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• HYDROLOGIC DOCUMENTATION <br />SMALL AREA EXEMPTION <br />ROCK DUST STORAGE AREA <br />The following calculations demonstrate the amount of sediment fence surface area required to <br />adequately handle the runoff from the rock dus[ area and that the existing diversion berm is <br />adequa[e to con[rol ninon. <br />Runoff volume and peak discharge calculations were performed utilizing the SEDCAD+ <br />computer model consistent with the methodology previously discussed in [his Exhibi[. The <br />sediment fence and diversion berm were designed to handle the peak discharge from a 10•yeaz, <br />24hour s[orm event. <br />1.0 West Diversion Berm) <br />1.1 Hydrology Lnouts <br />All hydrology inputs are shown on [he SEDCAD+ computer printou[s. <br />The CN numbers used for the berm watershed were obtained from Procedures for <br />De[ermining Peak Flows in Colorado and Technical Release No. 55 (USDA-SCS, 1980). <br />Based on soil type and vegetation cover, curve numbers were determined using Table <br />• 2-2a and 2-2d, USDA-SCS TR-55, for the following conditions: <br />Undisturbed <br />Soil Type: B <br />Ground Cover: <30°.(u, Poor <br />Cover Type: Pinyon -Juniper <br />CN: 75 <br />1.2 Hydrology Results <br />Peak Discharge <br />10-year,24hour event 0.32 cfs <br />1.3 Berm Desien <br />The berm was designed using Manning's equa[ion for open channel flow assuming a V- <br />shape channel. The results are summarized as follows: <br />Channel slope: 1% <br />Sideslopes: 3H:IV <br />Mannings n: .035 <br />Depth of flow: 0.3 feet <br />Veloci[y: 1.2 fps <br />Berm height: 1.5 feet <br />• Freeboard: 1.2 feet <br />:.,. <br />C\.V60TRIAMP <br />ivou» ~ Revised -November 1993 <br />