Figure 17. Silver Lake dunes, looking from Lake Michigan across 

 the dunes to Silver Lake. Spit extension probably 

 sealed off the two bodies of water soon after the 

 Nipissing high lake levels which, according to Hough 

 (1958), would have been about 3,000 years Before 

 Present (B.P.). Continued longshore transport and 

 prevailing west winds built the dune field along the 

 front of this low receptive embayraent. 



absence of an exposed beach across which the wind could blow make it difficult 

 to estimate the volume of sand actually transferred inland during the recent 

 period of high water. It is assumed that inland losses to the Silver Lake 

 dunes between 1969 and 1976 exceeded the gain of sediment supplied to the 

 adjusting profile from the dunes by only a small amount which can be neglected 

 in the calculation of an overall sediment balance for the larger study area. 



c. Measured and Predicted Shore Retreat . Because the initial 1967 survey 

 covered only a small area in the vicinity of Pentwater Harbor, an area subject 

 to less recession than the surrounding "undisturbed" beaches (Hands, 1979), 

 testing of the sediment balance approach was best done by using the 1969-76 

 survey data and excluding measurements made within 500 meters of the Pentwater 

 jetties. The extent of shore covered (25 profiles spread over 50 kilometers) 

 and the length of time monitored (7 years), together with the sizable increase 

 in mean water level during the study period and the generally near-ideal con- 

 ditions discussed previously, make this application the most realistic field 

 test of equilibrium profile migration to date. 



Measurements of the width of each profile from the vegetated dune line to 

 the pinch-out depth for each station were taken and averaged to obtain X = 923 

 meters. The heights of the scarps which waves had cut in the foredune were 

 also measured at each station. As the profiles had not yet developed a 



35 



