several days, represents a very large event, and winds would have needed to be much 

 stronger and of longer duration. Other sources of suspended sediment sufficient to supply 

 the mass needed to produce the large amplitude perturbations may be the additional regional 

 outfalls and CSOs located throughout New Haven Harbor. Data sufficient to quantify the 

 effects of these facilities on the regional suspended material field have been difficult to 

 acquire. It seems reasonable, since all other contributions can be eliminated, that such 

 sources may in fact dominate the observed events; however, the available data do not provide 

 conclusive evidence. 



4.0 DISCUSSION 



The first objective of this field investigation on dredge-induced resuspension was to 

 determine the normal background levels of suspended materials in New Haven Harbor 

 immediately prior to and during the dredging of the navigation channel. The DAISY data 

 indicate that, prior to dredging operations, background concentrations averaged 8 mg-1'. 

 After dredge operations began, short duration spikes on the order of 100 mg-l' were 

 observed, but concentrations decreased to background fairly quickly. Only during the latter 

 half of the deployment, when a number of environmental and anthropogenic factors 

 combined, did the mass of sediment in suspension increase to a point where the background 

 concentrations became consistently and considerably higher (20 mg-l*). 



The second objective was to monitor the plume of materials suspended by dredging 

 operations to determine the spatial extent of the plume and its trajectory relative to the areas 

 identified by the State of Connecticut Department of Environmental Protection as winter 

 flounder spawning areas. The acoustic data obtained during the field surveys document that 

 the sediment suspended by the dredging operations did, at times, migrate outside of the 

 channel into the adjacent shoal areas. Excursions onto the shoals tended to occur during 

 maximum tidal currents, and the plume was more likely to stay within the confines of the 

 channel during early or late ebb tides. Unless the currents were at a maximum, the plumes 

 became patchy, narrow, and difficult to identify within several hundred meters downstream. 

 This is supported by the water sample data which show that concentrations drop fairly 

 quickly away from dredging activity. 



The CTD data indicate that there is a slight decrease in surface salinity at the head of 

 the harbor, and water sample data do indicate considerable freshwater influence in the 

 surface waters immediately adjacent to the municipal outfalls. Elsewhere, the water column 

 is well mixed and vertically homogenous, with minimal salinity or temperature stratification. 

 This suggests that the water column had a negligible effect on the observed vertical 

 distribution of the plume material. Other confounding factors which can influence the 

 horizontal and vertical distribution of the resuspended sediment plume are related to the 

 physical and logistical characteristics of the barge operations. This includes bucket cycle 

 time, bottom sweeping, number of passes at a particular location, and disposal barge 



Dredged Sediment Dispersion in New Haven Harbor 



