concentrations of total suspended matter in tne water column and 

 acoustic profile observations. A diffusion model allowing 

 prediction of diffusion velocities and spatial variation has been 

 postulated and tested. 



The following relevant observations are taken from a 

 technical paper "SOME OBSERVATIONS ON DREDGED MATERIAL DUMPING IN 

 THE NEW YORf: BIGHT" , by Dr. John Proni and Dr. John Tsai at the 

 NOAA-AOML facility. 



1. Spatial and temporal variation during 

 diffusion following a dump predicts a two- 

 process diffusion with different diffusion 

 velocities and spatial variation. During the 

 active phase, heavy materials settle through 

 gravitation, reaching the bottom. The 

 downward momentum may generate vertical 

 mixing of the water column inside the plume, 

 and resuspension from the bottom. During the 

 passive diffusion phase, the sharp edges of 

 the plume disappear and dissipate into the 

 surrounding water. Rate of diffusion slows 

 down as the particle size distribution 

 changes from coarse heavy material to 

 smaller, lighter particulate matter. This 

 dual diffusion process was clearly observed 

 during the dredged material dump in 

 Massachusetts Bay in February 1983. 



2 . Acoustic backscatter measurements can be 

 correlated with measurements of total 

 suspended matter in the water column as: 



I = Q N 



where I is acoustic intensity, N is the 

 number of particles per unit volume, and a is 

 assumed to depend on particle shape, size, 

 density, compressibility and frequency. 

 Direct and linear relationships are found 

 between observed acoustic intensity and 

 measured total suspended matter. 



In the Rockland Disposal Area study, the following 

 tasks were attempted: 



1. Track and observe the extent of plume 

 dissipation and movement over a period of 

 time following the dump. 



