adjusting the fetch length. Wave prediction curves for waves passing through 

 shallow water with bottom friction ff = 0.01 are shown in Figures 3-21 and 

 3-22. For any given adjusted windspeed factor Ua and water depth d there 

 is a maximum (depth-limited) significant wave height Hsm which is generated 

 (long dashline in Fig. 3-21). 



When the initial wave height H-£ at the seaward or beginning edge of the 

 fetch is less than Hgm , the wave increases in height. Where the bottom 

 friction, ff is greater than 0.01, the wave will not become as high as a 

 wave traveling over a bottom where f^ = 0.01 , if the segment of fetch 

 distance Ax is the same in both cases. Therefore an adjusted fetch F^<ZUc 

 is used to describe the wave, using Figures 3-21 and 3-22 which were developed 

 for the case of ff = 0.01 . For specific water depths. Figures 3-27 to 3-36 

 show the same results as Figures 3-21 and 3-22. 



Where Hi > Hsm , the wave will decay. As a value of f/ > 0.01 will 

 cause a wave to decay a greater amount than if it were traveling over a bottom 

 where ff = 0.01 , an adjusted fetch F^^ > tax. should be used in this case. 



a. Fetch Adjustment . The fetch should be divided into segments to meet 

 three conditions. First, 



M < 0.25 di (3-42) 



where Ad is the change in depth over the distance across the segment in the 

 direction of wave motion and d{. is the depth at the seaward or beginning 

 edge of the segment; second 



Af_^ < 0.25 ffi (3-43) 



where Af^ is the change in the bottom friction factor over the segment 



distance, and ffi the bottom friction factor at the beginning edge of the 



segment; and third, after computation of the wave height at the end of the 

 fetch, 



AH < 0.5 H^ (3-44) 



where AH is the change in the wave height over the segment distance and 

 R-i the wave height at the beginning edge of the segment. Each segment of the 

 fetch can then be considered separately using the method indicated. 



The bottom friction ff can be obtained from Figure 3-37 for a known 

 type of vegetation. The decay factor Kf may be obtained from Figure 3-38. 

 Where H-^ < Hg;^ > the wave will increase in height, and the adjusted fetch 

 distance F^j for a segment distance Ax is then determined using an 

 adjustment factor a which is defined as 



^ - ^/ 01 

 a = -. —^ (3-45) 



1 - ^fa 



where Kf q^ is the decay factor for a bottom friction factor fj-" = 0.01 



3-67 



