so that d . varies directly with wave height and period. This water depth is 

 a seaward limit to usual wave agitation on a sandy profile. 



Both of these calculated water depths are to be taken with respect to 

 MLW. The median sediment diameter in equation (4-27) is that characterizing 

 the calculated buffer zone; e.g., that at a water depth of (1.5 d.). The 

 depth d . appears appropriate for applications requiring an estimated seaward 

 limit to moderate wave effects in onshore-offshore transport; e.g., desig- 

 nation of an offshore site as inactive and thus suitable for sediment 

 borrowing. The depth d. appears appropriate for applications such as 

 coastal structure design, m which an estimated seaward limit to relatively 

 intense onshore-offshore transport may be required. Hallermeier ( 1981a, b) 

 presented more detailed information on the calculation procedure and its 

 suggested applications, together with extensive example results. 



**************** EXAMPLE PROBLEM 3************** 



GIVEN ; The high-energy and low-energy coastal sites in Figure 4-30, with wave 

 conditions as follows: 



(a) Point Mugu, California (Thompson, 1977, p. 312) 



H = 1 meter (3.35 feet) 

 s 



a„ = 0.34 meter (1.12 feet) 

 H, 



T = 11.01 seconds 

 s 



(b) Sapelo Island, Georgia 



H = 0.25 meter (Howard and Reineck, 1981) 



T = 7 seconds (typical value for southern U. S. Atlantic 

 coast, Thompson, 1977) 



Presume quartz sand in seawater, with d^Q = 0.1 millimeter for each site. 



FIND: The values of d„ and d. for each site. 



* ^ 



SOLUTION ; The stated average significant wave height H can be used to give 



the needed annual wave height statistics, according to the modified 

 exponential distribution for nearshore wave heights presented in Section 

 III,3,b. Equation (4-12) yields 



»s50 = \ - °-3°7 ^H 

 and equations (4-13) and (4-14) provide 



a„ " 0.62 H 

 H s 



(a) Calculate 



^s50 " '"s " °*-^°^ °H " ^'^ " (0*307) (0.34) = 0.92 meter (3.01 feet) 



4-74 



