depth below datum (m) erosion of cohesive profile (m) 





6 





/ 



" 





4 



— Initial Profile 



— Cohesive Profile 



/ 







2 



■ -Final (d50=0.2mnn) 



// 











— Coh. Erosion (0.2mm) 

 • -Final (d50=2.0mm) 



// 



-0.05 





/ 



-2 

 -4 



— Coh Erosion (2.0mm) 



yp^ 



-0.1 





r 



— r:^^^^^^ 



-6 



/^^^22:-~_;-i:>----' 







-8 



X 







-10 



- 



-0.15 





-12 



- 







-14 



1,1.1,1,1.1.1. 



r\ r\ 





-200 200 400 600 800 1,000 1,200 1,400 





distance (m) 





k. Profile R8 cohesive profile erosion during 2 November, 1991 storm, d^^Q = 0.2 mm & 2.0 



mm 



actual W.L. 





Figure 21. (Sheet 6 of 6) 



The findings also indicate that the 2-mm grain size sediment is much more 

 effective than the 0.2-mm grain size sediment at mitigating downcutting for 

 those sections of shore where a beach deposit protects an underlying till layer. 

 For profiles which feature deep water at the toe of a shore protection structure 

 (and no beach), the coarse grain size sediment is no more effective than the 

 fine grain size sediment in protecting the underlying glacial till from 

 downcutting. 



Summary of the 3-D results 



A major limitation of the 3-D modeling was the limited number of profiles 

 available to describe the bathymetry along the study area shore. The 3-D 

 modelling was completed prior to the availability of detailed bathymetry from 

 the 1995 SHOALS survey. The implication of this limitation was that the 

 model results could only be interpreted in a general manner; detailed changes 

 to the bathymetry were either not predicted or were not entirely reliable. Not- 

 withstanding this limitation, several conclusions can be made based on the 

 results of the 3-D experiments. 



The 3-D results confirmed that the deep water located offshore of the 

 southern revetment-protected section of shore creates an impediment to along- 

 shore transport. For northwest wave events, this results in some deposition in 



56 



Chapter 4 Analyses of Coastal Processes and Geomorphology 



