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The road banks have a slope as steep as 1:1 on rock faces and a portion above the portal does approach <br />a 25% grade. However, using the flow rates shown in the engineering drawing, the associated velocities <br />are anticipated to be less than 1.5 fps, which should not cause any significant scouring following <br />mobilization of the surface fines. If we use the DRMS reviewer's value of 1.55 cfs (which is incorrect) at <br />the 25% grade, then the water velocity calculates to be greater than the than our target velocity of 3 fps. <br />However, since the portion of the road surface that is to carry the runoff is located at or very near <br />bedrock, the water would only scour to the top of the bedrock surface and then flow along it. Any <br />removed material would be deposited at the grade reduction point farther down the road and would be <br />returned back to the area that it was removed as part of normal road maintenance following the storm. <br />To once again to summarize, a flow rate of 0.02 cfs would produce a flow velocity of 1.5 fps, not enough <br />to do any significant scouring. <br />Thanks for the clarification on the Manning numbers. It appeared in the last response that DRMS was <br />suggesting the use of certain values, even though they may not fit the physical characteristics of the site. <br />It is good that the regulations allow us to have sufficient flexibility to make larger scale plan views and <br />sections of the standard base map, and we will continue to take advantage of that allowance. Thanks <br />once again for passing on the channel calculator spreadsheet. It saves quite a bit of effort as the <br />standard old method relies on multiple estimates to reach the proper solution. <br />7 <br />