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General comments applicable to all reaches <br />F iprap bedding is a necessary component of a riprap-- protected levee slope to provide a <br />surface for riprap placement which prevents loss of channel lining material through the <br />ri prap rock. Since the existing levee embankment is a constructed feature and since its <br />surface appeared to have the basic characteristics of a proper bedding material, the <br />embankment material was sampled and gradation tested. It was found to have slightly <br />more fines and slightly more coarse material than ideal, but otherwise its gradation was <br />within the range of a suitable Type 11 filter material_ The prepared levee embankment <br />was therefore accepted as a suitable rlprap bedding. <br />• Fiprap is typically either sized large enough or buried to protect it from theft for <br />landscaping purposes, vandalism, displacement by rock throwing recreationalists, or <br />other unintended uses. Rock L size and smaller is therefore normally burred anal <br />vegetated. However, in this instance we believe the rock need not be buried because <br />the rock ire most places is actUally closer to an M Classification than 2n t_, and the rock <br />is located away from convenient public access and the creek where it will not be subject <br />to loss to unintended uses. <br />• The onsite rock loft over from raining activity available for use as rlprap is skip - graded <br />(missing adequate - to -inch rocl as is the rook which has already been used as <br />rlprap on site. It was therefore mixed with an appropriate quantity of imported roof in <br />the proper size range to create a properly graded rlprap. <br />The an-site rock aVailable for use as riprap meets the gUdtative physical rocs <br />properties of size, hardness, durability, etc. with the exception of a preference for <br />angular over rounded rock which was party offset by supplementing on -site rock with <br />imported angular rock In the size range where it was ship- graded. <br />Examination of the rate of rise and duration of the 10o -ye flood indicates that the levee <br />is exposed to water against its face for only several hours during this rare flood. 'his <br />provides insufficient time for embankment saturatlon and instability to occur or for <br />flowing water to remove enough levee material, even if the levee is unarmored, through <br />general erosion to cause loss of embankment integrity. While general erosion is not a <br />primary concern for loss of embankment stability, the greater threat to embankment <br />stability is local erosion due to unpredictable anomalies. Therefore, a fully riprap- <br />protected embankment was felt to be a prudent level of protection for this levee at this <br />location. <br />The analysis by reach follows: <br />Reach ch 1 -- W@ter velocity is less than 5 fUsec. in this reach, therefore, non-- erodable, non- <br />vegetated, non-erosive earth would provide adequate levee erosion protection. The slope <br />protection which exists in this reach is close to type M rlprap_ While the rlprap is skip - <br />graded and not toed in, it provides better protection than a bare earth or even a vegetated <br />earth slope which is the level of erosion protection needed. It is also probable that a <br />specifically constructed rlprap bedding layer was not constructed. The levee embankment <br />itself and other erosion related characteristics are otherwise suitable as the levee eXists and <br />no modifications to this portion of the levee were necessary. <br />Ayres AssoC12te <br />