5 Conclusion 



This report elucidates the nature of frequency-direction spectra evolving 

 during storm events occurring at the FRF. The primary result is a series of 

 graphic presentations of spectra measured with a high-resolution directional 

 wave gauge in an 8-m depth approximately 900 m offshore. Data from a 

 5-year observation period have been searched for storm events defined bv a 

 characteristic wave height in excess of 2 m at two points at least 24 hr r.art 

 in the same storm system. A total of 29 events have been isolated for closer 

 scrutiny. Time series plots of climatic parameters and sequences of plots of 

 S(f,6) are used to reveal the evolutionary nature of storm wave fields. 



The data indicate that there are two basic types of events: (a) high waves 

 from strong but distant sources, and (b) localized wave generation from Cana- 

 dian high-pressure systems, frontal passages, and atmospheric low-pressure 

 cells passing the FRF from the west or south. Of the 29 events identified, 27 

 are of this latter type. Of the 27 localized events, 25 demonstrated very com- 

 mon patterns of spectral evolution. The patterns include initial localized 

 waves aligned nearly with the local wind, directional broadening of spectral 

 peaks as the wave fields grow, and a bifurcation of high-frequency spectral 

 tails into two modes: (a) one nearly aligned with the wind, and (b) another, 

 20 deg to 40 deg away, aligned nearer to the shore-normal direction. One- 

 quarter to one-half of the total energy is contained in the bimodal tails, a 

 consideration of consequence because such spectra occur at the peaks of 

 storms, and because the beating of such spectral waves against the shoreface 

 can affect such nearshore processes as the patterns of beach erosion and infra- 

 gravity wave generation. 



The main conclusions here are that storm waves occur at the FRF with 

 curious spectral shapes, and that accounting for the processes that give rise to 

 those shapes is important. It is suggested that a more detailed coverage of 

 wind, wave, and bathymetric observations over 100-km scales from the FRF 

 is warranted. It is certain that nearshore processes driven by waves having 

 such elaborately structured spectra will be different from estimates generated 

 by over-simplified wave models (typically unidirectional and monochromatic) 

 as even now still haunts engineering guidance. There is good reason to be- 

 lieve the spectra reported here are real and not some artifact of the analysis 

 method used. Use of these results for testing wave generation and transforma- 

 tion models at scales of the continental shelf width, and as seaward wave 

 boundary conditions for nearshore process models, will certainly yield more 



22 



Chapter 5 Conclusion 



