similarity between test and problem conditions. Initial consideration of both 

 estimates may be useful for placing high and low bounds on the expected re- 

 sponse. Of the two, the equilibrium approach is more objective and flexible 

 as it takes site-specific characteristics directly into account. 



Both approaches must be qualified, however, for the possible exposure of 

 nonsandy substrates, for the possibility of local intervention halting erosion 

 and changing longshore balances, and for the conditions that existed before 

 the period of application. 



Results reported here are promising. However, the contrast between the 

 extreme simplicity of the model and the intractable complexities of actual 

 beach and nearshore processes emphasizes the need for careful application and 

 further evaluation of these methods. Careful application during future lake 

 level cycles should provide a clear indication of weaknesses and usefulness of 

 these methods. If further research is then deemed necessary, the section of 

 shore studied here would serve as a good test site, for reasons discussed in 

 the text and because of the available past record. If such a study is neces- 

 sary, plans should be made to extend the study over at least a full cycle of 

 rising and falling lake levels with biennial surveys. The full longshore unit 

 should be covered from the Ludington pumped storage facility to the White Lake 

 jetties. The positions of station monuments used in the past studies are well 

 documented and can be reoccupied, but supplementary profiles should be estab- 

 lished between these sites because of the large variation in shore response 

 observed between adjacent stations. 



Because of the required profile length, boat positioning is critical. 

 Methods other than the usual siting on surveyed range markers are necessary. 

 The time of year for surveying is also important. A change in water tem- 

 perature from 24° to 13° Celsius within 2 hours was noted during sounding 

 operations in this study. Extreme temperature changes can affect the repro- 

 ducibility of soundings. In the spring, as waters warm, a sharp temperature 

 and acoustic gradient develops near the shore. Significantly cooler water is 

 sometimes trapped in a series of pools between the longshore bars. 



Even in late summer, when the thermocline is typically near 15 meters, a 

 change in wind direction can quickly flush the nearshore zone of warm water 

 and replenish a series of longshore pools with cold bottom water. Calibration 

 of the sounding instrument with a reflector suspended over the side of the 

 boat (a bar-check) should be done from the surface to the maximum profile 

 depth, and in a water column essentially like that at the profile site. 

 Variations which cannot be eliminated by field adjustments can be corrected 

 during data reduction stages if careful notes are kept of bar-check results. 



A good evaluation of the simple profile response model presented here 

 should be relatively easy after the lakes have undergone another long-term 

 cycle. However, obtaining the field data to significantly improve the situa- 

 tion would be a more difficult and expensive undertaking. 



55 



