The major activities associated with a navigation improvement 

 project are dredge operations and spoil disposal. A variety of eco- 

 logical disturbances may be associated with dredging and spoil dis- 

 posal within coastal water basins. Habitat alteration has particularly 

 high potential for generating damage to coastal ecosystems and reduc- 

 ing biotic carrying capacity. Major potential ecological effects in- 

 clude: (1) increased turbidity, (2) sediment buildup, (3) reduction of 

 oxygen content, (4) disruption and alteration of especially productive 

 estuarine bottoms and their biota, (5) creation of stagnant deepwater 

 areas, (6) disruption of estuarine circulation and (7) increased upstream 

 intrusion of salt water and sediments. 



4.1 .2 Dredging 



Adverse effects usually can be reduced by the proper choices of 

 location and design of the channel, channel alignment, minimum depth and 

 width dimensions, construction equipment, disposal of spoil, and perform- 

 ance controls on dredges (e.g., silt curtains, choice of season). 



Alignment : The general location of the navigation improvement is 

 usually dictated by selection of the onshore site. Nevertheless, there 

 is considerable opportunity for adjusting the channel alignment to avoid 

 vital habitats and to limit new dredging by using existing natural 

 estuarine channels. This will reduce one of the adverse effects of 

 channel dredging--the direct removal of vital habitat areas. The 

 identification of all vital habitat areas in the water body, therefore, 

 should be done before final channel alignments are decided. Vital areas 

 should not only be avoided but buffer strips around them should be 

 assured. 



Channels dredged too close to the shore in shallow-water areas may 

 result in severe shoreline recession, both from channel slumping and from 

 direct erosion of banks. The presence of a channel may increase the 

 frequency and speed of boat passage thereby increasing the intensity of 

 boat wake and shoreline erosion. In addition, the deepening of the 

 shoreline will decrease the dissipation effect that shallower water bottoms 

 have on incoming waves. 



A major environmental effect associated with dredging in shallow- 

 water areas is disruption of water circulation patterns. The effects are 

 particularly severe when channel cuts are made across low marshes in an 

 attempt to straighten winding creeks and rivers. A common effect is 

 sedimentation of cut-off "oxbows". 



Saltwater intrusion can be caused by dredging channels up shallow 

 tributary rivers or into wetlands (shorelands dredging is discussed in 

 Subproject 7). The resulting chemical and physical changes in the water 



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