Summit Park 



Pentwater 



Figure 16. Pumped storage facility south of Ludington. The shore south 

 of Ludington is a zone of general longshore divergence. The 

 jetties built at the pumped storage facility in 1971 further 

 restrict longshore transport in this area of divergence and 

 thus establish a specific northern limit for sources of sand 

 to the present study area. 



The assumption that there is no significant longshore input or losses 

 beyond the present study limits is reasonable, especially considering the 

 minor impact any imbalance would have on the 50-k,ilometer stretch of shore 

 during this period of rapid shore erosion. For example, a net inflow of 

 100,000 cubic meters per year (an improbably large figure) would be volu- 

 metrically equivalent to recession of only 0.2 meter per year, (10 m /yr)/ 

 (5 X 10 m X 10 m), while the observed shore recession actually averages 

 2.5 meters per year. So the maximum conceivable longshore input is small 

 relative to the enormous exchange of sediment onshore and offshore during this 

 period of rapid profile adjustment. 



b. A Possible Inland Loss . A possible inland loss on Little Sable Point 

 complicates the otherwise simple sediment balance for this area. The Silver 

 Lake dunes occupy about 6 kilometers of shoreline between profile stations 13 

 and 17 and extend more than a kilometer inland (Fig. 9). These actively 

 migrating dunes reach heights of 35 meters along the inland half of the dune 

 field (Fig. 17). Along the shoreline, the dune ridges crest about 7 meters 

 above lake level (Fig. 18) and some ponded interdune areas are at approxi- 

 mately the same level as Lake Michigan (177 meters. International Great Lakes 

 Datum). For many hundreds of years this dune field has been fed by the con- 

 vergence of longshore transport toward Little Sable Point from both the north 

 and south, and by the inland transport of sand by prevailing west winds. The 

 dune shoreline receded more than any of the adjoining beaches during the study 

 period (Fig. 19). The vastness of the dune field, the effect of 1- to 2-meter 

 wave-cut bluffs which marked much of the dune shoreline, and the virtual 



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