Figure 

 Island. 



Aerial view of St. Vincent 



aquifer conditions; all fresh water is 

 derived from rainfall. Silty clav 

 sediments at depths between 7.6 and P.? m 

 (25-30 ft) below the sandy surface create 

 an impermeable barrier to separate rain- 

 derived fresh water from the surrounding 

 salt water. There is a shallow lens of 

 fresh water beneath the island. Some of 

 this fresh water, modified by 

 transpiration and evaporation, is 

 eventually discharged into the Gulf and 

 lagoonal marine systems. 



?.2. CLIMATE 



2.2.1. Temperature 



The climate in the Apalachicola basin 

 is mild, with a mean annual temperature of 

 20° C (68° F). Temperature varies with 

 elevation and proximity to the coast. The 

 mean annual number of days with 

 temperatures at or below freezing is 20 at 

 Lake Seminole and 5 along the Gulf Coast 

 (National Oceanic and" Atmospheric 

 Administration, unpublished data; Clewell 

 1°77). Livingston (unpublished 

 manuscript), working with long-term 

 (40-year) climatological data, found that 

 temperatures usually peak in August with 

 lows from December to February, at which 

 time monthly variance is maximal. While 

 peak summer temperatures are similar from 

 year to year, winter minima vary. A time- 

 series (spectral) analysis indicates that 

 there is a long-term period of recurring 

 low winter temperatures of 118 months (P. 8 



Precipitation 



Mean annual rainfall in the 

 Aoalachicola River basin is approximately 

 150 cm (59 inches). There are, however, 

 considerable local differences in monthly 

 precipitation totals. In the Apalachicola 

 delta, areas west of the river receive 

 almost one-third less rainfall than those 

 east of the river (i.e., Tate's Hell 

 Swamp). Rainfall in the Georgia portion 

 of the watershed is 130 cm/yr (51 

 inches/yr). 



The rainfall patterns of Florida and 

 Georgia (Figure 9; Meeter et al. 1979) are 

 basically similar exceot for the timing of 

 rainfall peaks. Georgia rainfall has two 



MONTHS 



Figure 9. Seasonal averages of 

 Apalachicola River flow (Blountstown, 

 Fla.) and rainfall from Columbus, Georgia, 

 and Apalachicola, Florida. Standard 

 deviations (S.D.) are given for selected 

 months (after Meeter et al. 1979). 



11 



