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Rip Rap Size Calculation Worst Case - 625 cfs Station 6+50 <br />Calculate D30min for riprap. Based on Army COE 1991 Method. <br />"Hydraulic Design of Flood Control Channels" <br />12.01 fps=Va=average flow velocity <br />1000 ft=R=centerline radius of bend <br />25.32 ft=W=water surface width at upstream end of bend <br />39.49=R/W=to use in COE graph to read Vss/Va <br />1.00=VssNa= calculated; from COE Plate B-33 <br />12.01 fps=Vss=(Vss/Va)*Va <br />2.58 ft=depth of flow to toe of slope <br />2.064 ft=Y=local depth; use depth at 20% up slope from toe for side slopes <br />1.1 =SF=safety factor; minimum 1.1 <br />0.33 =Cs=stability coefficient for incipient failure; 0.3 for angular rock;0.375 for rounded rock <br />1.00 =Cv=velocity distribution coefficient; formula for outside of bends is entered here <br />1.25 d/s of concrete channels, and at end of dikes <br />1.283-0.2*log(RNV) for outside of bends <br />1.0 for straight channels and inside of bends; straight channel if (RNV)>26 <br />0.9 =Ct=blanket thickness coefficient <br />62.4 Ib/ft3=Gw=unit weight of water <br />2.65 =Gs=specific gravity of solids in stone (usually 2.65) <br />Gs = specific gravity of rock solids; solids only, no voids included <br />0.15 =n=porosity of an individual stone n = Vol. voids/Vol. of stone <br />141 Ib/ft3=GS=saturated surface dry unit weight of stone (riprap) <br />GS = (Gs*62.4)*(1-porosity of an individual stone) <br />NOTE: this does not add any wt. back in for water in the voids in the <br />individual stone, this is conservative. <br />O=SS=side slope; enter H of H:V (e.g., enter 2 for 2:1 side slopes) <br />26.6 degrees=theta=angle of side slope with horizontal <br />40 degrees=phi=riprap angle of repose <br />32.2 ft/s^2=g=acceleration due to gravity <br />Estrtaight <br />=K1 (Maynord)=from lookup table D90 "n" low "n" high <br />f bend (Cv=1.283-0.2*log(RNV): <br />ft=D30min=SF*Cs*Cv*Ct*Y*[([Gw/(GS-Gw)]"0.5)*(Vss/[K1*g*Y]^0.5)]^2.5 <br />inches 0.041 0.046 <br />channels and inside of bend (Vss/Va=1.0; Cv=1.0): <br />ft=D30min=SF*Cs*Cv*Ct*Y*[([Gw/(GS-Gw)]"0.5)*(Vss/[K1*g*Y]"0.5)]^2.5 <br />inches 0.041 0.046 <br />