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Report in Support of the Recertification of the <br />University of Colorado 's Flood Control Levee <br />Page 17 <br />"We opine our above referenced report conforms to the Embankment and Foundation <br />Stability and Settlement requirements cited in the copy of Article 65.10 e- mailed. "' <br />XI. EROSION PROTECTION <br />XI.1. Evaluated and Extended in 2008 <br />Ayres Associates, Inc. of Boulder, Colorado (Ayres) undertook an evaluation of the erosion <br />protection that existed on the Levee in 1997. Over the years, large rock had been installed by the <br />gravel mining company on the southern end (most upstream part of the upstream reach) of the <br />Levee from about station 135 +00 to 148 +50. Based on the Base Flood at the time, Ayres <br />indicated (see Appendix B -10) that the riprap: <br />• was poorly graded (missing the smaller rock sizes), <br />• was not toed into the ground, and <br />• did not rest on a filter layer. <br />In other locations along the upstream reach, the erosion protection which existed in September <br />1997 consisted of: <br />• a mixture of rock and grass; <br />• a reasonable stand of grass; <br />• a poor stand of grass; and <br />• no grass cover at all. <br />Ayres also determined that: <br />• The material forming the embankment itself was close enough to Type II filter material <br />that a separate filter was not required; <br />• The existing riprap installed at the south end of the Levee was sufficient for the low <br />velocities to be expected in that reach; and <br />• The areas of grass and rock, grass alone, and areas without any protection should be <br />replaced with properly designed and installed riprap. <br />Ayres designed appropriate rip rap for the areas that needed additional protection, concluding <br />that the large- and - rounded surplus rock which was available at the site could be mixed together <br />in a ratio of three to one with imported specified well - graded and angular rock of smaller size <br />(approximately equivalent to VL riprap). The mixed product satisfied the specifications of Type <br />L riprap. Because there was not enough of the large- and - rounded surplus rock on site to provide <br />for all of the riprap that was required, additional angular Type L riprap was imported for the <br />balance. The Ayres' analyses, documentation, riprap design, and description of rehabilitation are <br />contained in its report, "Levee Embankment Erosion Protection, Deepe Pit, South Boulder <br />Creek, Boulder Colorado," February 1998 (see Appendix B -10). <br />CTL /Thompson, Inc., letter "Geotechnical Engineering Consultation," June 2, 2008, page 1 (Appendix B -9) <br />© Leonard Rice Engineers, Inc. June 2009 — 207FIP05 <br />