2011-12-16_REVISION - M1977572 (71)

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Proposed Spillway Riprap Design Method: USACEs CHANLPRO Version 2.0 Riprap Design Program The proposed condition HEC -RAS modeling was utilized to obtain a worst case hydraulic condition through the spillway for riprap design. Three HEC -RAS models of the proposed condition spillway were prepared including 1) a model to analyze floodplain conditions which includes a single flow path through the study reach, 2) a model to determine the split flow occurring through the proposed spillway and 3) a model to determine the split flow occurring through the proposed spillway without tailwater conditions. Velocity and depth data through the spillway is attached. 100 -Year Event - Single flow path model The floodplain model, which treats the study reach as a single flow path, shows the worst case hydraulic conditions occurring during the 100 -year event with a spillway velocity of 12.26 ft /sec and a depth of 6.6 ft through the spillway. The resulting riprap specified can have max d50 between 12 and 14 inches. CHANLPRO output is provided below. PROGRAM OUTPUT FOR A CHANNEL WITH A KNOWN LOCAL DEPTH AVERAGED VELOCITY, STRAIGHT REACH INPUT PARAMETERS SPECIFIC WEIGHT OF STONE,PCF 165.0 LOCAL FLOW DEPTH,FT 6.6 CHANNEL SIDE SLOPE,1 VER: 3.00 HORZ LOCAL DEPTH AVG VELOCITY,FPS 12.26 SIDE SLOPE CORRECTION FACTOR K1 .99 CORRECTION FOR VELOCITY PROFILE IN BEND 1.00 RIPRAP DESIGN SAFETY FACTOR 1.10 SELECTED STABLE GRADATIONS ETL GRADATION NAME COMPUTED D30(MIN) D100(MAX) D85/D15 N= THICKNESS/ CT THICKNESS D30 FT FT IN D100(MAX) IN 3 .61 15.00 1.70 NOT STABLE 4 .73 .73 18.00 1.70 1.23 .94 22.2 5 .77 .85 21.00 1.70 1.00 1.00 21.0 D100(MAX) LIMITS OF STONE WEIGHT,LB D30(MIN) D90(MIN) IN FOR PERCENT LIGHTER BY WEIGHT FT FT 100 50 15 18.00 292 117 86 58 43 18 .73 1.06 21.00 463 185 137 93 69 29 .85 1.23 EQUIVALENT SPHERICAL DIAMETERS IN INCHES D100(MAX) D100(MIN) D50(MAX) D50(MIN) D15(MAX) D15(MIN) 18.0 13.3 12.0 10.5 9.5 7.1 21.0 15.5 14.0 12.3 11.1 8.3