EXECUTIVE SUMMARY 



Preliminary evidence of active bed transport at the Cornfield Shoals Disposal Site 

 (CSDS) prompted the National Marine Fisheries Service and the Connecticut Department of 

 Environmental Protection to express concern about possible sediment transport towards, and 

 impact on, shellfish beds located north of the site, north of Long Sand Shoal. This 

 preliminary study was designed to determine if the field-observed transport at the disposal site 

 is consistent with the predicted east- west transport pattern found in the historical record. 



This investigation at CSDS between July 1991 and May 1992 provided strong 

 circumstantial evidence for active bed transport. The study included a series of bathymetric 

 surveys, current meter and suspended sediment data collection, and REMOTS® photography of 

 the sediment-water interface. The circumstantial evidence for active bed transport included 

 shifts in areas of sediment accumulation and erosion, increased suspended sediment 

 concentrations in the bottom waters coupled with high bottom currents, and bedforms and lag 

 deposits at the sediment-water interface. In general, active bed transport appears to follow the 

 historical east- west current direction, and the extent of transport depends on the type of 

 material. The actual direction and magnitude of active bed transport apparently depend on 

 local topography and the nature of materials being transported. 



Sediment accumulated over a broad area near the disposal points of sand hydraulically 

 dredged from the Connecticut River in September 1991. Subsequent bathymetric surveys 

 showed an apparent movement of this material to the west. A clearly defined deposit formed 

 at the disposal point for fine-grained material mechanically dredged from North Cove, 

 Connecticut. This deposit of fine-grained dredged material apparently did not move, but was 

 partially covered by bedload transport of adjacent coarse-grained sediments. 



The present study concluded that: 



The predominant transport direction at the site appears to be east-west. This is 

 supported by current meter deployments and observed erosion and deposition patterns. 



Sediment disposed at the site was not immediately dispersed and was defined within 

 discrete deposits. This was observed for both fine-grained and sandy sediments. 



The dispersion process appears to occur over a period of weeks to months. The 

 dispersion rate for fine-grained materials may be markedly slowed by sand armor that 

 migrates over the more cohesive, less erosive silt-clays. 



The above findings, taken over the ten-month time period, reduce concerns about far-field 

 transport of material over oyster beds to the north. The dispersion of material over a time 

 scale of years, and the effectiveness of the sand armor over the silt-clays, are unknown. 



