H^/gT 2 = 0.0032. Follow the curve for tLJ/gT 2 to the point where (d/gT 2 ) 2 = 

 0.0018 and read off the ordinate (Hs/d) 2 = 0.81. The significant wave height 

 at location 2 is /« \ 



H s = i-^-j x d 2 = 0.81 x 1.0 = 0.81 



Note that the ratio of wave height to Stillwater depth is large because wave 

 setup increases the effective water depth in this case for a steep wave and a 

 steep beach. 



IV. SENSITIVITY ANALYSIS 



In any given design situation the quality of the input information may vary. 

 An important question t^ ask when predicting nearshore wave conditions is: How 

 sensitive are the predicted conditions to errors of uncertainty in the input 

 parameters? The sensitivity of the predicted nearshore significant wave height 

 to input parameters is illustrated below with an example. A reference condition 

 is chosen and nearshore significant wave heights are estimated. Each of the 

 input parameters is then systematically varied and the results compared to the 

 reference condition. 



The reference condition was selected to have the following input parameters: 



ILj = deepwater significant wave height (5 meters) 



T s = wave period (10 seconds) 



d = nearshore water depths (0.5 to 30 meters) 



m = beach slope (1/100) 



For the reference condition the predicted nearshore significant wave height is 

 slightly less than the deepwater wave height for water depth of 10 to 30 meters 

 due to wave setdown (Table 3) . The predicted height then decreases in shallow 

 water to a value of 0.96 meter in a 1-meter water depth (stillwater level). 

 Systematic variations are made from the reference condition and from the re- 

 sulting predicted nearshore wave heights given in Table 3. Comparisons with 

 the reference condition are shown in Figure 3. 



Table 3. Sensitivity analysis for nearshore wave height prediction 

 for a selected deepwater condition. 



Stillwater depth (m) 



0.5 



1.0 



3.0 



5.0 



10.0 



20.0 





30.0 



Reference d/H^, 



0.1 



0.2 



0.6 



1.0 



2.0 



4.0 





6.0 



Condition 



Pred: 



cted nearshore 



sign: 



ficant 



wave hei 



ght 



Cm) 



Reference 



0.7 



0.96 



2.1 



3.2 



4.9 



4.6 





4.6 



Variation 



















Water 1 m deeper 



1.3 



1.6 



2.7 



3.8 



5.0 



4.7 





4.7 



1/20 slope 



0.9 



1.3 



2.6 



3.9 



5.2 



4.8 





4.8 



Hq = 6 m 



0.7 



0.9 



2.2 



3.3 



5.4 



5.6 





5.8 



H^ = 4 m 



0.6 



0.9 



2.1 



3.1 



4.0 



3.8 





3.7 



a = 45°, S* = 4 



0.7 



0.9 



2.0 



3.1 



4.1 



3.9 





4.0 



T s = 6 s 



0.5 



0.8 



1.9 



2.8 



4.1 



4.8 





5.0 



T s = 18 s 



0.8 



1.1 



2.3 



3.5 



6.0 



5.2 





5.1 



Parameters: H^ = 5.0 meters; T s = 10.0 seconds; beach slope = 1/100; 

 no refraction 



18 



