Table 6. Predicted Duluth-Superior maximisn inlet 

 water velocities for a forcing wave of 

 1 hour (a^ = 3 centimeters) 





Velocities, cm/s (ft/s) 





Duluth 



Superior 



Flood 

 Ebb 



73 (2.4) 

 64 (2.1) 



43 (1.4) 

 49 (1.6) 



A unique feature of the North Pond inlets is that the maximum velocity 

 in the inlets is predicted to be approximately the same over a wide 

 range of forcing periods because of the approximately linear relation 

 between wave amplitude propagation in the bay and wave period (Fig. 18). 

 The velocities in the northern inlet at North Pond, the most recently 

 formed inlet, are predicted to be 1.4 times larger than those in the 

 older inlet. 



The numerical model for Pentwater was run using monochromatic forc- 

 ing waves with the various modal periods of oscillation of Lake Michigan 

 (Table 3) . The predicted amplification and maximum velocity for a forc- 

 ing wave of a^ = 0.1 foot are listed in Table 7. From this analysis, 

 the sixth through ninth longitudinal modes of oscillation of Lake Michigan 

 are predicted to cause the largest wave amplification and generate the 

 highest relative velocities. However, analysis of the node-antinode 

 pattern of Lake Michigan shows that only even modes of oscillation will 

 have antinodes, and cause significant water level fluctuations adjacent 

 to Pentwater (Fig. 3) . Since odd modes of Oscillation have a node near 

 Pentwater (Fig. 3), even the presence of one or more of the odd modes of 

 oscillation in Lake Michigan will cause only small water level fluctu- 

 ations near Pentwater. This means that the sixth and eighth longitu- 

 dinal modes of oscillation of Lake Michigan will probably have the 

 largest influence on the hydraulics of Pentwater. 



3. Observed Lake Level Fluctuations, Bay Response, and Inlet Velocities . 



The first obvious characteristic of Great Lakes water level fluc- 

 tuations is that they are not uniform (as assumed in the previous section) . 

 Therefore, the monochromatic analysis can be used to obtain an upper esti- 

 mate of bay wave amplification and inlet velocities; however, a complete 

 analysis is necessary for an accurate estimate of response to a particular 

 Great Lakes water level time history. Sample water level records from 

 Lake Michigan and Pentwater bay, along with spectral analysis of 42 -hour 

 records to show typical bay response, are plotted in Figures 19, 20 and 

 21. 



Figure 19 shows a storm event on Lake Michigan when several modes of 

 oscillation were excited by meteorological effects. The second longitu- 

 dinal mode of Lake Michigan (5.3 hours) and a 0.65-hour wave are partic- 

 ularly dominant. All of the 5.3-hour wave propagates into Pentwater 



47 



