In addition to spatial differ- 

 ences in the tidal structure of the 

 Florida Keys, a temporal pattern 

 also exists (Lloyd 1964). The daily 

 tidal amplitude changes in accor- 

 dance to well known lunar and solar 

 cycles as well as' in response to 

 short-term meterological events, 

 i.e., winter cold fronts and trop- 

 ical storms. The most dramatic 

 change is the storm tide associated 

 with the passage of hurricanes. A 

 combination of the cyclonic motion, 

 slope in the bottom topography, high 

 winds and extremely low atmospheric 

 pressures have resulted in tides 

 4.6 m (15 ft) above mean high water 

 line (Gentry 1974). 



A response unique to the Flor- 

 ida Keys is the tidally forced, 

 cyclic flow of groundwater from one 

 side of the islands to the other. 

 This lateral subsurface flow occurs 

 in response to: (1) the porous 



nature of the Miami and Key Largo 

 Limestone Formations; (2) the solu- 

 tion-cavities characterizing the two 

 formations; (3) the tidal gradients 

 (in some cases) developed from one 

 side to the next; and (4) the narrow 

 physiography of the islands (Gins- 

 burg 1956, Chesher 1974, Enos 1977). 

 In a Key West firewell located near 

 the center of the island and on one 

 of its highest parts, the tidal 

 amplitude is dampened but displays a 

 time lag of only a few minutes 

 (Parker et al. 1955). This indica- 

 tes that water passes fairly quickly 

 betwen the well and the marine re- 

 charge site. Similar results were 

 observed on Big Pine Key, particu- 

 larly during the dry season (Parker 

 et al. 1955, Hanson 1980), and in a 

 number of landlocked canals, lime- 

 stone rock quarries, and solution 

 formed ponds and holes throughout 

 the Florida Keys (Chesher 1974). 

 Keck (1969) and Chesher (1974) exam- 

 ined this tidal response of inland 

 waters and observed a consistent 



relationship between the dampened 

 amplitude (tidal range reduction) 

 and the distance from its marine 

 recharge source. 



The shallow depths, and the 

 open and exposed character of the 

 waters surrounding and permeating 

 the Florida Keys promote an environ- 

 mental setting conducive to wind- 

 driven currents. This relationship 

 between currents and the winds have 

 been well documented in the litera- 

 ture (Griffin 1974, Enos 1977). 

 Currents on a shallow reef bank on 

 the outer shelf margin have been 

 observed to respond rapidly to the 

 wind's direction and velocity over 

 3-day observation periods (Jones 

 1963). Chew (1954) reports that 

 currents off Key West (seaward) 

 correlate well with wind direction 

 but not wind velocity. Enos (1977) 

 observed strong notheast currents 

 for several days near Molasses Reef 

 moving approximately 45° downwind of 

 the prevailing winds and suggests 

 that bottom topography may have 

 channeled the flow or that a 

 spin-off eddy from the Florida 

 Current may have been "blown onto 

 the shelf". 



Other studies that have exam- 

 ined the wind-driven currents in the 

 Florida Keys include: (1) Koczy 

 et al. (1960) and Rehrer et al. 

 (1967) on the current patterns be- 

 tween the Tortugas and Cape Sable; 

 (2) Ball et al. (1967), Perkins and 

 Enos (1968), Gentry (1974), and 

 Warzeski (1976) on the effects of 

 tropical storm winds on the Keys' 

 hydrology; (3) Chesher (1974) and 

 USEPA (1975) on canal responses to 

 winds; and (4) Ginsburg (1956, 1964) 

 and Turney and Perkins (1972) on 

 Florida Bay's response to seasonal 

 winds. The winds driving these cur- 

 rents are primarily derived either 

 singly or in combination from three 

 types of wind force or energy levels 



89 



