 1987, Develoroment of Ripraro Design Criteria b~R~raro Testin¢ in Flumes: Phase I, section 3.4.3, the U.S. Army Corps of Engineers Method. The rock sizing is based on computing the sheaz stress, which is a function of velocity, slope, and depth. This method is suitable for situations where flow depth is small relative to riprap size. The channels will be constructed as the diversion berms are built with a bulldozer. As a result, the channel shape will be somewhat variable, but will approach an average triangular cross-section which will be over 10 feet wide by at least 2 feet deep. The slope will be approximately 0.10 where the natural gully of either subbasin intersects the diversion berms. Within a few tens of feet downstream, the gradient flattens, resulting in slower, wider, shallower flow. Therefore, riprap will only be placed at the intersection areas, unless observations during the life of the mine indicate the need for expansion. The following table shows the calculated DSO of riprap needed at each berm segment for both the 10-year and 100-year events. The unit weight of rock used in these calculations is that of the locally available sandstone, 1451b/ft': 10-yr 100-yr -cfs depth_ft V-ft/sec D o -cfs depth_ft V-ft/sec DSa Berm Se¢. 1 0.56 0.243 2.9 5.5 in 2.67 0.452 4.0 10.25 in Berm SQE. Z 1.36 0.345 3.5 7.8 in 6.64 0.648 4.9 14.7 in The berms will be protected during the mining operation life by rock that averages about 12 inches. The final footprint of the reclaimed waste rock dump will depend on the size of the pile attained during mining. The larger rock calculated for the 100- year event at berm segment 2 will not be placed until final reclamation is complete. At that time, particularly if the waste rock pile did not progress as far north as presently allowed, the berm and channel configuration will be re-evaluated.