wave parameters, and it is necessary to make simplifying assiomptions 

 about the waves to estimate design forces. If more accurate force esti- 

 mates 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 7.21, WAVE RUNUP. 



Model tests have shown that for waves breaking at a shore approxi- 

 mately 78 percent of the breaking wave height Hj^ is above the still- 

 water level. (Wiegel, 1964.) 



7.341 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 7-79.) 



Figure 7-79. Wave Pressures from Broken Waves: Wall Seaward of 

 Stillwater Line 



Using the approximate relationship C = /gd^ for the velocity of wave 

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



7-158 



