These formulas enabled the extrapolation of the known migration to a point 100 

 years into the future (Table 5) to gain some insight into the future migration 

 and orientation of Isles Dernieres (Figure 14). The area of the island was 

 also reduced in accordance with previous rates of area loss calculated from 

 topographic maps. 



Table 5 

 Projected Migration of Isles Dernieres 





Location 



Migration for Past 



93 Years (from 



formula), m 



Pro, 

 for 

 (fr< 



jected Migration 

 Next 100 Years 

 3m formula) , m 



90°4T 



994 



911 



90°47'30 M 



1,955 





1,909 



90°55' 



1,274 





1,167 



Eastern Spit 



1,210 





967 



Western Spit 



-212 





-600 



43. Figure 14 represents the best mathematical fit based on the limited 

 data available from historical maps. The data derived in this investigation 

 pertaining to individual processes controlling migration suggest that some 

 modification of this extrapolation may be necessary. For example, tidal in- 

 flux will probably increase considerably due to widening and deepening of the 

 present channels and possible creation of new channels. The decrease in the 

 importance of washover deposition and longshore drift relative to that of 

 tidal activity will have the effect of restricting landward and lateral migra- 

 tion. By restricting the ability of the island to migrate, the effects of 

 subsidence will be accelerated, causing sediments to sink below wave base and 

 to be lost from the island. These trends will likely increase with time and 

 Isles Dernieres will migrate much less in the future than it has since 1887. 

 By reducing the effect of overwash and longshore drift on sediment transport 

 and considering the limitations imposed by tidal channels and subsidence, 

 Isles Dernieres will ultimately become a shoal. Therefore, the Isles Der- 

 nieres in the year 2080 (presented in Figure 15) may represent too large an 

 area when considering the trend of the processes controlling island migration. 



34 



