Sensitivity tests 



501. To determine the influence of input wave and water level condi- 

 tions and to put the results in perspective, variant simulations using the 

 verification case 821207-821215 were performed. Since calibration was not 

 carried out for this case, changes in wave parameters and water level better 

 reflect model sensitivity to these input data. Parameter values given from 

 calibration were used in these simulations. First, the extent to which 

 changing water level improves or degrades model results was investigated. 



502. In one simulation, water level variation was neglected completely, 

 and neither the storm surge nor the tidal variation were represented. Figure 

 80 compares the measured 821215 profile and the simulated profile obtained by 

 omitting water level changes. A constant water level implied that only wave 

 height and period would determine the location of the surf zone and the amount 

 of energy dissipation. Comparison with Figure 79b shows that the bar closest 

 to shore developed a double-peaked shape. The most seaward bar was smaller 

 and not as smooth as the corresponding bar formed under a varying water level . 

 The sum of squares of the difference between measured and calculated profiles 

 was smaller for the case including the water level variation, thus giving a 

 better objective measure of agreement with the actual profile change. 

 However, the constant water level simulation showed less shoreline retreat, 

 which is artificial since the waves did not attack the beach as high as in the 

 variable water level case as would take place in the field. 



503. In another simulation, both wave height and period were kept 

 constant at their average values for the verification period, and the water 

 level was fixed at its mean position. The calculated result is shown in 

 Figure 81, together with the measured initial and final profiles. The 

 shoreward bar grew very steep and pronounced due to the constant wave and 

 water level conditions. Also, the seaward bar did not move, since, without 

 higher waves, all waves broke further inshore. This oversimplification of the 

 input wave parameters and water level variation did not adequately represent 

 the main features of the driving forces. When wave height and period were 

 held constant, but water level was allowed to vary, a pronounced bar develop- 

 ed. The main difference compared with the constant water level case was a 

 smoother bar and greater retreat of the shoreline. 



212 



