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level measurements at all sites, inlet velocity measurements at the primary site 

 (Pentwater, Michigan), and channel hydrographic surveys at the sites where more 

 recent data were needed. Available historic water level and velocity data for 

 some of the harbor sites were also used. 



Amplified harbor oscillations and generation of the highest inlet veloc- 

 ities are caused by the Helmholtz resonance mode which has a period of 0.6 to 5 

 hours for the inlet-bay systems studied. A recently developed, simple numerical 

 model is shown to be effective in predicting inlet-bay response over the range 

 of excitation periods encountered. A finite -difference form of the continuity 

 equation is shown to adequately predict inlet velocities if high-quality bay 

 water level records are available. Selected data from the study sites are 

 presented to demonstrate the hydraulic response of the inlet-bay systems and 

 the applicability of the prediction schemes. Examples to demonstrate use of 

 the concepts and techniques developed in the study are applied to the design 

 of a new inlet channel and to the modification of an existing channel. 



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