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Report in Support of the Recertification of the University of Colorado's Flood Control Levee Page 10 of Levee are in contact with the 100 -year flood, while the middle reach is not. The upstream reach will be re- certified, while the middle and downstream reaches will not be certified. The downstream reach is overtopped by the flood. See Figures 15 and 16. LRE also prepared more detailed profiles of the upstream reach of Levee using surveys by Robert M. Sayre, P.L.S. in 2007 and 2009. These profiles are shown on Figures 17 through 19, and on Mr. Sayre's plan and profile drawing, which is included as Appendix C. Boulder's hydraulic models and its one -foot contour map, and the Sayre field surveys are all based on the NAVD 88 vertical datum. This is the current datum used by FEMA. All of the previous flood plain and Levee certification work was based on NGVD 29, the datum previously used by Boulder and by FEMA. One of the flood profiles identified on Figures 15, and 17 through 19 is the result of Boulder's 1- D hydraulic model, which considers only the flood water that is conveyed in the vicinity of the Dry Creek Ditch No. 2. The ditch comes in contact with the Levee near station 142 +00 (in the middle of the east -west portion of the upstream reach), and it departs from the Levee at about station 101 +00 (the new downstream end of the upstream reach). The other flood profile included on Figures 15 through 19 is taken from the output generated by the four -meter grid of the 2 -D hydraulic model, which tracks the movement of the 100 -year flood over the entire flood plain, in four -meter cells. See Figures 20 and 21 for examples of model output from the 1 -D and 2 -D hydraulic models. VII.2. Cross Sections Twenty -four cross sections were prepared by LRE at 200 foot intervals for the upstream reach of the Levee using Boulder's one -foot topographic mapping. Three other cross sections were also drawn at other locations. The ground line represents the lines and grades of the Levee as of 2003 (see Appendix D). We added the surveyed top elevations, and the 1 -D and 2 -D flood levels (where applicable). Figure 22 shows the location of the Levee cross sections. Twelve cross sections were modified to show how they were raised in 2008 and 2009 to maintain the required freeboard, as described below. The cross sections show that the Levee has a minimum of ten feet of width at the top, and that the side slopes are a minimum of 3:1 on the interior and outside faces. VII.3. Raising of Levee- 1998, 2008, & 2009 Portions of the Levee were raised in 1998 as described in Appendices B, B -8, and B -9. Because Boulder's new hydraulic modeling results were higher than earlier flood studies at the lower end of the upstream reach of Levee, and because the 2007 flood plain was extended further along the levee than previous flood -plain delineations, it was necessary for the University to raise the levee to maintain the required level of freeboard for this portion of the Levee. LRE designed the lines and grades for the raising of the lower portion of the upstream reach Levee. The Levee needed to be raised over a length of about 1,000 feet. The design is shown on the appropriate cross sections (Appendix D), and on Figures 19 and 23. Robert Sayre, P.L.S laid out the grades for the work in the field. CTL /Thompson, Inc. prepared the specifications for the project, including preparation of the top of the existing Levee, the fill material, and its compaction (see Appendix E). As part of its ongoing maintenance effort, the University caused © Leonard Rice Engineers, Inc. June 2009 — 207FIP05