near the harbor Helmholtz period. Forcing waves are large because the 

 harbor is located on the converging end of the lake, which will always 

 be an antinode of longitudinal oscillations. 



Maximum water velocities observed in other inlets are much lower 

 than in Duluth-Superior; e.g., at Pentwater, all measurements and pre- 

 dictions show that velocities are less than 60 centimeters per second 

 (2 feet per second) for 99.5 percent of the time (Fig. 25). Predicted 

 inlet velocities for other locations show that Portage, Ludington, and 

 Pentwater have similar velocity distributions; Presque Isle, Muskegon, 

 and Little Lake have still lower velocities (Fig. 26). 



V. INLET DESIGN 



Great Lakes inlet design problems generally fall into one of two 

 classes: (a) a pond or lake to be connected to one of the Great Lakes 

 by a new channel, and (b) an existing inlet channel to be modified. The 

 concepts and techniques developed in this study can be used to aid the 

 design of an inlet in either class. An example application for each 

 class is given below. 



1. New Inlet Channel . 



The procedures for analysis of a new channel that is to connect a 

 lake to one of the Great Lakes are: (a) determine the approximate inlet 

 dimensions (length, width, and depth) based on physical limitations such 

 as the desired navigable depth and width and the distance between the 

 lake and Great Lakes; (b) estimate a Manning's n for the proposed channel 

 (see Sec. IV, 2, for typical values of n) ; (c) use the numerical model 

 to obtain monochromatic response characteristics of the harbor for the 

 range of expected lake seiching periods and a typical amplitude; (d) 

 compare the results to those of other nearby harbors; and (e) apply the 

 numerical model to predict inlet velocities, discharge, and bay levels 

 for the period of record (if Great Lakes water level fluctuation records 

 are available in the vicinity of proposed site) . 



For example, suppose an inlet is to be designed to connect Crystal 

 Lake to Lake Michigan (Fig. 27) . Crystal Lake, located on the eastern 

 shore of Lake Michigan 35 kilometers (22 miles) north of Portage Lake, 

 has a bay surface area of 4.12 x 10^ square meters (4.44 x 10^ square 

 feet). The inlet at this site would be approximately 1,200 meters 

 (4,000 feet) long. Assume that the inlet would be 61 meters (200 feet) 

 wide and 5.5 meters (18 feet) deep. Since the inlet is similar to Pent- 

 water (see Table 5), the Manning's n for this channel is estimated to be 

 0.036. 



The niimerical model was run for Crystal Lake using Lake Michigan 

 seiche periods of 9.3, 5.3, 3.5, 2.2, 1.85, and 1.4 hours with an 

 amplitude of 3 centimeters. The predicted response characteristics of 

 this inlet-bay system are shown in Figure 28. The model predicts that 



56 



