extreme excursions between surveys can safely be ignored depends on the energy 

 conditions and the temporal and spatial scales involved, as well as on the 

 application at hand. To reveal trends in long-term bathymetric adjustment to 

 higher water levels, profiles taken even several years apart are quite useful, 

 especially if all the profiles are obtained during similar phases in any 

 seasonal cycles but over a period of persistent annual change (see Fig. 8). 

 The magnitude of weekly to monthly profile changes is represented in Figure 8 

 by four surveys spanning the period from 19 July to 12 August 1967. Their 

 relatively close agreement contrasts with the difference that develops between 

 spring and fall as shown by the May and August 1969 surveys. The long-term 

 trend in bar migration can be seen in the overall change from 1967 to 1969 and 

 in the comparison of bar positions in those years with the final bar position 

 determined at this location in 1975. Careful measurements are necessary to 

 discern the small weekly changes from possible profile error. However, the 

 cumulative effect of long-term migration clearly exceeds both the margin of 

 error and the range of short-term fluctuations. 



26 f)UG 69 

 21 tlAY 69 



12 WG 67 



8 MG 67 



25 JUL 67 



19 JUL 67 



I0(» ISP 200 250 300 



Distance from Bose Monument (m) 



350 



450 



Figure 8. 



Short-term changes in bathymetry versus long-term bar migration. The 

 short-term changes are illustrated by four surveys in 1967. May and 

 August surveys in 1969 reveal larger changes. The final surveyed bar 

 position in 1975 illustrates the effect of long-term bar migration- 

 Details of intermediate surveys at other stations are shown in Appendix 

 A. To simplify the presentation of general trends, only the earliest and 

 latest surveyed bar positions are shown in Figure 9. The original survey in 

 1967 covered the area in the immediate vicinity of the Pentwater jetties 

 (stations 3 to 8). The remaining stations (1, 2, and 9 to 29), spread over 

 the adjacent 50 kilometers, were first surveyed in 1969. 



Continued monitoring of profile development throughout the remainder of 

 the rising phase in lake levels and for several years thereafter (until 1976) 

 confirms the original proposal (Saylor and Hands, 1970) that bars tend to rise 

 with the water level. However, landward migration of the bars was confirmed 

 only by trie two to three inner bars within 250 meters of shore. The outer 

 bars did not reveal the same tendency toward shoreward migration as the inner 



17 



