SEMIDIURNAL 



ONE TIDAL DAY 



MIXED 



ONE TIDAL DAY 



Distance* Phase Difference (min) Range (cm) 



Tide Prediction (km) High Tide Low Tide Mean Spring 



MEAN LOW WATER 



I 



Figure 38. Schematic of mixed 



and semidiurnal tides 

 (adapted from NOAA 

 1977). 



Figure 39. 



Delineation of tide 

 types in the Florida 

 Keys (adapted from 

 NOAA 1977). 



Channel) and west (Pine Channel) 

 sides of Big Pine Key. According to 

 Enos (1977) this phase difference in 

 tide crests through the length of 

 the reef tract, between Fowey Rocks 

 and Sand Key (Table 16), is of equal 

 or greater importance than the am- 



* Distance from Fowey Rocks measured along the reef arc, approximately at 

 the 18 m (60 ft) contour. 



t Fowey Rocks is near Miami; Sand Key is near Key West. Times are minutes 

 later than Fowey Rocks. Based on Tide Tables (ESSA 1967). 



§ These times are predicted relative to Key West Tides which bear no simple 

 relationship to Miami tides. They are referred to Miami times by estimating 

 an average phase difference of 2 hr. between Miami and Key West tides. 

 Actual daily differences vary between 1 and 3 hr. 



Table 16. Tidal ranges along 



the shallow slope break 

 (adapted from Enos 1977) 



plitude reduction. He observes that 

 the "...theoretical delay in twice- 

 daily tide crests between points 

 separated by about 1°45' longitude 

 would be 3 1/2 min. The actual 

 delay of more than an hour is pre- 

 sumably caused by friction intro- 

 duced by the topography of the 

 Florida Plateau and must involve 

 translation of water masses. This 

 tide-induced water movement is sug- 

 gested as a mechanism for a weak 

 counter-current southwestward along 

 the south Florida shelf margin". 



The Keys' tidal pattern is made 

 more complex by the effect of the 

 upper Keys physical alignment which 

 virtually blocks all direct inter- 

 action between Florida Bay and the 

 seaward reef tract, creating two 

 very distinct environments within a 

 few miles of each other (Ginsburg 

 1956, Marszalek et al. 1977). In 

 contrast to the tidal ranges report- 

 ed along the outer reef (Table 16), 

 the more restricted eastern part of 



87 



