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Reach 2 - VVater velocity is approximately 7.5 ft/ sec in this reach. A non - erosive earth levee <br />face would not withstand this velocity without surface erosion protection. Vegetation would <br />be marginally acceptable as erosion protection, especlally at a location such as this where <br />vegetation would not, in the near term, be irrigated or routinely maintained as landscaping. <br />Use of a riprap erosion protection facing would be appropriate. The slope protection which <br />exists in this reach was close to a type M riprap, however, the riprap characteristics fell <br />short in the following criteria: <br />* Rock was slip- graded missing generally a portion of the 2- to 6-inch rock fragment size <br />0 liprap was not toed in <br />a Rock surface was irregular and did not corer necessary slope face area <br />Due to this combination of deficiencies and the established nature of this slope, it was not <br />economically reasonable to rehabilitate this slope to a suitable condition. Therefore, we <br />recommended that the current armoring be removed for reuse, if possible; the slope be <br />regraded to a suitable subbase condition; adequate riprap toe protection be provided, and <br />adequate riprap be placed. This was accomplished in association with final levee <br />shaping /raising activity performed along this reach. <br />Reach 3 - Water velocity is approximately 9.5 fUsec in this reach. A non - erosive earth levee <br />would not withstand this velocity without surface erosion protection. Vegetation would not <br />be acceptable as erosion protection. Use of a riprap erosion protection facing would be <br />appropriate. There was no such erosion protection in this reach at the time. In addition, <br />significant regrading of the outside slope was needed to achieve a properly prepared <br />subbase for riprap placement. Therefore, we recommended that the unsuitable overburden <br />be removed, adequate ri rap toe protection be provided, the entire levee slope be regraded <br />to a suitable subbase condition, and adequate riprap placed. This was accomplished in <br />association with final levee shaping /raising activity performed along this reach. <br />DESIGN <br />The recommendations of the analysis phase ,ere accepted by Flatiron and design are <br />preparation of contract documents for the levee rehabilitation proceeded. The following <br />relevant design criteria were set: <br />• The average velocity rear the levee versus the lower velocity immediately adjacent to <br />the levee was used as a conservative assumption on velocity for sizing the erosion <br />protection <br />A consistent type of erosion protection was used for material economy, appearance, <br />2nd to provide a consistently greater level of protection than strictly needed <br />• Top of levee was set at a minimum of four feet of freeboard by others) and top of <br />erosion protect set a s two feet of freeboard (these are conservative assumptions, <br />one foot higher than typical criteria) <br />a Balance cuUfill to extent possible at each cross section <br />• Use a structural, vertical concrete wall too protection <br />Ayres Associates <br />