bars did, at least not between 1969 and 1975. Furthermore, the outer bar 

 during this period generally lost relief as a result of various combinations 

 of crest erosion (predominant at stations 2, 12, 16, and 18) and trough fill- 

 ing (predominant at stations 4, 8, 11, and 19). By 1975 these two processes 

 had progressed to the point of completely eliminating the outermost bar at 6 

 of the 33 stations (4, 9, 11, 13, 19, and 24). 



5. Depths of Profile Closure . 



All profiles collected were examined for evidence of a limiting depth 

 below which there were no bottom changes over the period of study. In 1967 

 the bathymetric surveys terminated at the 5-meter contour. Over the 2-year 

 period from 1967 to 1969, substantial bottom changes occurred throughout the 

 zone from the shoreline to the 5-meter contour. This evidence of deep profile 

 fluctuation prompted the extension of surveys to greater depths — 11 meters in 

 1969 and 21 meters in 1971 and 1975. Although probable depth error increased 

 with distance from shore, the longer profiles converged at their outer ends. 



Because relief on the longshore bars increased significantly from one bar 

 to the next in the lakeward direction and the bars migrated yearly, the enve- 

 lope of bottom change also increased from the shoreline lakeward across the 

 barred zone (Fig. 10). Beyond the outer bar, the envelope of bottom change 

 narrowed abruptly. 



185 r 



Water Surface 



^u 150 



Figure 10. 



Envelope of bottom change, station 4 (1967-75). After several years of pro- 

 file adjustment to higher water levels, the envelope of changes in bottom 

 elevation is thickest in the zone traversed by the largest migrating bar and 

 narrows abruptly above the wave uprush and below the barred zone. 



20 



