Introduction:

        The DROG3D tracking program was used to track  particles over the stw2 grid (high definition in the area of Stellwagen Bank), whose borders can be seen in the image below.  This grid can be found here.  The drogues were tracked through a period of 31 days and the resulting paths plotted.  The velocity field used was the residual averaged velocities for the period of July/August (M2.vel), which can be found here.

        Launches of particles were made at depths ranging from 1 to 50 meters along the two lines specified (1. across from Cape Elizabeth and 2. across from Cape Neddick).   Launches were also made at depths ranging from 1 to 25 meters for particles located at the GPS coordinates of the Mussel Project Sites.   Two types of tracking were implemented for each launch position.  The first type being fixed depth tracking in which the particles are held at locked vertical positions unless a change is dictated due to restraints imposed by the depth of the water column.  The second type being passive tracking in which particles are allowed to move freely both horizontally and vertically as dictated by the velocity field.  Study of Bathymetry data also revealed a deep trench (> 150 meters) to the norhteast of Cape Ann) so passive tracking was used to estimate the retentive properties of this trench.

Borders of stw2 grid:

 
 
 

Results:

A.)      For the fixed depth particle tracking along line 1 all particles launched at or above depths of 30 meters tend to exit the area in a direct path as can be seen in the example image for a depth of 10m.  At a launch depth of 40 meters this pattern begins to change and paths that indicate a mild degree of possible retainment are observed (see example image).  The pattern of retainment strengthens at a depth of 50 meters (see example image).

Fixed Depth Tracking from launches along line 1 at a depth of 10 meters:

Fixed Depth Tracking from launches along line 1 at a depth of 40 meters:

Fixed Depth Tracking from launches along line 1 at a depth of 50 meters

 
 

B.)      For the passive tracking the same general trend holds.  Launches at depths at or above 30 meters result in particles exiting the area in a direct path (see example image for a 10 meter depth).  Once again, the first signs of retainment occur at a depth of 40 meters and to a more noticable degree than with the fixed depth launches (see example image).  At a depth of 50 meters the degree of retainment becomes quite extreme (see example image).

Passive Tracking from launches along line 1 at a depth of 10 meters:

Passive Tracking from launches along line 1 at a depth of 40 meters:

Passive Tracking from launches along line 1 at a depth of 50 meters:

 
 

C.)     For fixed depth tracking of launches along line 2 most drogue paths indicate a quick exit from the study area for launch depths of less than or equal to 40 meters.  The only exception being what appears to be a little bit of near-shore upwelling (see example image for 10 meter depth).  Then at a depth of 50 meters retentive paths begin to appear (see example image).

Fixed Depth Tracking from launches along line 2 at a depth of 10 meters:

Fixed Depth Tracking from launches along line 2 at a depth of 50 meters:

 
 

D.)     The results for passive tracking of launches along line 2 are similiar to those for fixed depth.  Most drogue paths indicate a quick exit from the study area for launch depths of less than or equal to 40 meters.  Again, the only exception being what appears to be a little bit of near-shore upwelling (see example images for 10 & 20 meter depths).  The retentive paths at the 50 meter depth do not appear as clearly (see example image).

Passive Tracking from launches along line 2 at a depth of 10 meters:

Passive Tracking from launches along line 2 at a depth of 20 meters:

Passive Tracking from launches along line 2 at a depth of 50 meters:

 
 

E.)     For fixed depth tracking of launches at the Mussel Project Sites most drogue paths either run into the shore or exit the study area for launhes at depths of less than or equal to 15 meters (see example image for 10 meters).  Then at a depth of 20 meters drogue paths with a small degree of retentive properties can be observed (see example image).

Fixed Depth Tracking from launches at project sites at a depth of 10 meters:

Fixed Depth Tracking from launches at project sites at a depth of 20 meters:

 
 

F.)     For passive tracking of launches at the Mussel Project Sites most drogue paths exit the study area for launhes at depths of greater than or equal to 5 meters (see example image for 10 meters).  At depths of greater than or equal to 10 meters some drogue paths with possible retentive properties can be observed near shore (see example images for 10 & 15 meter depths).

Passive Tracking from launches at project sites at a depth of 10 meters:

Passive Tracking from launches at project sites at a depth of 15 meters:

 

G.)       There is a deep trench to the north-east of Cape Ann.  The retentive properties of this trench were also tested.  Passive tracking was implemented on particles placed at varying depths in this trench.  It was found that for depths of 130 meters or greater the particles escaped the boundaries of the trench (see example image for 130 meter depth).  For a depth of 140 meters there was partial retention (see example image) and for a depth of 150 meters all particles were retained in the trench (see example image).

Passive Tracking from launches in trench at a depth of 130 meters:

Passive Tracking from launches in trench at a depth of 140 meters:

Passive Tracking from launches in trench at a depth of 150 meters: