differential barometric pressures and are superimposed on the longer period 

 variations in the lake level. Large short-period rises in local water levels are 

 associated with the most severe storms, which generally occur in the winter when 

 the lake level is usually low; therefore, the probability that a high lake level and a 

 large wind tide or seiche will occur simultaneously is relatively small. 



Lake levels of +0.52 and +1.07 m (+L7 and +3.5 ft) were selected by the 

 Detroit District for use during the model experiments. The lower value (+0.52 m 

 (+L7 ft)) represents the long-term summer (April-October) average for the period 

 of record. The higher value (+1.07 m (+3.5 ft)) represents the summer average for 

 Lake Huron during 1997, when the lake levels were unusually high. 



Factors influencing selection of experimental wave characteristics. In 



planning the experimental program for a model investigation of harbor wave- 

 action problems, it is necessary to select heights, periods, and directions for the 

 experimental waves that will allow a realistic study of the proposed improvement 

 plans and an accurate evaluation of the elements of the various proposals. 

 Surface-wind waves are generated primarily by the interactions between tangential 

 stresses of wind flowing over water, resonance between the water surface and 

 atmospheric turbulence, and interactions between individual wave components. 

 The height and period of the maximum significant wave that can be generated by 

 a given storm depend on the wind speed, the length of time that wind of a given 

 speed continues to blow, and the distance over water (fetch) that the wind blows. 

 Selection of experimental wave conditions entails evaluation of such factors as 

 follows: 



a. Fetch and decay distances (the latter being the distance over which waves 

 travel after leaving the generating area) for various directions from which 

 waves can approach the problem area. 



b. Frequency of occurrence and duration of storm winds from the different 

 directions. 



c. Alignment, size, and relative geographic position of the navigation 



structures. 



d. Alignments, lengths, and locations of the various reflecting surfaces in the 

 area. 



e. Refraction of waves caused by differentials in depth in the area lakeward 

 of the site, which may create either a concentration or a diffusion of wave 

 energy. 



Deepwater wave data. Measured prototype wave data covering a 

 sufficiently long duration from which to base a comprehensive statistical analysis 

 of wave conditions were unavailable for the Port Huron area. However, statistical 

 wave hindcast estimates representative of this area were available from Resio and 

 Vincent (1977). This hindcast was developed for 28 points along the U.S. Lake 

 Huron shore using historical wind data from three climatological stations. 

 Significant wave heights and peak wave periods were calculated for 5, 10, 20, 50, 

 and 100 years for three wave approach angles to shore. 



36 Chapter 6 Physical Model 



