d. Line 4. Downdrift cohesive profile (not influenced by reduced sedi- 

 ment supply from the north - representative of natural conditions or 

 background erosion rate). 



Model runs were completed for profiles firom the four available bathymetric 

 surveys: 1945/46, 1964/65, 1991, and 1995. Changes in these profiles are 

 discussed in a later section titled 'Trends in Profile Change" (page 57), and the 

 changes are illustrated in Figures 11 to 13. The results of the model runs are 

 summarized in Table 6. 



Decreased depths at Line 2 in the vicinity of the depositional fiUet beach 

 have increased the potential for alongshore sediment transport because the zone 

 of breaking waves is wider. However, this increase may be offset by the 

 change in shoreline and contour orientation at this location. 



The large depression offshore of R12 and R14 and the associated steeper 

 nearshore slopes at Line 3 resulted in a 24-percent reduction in southerly 

 potential transport from 259,000 to 198,000 m^/year from 1945 to 1995 (see 

 Table 6). At Line 3 the northerly transport component was reduced by 32 per- 

 cent from 207,000 m^/year in 1945 to 142,000 m^/year in 1995. 



At Line 4, located 8.2 km south of the harbor jetties, the predicted transport 

 rates were also much lower for the 1995 profile (see Table 7). From 1945 to 

 1995, southerly transport decreased 31 percent and northerly transport 

 decreased by 41 percent. 



In summary, long-term profile changes at St. Joseph have influenced the 

 potenfial for northerly and southerly alongshore sediment transport. At the 

 north fillet beach, the reduction in nearshore depths due to deposition has 

 increased the potential for sediment transport. South of the harbor jetties, the 

 deeper nearshore profiles off the revetment and the unprotected shores further 

 to the south have significantly reduced the potential for northerly and southerly 

 transport. 



Bypassing and channel infilling at St. Joseph Harbor 



Since the construction of the jetties in 1903, the fillet beach deposits north 

 and south of the harbor have increased in size, resulting in increased potential 

 for channel infilling during northerly and southerly wave attack. Profile data 

 from the detailed 1995 bathymetry were used as input for the C0SM0S-2D 

 model to assess the existing potential for channel bypassing and/or infilling. 



Annual rates of alongshore transport were calculated beyond the end of the 

 north and south jetties. Landward of the channel entrance, the harbor jetties 

 due to their sheet-pile construction, were assumed to be complete barriers to 

 alongshore transport. The average annual potential for channel infilling from 

 the north was estimated to be 15,000 m /year (see Figure 14a) based on the 



Chapter 4 Analyses of Coastal Processes and Geomorphology 



27 



