VII. SUMMARY AND CONCLUSIONS 



Methods developed by Goda (1975a, 1975b) and suggested by Goda, Takayama, 

 and Suzuki (1978) for predicting nearshore irregular wave conditions for the 

 case of continuously shallowing bottom contours have been presented in forms 

 convenient for designers. A sensitivity analysis of the methods shows the 

 relative importance of the input parameters on the predicted nearshore sig- 

 nificant wave height. Comparison with observed wave height changes at the 

 CERC FRF pier indicates that the methods may be suitable for preliminary de- 

 sign, although the influence of the pier piles and variable hydrography 

 caused by the pier on wave activity has not been determined. Examples are 

 presented and design curves are given in Appendixes A, B, and C. 



The design curves in Appendixes B and C were produced by assuming that 

 the deepwater wave heights have a Raleigh distribution. In a design situa- 

 ation where the deepwater waves are known to be non-Raleigh, which may occur 

 with multipeaked spectra, methods described in this report should not be used. 



The analytical model also assumes that the beach has continuously shal- 

 lowing bottom contours; the effect of offshore bars on nearshore wave height 

 is unknown. As a first approximation for barred coasts the wave height shore- 

 ward of the bar should be taken as equal to the predicted height at the bar 

 crest location (Y. Goda, personal communication, 1979). Where the water depth 

 becomes less than the depth at the bar crest, the curves can once again be 

 used to predict wave heights shoreward of the bar. 



The wave predictions for structural design in very shallow water (approxi- 

 mately d/H' < 0.1) should be used with caution. In very shallow water the 

 wave begins to behave like a runup bore with a large forward momentum, and 

 for this case the wave height alone may not provide enough information for 

 design of a structure. 



When this report was prepared, little wave data were available; therefore, 

 only a few observations are presented in Section V. However, large amounts of 

 wave data are now becoming available from CERC's Field Research Facility at 

 Duck, North Carolina, and CERC is in the process of making a more comprehen- 

 sive evaluation of methods described in this report. Preliminary results sug- 

 gest that on the average, predictions are conservative for d/H g > 1.5 while 

 the predicted significant wave height may be underestimated for d/H s < 1.5. 

 Results of CERC's analysis will be published in a later report. 



27 



