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Memorandum <br />January 3, 1992 <br />Page two <br />Discussion <br />After examining and taking measurements at the site with Jim Norfleet of DWR on <br />November 14, 1991, I performed an evaluation of current and possible revised <br />conditions. Pertinent conclusions are as follows: <br />(1) The timber crib side walls are rotting, broken, and in poor condition, <br />and provide very limited protection for the channel sides under higher <br />discharge conditions. <br />(2) Existing channel capacity with the boulders in place across the inlet is <br />only sufficient to pass a snowmelt runoff discharge with a recurrence <br />interval of about 2 -5 years without causing serious problems with the <br />timber crib sidewalk. <br />(3) Original channel capacity at the time of the timber crib overflow <br />structure completion was sufficient to pass a sustained runoff with a <br />recurrence interval of about 60-70 years. <br />(4) By removing the timber crib side walls, and laying back the slopes at <br />the channel entrance to a 3:1 slope,channel capacity, without removing <br />the boulders, would be sufficient to pass approximately a 40 -year <br />discharge. <br />(5) Channel capacity downstream, including the bridge section, is sufficient <br />to pass any of the above flows. <br />(6) The existing channel is currently cut into mostly angular sand, gravel, <br />and cobble -sized materials which are undersized to resist erosion from <br />channel- capacity discharges. <br />(7) Riprap of approximate D50 size of 18 inches could be placed directly <br />in the channel to stabilize the outflow section from erosion. The <br />existing channel bed would perform well as riprap bedding. <br />Recommendations <br />To stabilize the channel inlet section, the existing timber crib sidewalls should be <br />removed by excavating back at about a 3:1 side slope from the toe of each sidewall. <br />The excavated slopes should be rounded into the lake shore and armored with riprap <br />