7.383 Armor Stone . The equation used to determine the armor stone 

 weight is a form of Equation 7-105, 



w H^ 



W = -^- rr , (7-110) 



N|(S,-1)3 



where, 



W = mean weight of individual armor unit, lbs. 



Wj, = unit weight of rock (saturated surface dry), Ibs./ft^ 



H = design wave height (the incident wave height causing 

 no damage to the structure) . 



S^ = specific gravity of rubble or armor stone relative to 



the water on which the structure is situated (Sj, = w^/w^^) . 



Wy = unit weight of water, fresh water = 62.4 Ibs./ft^ 

 sea water = 64.0 lbs. /ft r 



Ng = design stability number for rubble foundations and toe 

 protection. (See Figure 7-99.) 



7.4 VELOCITY F0RCES--STABIL1TY OF CHANNEL REVETMENTS 



In the design of channel revetments, the armor stone along the 

 channel slope should be able to withstand anticipated current velocities 

 without being displaced. (Cox, 1958, and Cambell, 1966.) The maximum 

 velocity of tidal currents in midchannel through a navigation opening as 

 given by Sverdrup, Johnson, and Fleming (1942), can be approximated by 

 the following formula: 



4 TT A h 



V = ———r- . (7-111) 



3 T S ^ 



where V is the maximum velocity of tidal current at the center of the 

 opening, T is the period of tide, A is the surface area of harbor 

 basin, S is the cross-section area of openings, and h is the range 

 of tide in the basin. The current in midchannel is about one-third 

 swifter than at each side of the channel. 



If the stable stone weight 



W = -^ d| w^, (7-112) 



where d is the diameter of a stone sphere of equivalent weight, and 



V = y (2„r (cos0-sin0)'/^ d'^ , (7-113) 



\ SI y w^ j & 



7-203 



