Under extreme storm conditions, the largest velocities of surface 

 currents due to winds in the area are about 1.5 knots. Such strong 

 currents would be due to gales with force of 40 miles per hour, predom- 

 inantly from the northwest. Since the prevailing winds are from the 

 northwest, about 10 months of the year, the net movement of surface 

 water and its suspended material, during these months, would be in a 

 south or southeasterly direction. 



In July and August, when prevailing winds are southeasterly, net 

 movement of surface water and of suspended matter in the upper water layer 

 would be in a north, northeast direction. Such surface flow was confirmed 

 by the SHL drifter studies. 



The layer of water that may be affected by storm winds would be the 

 upper layer, to 50 feet thick. Below that depth, net movement of the 

 water due to subsurface currents may be in any direction and even in a 

 direction opposite to the surface flow. 



(3) General Surface Circulation . General patterns of surface 

 circulation can be obtained inexpensively over a large area by the use 

 of surface drifters. Such a surface drifter study was undertaken by the 

 Sandy Hook Laboratory. 



Surface drift bottles were released intermittently at several points 

 of the Bight (Figure 9) to determine the seasonal and spatial character 

 of the surface currents. Of 1,886 surface drifters released by SHL, 497 

 (26 percent) were recovered. The total percent recovery of surface 

 drifters is illustrated in Figure 12, and the origin of surface drifters 

 recovered on the Long Island and New Jersey shores on Figures 13 and 14. 

 To estimate speed, the SHL study assumed a straight-line course between 

 release and recovery. To estimate time at sea, the duration between re- 

 lease and recovery was used. By this method, changes in the direction 

 of currents were only roughly depicted, and speed could be underestimated. 



The SHL study concluded that there is a general clockwise circulation 

 in the Bight, which was associated with bifurcation at the head of the 

 Hudson Channel. Surface drift patterns suggested strong seasonal sur- 

 face circulation. During winter, surface flow was predominantly south- 

 east, in summer the flow tended northward toward the south coast of 

 Long Island. These results are in agreement with earlier observations 

 of Bumpus and Lauzier (1965) . 



Density patterns derived from temperature-salinity values for a cross 

 section aligned with the axis of the Hudson Channel near Station C where 

 current measurements were obtained, infer according to the SHL study, an 

 estuarine type of circulation. Although not quantitatively definable, 

 according to the SHL study, a landward flow of water near the bottom 

 should occur preferentially in the Hudson Channel region of the Bight. 

 The force driving the estuarine and coastal circulation, according to the 

 SHL study, is the horizontal pressure gradient. 



44 



