60 



Short-term profile change 



Changes in profile volumes were calculated by CHL for 14 stations moni- 

 tored over a 4-year period from 1991 to 1995 (Figure 4). Three distinct zones 

 for the volume calculations were selected: beach/nearshore bar, offshore bar, 

 and offshore. The three zones identified distinct characteristics of the offshore 

 zone south of St. Joseph. However, given the size of the study area and the 

 diversity of the nearshore conditions, the locations of these zones could not be 

 standardized by distance (shore-perpendicular) or depth. Consequently, their 

 location on each profile was based on individual morphology. In all cases, the 

 earliest profile was used as a baseline to compare changes in the volumes of 

 sediment on the profile from 1991 to 1995. Positive volumetric changes indi- 

 cate the amount of sand on the profile has increased since the base year of the 

 comparison. Negative volume changes occur when there is a reduction in sand 

 cover and/or irreversible lowering of the cohesive profile. For the wide off- 

 shore zone in particular, it is noted that small errors in the profile surveys 

 could result in large errors in estimated profile volume changes. 



An overlay of the long (beach and offshore) profiles for R8 is presented in 

 Figure 23. Line R8 is located in a transition zone between the south fillet 

 beach and feeder beach. The bathymetry comparison showed that the lake bed 

 north of R8 was stable or accretional. This area is in the lee of the harbor 

 jetties and any sand transported into this zone is effectively trapped (i.e., 

 because of sheltering from northerly wave attack). 



The results of the profile volume calculations and the timing and volume of 

 beach nourishment for Profile R8 are presented in Figure 23. The beach/ 

 nearshore bar showed deposition from 1991 to 1995; however, the offshore bar 

 continued to erode despite the beach nourishment. 



Profile RIO (Figure 24) is located in the feeder beach zone. The volumetric 

 results suggest that the beach nourishment has been successful in maintaining 

 the profile volumes in all three zones: beach/nearshore bar, offshore bar, and 

 offshore (see Figure 24). Over 1 00,000 m of sand was placed on the feeder 

 beach in 1991, which initially added approximately 300 m /m of sand to the 

 RIO profile. In 1993, the volume of sand on the profile increased to 

 600 m / m above the volumes recorded on August 14, 1991 (the base profile). 



Profile Rl 1 (Figure 25) is located at the southern end of the feeder beach 

 and is in a transitional zone between depositional and erosional profiles. All 

 three profile zones, especially the offshore bar, experienced an erosional trend 

 from 1991 to 1995 (see Figure 25). One possible explanation is the influence 

 of the nearshore beach slope, which increased from 1:85 at R8 (which was 

 depositional in the beach/nearshore bar zone) to 1:30 at profile Rl 1. The 

 numerical modeling indicated significant quantities of sediment could be trans- 

 ported in a cross-shore direction during a severe storm, especially when the 

 nearshore slopes are steep. 



Chapter 4 Analyses of Coastal Processes and Geomorphology 



