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Report in Support of the Recertification of the University of Colorado's Flood Control Levee Page 4 SCA's as -built survey, included here as Appendix B -8, has been superseded by new surveys completed by Robert M. Sayre, P.L.S. Mr. Sayre's plan and profile drawing is included as Appendix C. • The geotechnical evaluation of the Levee was performed by CTL /Thompson, Inc. (CTL /Thompson). The Levee was found it to be safe from sliding and seepage during the 100 -year flood, and resistant to settling over time. CTL /Thompson's final report is titled, "Levee at Deepe Farm Pit, Boulder, Colorado," September 28, 1998. See Appendix B -9. • The rock rip rap that the gravel mining company originally placed on the upstream face of the Levee was evaluated by Ayres Associates, Inc. (Ayres) in 1998. The reach (from approximately station 135 +00 to approximately 149 +00) was found to provide adequate erosion protection. Additional rip rap was required for the reach of Levee between stations 105 +00 and 135 +00. Type L riprap was designed by Ayres and placed on the face of the Levee in that reach by L &M Enterprises of Berthoud, Colorado during the period November 1997 through February 1998 (see Appendix B -10). • An operation and maintenance plan was developed for the Levee and adopted by its owner, the University. It is included as here as Appendix B -11. Bi- annual inspections have been made by Love and Associates, Inc. on behalf of the University beginning in the spring of 2001(see Appendix H), and maintenance of the Levee has been undertaken as required. The current report is intended to support the re- certification of the Levee, based on the latest hydrologic, hydraulic, geotechnical, erosion protection, and field survey information. V. REVISED HYDROLOGY AND FLOOD -PLAIN DELINEATIONS Since FEMA's certification of the upstream reach of Levee in 2000 (see Appendix A), Boulder commissioned another study of the flood hydrology and another study of the flood plain. The hydrology study was submitted to FEMA for review in 2007, and the hydraulic analyses and two interpretations of the flood plain were submitted in 2007 and 2008. LRE reviewed the output of the 1 -D and 2 -D hydraulic models, and the delineation of the flood plain in the vicinity of the Levee. We found that the 2007 version of the flood plain that was submitted to FEMA extended the 100 -year flood plain further along the Levee than any previous flood -plain delineation. This thin ribbon of flood plain was extended about 400 feet farther to the west, following the alignment of the Dry Creek Ditch No. 2 (see Figures 7 and 8). In a meeting of interested parties, including representatives from Boulder, the University, Boulder's consultants, Flatiron Companies, and LRE, on January 10, 2008, and from the subsequent reported feedback from FEMA, it was learned that this new area was to remain part of the flood -plain delineation. In response, the downstream end of 1999's upstream reach of Levee was extended to include the new flood -plain area (see Figures 8 and 9). In addition, a 1,100 -foot reach of the Levee was raised by the University so that the required freeboard could be maintained (Figure 10). In Boulder's 2008 submittal to FEMA (see Figure 11), the thin ribbon of flood plain was eliminated, so a substantial portion of the Levee that was raised in 2008 may not have been necessary. With the 2008 submittal, Boulder also made a second change in the delineation of the flood plain that affects the Levee. Figures 12 and 13 show the two versions of the flood plain at the © Leonard Rice Engineers, Inc. June 2009 — 207FIP05