Analysis o£ experimental data shows that the relationship between 

 depth at breaking d^, and breaker height Hj is more complex than 

 indicated by the equation db = 1.3 H^. Consequently, the expression 

 d^ = 1.3 H^j should not be used for design purposes. The dimensionless 

 ratio d^/H^j varies with nearshore slope m and incident wave steepness 

 Hj^/gT^ as indicated in Figure 7-2. Since experimental measurements of 

 d^/H^p exhibit scatter, even when made in laboratory flumes, two sets of 

 curves are presented in Figure 7-2. The curve of a vs. H^^/gT^ repre- 

 sents an upper limit of experimentally observed values of d^/H^, hence 

 a = (d^/H^)max* Similarly, B is an approximate lower limit of measure- 

 ments of d^/H^; therefore, g = (db/iil))min' Figure 7-2 can be used with 

 Figure 7-3 to determine the water depth in which an incident wave of known 

 period and unrefracted deepwater height will break. 



************** EXAMPLE PROBLEM *************** 



GIVEN: A wave with period T = 10 seconds, and an unrefracted deepwater 

 height of H^ = 5 feet advancing shoreward over a nearshore slope of 

 m = 0.050 (1:20). 



FIND: The range of depths where breaking may start. 



SOLUTION : The breaker height can be found in Figure 7-3. Calculate, 



= 0.00155 



gT^ 32.2 (10)2 



and enter the figure to the curve for an m = 0.05 or 1:20 slope. 

 Hb/tio is read from the figure 



Therefore, 



Hy = 1.65 Hj = 1.65(5.0) = 8.3 ft . 

 Hj,/gT^ may now be computed. 



8.3 



H, 



gT^ (32.2) (10)2 



0.0026 



Entering Figure 7-2 with the computed value of H^/gT^ the value 

 of a is found to be 1.51 and the value of 6 for a beach slope of 

 0.050 is 0.93. Then. 



and 



i^)ma. =«Hf, - 1.51(8.3) = 12.5 ft , 

 Nmin = ^^b = 0.93(8.3) = 7.7 ft . 



NOTE: When results of computations are used in subsequent problems or steps of the same problem, the 

 number of significant digits carried is the number of digits that can be read on a slide rule. Final 

 answers should be rounded to reflect the accuracy of the original given data and assumptions. 



7-5 



