the wave amplitude will be smaller in the bay than in Lake Michigan, pri- 

 marily because the bay surface area is much larger than the inlet design 

 cross-sectional area (a ratio of approximately 10^) . 



The model also predicts that monochromatic seiches with an amplitude 

 of 3 centimeters will generate maximum velocities of 43 centimeters per 

 second (1.4 feet per second) for wave periods of 4 to 9 hours (Fig. 28). 

 Since maximum velocities decrease for waves shorter than 4 hours, a wave 

 with a 1-hour period produces insignificant inlet velocities. 



The first three modes of oscillation of Lake Michigan (9.3-, 5.3-, 

 and 3.5-hour waves) will generate the highest velocities for the Crystal 

 Lake inlet design. Portage is located near Crystal Lake; therefore, 

 forcing amplitudes of the first three modes of oscillation of Lake 

 Michigan will be similar at both locations (Fig. 3). The predicted vel- 

 ocities for a given wave are different at Portage and Crystal Lake 

 (Fig. 29) due to differences in inlet and bay geometry. However, Portage 

 water level data can be used to estimate Crystal Lake inlet velocities. 



To predict inlet velocities at Crystal Lake using Portage data, the 

 measured Portage bay level fluctuations must first be adjusted to esti- 

 mate the nearby Lake Michigan wave amplitudes. These amplitudes are then 

 used to predict velocities at Crystal Lake; e.g., a measured Portage bay 

 level fluctuation has a period of 3.5 hours and amplitude of 0.15 foot 

 (4.6 centimeters). This wave was amplified by a factor of 1.3 by Portage 

 harbor (Fig. 16), so the Lake Michigan wave amplitude was 0.15/1.3 = 

 0.12 foot. A 0.1-foot wave amplitude in Lake Michigan produces a maximum 

 velocity of 1.3 feet per second at Crystal Lake inlet (Fig. 28); there- 

 fore, the 0.12-foot wave produces 1.3 (0.12) = 1.6 feet per second maxi- 

 mum velocity. This procedure could be followed for other seiche modes 

 to estimate the maximum velocities expected at Crystal Lake. 



If a complete analysis of inlet velocities is required, water levels 

 should be measured in Lake Michigan adjacent to Crystal Lake for at least 

 several months. These levels can be used as the forcing function in the 

 numerical model to produce a predicted time history of inlet velocities, 

 discharge, and bay levels for the period of record. 



2. Inlet Channel Modification . 



Procedures for investigating the effect of a modification to an inlet 

 are: (a) Determine the geometry of the present system and obtain proto- 

 type hydraulic data (i-e., concurrent bay levels. Great Lakes levels, 

 and inlet velocities); (b) calibrate the numerical model; (c) obtain 

 monochromatic response characteristics of the inlet-bay system, (d) 

 modify the model geometry to reflect the proposed inlet change and pre- 

 dict the response characteristics of the new condition; and (e) use the 

 water level records in the Great Lakes to force the model to produce a 

 time history of inlet velocities, discharge, and bay levels for the 

 proposed design. 



