80 



r. S. BUEEAU OF FISHERIES 



The tides around Doboy Island are characterized by the very high 

 velocity of the ebb tide and the rather weak irregular velocities of 

 the flood tide. The highest velocity of the surface current occurs 

 in most cases between three and one-half and four and one-half hours 

 after high water. There is no significant difference between the 

 surface and bottom current. (Fig. 18.) 



30 



20 - 



10 



10 



A.M. 



12 2 



HOUR 



P.M. 



Figure 12. — Salinity and surface currents during the tidal cycle at Doboy 

 Island, July 3, 1928, spring tide 



The time of slack water (zero velocity) is influenced by the stage 

 of the river. On July 3, 1928, and April 24, 1929, it nearly coincided 

 with the time of high and low water. (Figs. 12, 18.) In August 

 1928, Avhen the Altamaha River was approaching flood stage, the zero 

 velocities were observed about two hours after the low water and one 

 and one-half hours before high water (August 16, fig. 14). In all 

 the observations, the velocities of the flood current were rather 



I 



