Laserfiche WebLink
<br />David Berry -13- June 20, 1996 <br />other. Why are there two different presentations for these <br />ditches and which presentation applies to the in-the-field <br />situation? <br />Runoff control ditches presented in Appendix B represent <br />preliminary ditch geometry for a simplified overall hydrology <br />scenario. Conservative results from hydrology analyses then <br />were taken and refined for site-specific ditch design. <br />Refined ditch geometry is presented in Appendix C. <br />To avoid any confusion, the ditches used for hydrological <br />analysis presented in Appendix B have been changed to 2H:lV <br />geometry. This change in geometry has no affect to site- <br />apecific ditch calculations. <br />56. Drawing 95266-04 shows that the side slopes for the runoff <br />control ditches are 2H:1V. However, the ditch designs in <br />Appendix B of Volume IV list 1H:1V for the side slopes for all <br />the ditches. In Appendix C, the ditch designs for the crest <br />ditch and the upper diversion show side slopes of 1H:1V. <br />Please reconcile these differences. <br />Runoff control ditch geometry presented on the design drawings <br />are those required to be constructed in the field. They are <br />based on the refined ditch geometry worksheets presented in <br />Appendix C. The calculations presented in Appendix C have <br />been changed to reflect the geometry shown on the design <br />drawings. <br />57. Drawing 95266-04 shows that the emergency spillway side slopes <br />are 2H:1V. However, the sediment pond spillway worksheet in <br />Appendix C shows side slopes of 1H:1V. Please reconcile this <br />difference. <br />Sediment pond emergency spillway side slopes were re-analyzed <br />with 2H:1V side slopes to provide assurance that the 2H:lV <br />geometry specified on the drawings and in Volume IV text is <br />adequate. Results indicate the spillway is adequate, and the <br />corrected calculation is included in updated Appendix C. <br />58. In Appendix B of Volume IV, a curve number of 63 is used for <br />basin A3b. However, examination of Map 3, Vegetation, and Map <br />20, Sedimentation Control Plan, suggest a larger curve number <br />may be appropriate. It appears that the drainage basin for <br />A3b is composed of about 75$ disturbed area and about 258 <br />burned area. Using a curve number of 89 for the disturbed <br />area and 65 for the burned area, and average curve number of <br />about 83 would seem appropriate. Please justify a curve <br />number of 63 for basin A3b. <br />We believe that the curve number of 63 used in the initial <br />design is appropriate for this area. However, the hydrology <br />