H. = R. H (3-52) 



(e) Determine the equivalent fetch length Y„ for the wave height 



^e 



(f) Determine an adjusted fetch length F for the segment length, 

 Ax as discussed in Chapter 3, Section VI, 2, a using equations (3-47) and 



(3-48). 



(g) Determine the total fetch F from equation (3-49) . 



(h) Determine an equivalent wave height H for the total fetch and 

 the given windspeed and water depth. 



(i) Calculate the fractional growth by 



h = /- (3-53) 



sm 



(j) Calculate the decayed wave height at the end of the fetch by 



H„ = H - G. (H - H ) (3-54) 



As a conservative estimate, it is assumed that the wave period remains 

 constant as the wave decays. 



*************** EXAMPLE PROBLEM 6*************** 



GIVEN : A flooded coastal area is covered with thick stands of tall grass. 

 The water depth d^ at the seaward edge of the area is 7 meters (23 

 feet), and at the landward edge of the area the depth is 4 meters (13 

 feet) . The distance across the area in the direction of wave travel is 

 3050 meters (10,000 feet). The wave height H^ at the seaward edge of 

 the area is limited to 0.9 meters (3 feet) by the flooded beach dune 

 system seaward of the area being considered, and the wave period is 2.6 

 seconds. The adjusted windspeed factor is 31.3 meters per second (70 

 miles per hour or 103 feet per second). 



FIND: The height and period of the significant wave at the landward 

 edge of the area. 



SOLUTION : From the long dashline in Figure 3-21, for an adjusted wind- 

 speed factor of 31.3 meters per second and a water depth of 7 meters, 



M = iJ_2L7= 0.0700 

 U^ (31.3) 



giving (at the intersection of the above line with the long dashline) 



^= 0.02 



"a 



so that the maximum significant wave height is 



3-71 



