results from dredging in aquatic and 

 wetland habitats. Spoil material is 

 commonly piled adjacent to the dredged 

 site where it rises above the sur- 

 rounding natural landscape and is called 

 a spoil bank. The distribution of this 

 habitat within the MDPR is illustrated 

 in Figure 36. 



Spoil banks are highly variable, 

 depending on such factors as age, sedi- 

 ment type, dredging method, elevation, 

 and location. For example, hydrauli- 

 cally dredged sediment that is high in 

 clay may remain fluid for a long time, 

 while bucket-dredged sediment from an 

 organic rich area may be relatively 

 consolidated. Hydraulically dredged 

 sediment will spread out unless con- 

 tained by a dike, while bucket-dredged 

 sediment may initially remain in place 

 without being confined. All uncon- 

 strained spoil will inevitably slump and 

 spread out to some extent, blanketing a 

 surface area of wetland much larger than 

 the area dredged. Thus, the dredging of 

 canals in wetlands creates spoil banks 

 that are three or more times greater in 

 area than the canal from which the spoil 

 was removed . 



A typical spoil bank in the MDPR is 

 a linear structure resulting from the 

 construction of an oil well access 

 canal, a pipeline canal, or a navigation 

 canal (Figure 37). A new spoil bank may 

 initially rise as much as three meters 

 (10 ft) above the surrounding wetland 

 elevation, with a width of 30 m (100 ft) 

 (Monte 1978). Most older spoil banks 

 from oil access canals are lower, aver- 

 aging perhaps 1 m. 



Monte (1978) estimated that over 

 200,000 ha (494,000 acres) of spoil bank 

 habitat existed in wetland regions of 

 Louisiana at the time of her study. 

 Estimates from the MDPR habitat mapping 

 study (Table 5) indicate the presence of 

 about 33,600 ha (83,000 acres) of spoil 

 habitat in the MDPR in 1978, but this 

 may be an underestimate because of the 

 difficulty of measuring the area of 

 spoil banks from aerial imagery. 



Spoil area is rapidly increasing. 

 For example, Louisiana receives about 



2,200 permit applications yearly for 

 various wetland modifications. The 

 majority of the requests come from 

 Terrebonne, Plaquemines, Lafourche, 

 Jefferson, and St. Bernard Parishes. 

 During 1981, 70% of all petroleum- 

 related dredging permit requests in- 

 volved saline and brackish marsh and 

 estuarine open water habitats (Louisiana 

 Department of Natural Resources 1982) . 

 Most of these projects create spoil 

 banks, although many pipeline canals are 

 Dackfilled after the pipe is laid. 



The vegetation on wetland spoil 

 banks usually follows a pattern of suc- 

 cession toward typically upland plant 

 communities (Monte 1978). In salt 

 marshes, the high soil salt content of 

 newly created spoil banks retards colo- 

 nization by plants other than salt marsh 

 cordgrass. After several years as 

 leaching decreases the spoil salt con- 

 tent, the bank becomes dominated by salt 

 meadow grass. A ten year old spoil bank 

 contains little salt and is dominated by 

 shrubs such as eastern silverling and 

 marsh elder. After 30 years, salt marsh 

 spoil banks contain trees up to 25 cm 

 (9.8 inches) diameter, including tooth- 

 ache trees and hackberry. Sixty-four 

 percent of the plant species found on 

 thirty-year-old salt marsh spoil banks 

 are typical of upland rather than marsh 

 habitats. 



Succession on brackish marsh spoil 

 banks follows a similar pattern, but 

 lower initial soil salt content allows 

 more rapid colonization by upland spe- 

 cies. Thirty-year-old brackish marsh 

 spoil banks are typically dominated by 

 hackberry, toothache tree, chinaberry 

 ( Melia azedarach ) , and black willow, up 

 to 10 m (33 ft) in height. Seventy-one 

 percent of the plant species found are 

 typical of upland rather than wetland 

 habitats (Monte 1978). 



Fresh marsh and swamp spoil bank 

 succession proceeds even faster because 

 of the absence of soil salts, and be- 

 cause seed sources are closer. Ten- 

 year-old spoil is often vegetated by 

 such bottomland hardwood species as 

 cottonwood ( Populus deltoides ) , red 

 maple ( Acer rubrum ) , black willow ( Salix 



78 



