PART VII: FUTURE PROSPECTS FOR ISLES DERNIERES 



41. In order to predict the future migration of Isles Dernieres, past 

 migration must first be documented. To measure historic island migration, to- 

 pographic maps from the years 1887, 1906, 1935, 1953, and 1980 were obtained. 

 Before any measurements were taken, the scales of the maps were adjusted to 

 1:24,000 and the maps were overlaid by aligning selected points of latitude 

 and longitude. The change in beach front position could then be measured di- 

 rectly from the maps. Three points of longitude were selected, along which 

 landward migration was to be measured (90°41', 90 o 47'30", 90°55'). Eastward 

 and westward accretion of the terminal spits was measured directly from the 

 overlays. The values for island migration are found in Table 4. 



Table 4 

 Landward and Lateral Migration of Isles Dernieres 



90°41' 90°47'30" 90°55' 



Landward Migration 



1887-1906 = 318 m 1887-1906 = 480 m 1887-1935 = 942 m 



1906-1935 = 360 m 1906-1935 = 630 m 1935-1953 = 30 m 



1935-1953 = 60 m 1935-1953 = 330 m 1953-1980 = 162 m 



1953-1980 = 180 m 1953-1980 = 450 m 



Lateral Migration 



Eastern Spit Western Spit 



1887-1906 = 690 m 1887-1935 = 660 m 



1906-1935 = 180 m 1935-1953 = -120 m 



1935-1953 = 72 m 1953-1980 = -210 m 

 1953-1980 = 150 m 



42. Using the time interval and the migration within that interval the 

 least squares regression formula was used to find a value for future migration 

 (Y) as a linear function of X(Y=mX+B) 



where ay 2 



m = nl(x y ) = - (Ex ) 



. nl(x.) 



and l 



2 

 Zy.Zx. - xEx.y. 

 J l l i J l 

 b = — 



nz(x.) 2 - (ix.) 2 

 i i' 



33 



