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summation of the two curves and predicts a maximum flow of .017 cfs. The number used for the <br />calculations was conservatively raised to 0.02 cfs. This remains our best estimate and we will leave it <br />unchanged for our channel design. <br />For discussion, we can test the channel design against the DRMS reviewer's suggested number of 1.55 <br />cfs. We need to once again go back to the Manning equations, and solve them for channel area/ wetted <br />perimeter. For this higher flow rate, the Manning number is reduced to 0.03 from the 0.04 value which <br />we continue to use for the real current runoff model. The 0.04 value betters represents the flow of a <br />typical mountain stream, for which the low flow rate. With the higher flow rate suggested by the <br />reviewer, and using the configuration shown in the design drawing B Section, a bottom channel width of <br />1.25 feet solves the equation. I also used the Excel calculating tool you sent me, to check my <br />calculations confirming that the Section B channel is sized large enough to carry this higher flow. I made <br />one change in your already filled in table, by reducing the channel bottom width "B" to zero as our <br />calculations are based on the 10 percent cross- grade (super) of the road surface with no gutter. Your <br />calculating tool (thanks for sharing it — It is a great help in zeroing in on a design rapidly) produced a <br />lower flow velocity number than ours, but both calculations produce flow velocities that are sufficient to <br />keep the diversion channel from silting. <br />Comment 3c Demonstrate that south run-on control is adequate to divert run-on away from work <br />area. <br />Response: <br />The area was so small and the calculated flows were so low, we left them off of the engineering drawing <br />as they made little difference to our calculations. To address the comment we use the same method as <br />above to produce a calculated flow rate of 0.006 cfs, a volume that can easily flow through an ordinary <br />garden hose. The diversion channel above the work area is designed as an 18 -inch wide native earth <br />trench with the edges set to a 1:2.5 (V:H) slope, and a base slope set at a grade of 4 percent. Our <br />calculations show that the channel has sufficient capacity to allow a free board of 11.5 inches; <br />approximately the same result produced using the Excel calculation tool. There is once again some <br />difference in my velocity value versus the value produced by the spreadsheet, but both results are well <br />below any velocities that might produce scouring. The existing cut that drains down the hillside is <br />obviously stable, since it likely more than 50 years old and no evaluation was done on it. A section of <br />the channel has been added to the design drawing. <br />Comment 4b There appears to be a steeper reach of the north run -on that should be analyzed for <br />stability. <br />Response: <br />2 <br />