HYDRAULICS OF GREAT LAKES INLETS 

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William N. Seelig and Robert M. Sorensen 



I. INTRODUCTION 



Numerous bays and harbors are connected to the Great Lakes by 

 jettied inlet channels. These inlet channels are important because they 

 allow (a) access to commercial shipping and recreational boating, (b) 

 migration of fish, and (c) flushing of pollutants from the bays and 

 harbors . 



Great Lakes inlet-bay systems are generally smaller than those on 

 the Atlantic, Pacific, and gulf coasts of the United States and respond 

 primarily to the long wave seiching modes of the Great Lakes rather 

 than to the astronomical tides. These seiches have smaller amplitudes 

 and shorter periods than the tides on the ocean coasts . 



The major effort of this study involved the collection and analysis 

 of hydraulic data at several inlet-bay systems throughout the Great Lakes 

 during 1974 and 1975. Measurements at Pentwater, Michigan, the primary 

 study location, included simultaneous recording of inlet current veloc- 

 ities and water levels in the bay and in Lake Michigan. At the other 

 locations, only bay water levels were measured. However, hydrographic 

 surveys were obtained for all the inlets investigated, and historic 

 hydraulic data from selected sources were analyzed. 



This study defines the hydraulic mechanisms important to Great Lakes 

 inlet-bay systems, develops analytical techniques for the prediction of 

 inlet currents and bay water level oscillations, and presents design 

 data and system response curves for selected inlets. 



Field data were analyzed using (a) a formula for estimating the 

 seiche periods of the Great Lakes which are important in producing 

 reversing currents at an inlet; (b) a model that uses bay water level 

 time histories to predict inlet velocities; and (c) a simplified numer- 

 ical inlet hydraulic model that, when calibrated for friction effects, 

 can be used to predict inlet velocities and bay water level oscillations 

 generated by lake oscillations. These analysis techniques are used with 

 the field data to develop response curves and cumulative inlet current 

 velocity distribution curves for the inlets studied. 



II. LAKE AND INLET HYDRAULICS 



1. Great Lakes and Inlet-Bay System Hydraulics . 



An inlet is a relatively narrow channel which connects a "sea" (or 

 one of the Great Lakes in this study) to a lake or harbor (a "bay" in 

 this study). The bay is large compared to the inlet (i.e., the radius 



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