Table 1. Canal area expressed as a percentage of land area in the 

 deltaic plain in 1955 and 1978 for each of seven hydrological units, 

 Data from Wicker (1980). 



redistribution of sediments is greatest near the coast, particularly for the fine-grained 

 sediments of the delta tip (Coleman 1976). 



We therefore assigned a delta age based on Frazier's (1967) maps and a distance to 

 the coast for each mapping unit. Land loss was higher nearer the coast in younger delta 

 substrates. But within groups of similar soils, the same pattern emerged: (I) land loss 

 rate was directly related to canal density, and (2) land loss rate was very near zero 

 when canal density was zero. An example of the analysis is shown in Figure 4. The only 

 exception was the Atchafalaya delta where land building is occuring. The direct 

 relationship otherwise holds for land areas both near and far from major sediment 

 sources. Proportionally, more land is lost per canal in younger rather than older deltas, 

 and in areas nearer the coast. New "holes" or ponds in the marsh also appear in 

 association with canals and away from natural channels (Figure 5). 



A summary of our present linear regression analyses of canal density vs. land loss 

 rates is in Table 2. There is a consistent pattern within similar substrate types, among 

 hydrological units, and across the coast for the three survey intervals since 1890. 

 Further, the estimate of the land loss that would occur at zero canal density ranges from 

 10% of the present total land loss rate to a net gain. The average "intercept estimate" 

 of the three methods, (A, B, and C in Table 2) is almost exactly the same as the 

 historical average land increase we might expect, judging from the 7,000-year history of 

 land building in the coastal zone. 



Put another way, the indication is that canal densities, since 1890, are high where 

 land loss is high and near zero where land loss is zero (except for the Atchafalaya delta 

 region) for areas with a variety of substrates and of varying distances from the coast. 

 The slopes of the regression lines vary with delta age and distance to the coast. One 



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