as purely incident energy. (A amp ) a 

 to 1 .0 in this calculation. 



, was constrained to be greater than or equal 



Table 20 



Percent Occurrence of W s/ong ^10 cm at 



Field Gages 



Gage 



Wave Period Range (sec) 



100-400 



30-100 



Pier 2 



3.8 



1.4 



Canoe Club 



0.8 



2.1 



Back Basin 



0.1 



0.2 



Channel Entrance 



2.2 



1.6 



Array 



0.4 



3.0 



Using Equation 32 and the 1 1 -month field data set, the percent of obser- 

 vations with H sU>ng z 10 cm was calculated. Results for the 100-sec to 400-sec 

 range are similar to the RMS amplification factor results (Figure 57). Results for 

 the 30-sec to 100-sec range are more scattered (Figure 58). Corresponding 

 information from the field gages is given in Table 20 for comparison. 



A slope criterion as 

 suggested by Wilson 

 (1967) was also eval- 

 uated. Wave height for 

 the criterion was an H sjmg 

 as in Equation 32, with 

 the summation taken over 

 nine successive model 

 frequencies. The number 

 nine was chosen because 

 nine successive frequen- 

 cies encompass a broad 

 enough band to include 

 most or all of any peak in 

 the model spectral 

 response. The// Jtong was 

 multiplied by the center 



frequency to give a slope. If any combination of nine successive frequencies 

 gave a slope exceeding Wilson's criterion, the record was counted as having 

 exceeded the threshold. Period ranges of 30-100 sec and 100-400 sec were 

 evaluated separately as before. Results are given in Appendix G. 



An additional operational guideline is based on the value of A amp/ for the 

 higher resonant peaks. Experience with Los Angeles and Long Beach Harbors 

 has indicated that if A ampl is greater than about 5, some operational difficulties 

 may be encountered. If A ampJ is greater than 10, major operational problems can 

 be expected. 1 This guideline may be applied to the plots in Appendix G. If the 

 very low frequency Helmholtz peak is excluded, Plans 1, 2, 5, and 7 all appear to 

 be operationally unacceptable as presently formulated. They all have basins at 

 which A^, exceeds 10. 



Results are best judged by comparison to the existing piers. Plans 1 and 

 2 clearly have potential problems at the passenger pier (Basin 23) in the 100- to 

 400-sec range. The magnitude of response in a range which affects ships of this 

 size is large enough that this facility would likely be unacceptable. Plans 5 and 

 7 also tend toward elevated responses. 



Personal Communication, William C. Seabergh, Research Hydraulic Engineer, U.S. Army Engineer Waterways 

 Experiment Station, Vicksburg, MS. 



84 



Chapter 6 Harbor Oscillations 



