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e. Channel Data - Design Flow: Exhibit U -1 does not list a peak flow result for either subbasin PA -N1 <br />or PA N2. Please provide appropriate calculations, including: <br />i. CN rationale for the curve numbers (CN) selected other than the "Arid Rangeland, Pinyon - <br />Juniper, Poor Condition ". <br />ii. Time of concentration estimates. <br />iii. Contributing areas. <br />Response - Flow information has been added for sub - basins PA -N1 and N2. Reference prior <br />responses on CN rationales. <br />f. Channel Data - Slope: The maximum slope is listed as 0.063 ft/ft. The Plan View shows a reach with <br />a 6.63% slope. Please revise the calculations to reflect the steeper design slope. <br />Response - Calculations updated to reflect steeper slope. <br />g. Channel Data - Manning's n: The value of 0.028 appears too high for bare soil and too low for <br />riprap. Please provide rationale for the selection of 0.028. Note flow velocities exceeding 5.0 fps <br />will require a discussion on armoring/erosion protection. <br />Response - Value of 0.028 was chosen from typical channel design charts and represents a earthen <br />channel with rubble sides. This appeared to be the best fit among the examples listed in the <br />reviewed criteria as the dikes and berms will be constructed using neutral mine waste rock <br />h. Section Thru Spillway: The specified geotextile/filter fabric indicated is Mirafi 140N. DRMS <br />believes the unit weight of this material is approximately 5 oz/'yd Given the size and thickness of <br />the riprap layer, we strongly recommend using a minimum 12 oz/yd" fabric. <br />Response - Geotextile specification has been revised to Mirafi 1120n or equivalent An alternate <br />granular filter has been added <br />i. Section Thru Spillway: The designed riprap layer is 1.5 thick on the embankment slope and for some <br />distance downstream before the thickness is reduced to 0.76 feet. Please provide a distance <br />dimension for each of the two riprap blanket thicknesses. <br />Response - Upon reviewing the design the reduced thickness portion of the riprap has been <br />eliminated A dimension has been added to the downstream riprap extension. <br />j. Section Thru Spillway: No cross - sections perpendicular to the flow direction are provided. Please <br />provide lateral cross - sections through the embankment and through the run out downstream to <br />enable an evaluation of flow' containment. <br />Response - A typical section has been added to the plans. <br />