Florida Bay exhibits an average 

 range of less than 15 cm (6 in). 

 Table 17 provides tide range values 

 from the shallow slope break to 

 Florida Bay. This reduction occurs 

 quite abruptly just inside the Keys 

 (Enos 1977). 



Table 17. Profiles of tidal ranges 

 from the shallow slope 

 break to the inner shelf 

 (Florida Bay) (adapted 

 from Enos 1977). 



Jones et al. (1973) and Ross 

 (1975) relate the Florida Bay and 

 Atlantic tidal range differences to 

 a tidal height gradient developing 

 between the two environments result- 

 ing in a net water movement from 

 southeast to northwest. Ross (1975) 

 summarizes this dicotomy of reef 

 tract and Florida Bay tidal regimes 

 and their subsequent effect on the 

 Keys' hydrology: 



"Long waves (tides) generated 

 by the passage of astronomical 

 bodies at this latitude tend to lag 

 the time of passage. Thus, high 

 tide at Miami, Florida, high tide at 

 the western extremities of the Gulf 

 of Mexico, say Galveston, Texas, and 



low tide at the eastern extremities 

 of the Gulf of St. Petersburg, Flor- 

 ida, all occur at approximately the 

 same time. This occurs because the 

 tidal wave generated in the Atlantic 

 cannot move into the Gulf around the 

 Keys, and the Gulf of Mexico gives 

 rise to a new tidal wave which meets 

 the Atlantic wave in the Key West 

 area. The tidal wave which moves 

 down the Atlantic side of the Keys 

 has a normal range (height between 

 higher high and lower low, NOAA 

 1977) of approximately 1.5 feet as 

 does the normal tide in the Gulf of 

 Mexico. Florida Bay because of its 

 depth, has a limited response to the 

 astronomical passage and derives its 

 changes in water heights from flows 

 from the Gulf of Mexico and the 

 Atlantic. The result is a normal 

 tidal range of approximately 0.5 

 feet, more in phase with Gulf tides 

 than with Atlantic tides. 



"When tide heights on each side 

 of the Keys are plotted for various 

 locations, it can be seen that a 

 considerable difference in water 

 heights exists from east to west 

 during portions of the tidal cycle. 

 A lesser tidal height difference 

 exists in the west to east portion 

 of the tidal cycle because of the 

 phasing of the tides. As a result, 

 a net flow from east to west is ex- 

 pected through any openings in the 

 northern section (upper keys) of the 

 Florida Keys. The difference in 

 water levels between the two sides 

 of the Keys may be as much as one 

 foot at times in the northern sec- 

 tion, tapering to a fraction of an 

 inch in the lower section, near Key 

 West... . 



"In the southern portion of the 

 Keys very small tide height differ- 

 ences exist. Flow through these 

 bridges is predominantly the result 

 of easterly wind and wave-driven 

 water." 



88 



