these areas are frequent locations of borrow activity. When located on 

 uplands, borrow activity involves stripping away the topsoil followed 

 by excavation and hauling of the underlying material. Borrow areas may 

 be quite large, and upon completion of construction, these areas may be 

 contoured and seeded to minimize erosion. 



Both spoil from channel dredging and unconsolidated marsh muck are 

 often used for embankments because they are cheap, undesirable for other 

 uses, and immediately available. The solid material in dredge spoil 

 is often composed of silt or organic accumulations which may range to 

 well over 90 percent of the solid material. Once built, these organic 

 levees undergo a loss of over 60 percent of their original height. The 

 reductions in height may result from shrinkage, compaction, edge erosion 

 or ground subsidence [161] [162]. Compaction is a major factor affecting 

 levee height [73]. Stresses can produce cracks or even failure, depend- 

 ing on the load added, the depth of the deposit, and the amount of vertical 

 and horizontal variation within the peat [163]. 



To retard erosion and subsequent filling of channels, levees exposed 

 to river or tidewater currents are often riprapped with rock or broken 

 concrete. 



Potential disturbances to coastal systems by dike and levee systems 

 include: (1) elimination of surface waters; (2) lowering of water table; 

 (3) elimination of periodic flooding and fertilization; (4) reduction of 

 groundwater recharge; (5) increased erosion; (6) more streamflow sent 

 downstream as surge; (7) increased or decreased saltwater penetration; 

 and (8) exposure to deforestation, agriculture, construction, and other 

 human use [142]. 



The trend now is toward flood management systems that discourage 

 occupancy of floodprone areas, and control land use and construction in 

 ways that protect life and property without reliance on dikes, levees, 

 and other structures. In general, areas that are flooded every few years 

 should be reserved for uses which do not expose life and property to 

 risk or can withstand periodic flooding. The need for dikes and levees 

 as flood control measures can be reduced by prescribing land uses that 

 retain stormwaters in the watershed. 



Coastal salt marshes are seriously disturbed by modification of the 

 level of the water table or the rate of surface freshwater flow. A 

 levee placed across the upper end of a coastal marsh has the following 

 primary effects: (1) cuts off all tributaries feeding the marsh; (2) 

 prevents freshwater flooding and fertilization, (3) prevents annual 

 flushing, (4) prevents annual renewal of sediments and nutrients, and 

 (5) ends formation of new marshes [142]. 



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