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Section 2 <br />Topaz Mine <br />To determine the channel capacity, CDM performed a Manning's equation analysis. <br />Flow depth and velocity were calculated using the following equations for the 100- <br />year peak discharges, cross section geometry (rectangular), and Manning's n values <br />listed in Table 2-2. <br />Q=VA <br />A = (b + zh)h <br />V =1.49 _(b+zh)h 2/3 Sul <br />n b+2h 1+z2 <br />where: <br />Q = discharge in cfs <br />V = velocity in feet per second (ft/sec) <br />z :1 = side slope <br />A = flow area in square feet (W) <br />b = bottom width of the cross section in feet (ft) <br />h = flow depth in ft <br />S = channel slope in feet/feet (ft/ft) <br />n = Manning's roughness coefficient (unitless) <br />• <br />Table 2-2 Innut Values for Channalc I and 9 CanaA#w Anal-1. <br />Channel 100- r Q S n z b <br /> cfs ft/ft ft/ft ft <br />1 5.79 0.025 0.035 3 3 <br />2 4.25 0.037 0.035 3 3 <br />The calculated channel depths and velocities of Channels 1 and 2 are shown in <br />Table 2-3. CDM recommends adding 2-feet of freeboard to the calculated flow depth <br />to account for potential channel overtopping. Given rectangular channels with bottom <br />widths of 3 feet each, a design depth of 2.5 feet is recommended for Channels 1 and 2. <br />Table 2.3 Calculation Summary fnr Channalc 1 and 9 <br />Channel h Freeboard esi n De th V <br /> ft ft ft ft/sec <br />1 0.43 2 2.43 3.16 <br />2 0.32 2 2.32 3.30 <br />To determine the appropriate channel lining (e.g., vegetated or riprap) for Channels 1 <br />and 2, CDM calculated flow velocities using information from the Urban Drainage <br />and Flood Control District (UDFCD) Drainage Criteria manual (UDFCD 2005). <br />UDFCD recommends flow velocity be less than 5 feet per second (ft/sec) for grass- <br />lined channels and velocities less than 12 ft/sec for riprap channels (UDFCD 2005). <br />Based on UDFCD remaunenda*ins, a Mamdnes n value of 0.035 was selected for <br />design calculations to check the capacity of grass-lined channels. Based on these <br />2-3 <br />0484986 - Denis Walk Order 1 - Sunday Mims Drainage StudyWWporllfi ml RepodVFkml Sunday Mines Drainage Report 052208.doc