Long Island Sound is technically described as a co-oscillating 

 tidal basin ( 33) characterized by minimum tidal range and maximum tidal cur- 

 rent at its mouth and maximum tidal range and minimal tidal currents at the 

 almost closed western end. At the eastern passage known as The Race the 

 tidal range is 2.5 feet and the maximum currents are over 5 knots (5.8 mph) . 

 The tide range increases to the west, whereas the current velocities decrease. 



The dominant horizontal motion of the waters of the Sound are the 

 semidiurnal tidal currents. The direction and speed of tidal currents in the 

 upper waters at the time of full moon and under normal weather conditions are 

 shown on tidal current charts prepared by the National Ocean Survey (22) . An 

 example of tidal surface currents at the eastern end of the Sound is shown on 

 Figure 16. While the tidal circulation pattern of the surface and near sur- 

 face waters is well defined relatively little is known about the deep current 

 circulation. 



Tidal currents shown on such charts are subject to modification 

 by nontidal currents due to winds and fresh water inflow from rivers. For 

 example offshore and onshore winds modify the currents along the coast and 

 during periods of very high runoff the fresh water inflow from the Connecticut 

 River creates a distinct plume of lighter and fresher water that moves gener- 

 ally eastward toward Block Island Sound ( 29» 51 » 52). 



10 



20 



30 



60 



go 



100 120 



CENTIMETERS PER SECOND 



140 



160 



Figure 17. Observations of tidal current speed at various depths, 

 ments made at an anchor station in east-central Long Island Sound 

 (Lat 4l°11.9'N, Long. 72°29.^'W) in 1953. After Riley (1956, Fig. 



Measure- 



7) 



39 



