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The 100 yr discharge was recalculated to be 43 cfs instead of 35 cfs because of changes <br /> in Time of Concentration (see responses below for further information). A 30-inch pipe <br /> would still be sufficient, but marginal with an upstream&D of 150%. <br /> • If not how is traffic to cross the ri ra -lined spillway? <br /> P P <br /> RESPONSE. The spillway from the stream for overtopping flows will be a 6-inch <br /> deep x 6 foot wide armored Swale from the ditch across the access road to the point <br /> shown on Photo 1. The armoring will be configured and the rock consolidated so <br /> that normal traffic will drive across it. The swale will be armored with 3-inch <br /> riprap as shown on Drawing CCVSAI I-6. See Attachment 13. <br /> 52. Appendix 10, Chicago Tunnel Site (p. 6) <br /> • The Chicago Tunnel site is to be considered a designated mining operation(DMO)with <br /> the approval of AM-11. As such stormwater conveyances are required to pass the peak <br /> flow resulting from the 100-year, 24-hour design storm. The first paragraph states the <br /> upper channel has been designed for the 10-year/24-hour event. This channel must be <br /> redesigned to convey the 100-year event. <br /> RESPONSE: The stormwater hydrology for the Chicago Tunnel site was recomputed to <br /> address comments about Time of Concentration. The actual site related to the Chicago <br /> Tunnel mining operation was also divided into two basins (ChiTunPond and <br /> ChiTunBypass). The hydrograph for that upper channel is shown on Photo 2, with a <br /> peak discharge of 7 cfs for just a few minutes because of the short time of concentration, <br /> and then decreasing to less than one cfs. The peak discharge from a 10 year storm is 3.4 <br /> j cfs. The channel was designed to handle the 100 year flow, and meanwhile the sediment <br /> pond can accept two times the 10 year storm volume or the volume of a 100 year storm. <br /> Therefore, if there is an erosion issue with the channel design, any sediment will report <br /> to the pond and the Poverty Gulch stream will be protected. <br /> 8 - <br /> Combined SWS Peak Flow <br /> 7.04 cfs at 12.10 hrs <br /> 6. <br /> 5. <br /> m <br /> � 4- <br /> 3- <br /> 2- <br /> 0 <br /> 1 . <br /> 0 Photo 2:Hydrograph of ChiTun Pond Basin 50 <br /> The channel is shown on Detail 3, Section B of Drawing CCVSA11-6 as a two foot wide <br /> armored swale with 6-inches of depth. That profile can either be a separate ditch or the <br /> Page 24 of 30 <br />