22 



was on its side, and data were not obtained; the data from the mid-water meter showed that 

 the mid-day flood velocity was reduced by more than half. The succeeding flood tide current 

 was normal. The near bottom current meter was operational between August 28th and 

 September 26th, and again between October 21st and December 12th. At the end of October 

 1991, a major storm occurred that lasted 114 hours with sustained winds of 40 knots over 

 October 30 and 31. The National Weather Service determined this to be a 100-year storm; 

 therefore, the potential for erosion could have been high. During this "Halloween" storm, 

 the current meters showed no change in current strength, yet change did occur in the net 

 drift. The mid- water drift, normally 305° true, shifted to the west and then south for three 

 days. The near-bottom current net drift, normally 256° true, shifted to the west. The 

 combined effects of the October storm were to produce an offshore displacement in the mid- 

 depth waters, and shoreward displacement of bottom waters, intensifying the rate of 

 upwelling in the area. 



3.3 Suspended Sediment Concentrations 



Background levels of suspended sediment concentrations were measured at 

 approximately 6.5 mg-1 1 prior to the release of dredged material at CSDS on September 12, 

 1991. There was a weak tidal dependence in the background suspended sediment 

 concentrations. With the release of dredged material at buoy A, the background levels of 

 suspended sediment, measured approximately 1 m above the seafloor, increased by an order 

 of magnitude at BTM-A. The initially weak tidal dependence was increased with the advent 

 of dredged material disposal. In addition to the general increase in water column turbidity 

 during dredged material disposal, there were definite peaks during the discrete disposal 

 events (Figure 3-11). 



The background turbidity levels at BTM-A did not increase significantly until three 

 days into the Saybrook Outer Bar disposal. Since the Saybrook Outer Bar contained medium 

 to fine sands, the initial increases in suspended sediment concentrations were due only to 

 discrete disposal events. As material accumulated on the seafloor, background levels 

 increased, presumably due to tidal resuspension and winnowing. Once the material eroded 

 or formed a lag deposit, the background turbidity levels began to decrease. A gradual, but 

 lower magnitude increase in background levels occurred during disposal from the Calves 

 Island Bar and Essex Island Bar projects. However, the amount of the resuspended material 

 in the bottom water decreased, from the Saybrook Outer Bar to the Calves Island Bar and 

 Essex Island Bar projects, as the material became coarser (Bohlen et al. 1992). 



3.4 REMOTS® 



The REMOTS® sediment-profile survey was conducted in May, after the completion 

 of dredged material disposal at CSDS. The REMOTS® photographs detected dredged 

 material at 15 out of 45 stations. Most of these stations were within 400 m of disposal 



Synthesis of Monitoring Surveys at the Cornfield Shoals Disposal Site, July 1991 to May 1992 



