v r 



v r 



where 



Vr = volume of sediment lost 



E = volume of eroded sediment 

 V n = volume of sediment deposited 



38. The volumes of net sediment lost from Isles Dernieres are presented 

 in Table 3A. These values demonstrate that the percentage of eroded sediment 

 increased from 11 percent (between 1887 and 1935) to 24 percent (between 1953 

 and 1980) — reflecting an increase in the effects of tides on the migration of 

 Isles Dernieres. The annual rates of erosion and sediment loss, shown in Ta- 

 ble 3B, further support the data presented in Table 3A. The amount of eroded 

 sediment lost from Isles Dernieres has remained about the same, but the amount 

 of erosion has been greatly reduced. Thus, the importance of sediment lost by 

 tidal activity has proportionately increased. This trend directly correlates 

 with the evolution of tidal inlets on Isles Dernieres. In 1853, there were no 

 tidal inlets over the entire length of Isles Dernieres; by 1980, there were 

 three. Because these inlets are continuing to widen and deepen, it can be ex- 

 pected that an ever-increasing amount of sediment will be lost in the future. 



39. By combining the data for the annual rates of eroded sediment rede- 

 posited by each of the three processes on a graph, the relative importance of 

 these factors with respect to island migration can be illustrated (Figure 14). 



Table 3 

 Comparison of Total Erosion to Amount of Sediment Lost 

















A. 

 Time 



Total Amount of 

 Eroded Sediment 



10 6 m 3 



Amount of Eroded 



Sediment Lost From 

 c 



n 3 



Percentage of Total 

 Lost from 



Interval 



Isles Dernieres 

 9.1 



10 l 



Isles Dernieres 



1887-1935 



82.1 



11 



1935-1953 



16.1 



2.6 









16 



1953-1980 



19.3 



4.5 









23 



B. 



Amount 



of Sediment 







Amount 



; of Eroded Sediment 





Eroded Annually 









Lost Annually 





• 



I0 6 m 3 









10 6 m 3 



1887-1935 





1.71 





0.19 



1935-1953 





0.89 









0.14 



1953-1980 





0.71 









0.17 



29 



