M' = 309 [1.94] = 600 kN-m/m (134,900 ft-lb/ft) (T = 6 s) 

 A similar analysis for the maximum breaker with a 10-second period gives 



r^ = 0.79 



m 



a = 0.86 m (2.82 ft) 



R^ = 153 kN/m (10,484 lb/ft) 



kN-m ,^„ ^^^ Ib-ft 



K = 348 

 m m 



(78,237 ^^^^ ) (T = 10 s) 



The hydrostatic part of the force and moment can be computed from the 

 hydrostatic pressure distribution shown in Figure 7-99 by assuming the 

 hydrostatic pressure to be zero at H%,/2 above SWL and taking only that 

 portion of the area under the pressure distribution which is below the crest 

 of the wall . 



*************************************** 

 4. Broken Waves . 



Shore structures may be located so that even under severe storm and tide 

 conditions waves will break before striking the structure. No studies have 

 yet been made to relate forces of broken waves to various wave parameters, and 

 it is necessary to make simplifying assumptions about the waves to estimate 

 design forces. If more accurate force estimates are required, model tests are 

 necessary. 



It is assumed that, immediately after breaking, the water mass in a wave 

 moves forward with the velocity of propagation attained before breaking; that 

 is, upon breaking, the water particle motion changes from oscillatory to 

 translatory motion. This turbulent mass of water then moves up to and over 

 the Stillwater line dividing the area shoreward of the breakers into two 

 parts, seaward and landward of the Stillwater line. For a conservative 

 estimate of wave force, it is assumed that neither wave height nor wave 

 velocity decreases from the breaking point to the Stillwater line and that 

 after passing the Stillwater line the wave will run up roughly twice its 

 height at breaking, with both velocity and height decreasing to zero at this 

 point. Wave runup can be estimated more accurately from the procedure 

 outlined in Section 1, Wave Runup. 



Model tests have shown that, for waves breaking at a shore, approximately 

 78 percent of the breaking wave height H, is above the Stillwater level 

 (Wiegel, 1964). 



a. Wall Seaward of Stillwater Line . Walls located seaward of the 

 Stillwater line are subjected to wave pressures that are partly dynamic and 

 partly hydrostatic (see Figure 7-104). 



Using the approximate relationship C =Vgd, for the velocity of wave 

 propagation, C where g is the acceleration of gravity and d, is the 



7-192 



