2014-02-07_REVISION - M1979094HR (5)

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JD -7 Mine - Drainage Design Plan 13 where : nb = a base value of n for a straight, uniform, smooth channel in natural materials nj = a correction factor for the effect of surface irregularities nZ = a value for variations in shape and size of the channel cross section, n3 = a value for obstructions n4 = a value for vegetation and flow conditions m= a correction factor for meandering of the channel The values selected for the six roughness factors for natural channels, borrow ditches, diversion ditches, and short natural channels at the JD -7 Mine site are shown in Table 6. These n values were used to calculate channel capacity and were decreased, where appropriate, to calculate channel stability (Section 2.3.2). Table 6. Manning's "n" Values Used in Cowan's Method for Channel Roughness Natural Borrow Diversion Short Channel Condition n Values Channels Ditches Ditches Natural Channels Material Involved nb 0.02 Severe 0.040 -0.060 Earth 0.02 n4 0.02 Rock cut 0.025 0.022 0.022 0.022 Fine gravel 0.024 Very high 0.050 -0.100 Coarse gravel 0.028 m Minor Degree of Irregularity n 1 Appreciable 1.15 Smooth 0 Calculated Manning's n value Minor 0.005 0.005 Moderate 0.01 0.01 0.01 0.01 Severe 0.02 Variations of Channel Cross Section nZ Gradual 0 Alternating occasionally 0.005 0.005 0.005 0.005 Alternating frequently 0.010 -0.015 0.01 Relative Effect of Obstructions n3 Negligible 0 Minor 0.010 -0.015 0.01 0.01 0.01 Appreciable 0.020 -0.030 0.02 Severe 0.040 -0.060 Vegetation n4 Low 0.005 -0.010 0.005 0.005 0.005 0.005 Medium 0.010 -0.025 High 0.025 -0.050 Very high 0.050 -0.100 Degree of Meandering m Minor 1 1 1 1 1 Appreciable 1.15 Severe 1.3 Calculated Manning's n value 0.067 0.052 0.047 0.05 2.3.2 Channel Stability Channel stability was evaluated using the momentum and energy equations, in which gravitational forces that cause water to move downhill are balanced by frictional forces at the channel boundary that resist 4149A.140207 Whetstone Associates