PREDICTION OF SHORE RETREAT AND NEARSHORE PROFILE 

 ADJUSTMENTS TO RISING WATER LEVELS ON THE GREAT LAK.ES 



By 

 Edward B. Hands 



I. INTRODUCTION 



1 . Purpose . 



This report demonstrates that increased shore retreat during periods of 

 sustained high water is merely the most visible expression of a massive 

 adjustment affecting a much wider area offshore. An equilibrium sediment 

 balance model realistically describes the ultimate, broad profile response to 

 increased water levels. Beach and nearshore surveys along a section of the 

 eastern shore of Lake Michigan (Fig. 1) in 1967, 1969, 1971, 1975, and 1976 

 provide the basis for this analysis. The results are generalized to provide a 

 simple but rational approach for estimating the response of sandy shore areas 

 throughout the Great Lakes to future long-term change in water levels. 



2. Background. 



Because of variations in climatic factors within their regional drainage 

 basins, the Great Lakes experience water level fluctuations uncharacteristic 

 of ocean shores (Fig. 2). Dry periods are common during which the mean 

 elevations of the lakes decline for many years in succession. After these 

 long periods of falling lake levels, it is easy for new property owners to 

 overestimate the stability of the shores and build structures too close to the 

 lakes. Storm erosion during later years of high water accelerates shore 

 recession and creates costly property damage. The persistence of high water 

 conditions for many years permits extensive profile adjustment via erosion and 

 offshore sediment transport. 



Recurrently during periods of extreme shore erosion there has been public 

 interest in gaining greater control over lake level fluctuations. However, a 

 study by the International Great Lakes Level Board (1973) concluded that regu- 

 lation of the five Great Lakes, while possible, would not provide benefits 

 commensurate with costs; outflows from Lake Superior and lake Ontario have 

 been controlled since 1921 and 1958, respectively. Natural variations in the 

 water supply to these basins are too large, however, to maintain constant lake 

 levels, so adjustments are made in the flows to benefit the many interests 

 involved. Reliable estimates of shore erosion for various water level condi- 

 tions are important in evaluating the impact of regulation plans on riparian 

 interests. An improved understanding is also needed for the proper design of 

 coastal construction projects and beach-fill operations, and the recommenda- 

 tions of setback distances, etc. 



A report on recent changes in rates of shore retreat summarized data from 

 the same set of surveys used here, but considered only the changes within 100 

 meters of the shoreline (Hands, 1979). Dates, types of data collected, and 

 reports on the earlier surveys are discussed in Section II. 



