where 



V = average local velocity in the vertical 



d = depth at site (V is average over this depth) 



If the channel is curved, the computed local boundary shear should be 

 multiplied by a factor appropriate for that cross section (available in 

 EM 1110-2-1601, Office, Chief of Engineers, 1970). If the conditions 

 described above leading to a uniform channel flow at normal depth and velocity 

 do not exist, as they will not for most tidal channels, the local boundary 

 shear computed from the equation above should be increased by a factor of 1.5. 



If the local boundary shear can be calculated by using the average 

 velocity over depth, it should also be calculated using an estimated velocity 

 at the revetment surface, as described in the two methods above. The 

 calculated local boundary shears can be compared and the most conservative 

 used. 



Calculate the riprap design shear or armor stone design shear using 



T = 0.040 (w - W ) d (7-131) 



r w g 



where t = design shear for the channel bottom if essentially level, and 



,' = Jl -liH-i) (7-132) 



y sin (j)/ 



where 



t' = design shear for channel side slopes 



Q = angle of side slope with horizontal 



(fi = angle of repose of the riprap (normally about 40°) 



For all graded stone armor (riprap), the gradation should have the 



following relatins to the computed value for W^_ . : 



50 rmn 



W,__ = 5 W,. . (7-133) 



100 max 50 rmn 



W,_. . = 2 W.- . (7-134) 



100 rmn 50 rmn 



W.„ = 1.5 W,„ . (7-135) 



50 max 50 rmn 



W,. = 0.5 W.„ (7-136) 



15 max 50 max 



7-251 



