with varying success, since they cease to 

 velocity currents or in cases where there 

 traffic (Figure 10) . 



function in moderate to high 



is wave action from wind or boat 



Figure 10. Concentration of suspended sediments in a plume caused 

 by dredging (Source: Reference 37). 



y 



? M 



Bockground Turbidity 



Outside Edge of Leaking 

 Turbidity Diaper ^ 



Nautical Miles 



Schedule : Dredging may be more adverse at one time of the year than 

 another. Dredging operations along migration routes of fish and other 

 marine animals might be suspended near known nursery areas during periods 

 when the young of a species are passing through critical development stages, 

 Turbidity and poor water quality created by dredging operations usually 

 have a more significant impact on larval and juvenile populations. Timing 

 for dredging restrictions must he developed by knowing the life cycles of 

 the critical species of the ecosystem involved. 



4.1.3 Spoil Disposal 



Spoil is the common term for sediments and other material excavated 

 by dredging a navigation channel. Its disposal may cause economic and 

 environmental problems. In some cases, spoil becomes a resource for 

 shoreline landfill or for mining of aggregate sand and gravel for concrete. 

 Environmental considerations have fostered a new trend away from casual 

 open-water disposal and toward highly engineered land and contained dis- 

 posal [31]. 



90 



