material concentrations from near average values to more than 100 mg-l'. There appears to 

 be no relationship between elevated concentrations and wind events (Figure 3-30; C and D), 

 stream flow events (Figure 3-31; B), or municipal outflow data (Figure 3-31; C,D, and E). 

 Wind speeds averaged only 5 m-s', and the mean river discharge is below average at 3 m^-s 

 during this period. However, the dredge was operating in reaches 2, 3, 4, and 5 from 

 October 25 to November 5 when the spikes are most obvious. After November 5, the barge 

 moves outside of the entrance breakwaters to reach 8 (off the definition map in Figure 3-1) 

 during which time the frequency of the spikes decreases dramatically. This suggests that the 

 concentration spikes observed are most likely the result of intrusions of the dredge-induced 

 sediment plume. The spikes are of short duration and tend to occur at times of maximum 

 current velocity, evidence that the suspended material is being advected from a farfield 

 source, as opposed to local resuspension which usually occurs just as tidal currents are 

 increasing, or from sediment settiing at slack water. 



During the latter half of the DAISY deployment period (November 11 to December 7, 

 1993) several major events are recorded in the suspended material concentration data. These 

 disturbances differ substantially in character from those that were observed during the first 

 part of the deployment. In contrast to the short duration, spiky perturbations of the first 

 deployment, the perturbations of the second deployment were longer lived and significantiy 

 larger in amplitude. These events also had a residual effect in that the average background 

 concentrations increased to near 20 mg-l'' (Figure 3-32; A). 



The first sustained event, beginning on November 19, persisted for more than three 

 days and increased concentrations to more than 700 mg-1'. These concentrations exceed the 

 maxima indicated by water samples taken in the vicinity of the operating dredge (Table 3-3). 

 The dredge was working in Reach 5, 1 km south of the DAISY site. We believe this 

 perturbation was not simply the result of dredge-induced resuspension. Even when the barge 

 was operating much closer to the DAISY (Figures 3-6; A, 3-9; A, 3-10; A), resuspension 

 events of this magnitude were not observed in the data (Figure 3-30; A). The dredge did 

 move into Reach 2 on November 21, and may have contributed some amount of material to 

 the final day of the event and possibly slowed the recovery of the system. Again, both the 

 echo sounder and DAISY data indicate that the dredging process is incapable of producing 

 such large amplitude and persistent perturbations at any site removed from the immediate 

 dredging point. A more typical data record would show the sharp short-duration spikes in 

 the suspended material concentrations (as seen in the first part of the deployment), not the 

 long duration, high concentrations records observed here. There is no indication of increased 

 stream flow (Figure 3-31; B) contributing to the suspended material field. However, effluent 

 data from the nearby East Shore Water Pollution Abatement Facility (Figure 1-1) does show 

 a significantly higher discharge of suspended solids (Figure 3-33; C) on November 19, a 

 Friday, which could be the source material for the event. Records are not kept on weekends 

 at the municipal facilities, and it may be that the higher than average effluent flow continued 



Dredged Sediment Dispersion in New Haven Harbor 



