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b. Central Detention Overflow, Section E- E/Channel Data: The maximum slope is listed as 0.125 ft/ft. <br />The Plan View shows a reach with an 18.08% slope. Please revise the calculations to reflect the <br />steeper design slope. Also, please confirm in the data that the channel is intended to be a "V" ditch <br />by listing the bottom with as 0.0 feet. <br />Response - As with the prior channel comment on Section H -H, channel dimensions were not <br />current, calculations and dimensions have been updated <br />c. Central Detention Overflow, Channel Data - Manning's n: The value of 0.028 appears too high for bare <br />soil and too low for riprap. Please provide rationale for the selection of 0.028. Note flow velocities <br />exceeding 5.0 fps 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/gravelly channel. This appeared to be the best fit among the <br />examples listed in the reviewed criteria as the dikes and berms will be constructed using neutral <br />mine waste rock <br />d. East Run On Diversion Swale, Sections E -E and F -F, Channel Data - Manning's n: The value of <br />0.028 appears too high for bare soil and too low for riprap. Please provide rationale for the <br />selection of 0.028. Note flow velocities exceeding 5.0 fps will require a discussion on <br />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/gravelly channel. This appeared to be the best fit among the <br />examples listed in the reviewed criteria as the dikes and berms will be constructed using neutral <br />mine waste rock <br />e. East Run On Diversion Swale, Section E -E, Channel Data - Slope: The maximum slope is listed as <br />0.125 ft/ft. The Plan View shows a reach with an 18.08% slope. Please revise the calculations to <br />reflect the steeper design slope. <br />Response - Calculations have been revised <br />f. East Run On Diversion Swale, Plan View: The note indicates topsoil will be stripped and 4 -inch <br />cobble will be placed to maintain "travel surface ". 4 -inch cobble is unlikely to remain on bedrock <br />either during a storm event or with infrequent vehicle traffic on an 18% slope. Please provide some <br />discussion on the purpose and maintenance of the 4 -inch cobble. <br />Response - The 4 in cobble (not a D50, should perhaps have been minus) is intended to fill any <br />significant cavities created in recovering topsoil. Without 'potholes' that could swallow a tire, <br />even an 18 -20% expanse of bedrock is an acceptable travel surface. Depressions regraded/filled <br />with fine material would be significantly more susceptible to erosion. <br />Additional notation has been added to the plans for two sections of riprap lining for the channel <br />should there be erodible material remaining after the topsoil is removed As noted above, if the <br />surface after the topsoil is removed is exposed bedrock the riprap will be placed as necessary to <br />fill any significant depressions that would impair vehicular transit. <br />