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The Altamaha River in Georgia and the Suwannee River in Georgia and Florida were the major rivers sampled regularly for this study. The Altamaha is an alluvial river and the Suwannee has blackwater and springfed features, as do many rivers in the study area (Berndt and others, 1996). About 80 percent of the 9 million people residing in the study area obtain drinking water from ground water (Marella and Fanning, 1996). Nearly 94 percent of this ground water is from the limestone and dolomite rocks that comprise the Upper Floridan aquifer. In much of the area, the Upper Floridan aquifer is unconfined, contains many karst features (sinkholes, sinking streams, and springs) and is vulnerable to the same land-use effects as the sandy surficial aquifers. |
The Upper Floridian aquifer, the primary drinking-water aquifer, is poorly confined and vulnerable to contamination from the surface in much of the study area. |
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Ground-water/surface-water interaction is an important factor affecting water quality in much of the study area, particularly in the Suwannee River Basin. This area contains numerous springs and other ground-water inputs that supply base flow to the Suwannee River during low flow. The quality of spring water also reflects the drinking-water quality in the Upper Floridan aquifer in areas where it is most vulnerable to contamination from land uses. |
More than one-half of the water used in the study area is ground water; most is used for public supply and irrigation. |
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More than one-half of the study area is forest land used for the production of paper products and lumber (Berndt and others, 1996). Agricultural land covers about 25 percent of the study area. Field crops (including cotton, peanuts, corn, soybeans, and wheat) are grown in the central part of the study area, vegetables are grown throughout, and citrus crops are grown in the southern part of the study area. Dairy and poultry farms are present in northern and central parts of the study area. |
The study area contains large agricultural areas and numerous large urban areas. |
Winter frontal systems that move across the continent affect northern and central parts of the study area. The central and southern parts are subject to subtropical air masses from the Gulf of Mexico and the Atlantic Ocean. Northern Florida receives the most rainfall. The long-term average is about 65 inches per year (in/yr) in Tallahassee, Fla. North-central Georgia (45 in/yr in Macon) and west-central Florida (44 in/yr in Tampa) receive less rain. Rainfall amounts in 1993 and 1995 throughout the study area were below or near the long-term average.
Numerous tropical storms and hurricanes in the summer and fall of 1994 caused very high rainfall in central and southwestern Georgia and northern Florida. These high rainfall amounts were reflected in the river flows in 1994. Flows in the Altamaha and Suwannee Rivers were higher in 1994 than the 30-year mean. In 1994 in the Altamaha River, the highest monthly mean discharge in 30 years was observed for five months (January, July, September, October, and November).
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Rainfall amounts vary from north to south. Tropical storms and hurricanes caused high rainfall in 1994, during the 3 years of the most intensive data collection, 1993-95. Flows in the Altamaha and Suwannee Rivers reflect the varying rainfall amounts in these 3 years.
