As a first approximation, the wfave decay may be assumed to occur 

 exponentially at a rate similar to the rate of wave growth; i.e., the 

 wave height will decay from a maximum stable wave height given by the 

 shallow-water condition 



H„ 



0.78 d 



(15) 



to a height equal to the maximum significant height in a distance approx- 

 imately equal to the shallow-water fetch length required for a wave to 

 grow from a zero height to the maximum generated significant wave height 

 (the fetch length defined by the long dashlines in Fig. 1). 



1. Wave Height . 



The means of determining the decayed wave height is shown schematic- 

 ally in Figure 19. Steps to predict the decay of a wave are: 



Figure 19. Schematic of wave decay calculations, 



(a) Determine the maximum significant wave height that would be 

 generated for the given windspeed and water depth, assuming an unlimited 

 fetch, and using Figures 1 to 12 or equation (3). 



(b) Determine the fractional reduction, R^, represented by the initial 

 wave at the seaward edge of the segment of fetch under consideration 

 given by 



37 



