EXECUTIVE SUMMARY 



Maintenance dredging involving the removal of 840,000 yd^ from the New Haven 

 Harbor main navigational channel took place between October 1993 and January 1994. 

 Concern about the transport and fate of the resuspended sediments resulting from the 

 dredging operations was expressed by the State of Connecticut's Department of 

 Environmental Protection (DEP). The problem centered on the shallow water areas flanking 

 the navigation channel which had been identified as winter flounder spawning grounds. An 

 agreement was reached wherein field surveys, using an acoustic echo sounder, would be 

 conducted while the dredge was operating. Additionally, a bottom-mounted instrument 

 array, recording suspended sediment concentrations and other hydrographic parameters, 

 would be deployed near the site of the flounder spawning grounds. This monitoring of the 

 dredged sediment plume would provide a case history for future reference. 



The two major objectives of the study were to 1) establish what the background 

 suspended sediment concentration is before and after dredging, and 2) document the 

 movement of the dredge plume relative to fishery resource areas such as winter flounder 

 spawning grounds. 



The results of the acoustic surveys revealed that the dredge-induced sediment plume 

 did protrude into the shoal areas to the east and west of the main navigation channel. These 

 excursions onto the shoals occurred only when the dredge was in the immediate vicinity. 

 The DAISY, which was deployed on the eastern edge of the winter flounder spawning area, 

 also showed elevated suspended material concentrations attributable to the dredge operating 

 in the upper reaches of the harbor. The time series of DAISY data showed numerous 

 aperiodic short duration spikes of approximately 100 mg-l'^ The observed concentrations 

 were an order of magnitude larger than the predredging background concentrations. 

 However, in the last half of the deployment, while the dredge was located well south of the 

 DAISY site, there were several long duration (1-3 days), very high concentration 

 perturbations. During these events concentrations reached 700 mg-1"* which could not be 

 related to dredging operations. Evidence from meteorological data and sewage effluent 

 records indicate that these events are likely a result of winds and wind-generated waves, 

 alone or in combination with, discharges from wastewater treatment plant outfalls. 



Based on these findings, dredge-induced sediment resuspension is a minor 

 perturbation relative to the much longer duration, larger amplitude events associated with 

 wind, wind waves, and effluent discharges from outfalls. The effects of dredging related 

 spikes in suspended sediment on the winter flounder spawning grounds, and the regional 

 water quality in general appear limited in duration and of relatively low amplitude. 



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