2002-03-07_REVISION - M1976020 (2)

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SS =angle of the bank @ O.SH:I.OV. S = bedslope angle based on river slope in this area of 0.733% grade. This is the same as Z for this case. O =angle of repose of rock, due to large size, hand placed, this angle can reach 70 degrees or higher. D =flow depth, assuming upper boulders of 5.0 feet height and water level is 11.5 feet above the base of the boulder. Results show that boulders are stable for both cases, however, shear in the bend has not been taken into account. Since the jetty will be placed at an angle of 42 degrees, sheaz forces can be double than that for the side of a channel where the flow is pazallel to the rock. However, if the safety factors are reduced by half, they are still over 2.0 for the Test 1 case and 1.02 for the Test 2 case, therefore the boulders should be stable. See Map C-6 for complete details of the jetty design. The rock boulders will be buried at least 3.0 feet into the surrounding ground for the part that extends in the river bed itself and at least 2.0 feet in the ground for the part above the bed that forms the slope of the existing river embankment. This will help the foun- dation stability of the boulders and prevent scouring. To further increase the safety factor, the specified diameter of the rock will be 4.75 feet in size instead of 4.5 feet. The rock is also specified that no boulder can be less than this size, therefore, it is not an average size; it is a minimum size. Since water can flow over the jetty toward the west riverbank, pit run material will be backfilled in the wedge between the jetty and the bank to a depth of approximately 4 feet and [he grade will be mild 8-lOH:1V toward the river. Looking at the jetty with regard to the 100 year flows of approximately 25000 cfs and a water elevation of 666.5 feet, the jetty has been placed at a height to divert almost all of the flows at an approximate angle of 42 degrees from the flow direction immediately upstream. During the large storm event, as seen from Exhibit C-2 and C-6, the water will move to the southeast and will likely cut out a portion of the dike at its southern location. This will not cause a problem since the dike berm is not near anything in the river that could be adversely affected. There are plans to remove this dike berm anyway and restore the channel to its former condi- tion as a wide shallow channel with a grade resembling that of the original. The cutting would only occur if the dike berm still exists before it is removed in the channel restoration Received Thomas Pit 2/02 16 MAR072~2 view once