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A total of 18 inches of Type L riprap (nominal diameter nine inches) was installed during the <br />period October 1997 through January 1998 on the outside face of the Levee from station 108 +00 <br />to 135 +00. The design height of this riprap was to be two feet higher than the higher of the <br />G &O and Taggart flood profiles. <br />A fiber -mesh reinforced concrete cutoff wall was constructed at the toe of the South- Boulder- <br />Creek side of the Levee from station 106 +00 to 135 +30. It extends to a depth of three feet below <br />the elevation of the bottom of Dry Creek Ditch No. 2, which parallels the Levee. No specifically <br />constructed filter layer was required, because of the nature of the material that the Levee is <br />constructed of. The typical section of the Levee and its erosion protection are shown on Ayres' <br />as- constructed drawings. Certifications for the design and installation of the riprap and cutoff <br />wall are included with Appendix 10 of the August 1999 submittal (included here as Appendix B- <br />10). <br />XI.2. Re- Evaluated and Replaced in 2009 <br />LRE asked AMEC Earth and Environmental (AMEC) of Boulder and Lakewood Colorado to <br />evaluate the effectiveness of the erosion protection of the Levee as it existed in 2008 in light of <br />Boulder's updated hydrologic and hydraulic studies. Mr. Doug Laiho undertook the original <br />evaluation of the erosion protection work while he was at Ayres. Since he was working for <br />AMEC at the time of our request, it made sense for him to do the follow -up review. AMEC's <br />reviewed the 1998 evaluation by Ayres (Appendix B -10) and made a field evaluation of the rip <br />rap on the Levee. AMEC's report is included as Appendix G. <br />AMEC divided the erosion protection into three reaches: <br />• Reach 1- station 135 +00 to 148 +65 (the most upstream reach); <br />• Reach 2- station 128 +60 to 135 +00; and <br />• Reach 3- station 105 +00 to 128 +80 (the most downstream reach). <br />Report in Support of the Recertification of the <br />University of Colorado's Flood Control Levee <br />Page 18 <br />AMEC concluded that "... the riprap present in July, 2008 at Reach 1 and Reach 3 was found to <br />provide adequate protection against the water velocities of the 100 year flood. The erosion <br />protection at Reach 2 needed to be redesigned and reconstructed " <br />AMEC designed new rip rap for Reach 2. Using permissible velocity criteria design (UDFCD <br />2001), AMEC determined that rip rap with an average diameter (D of 12.8 inches would be <br />required to provide adequate protection against the water velocities of the 100 -year flood. The <br />plan for replacing the erosion protection is shown on Figure 30 and spelled out in detail in <br />Appendix G. It called for removal of the existing rip rap in Reach 2 from the "lower portion" of <br />the slope and placing it on the "upper portion" of the slope. The lower portion of the face of the <br />Levee extends from a point one foot above the 100 -year flood level down to the existing concrete <br />cutoff wall at the toe of the slope (visible in Figure 31). The upper portion is above the lower <br />portion, and extends from there to the top of the Levee. The old rip rap that was relocated to the <br />$ AMEC, "Embankment Erosion Protection, South Campus Levee," May 14, 2009, page 4 (Appendix G). <br />9 Ibid, pages 4 & 8. <br />© Leonard Rice Engineers, Inc. June 2009 — 207FIP05 <br />