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Craig Ranch Pit — Response to Adequacy Stormwater Comments <br />Page 3 <br />October 27, 2011 <br />a. Again, note the design storm is the 100 -year, 24 -hour precipitation event, and that <br />the collection channels will not "be able to handle the maximum stormwater <br />channel flow that enters them ". <br />9. Page G -3, first paragraph, spillways: Please provide clarification that the storage volume <br />in the sediment ponds discussed in the first paragraph on page G -2 is below the effective <br />crest of the spillway invert (i.e., the 1.0- and 5 -foot incised depths is in fact dead storage). <br />Note: the effective invert of the spillway is the contact between the bottom of the riprap <br />and the top of the subgrade /filter layer on which it lies, unless a spillway detail is <br />included to demonstrate otherwise. <br />10. Page G -3, second paragraph, transition channels: Please provide additional clarification <br />of the design intent. The description does not state what material is to be grouted. Is it <br />the in situ material as implied or the 8 " -18" diameter riprap stated in Item 10 of the Ellis <br />Letter? The Division engineering staff is familiar with the Urban Drainage and Flood <br />Control District's (UDFCD) grouted boulder design in which the lower half of the <br />boulder is grouted. Please provide a reference for the design if different than the <br />UDFCD's. <br />11. Map G, Spillway Conceptual Detail: The depth of rock is given a range of 6 " -12 ". The <br />riprap layer thickness should be twice the D50. Please revise the depth of rock to be 12" <br />minimum. <br />If either you or the applicants have any questions regarding the comments above, please call me <br />at (303) 866 -3567, extension 8169. <br />c:\ users \thm \appdata \local\microsoft\windows \temporary internet <br />files \ content. outlook \3nyv6den\stormwatercomments mem27octl1.docx <br />