this area, including deposition at Line R12 which relates to the extension of 

 the ephemeral beach south of the Waterworks revetment. 



Southwesterly storms resulted in redistribution of sediment from the beach 

 immediately south of the Waterworks revetment and from the south end of the 

 feeder beach northwards to the fillet beach area. 



The beachfill was predicted to respond very rapidly in the cross-shore 

 direction, with the upper beach sediment being eroded and transported offshore 

 as the profile readjusted to equilibrium form. However, the influence of along- 

 shore transport had less immediate effects on the redistribution of sediment 

 outside the feeder beach area. The sediment was predicted to move along the 

 shore at a relatively slow rate, with deposition only perceptible at Lines R12 

 and R14 during the NW storm event. This result is in part related to the issue 

 of actual versus potential alongshore transport rates for Lines R8 and R9. If 

 the actual transport rates are less than the potential values predicted for 

 Lines R8 and R9 during a northwest storm event, the volume of sediment 

 transported to the feeder beach from the north will be much lower than the 

 model predictions. A reduction in the rate of sediment transport from the 

 north will accelerate erosion of the feeder beach and the associated alongshore 

 transport of sediment may occur more rapidly than predicted during a north- 

 west storm event. 



The influence of alongshore transport on the movement of bars can result in 

 significant changes to the exposure of glacial till over the duration of a single 

 storm. Presumably, it is these changes which contribute to the ongoing down- 

 cutting of the underlying glacial till in the vicinity of thick bar deposits. The 

 volatility of the sand cover is diminished along the southern section of shore, 

 which features deeper water offshore of the toe of the revetment. Predicted 

 downcutting rates are much lower in this area and only occur for isolated 

 sections of lake bed. The 3-D runs with a 2-mm grain size support the 2-D 

 findings: because of the stability of the sand cover, existing exposures of till 

 remained exposed and buried sections remained protected. The influence of 

 fluctuating lake levels on the exposure of the underlying glacial till has also 

 been shown to be an important factor (see section titled "Bathymetry Compari- 

 sons and Sediment Budget Calculations"). 



Trends in Profile Change 



In the past 50 years, several factors have influenced the volume of sand 

 above the cohesive profile at St. Joseph, including: obstructions to alongshore 

 sediment transport (harbor jetties), construction of shore protection structures, 

 the Section 1 1 1 beach nourishment program, and annual variability in along- 

 shore sediment transport. The quantity and stability of the sand cover above 

 the glacial till has an important impact on the magnitude and location of cohe- 

 sive downcutting. Long-term profile comparisons were made from the four 

 snapshots of the lake bed bathymetry (1945/6, 1964/5, 1991, and 1995) and are 

 discussed below. A review of the profile data collected from 1991 to 1995 



Chapter 4 Analyses of Coastal Processes and Geomorphology 



57 



