then ^ = ^ 1 ^^ 



= 536 + 200 



= 536 + 200 = 736 pounds per square foot, 

 536 - 200 = 336 pounds per square foot. 



The assumed design is also safe for wave forces « 



U83o Rubble-Stone Groins, - Assume a rubble-stone groin to end in 

 k feet of water with a 5-foot tide. From the wave studies, the wave 

 with the greatest energy is a lO-second wave with a wave height of 10 

 feet in deep T^rater, The wave orthogonals approach the structure at an 

 angle of 0^ = 11 , 



U8ho Maximum Design Wave Hei^t , - The highest wave that can strike 

 the seaward end of the groin is 



H - U (depth of -water) + 5 (tide) _ „ fept 



Any larger waves will break before reaching the structure and only a 

 reformed wave or wave uprush xd.ll be propagated forward,. Inspection of 

 the orthogonal .pattern indicates a uniform bottom with little divergence 

 so that 7-foot waves can occur where the deep water design wave is 10 

 feet, 



US^o Along the sides of the groin, however, the wave energy between 

 two adjacent orthogonals is spread out along a considerable length of groin 

 such that x-irith orthogonals 1 foot apart, the length along the groin 

 would be 



= 5o2l; 



Accordingly, the wave energy impinging on the side of the groin is only 

 1/5 of the wave energy impinging on the end. Also, H is proportional t o 

 the sfe" or the eqiiivalent height of wave striking the side of the structure 

 would be 



= 7 X „U5 = 3o2 feet. 



The s tability of the s tructure is dependent on the stability of each 

 individual stone o Because of the irregularities of the surface, the 

 equivalent wave is able to impinge on any single stone with the same force 

 as if the wave were normal t o the structure. Accordingly, no further 

 reduction is made „ 



229 



