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occur to an entire estuarine system, depending on the nature and size 

 of the change. The impact may be temporary, if it is possible to return 

 the environment to its original form, or it may be permanent. 



Any use or activity requiring physical modification of the shoreline, 

 marshes, or bottom of an estuarine system may have a prohibitive 

 impact. Modification of water circulation also tends to be prohibitive 

 when it has any conflicting impact. 



Navigation channel dredging 



This is probably the most widespread and constant permanent 

 modifying activity in the estuarine system. It is carried out solely to 

 maintain and improve navigation needed for commercial and recrea- 

 tional purposes and for national defense. Dredged navigation channels 

 must be kept clear for navigational purposes, and the bottom is 

 constantly being removed. Both of these conditions preclude the large- 

 scale use of such areas for purposes other than navigation. 



The disposal of dredging spoil may also be a prohibitive estuarine use 

 when it is deposited in other parts of the system or on adjacent 

 marshes or land. The destruction of habitat which can result from 

 such disposal will, at a minimum, remove the areas used for productive 

 participation in the estuarine ecosystem. 



The prohibitive impact of navigation dredging may, however, 

 affect an entire system, particularly where a major channel realine- 

 ment or channel deepening occurs. The prohibitive impact of such 

 modification may not be in direct destruction of habitat, but may 

 result from a change in water circulation patterns. 



For example, a change in current structure associated with channel 

 deepening in the James River prevented the upstream transport of 

 oyster spat to the beds where they normally settled and grew to edible 

 size(IV-6-l). ^ 



Such prohibitive use impacts are not always associated with the 

 dredging of navigation channels; in fact, such activities can enhance 

 the environment by improving water circulation and creating new 

 habitat. When there is an impact, however, it is prohibitive in that it 

 permanently excludes other uses while the channel exists. 



Land fits 



The operations of dredging and filling associated with the creation 

 of dry land from marshes and estuarine shallows may have severe 

 prohibitive impact on other estuarine activities. The massive areas 

 ifilled for large residential and industrial developments destroy much 

 of the envronment directly; and, in many cases, the areas involved 

 are large enough to make a significant impact on water circulation 

 and even on the total volume of water in an estuarine system. 



Large fills, such as those made for airports, also limit access to 

 estuarine waters, thereby permanently limiting the recreational 

 potential of such areas. 



Solid Waste Disposal 



The use of undeveloped estuarine shoreline areas for final disposal 

 of garbage and other solid waste materials is not only prohibitive 

 in the same sense as other filling operations, but also the drainage and 

 runoff from such sites can have a severe and continuing impact on 

 water quality. 



