7.32 NONBREAKING WAVE FORCES ON WALLS 



7.321 General. In an analysis of wave forces on structures, a distinc- 

 tion is made between the action of nonbreaking, breaking, and broken 

 waves. (See Section 7.12, SELECTION OF DESIGN WAVE.) Forces due to non- 

 breaking waves are primarily hydrostatic. Broken and breaking waves exert 

 an additional force due to the dynamic effects of turbulent water and the 

 compression of entrapped air pockets. Dynamic forces may be much greater 

 than hydrostatic forces. Therefore, structures located where waves break 

 are designed for greater forces than those exposed only to nonbreaking 

 waves . 



7.322 Nonbreaking Waves . Typically, shore structures are located in 

 depths where waves will break against them. However, in protected regions 

 or where the fetch is limited, and when depth at the structure is greater 

 than about 1„5 times the maximum expected wave height, nonbreaking waves 

 may occur. 



Sainflou (1928) proposed a method for determining the pressure due to 

 nonbreaking waves. Tlie advantage of his method has been ease of applica- 

 tion, since the resulting pressure distribution may be reasonably approxi- 

 mated by a straight line. Experimental observations by Rundgren (1958), 

 have indicated Saniflou's method overestimates the nonbreaking wave force 

 for steep waves. The higher order theory by Miche (1944) , as modified by 

 Rundgren (1958) , to consider the wave reflection coefficient of the struc- 

 ture, appears to best fit experimentally measured forces on vertical walls. 

 Design curves presented here have been developed from the Miche -Rundgren 

 equations. 



7.323 Miche -Rundgren: Nonbreaking Wave Forces . Wave conditions at a 

 structure and seaward of a structure (when no reflected waves are shown) 

 are depicted in Figure 7-63. The wave height that would exist at the 

 structure if the structure were not present is the incident wave height, 

 H^. The wave height that actually exists at the structure is the sum of 

 H-^, and the height of the wave reflected by the structure, H^. The wave 

 reflection coefficient, x> is defined as the ratio of H^ to H^ 



(x = Hp/H^). Wave height at the wall, H^j, is given as 



^w ^ ^i + "r = (1+X) H,. (7-65) 



If reflection is complete, and the reflected wave has the same amplitude 

 as the incident wave, then x = !» ^nd the height of the clapotis or 

 standing wave at the structure will be 211^. See Figure 7-63 for defini- 

 tion of terms associated with a clapotis at a vertical wall. The height 

 of the clapotis crest above the bottom is given by 



Yc = d + h^ + -^ H,. (7-66) 



The height of the clapotis trough above the bottom is given by, 



Jt- ^ + K-~r^ H. (7-67) 



7-127 



