Spillover effects : Proper management of dredging operations is 

 aimed at controlling effects from reintroduction of dredged materials 

 into the water column and the possible release of polluted bottom 

 sediments. Problems associated with dredging are increased water 

 turbidity and the release of large quantities of trapped nutrients, 

 organic materials, and toxic pollutants. The turbidity plume from 

 released material will usually form a visible, elliptical pattern from 

 the dredge or dumping site, as shown in Figure 9. 



Figure 9. Example of a "fugitive" dredge plume with a 

 protective turbidity diaper in place (Source: Reference 36) 



The above conditions are usually temporary, lasting for the period 

 of dredging and a few days after its completion; however, the environmental 

 effects created during the work periods can be of sufficient magnitude to 

 require that steps be taken to eliminate or control their extent. Included 

 in the short-term effects that may be expected are: clogging of gills of 

 aquatic organisms with silt; reduced light penetration; increased release 

 of nutrients; depletion of dissolved oxygen; and resuspension and possible 

 uptake by organisms of heavy metals, pesticides, or other toxic substances. 

 In an attempt to contain turbid water near the dredge site, preventive 

 "silt curtains" or "diapers" have been developed. These floating vertical 

 barriers have been used around both dredging and spoil disposal operations 



89 



