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Publication #FE757

Florida's Water Resources1

Tatiana Borisova and Roy R. Carriker2

Introduction

Water is important to Floridians for household uses, to industry for cooling and processing, to agriculture for irrigation, and to recreationists for boating and swimming. Water sustains wildlife and is an integral part of Florida's environment. Total freshwater withdrawals from ground and surface water sources have been high (Marella 2014), causing many Floridians to pay closer attention to plans for further development of water supplies. A better understanding of Florida's water resources is a first step toward assuring adequate future freshwater supplies.

The Hydrologic Cycle

Where does water come from? How much water is available? These questions pertain to the fundamental nature of water as it "cycles" through the environment. The continual circulation/distribution of water on the surface of the land, in the ground, and in the atmosphere is referred to as the "hydrologic cycle" or "water cycle." There are five basic processes in the hydrologic cycle: 1) condensation, 2) precipitation, 3) infiltration, 4) runoff, and 5) evapotranspiration (Figure 1). These processes can occur at the same time and, except for precipitation, continuously.

Figure 1. 

Water cycle (Source: SWFWMD).


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Condensation occurs as moist air cools. The cooling water vapor at first forms tiny droplets that cling to dust particles in the air and then forms clouds or fog. As the droplets increase in size, they gain weight, causing them to fall as rain (or as snow, hail, or sleet, depending upon conditions). When raindrops or snowflakes fall, the second stage of the hydrologic cycle, precipitation, has started. Rainfall varies in amounts and in intensity from one season to another and from one region to another. Differences in rainfall patterns result from general differences in climate across time and space. When rainfall reaches the Earth's surface, it can do one of three things: 1) enter the ground (infiltration), 2) collect into surface streams and lakes (runoff), or 3) return to the atmosphere as water vapor (evapotranspiration). The phases of runoff and infiltration are highly interrelated and are influenced by the form of precipitation, the type and amount of vegetation upon which the precipitation falls, topography, and permeability of the soil.

When water infiltrates the soil, it first enters the surface zone where it can be absorbed by plant roots. Some soil types (e.g., sandy soils) do not retain water readily. When this is the case, the water quickly percolates (seeps) downward until it encounters a stratum (zone) where the pores in the soil or rocks are saturated. Water in this zone of saturation is called groundwater. Underground layers of porous material that are saturated with water are called aquifers. The water level can rise and fall in shallow or surface aquifers, depending upon local rainfall conditions. When a shallow groundwater aquifer is underlain by a stratum of low permeability called an aquiclude, water is forced to move laterally through the aquifer and emerge into a surface stream or lake. On the other hand, when groundwater levels are low, water may flow in the opposite direction – from surface streams and lakes into the shallow aquifer.

Sometimes freshwater exists deep underground in "confined aquifers," so-called because the water-bearing aquifer is confined below a stratum of low permeability. A confined aquifer can sometimes hold water under sufficient pressure such that water will rise above the confining layer when a tightly cased well penetrates the aquiclude. These are known as "artesian aquifers." When tapped, they sometimes produce free-flowing artesian wells. Naturally occurring springs also result from this same phenomenon.

Water enters the aquifer through recharge areas which are zones where the water-bearing stratum emerges at the surface or where the confining layer is broken up by faults or natural sinkholes that allow downward infiltration of water. Recharge areas may be some distance away from the spring or well that is fed by the aquifer.

Water that does not enter the ground collects in rivers and streams, comprising the runoff phase of the hydrologic cycle. This water evaporates, percolates into the ground, or flows out to sea. Some of the surface water is tapped as a water supply for agricultural, residential, or industrial use.

An additional stage of the hydrologic cycle is evapotranspiration. "Evaporation" is the process by which water is changed into its gaseous form (water vapor). "Transpiration" is the process whereby moisture in plants is returned to the atmosphere through plant leaves. To prevent wilting, plants must absorb water through their roots to replenish water lost through evapotranspiration.

Florida's Hydrologic Cycle

This overview of Florida's water resources is organized with reference to the hydrologic cycle. Describing the resource in this fashion provides a sense of where the water is at any point in time and a perception of how much water is accessible in each phase of the hydrologic cycle.

Rainfall

Florida receives an average of 54 inches of rainfall per year. For comparison, rainfall averages 30 inches per year for the nation as a whole, and only 10 inches per year in Nevada (NOAA 2014a). Total rainfall for Florida varies from one part of the state to another, from one season of the year to another, and from one year to the next.

Florida's highest mean annual rainfall occurs in the Panhandle (in northwestern Florida) and in West Palm Beach (in southeastern Florida), with averages exceeding 60 inches per year. The Pensacola, Tallahassee, and West Palm Beach weather stations are listed among the 10 "wettest" stations in the nation, with 30-year average precipitation of 64 inches, 63 inches, and 61 inches per year, respectively (NOAA 2014b). In contrast, the Florida Keys receive on average 47 inches of rainfall annually, and Tampa (in southwestern Florida) receives approximately 48 inches per year (NOAA 2014a).

Seasonal variations in rainfall are evident. Traditionally, summer is the wettest season in Florida, with more than half of the annual rainfall occurring during the June to September "wet season" (Figure 2). However, this pattern of seasonal precipitation varies. And while precipitation during the wet season is always greater than that during the dry season (December to March), the difference is much more significant in South Florida, compared with the Panhandle.

Figure 2. 

Average monthly precipitation, Jan 1895 to Dec 2013 [Florida Climate Center (2014)]


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Annual variations in rainfall can be extreme. For example, in 1927, annual rainfall in Florida measured about 41 inches while, in 1947, it measured almost 73 inches (FSU). Extremes in annual rainfall have been recorded for various regions of the state, and are responsible for the drought conditions of some years and the periods of frequent flooding in other years.

Tropical storms are normal in Florida, with some delivering over 10 inches of rainfall during a 24-hour period, which usually causes flooding. The highest estimated rainfall of almost 39 inches in 24 hours was in Yankeetown (in west-central Florida) during Hurricane Easy in 1950. The official measured state record rainfall was approximately 23 inches within a 24-hour period (Hurricane Jeanne in 1980) (Florida Climate Center 2014).

Flow characteristics of streams, groundwater recharge, and levels of lakes and reservoirs are all functions of the amount and intensity of rainfall. Plans for water supply development and flood control must take into account short- and long-term variations in rainfall volume.

Evapotranspiration

Evapotranspiration is the sum of evaporation and transpiration. Generally, evaporation is the process by which water is changed into its gaseous form (water vapor). Part of the rainfall evaporates from the land surface back to the atmosphere. The potential for evaporation from an area depends upon atmospheric conditions such as temperature and wind speed. Evaporation is also affected by factors such as soil permeability, the type and amount of vegetative ground cover, and slope of the land. For example, evaporation is relatively low in parts of northwestern Florida. This area is well-drained and, compared with other parts of Florida, has steep slopes. Much of the area is covered by permeable soils that readily pass rainfall into a shallow aquifer. An aquiclude (impermeable ground layer) underlying the shallow aquifer in this area ensures that most of the rainfall appears in streams. On the other hand, for portions of extreme southern Florida, where topography is flat and drainage is poor, water is readily available for evaporation.

In turn, transpiration is the process whereby moisture in plants is returned to the atmosphere through plant leaves. Water that the plants rely on is usually part of the rainfall that infiltrates the soil from the surface (of course, people can supplement rainfall with irrigation).

A water deficiency exists when potential evapotranspiration (i.e., evaporation plus the moisture demand by plants) exceeds actual evapotranspiration (i.e., soil moisture that is actually available for evaporation and the plants to use). Monthly climatic water budgets indicate that in Key West, water deficiency persists throughout the year, while in the Panhandle, a deficit rarely happens. In the rest of the state, deficiencies are common in winter and spring.

Surface Runoff, and Groundwater Infilitration, and Discharge

Surface runoff is rainfall that runs over the landscape, usually reaching streams, lakes, or the ocean. Some of the rainfall can infiltrate the ground and reach groundwater aquifers. In turn, groundwater can run close to the surface and then discharge (e.g., to feed springs, streams, rivers, or lakes), or it can move vertically, into the deeper land layers (sometimes referred to as groundwater storage). Surface runoff, as well as groundwater infiltration and discharge rates, depend on land cover, soils, and weather conditions.

Florida's Rivers

Surface runoff and groundwater discharge feed several major streams and rivers. Of Florida's five largest streams, four are in the drainage basins of northern Florida. They are the Apalachicola, Suwannee, Choctawhatchee, and Escambia Rivers. The fifth largest stream is the St. Johns River that flows north from headwaters near Vero Beach to the Atlantic Ocean at Jacksonville in northern Florida.

The largest of Florida's streams is the Apalachicola River (Figure 3). Its headwater is located in Georgia, north of Atlanta, but the stream receives its name only at the Georgia-Florida line, at the confluence of the Flint and Chattahoochee Rivers. The Apalachicola River drains 17,200 square miles in Alabama and Georgia, and 2,400 square miles in Florida. From 1978 to 2012, mean discharge of the river at Sumatra (a midpoint of river length in Florida) was 24,000 cubic feet per second (or 15 billion gallons per day), with a variation between approximately 10,000 and 37,000 cubic feet per second (or from 6 billion to 24 billion gallons per day) (USGS 2014a).

Figure 3. 

Apalachicola Watershed (USDA 2007)


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The Suwannee River (Florida's second-largest river) drains about 11,000 square miles from its headwaters in southern Georgia to its mouth at the Gulf of Mexico (Figure 4). At the measuring station in Wilcox (33 miles above the mouth), the river discharges about 10,000 cubic feet per second (6 billion gallons per day, average for 1930–2013). The variation is between 3,000 and 25,000 cubic feet per second (or from 2 billion to 16 billion gallons per day) (USGS 2014b). The Santa Fe River flows into the Suwannee River, as do a number of springs, such as Troy, Ichetucknee, Fanning, and Manatee.

Figure 4. 

Suwannee River Watershed (USDA 2007)


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The Choctawhatchee River (Florida's third-largest river) drains 3,100 square miles in southeastern Alabama and 1,500 square miles in Florida (Figure 5). Choctawhatchee Bay opens to the Gulf of Mexico in the vicinity of Fort Walton Beach and Niceville. At the measurement station near Bruce, 21 miles above the river's mouth, average discharge is about 7,000 cubic feet per second (more than 4 billion gallons per day, average for 1931–2013). The variation is between 3,000 and 12,000 cubic feet per second (or from 2 billion to 8 billion gallons per day) (USGS 2014c).

Figure 5. 

Choctawhatchee River Watershed (USDA 2007)


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The Escambia River and its tributaries (Figure 6) drain 3,760 square miles in Alabama and 425 square miles in Florida before flowing into Pensacola Bay at a rate of almost 7,000 cubic feet per second (more than 4,000 million gallons per day, measured near Molino, FL, in 1988–2013) (USGS 2014d).

Figure 6. 

Escambia River Watershed (USDA 2007)


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The St. Johns River drains about 9,400 square miles from marshes west of Vero Beach to its mouth at the Atlantic Ocean in Jacksonville (Figure 7). It is one of the few rivers in the United States that flows north. At the mouth, near Jacksonville, flow is about 7,000 cubic feet per second (more than 4 billion million gallons per day, an average for 1970–2011) (USGS 2014e). The St. Johns River connects seven major lakes, from Lake Washington to Lake George. Its tributary, the Oklawaha River, connects nine lakes, from Lake Apopka to Lake Lochloosa.

Figure 7. 

St. Johns River Watershed (USDA 2007)


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Other significant streams include the Kissimmee River (with headwaters near Orlando, flowing south down the center of the Florida Peninsula, and emptying into Lake Okeechobee), the Peace River (that flows into Charlotte Harbor), and the Withlacoochee River (that flows to the northwest from an area called the Green Swamp in Polk, Sumter, and Lake Counties, and emptying into the Gulf of Mexico near Yankeetown). In addition, the St. Lucie Canal connects Lake Okeechobee to the Atlantic Ocean near Stuart, and the Caloosahatchee Canal and River connect Lake Okeechobee with the Gulf of Mexico near Fort Myers. Together, these two canals form a navigable cross-state waterway. Other canals from Lake Okeechobee to the Atlantic Ocean are the Hillsboro, North New River, Miami, and West Palm Beach Canals (Fernald and Purdum 1998).

The streams, rivers, springs, and lakes produced by the runoff phase of Florida's hydrologic cycle are familiar to Floridians as water supply sources, recreational attractions, transportation routes, and havens for the state's abundant fish and wildlife populations. Closely related to Florida's surface water systems, but much more important as a source of water supply, are Florida's major groundwater systems.

Principal Aquifers in Florida

Florida has several prolific aquifers that yield large quantities of water to wells, streams, lakes, and some of the world's largest springs (Figure 8). The principal source of groundwater for most of the state is the Floridan aquifer—the source of the municipal water supply for the cities of Tallahassee, Jacksonville, Gainesville, Orlando, Daytona Beach, Tampa, and St. Petersburg. It also yields water to thousands of domestic, industrial, and irrigation wells throughout the state.

Figure 8. 

Florida's aquifers (FDEP 2007)


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Thick layers of porous limestone of the Floridan aquifer underlie all of the state, although in South Florida the water it contains is too highly mineralized (salty) to be usable. Except in those areas where its limestone formations break the surface of the ground, the Floridan aquifer underlies several hundred feet of sediment, including thick beds of relatively impermeable material that restrict upward movement of the water. This restriction causes the aquifer to have artesian pressure. Water in the Floridan aquifer is replenished by rainfall in central and northern Florida, where the aquifer emerges at the surface or is covered by permeable materials, or where the confining material is broken up by sinkholes.

The non-artesian Biscayne aquifer underlies an area of about 3,000 square miles in Dade, Broward, and Palm Beach Counties on Florida's lower east coast. Water in the Biscayne aquifer is derived chiefly from local rainfall and, during dry periods, from canals ultimately linked to Lake Okeechobee. The Biscayne aquifer is an important water supply for lower east coast Florida cities.

A non-artesian, sand-and-gravel aquifer is the major source of groundwater in the extreme western part of the Florida Panhandle. Water in the sand-and-gravel aquifer is derived chiefly from local rainfall and is of good chemical quality. Wells tapping this aquifer furnish most of the groundwater used in Escambia and Santa Rosa Counties, and part of Okaloosa County.

A shallow, non-artesian surficial aquifer is present across much of the state, but in most areas it is not an important source of groundwater because a better supply is available from deeper aquifers. However, in rural areas where residential water requirements are relatively smaller by comparison to other areas, this aquifer is tapped by small-diameter wells. The water in this shallow aquifer is derived primarily from local rainfall. For more information about Florida aquifers, see FDEP (2007).

Salt Water Intrusion

Florida's geography as a peninsula between two bodies of salt water creates the potential for salt water intrusion into the fresh groundwater supply. Salt water is denser than freshwater and exerts a constant pressure to permeate the porous aquifers. As long as freshwater levels in the aquifers are above sea level, the freshwater pressure keeps salt water from moving inland and upward into the aquifers. For example, the level of water flowing through south Florida's coastal canals is generally several feet above sea level, which is enough to prevent ocean water from moving inland and upward into the aquifer. However, if during dry periods the freshwater levels in canals without locks and dams fall to or below sea level, this would allow salt water to move upward in the canals.

In some places, excessively pumping a well can increase salt water intrusion. If water is pumped at a rate faster than the aquifer is replenished, the pressure of freshwater over salt water in the land mass is decreased. This decrease may cause the level of the saltwater-freshwater interface to rise in the aquifer, degrading water quality. This problem must be controlled by careful attention to well location and pumping rates. The problem of saltwater intrusion is aggravated by drought periods when there is not enough rainfall to replenish the freshwater aquifers.

Florida's Springs

There are over 700 springs in Florida, including more than 30 first-magnitude springs with an average flow of over 100 cubic feet per second (64.6 million gallons per day). There are also about 200 second-magnitude springs, with average flow between 10 and 100 cubic feet per second (6.46 million to 64.6 million gallons per day) (Scott et al. 2006). Spring water emerges from cavities in the porous limestone of the Floridan aquifer and mixes with the water in streams and lakes. The Floridan aquifer is replenished by rainfall across northern and central Florida, southern Alabama, and southern Georgia.

Summary

A description of Florida's water resources is usefully organized in terms of the hydrologic cycle. Since the cost and feasibility of making water supplies available for municipal, agricultural, and industrial uses is determined to a great extent by the patterns of rainfall, runoff, and infiltration over time and space, it is important that Florida citizens become familiar with the water cycle.

References

Ackermann, W.C., E.A. Colman, and H.O. Ogrosky (editors). 1955. Where we get our water. Water: The Yearbook of Agriculture. Washington. D.C.: The United States Government Printing Office.

Fernald E.A. and E.D. Purdum (editors). 1998. Water Atlas of Florida. Tallahassee, FL: Institute of Science and Public Affairs, Florida State University.

Florida Department of Environmental Protection (FDEP). 2007. Aquifers. Florida Department of Environmental Protection, Last updated: January 03, 2007, Accessed on November 3, 2014. http://www.dep.state.fl.us/swapp/aquifer.asp#

Florida Climate Center. 2014a. Precipitation. Florida Climate Center, Florida State University Center for Ocean-Atmospheric Prediction Studies, 2000 Levy Avenue, Room 241, Building A, Tallahassee, FL 32306-2741. http://climatecenter.fsu.edu/products-services/data/statewide-averages/precipitation (accessed on November 3, 2014).

Florida Climate Center. 2014b. Hurricanes. Florida Climate Center, Florida State University Center for Ocean-Atmospheric Prediction Studies, 2000 Levy Avenue, Room 241, Building A, Tallahassee, FL 32306-2741. http://climatecenter.fsu.edu/products-services/data/statewide-averages/precipitation (accessed on November 3, 2014).

Marella, R., 2014. Water withdrawals, use, and trends in Florida, 2010. U. S. Geological Survey Scientific Investigations Report 2014-5088, 59 p. SIR 2014-5088. http://pubs.usgs.gov/sir/2014/5088/

McCann, A. 2006. Groundwater Movement and Protection. URI Home*A*Syst. The University of Rhode Island. http://www.uri.edu/ce/wq/has/Private%20Wells/GROUNDWATER.htm . Accessed on November 3, 2014.

National Oceanic and Atmospheric Association (NOAA). 2014a. Climate at a Glance. http://www.ncdc.noaa.gov/cag/. Accessed on November 3, 2014.

National Oceanic and Atmospheric Association (NOAA). 2014b. Extremes in U.S. Climate. NOAA National Climatic Data Center, http://www.ncdc.noaa.gov/extremes/extreme-us-climates.php .Last updated on January 16, 2008. Accessed on Oct. 31. 2014.

Scott T.M., G.H. Means, R.P. Meegan, R.C. Means, S.B. Upchurch, R.E. Copeland, J. Jones, T. Roberts, and A. Willet. 2006. Springs of Florida. Bulletin Number 66. Florida Department of Environmental Protection, Tallahassee, FL. http://www.dep.state.fl.us/geology/geologictopics/springs/bulletin66.htm

USGS. 2014a. Surface-Water Annual Statistics for Florida. USGS 02359170 Apalachicola River Nr Sumatra, Fla. http://waterdata.usgs.gov/fl/nwis/annual/?referred_module=sw&site_no=02359170&por_02359170_1=2396790,00060,1,1978,2014&year_type=C&format=html_table&date_format=YYYY-MM-DD&rdb_compression=file&submitted_form=parameter_selection_list

USGS. 2014b. Surface-Water Annual Statistics for Florida. USGS 02323500 Suwannee River Near Wilcox, Fla. http://waterdata.usgs.gov/nwis/annual?site_no=02323500&agency_cd=USGS&por_02323500_7=2396494,00060,7,1931,2013&year_type=W&referred_module=sw&format=rdb

USGS. 2014c. Surface-Water Annual Statistics for Florida. USGS 02366500 Choctawhatchee River Nr Bruce, Fla. http://waterdata.usgs.gov/fl/nwis/annual?site_no=02366500&agency_cd=USGS&por_02366500_2=2396875,00060,2,1931,2014&year_type=W&referred_module=sw&format=rdb

USGS. 2014d. Surface-Water Annual Statistics for Florida. 02376033 Escambia River Nr Molino, Fla. http://waterdata.usgs.gov/fl/nwis/annual?site_no=02376033&agency_cd=USGS&por_02376033_1=2396992,00060,1,1984,2014&year_type=W&referred_module=sw&format=rdb

USGS. 2014e. Surface-Water Annual Statistics for Florida. USGS 02246500 St. Johns River at Jacksonville, FL. http://waterdata.usgs.gov/fl/nwis/dv?cb_00060=on&format=rdb&site_no=02246500&referred_module=sw&period=&begin_date=1971-10-01&end_date=2014-11-02

U.S. Geological Service (USGS). 2007. EDNA Derived Watersheds for Major Named Rivers. KML Watershed Index. Last modified June 19, 2007. Accessed on November 3, 2014. http://edna.usgs.gov/watersheds/kml_index.htm

Footnotes

1.

This document is FE757, one of a series of the Food and Resource Economics Department, UF/IFAS Extension. Original publication date December 2008 as a major revision of WQ101. Revised November 2014. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Tatkiana Boriosva, assistant professor, and Roy R. Carriker, emeritus professor, Food and Resource Economics Department, UF/IFAS Extension, Gainesville, FL.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.