bypassing, approximately 80,000 m annually must be eroded from the lake 

 bed to supply the potential for net southerly alongshore transport and an 

 additional 8,000 m is lost annually to deposition in the navigation channel. 

 Considering that the annual nourishment volumes between 1991 and 1995 

 were 41,000 m / year, approximately 47,000 m /year of lake bed erosion 

 would be required to supply the additional losses to alongshore transport and 

 channel infilling. Consequently, of the 367,000-m loss related to lake bed 

 lowering, up to 320,000 m may have been attributed to the irreversible 

 lowering of the cohesive profile or approximately 35.5 m /m/year. 



1945/46 to 1995 



Figure 33 compares 1945/6 and 1995 bathymetry, and represents 50 years 

 of lake bed evolution at St. Joseph. With the exception of the northern and 

 southern fillets (Panels 2 and 3), the entire lake bed has experienced dramatic 

 lowering. A large depression in the lake bed has been created by 2 to 5 m of 

 vertical erosion in the nearshore zone between St. Joseph and Shoreham. 

 Given the approximate size of the depression, over 3,000,000 m of sediment 

 has been eroded from the lake bed in the last 50 years. 



75 



Chapter 4 Analyses of Coastal Processes and Geomorphology 



