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AREA DELTA SYSTEM #5 

 DISTANCE FROM COAST 3' 



25 30 35 JO 45 50 55 60 

 CANAL AREA /LAND AREA « 100 (1978) 



Figure 4. Land loss per 7 1/2' quandrangle for the delta system outlined 

 in the map. Canal area is expressed as a percent of the total land area 

 in 1978. This analysis and other examples are provided in detail in 

 Scaife et al . (in press) . 



explanation might be that this relationship is the result of only the direct removal of land 

 by the canal dredging operations, that is, the direct loss. But this is not supported by an 

 analysis of the available data (Figure 6). Canal surface area accounts for less than 10% 

 of the total land loss from 1955 to 1978, though from the I930's to 1958 it amounted to 

 39%. Rather, the relationship must be explained on the basis of indirect impacts. It is 

 probably associated with a combination of the canal, the dredging activity, subsequent 

 use of the canal, and coincidental engineering (such as levees). 



Given these relationships, it is worth examining the present trend in canal area 

 added each year (Figure 7). the Louisiana Department of Natural Resources has records 

 of the canal area it has permitted for the first 105 days of 1981. We prorated that 

 amount for 365 days. Since the actual area of a canal is 1.46 times the permitted area 

 (Johnson and Gosselink 1982), the amount of new canal area added each year is still 

 accelerating. Further, many, but not all, canals widen with age (Craig et al. 1980; 

 Johnson and Gosselink 1982). If the amount of canal area added each year approaches 

 anywhere near a 1% annual widening rate, an area equal to the permitted area should 

 also be added to the 1981 estimate of new canal area. The geometric increase in canal 

 density is thus still occurring. 



79 



