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Susan Burgmaier <br />-3- December 31, 2012 <br />coincide with the SEDCAD report on pages App. B -17 through App. B -41. <br />BRL: Appendix B as shown on page App. B -2 has been revised per the changes as <br />noted in the table provided by DRMS. The diameter of culvert determined by <br />SedCad is a minimum diameter. A 42" is in place, so it was left in the table, but an <br />'in- place' has been added to the table. For the West Diversion Ditch #2, we <br />consider D50 = 1.5" riprap to be no rip rap required. However, the design for the <br />West Diversion Ditch #2 has been revised and the D =1.5" is no longer applicable. <br />West Diversion Ditch #1 and #2 have been constructed, and the grade has been <br />revised from a 2% to a 3.5% as well as the shape of the channels. Revised <br />SedCad designs are attached as pages App. B -41, 42, and 42i. <br />10. Page App. B -6 indicates that the anticipated runoff from the 10 yr -24 hr event to Pond <br />F is 3.74 ac ft. We are unable to locate supporting documentation, such as a <br />SEDCAD run or other calculation, for this runoff estimate. Please provide the <br />SEDCAD report or other information to document the runoff calculation for the <br />10 yr -24 hr event. <br />BRL: Runoff from the 10 -year 24 -hour event as shown on page B -4 is calculated using <br />the SCS (NRCS) Runoff Equation, which is the equation used in TR -55, and what <br />SedCad is based on. Prior to use of SedCad, TR -55 was the method for <br />determining runoff. Given a curve number and precipitation amount, a value for <br />runoff could be picked off from the table. For simplification, our office input the SCS <br />equation into excel so it wasn't necessary to use the table for each runoff <br />determination. Clarification has been added to pages App. B -4 & 6 specifying the <br />methodology being used. <br />11. Pond F, as designed, appears to be adequate to contain the 10 yr -24 hr storm event <br />(3.74 ac ft), with storage capacity for approximately two years of sediment <br />accumulation (0.20 ac ft). There is an additional 0.03 ac ft of excess capacity in the <br />pond, which equates to roughly 5945.1' elevation. Because there is so little excess <br />capacity in Pond F, it will be imperative that the pond be maintained so that water and <br />sediment are at or below 5945'. Upon approval of TR -76 and prior to <br />implementation of the revision, BRL must install a durable marker in the pond <br />that clearly indicates the 5945' elevation so that maintenance personnel can <br />identify when the pond will require pumping and /or sediment cleanout. <br />BRL: A sediment marker will be installed once the weather allows for it, most likely in the <br />Spring. The currently approved Pond F configuration allows for a two year sediment <br />storage volume. Since Pond F was cleaned out in June of 2012, adequate storage <br />capacity for sediment will be available prior to a sediment marker installation. <br />12. Page numbers are missing for the designs of ditches F3, F5 and F6; presumably they <br />would be App. B -19, App. B -21, and App. B -22. Please revise these pages to <br />include page numbers. <br />