Water and Land Uses:
Agricultural Water and Land Uses

Surface and ground water are used to meet the needs of agricultural producers in Miami-Dade, Broward, and Palm Beach Counties. In Palm Beach County, agricultural users rely on surface water from Lake Okeechobee and canals for the cultivation of sugar cane and other field and row crops in the Everglades Agricultural Area (fig. 1). In this region, the underlying surficial aquifer system contains ground water that is highly mineralized, and the yield to wells is low (Miller, 1988). Regulatory release of surface water from Lake Okeechobee is made to major conveyance canals and agricultural canals including the L-10 borrow canal, Miami Canal, North New River Canal, and Hillsboro Canal (fig. 3). In the Everglades Agricultural Area, growers have developed local canal systems to complement the regional conveyance systems; subirrigation systems are used to maintain desired water levels in fields used for sugar cane and vegetable crops. The same fields are used in rotation with rice crops, which are flooded with surface water during the summer.

In Miami-Dade County, ground water is the principal source of water for irrigation. Water is withdrawn from shallow uncased wells and conveyed using truck-mounted pump and spray irrigation systems. Ground-water levels generally are maintained by closing control structures on the eastern edge of the Everglades Agricultural Area in Miami-Dade County. Most agricultural land in southern Miami-Dade County is used for field and row crops (truck crops), primarily tomatoes and small vegetables.

Figure 21. Workmen cultivating a field of tomatoes near Pompano Beach. Photo courtesy of the Historical Museum of Southern Florida, January 1942.[larger image]

Once considered the Nation's principal source of winter bean, tomato, and pepper crops during the1920s and 1940s, the agricultural industry of Broward County has been largely displaced by residential and urban development (fig. 21). Broward County agricultural producers relied mostly on surface-water supplies between 1945 and 1960, subsequently converting to ground water as a primary source of water for irrigation.

Land-Use Classification

To better understand agricultural water use, the hierarchical Anderson land-use classification system (Anderson and others, 1976) was used in this study to categorize 1953, 1977, 1988, and 1995 agricultural land types from general to specific-use characterizations. Different land-use databases were developed separately with different classification schemes and contain inherent inconsistencies. For example, the 1953 land-use data (Costanza, 1975) were developed as part of an analysis of vegetative changes in the Everglades. Acquired from the USGS Geographic Information Retrieval and Analysis System (GIRAS), 1977 land-cover spatial data were compiled and redefined using aerial photography. The 1988 and 1995 land-use spatial data sets, prepared by the SFWMD, employ different classification schemes, use digital data obtained from county land-use planning maps, and include field and aerial photographic verification. The 1988 and 1995 data sets were classified by SFWMD using its own land-use coding system, patterned after the Florida Land Use and Cover Classification System used by the Florida Department of Transportation (1985).

As part of this analysis, agricultural land-use data were reassembled using Anderson categories in separate spatial data layers and redefined using a standard classification scheme. Where possible, crop types were grouped in the following major categories: improved pasture, sugar cane, citrus groves, grass, container ornamentals, tomatoes, and small vegetables.

Methods Used to Estimate Water Use

Agricultural consumptive water use can be estimated using direct or indirect methods. A direct method requires use of metering devices to accurately assess the amount of water applied to a cultivated field (R.L Marella and V.D. Singleton, U.S. Geological Survey, written commun., 1988). However, most agricultural areas in southeastern Florida are not metered. Therefore, the water-management districts in Florida indirectly estimate agricultural water use on the basis of crop acreage, a use coefficient, and a crop irrigation model (Marella, 1999, p. 4). This indirect methodology was applied for 1953, 1977, 1988, and 1995 and used to develop multicounty spatial and temporal agricultural water-use maps (figs. 22A and 22B). Agricultural water-use estimates in this report may not directly correspond to previous estimates (Marella, 1999) due to the assignment of variables weighed differently herein by the USGS or those by the SFWMD. For purposes of this analysis, agricultural withdrawals were limited to irrigation withdrawals; nonirrigation withdrawals (mostly for livestock purposes) were not estimated.

Figure 22A. Estimated agricultural water use in Miami-Dade, Broward, and Palm Beach Counties during 1953 and 1977. [larger image]

 

Figure 22B. Estimated agricultural water use in Miami-Dade, Broward, and Palm Beach Counties during 1988 and 1995. [larger image]

A modified Blaney-Criddle formulation with crop coefficients is used by three State of Florida water-management districts, including the SFWMD (Jacobs and Satti, 2001), to estimate consumptive crop water use. Consumptive water use includes both losses mostly associated with evapotranspiration but also the small amount of water consumed by incorporation in the plant tissue. For purposes of this report, the modified Blaney-Criddle equation (Blaney and others, 1952) was used to estimate evaporative losses (Jensen and others, 1990). The empirical equation relates rates of evapotranspiration with mean air temperature and mean percentage daytime hours. The original procedure was developed for estimating seasonal evapotranspiration, but later modified to estimate short-period use. Modifications include the use of climatic coefficients directly related to the mean air temperature for consecutive short growing seasons and coefficients that reflect the influence of the crop growth stage on consumptive use rate. Consumptive use rates may vary with temperature, length of day, and available moisture. Additionally, an allocation program was used to calculate a maximum monthly supplemental crop requirement and an average annual supplemental crop requirement using the modified Blaney-Criddle program.

Input data for the modified Blaney-Criddle program include mean rainfall, evapotranspiration, crop type, the number of plantings and plant growth duration (dependent on the crop type), an allocation coefficient, soil type, and the method of irrigation. Rainfall estimates were determined by averaging information from selected cities in Miami-Dade, Broward, and Palm Beach Counties. For example, Belle Glade, Jupiter, and West Palm Beach (fig. 15) were used to estimate precipitation in Palm Beach County. The period of record for mean rainfall in Palm Beach County was 35 years; Broward County (fig. 15, Pompano Beach and Fort Lauderdale) estimates are based on 41 years of record, whereas Miami-Dade County (fig. 15, Hialeah, Miami, and Homestead) includes 46.5 years of rainfall data. Consumptive water use was determined for crop types that include sugar cane, tomato, small vegetable, grass, citrus, and pasture. Tomatoes and small vegetable plants were assumed to be cultivated three times annually, whereas other crop types were considered to have been under cultivation for the entire year. An allocation coefficient was applied to different crop types, and a soil type factor of 0.8 was applied for all crops, except container ornamentals in which a factor of 1.5 was used. In this analysis, it is assumed that a sprinkler irrigation system is used for all crop types. Consumptive water use for specific crop types was estimated by county and used to determine evaporative losses for selected years.

Findings on Agricultural Water Use

Agricultural acreage in Miami-Dade, Broward, and Palm Beach Counties expanded dramatically during the latter half of the 20th century. Areas under cultivation increased from more than 223,000 acres in 1953 to more than 535,000 acres in 1995 (fig. 22B). Completion of the West Palm Beach, Hillsboro, North New River, and Miami Canals by 1921 and construction of a levee along the southern rim of Lake Okeechobee provided opportunities for expansion of cultivated land near the lake, along major canals, and near some coastal areas. Areas under cultivation expanded nearly continuously in both Miami-Dade and Palm Beach Counties between 1953 and 1988 (fig. 22A). Southeastern Florida has experienced a decline in cultivated land since 1988 (fig. 22B); reduction in the agricultural economy of Broward County began in the 1950s largely due to encroachment by urban and residential areas. By the late 1980s, urban and residential development reduced Broward County agriculture to a minor factor in the county economy (Knetsch and Ethridge, 1992). In 1992, powerful winds from Hurricane Andrew swept across the southern Miami-Dade agricultural area, causing widespread damage and a financial loss to the agriculture industry that exceeded $1 billion (Hebert and others,1992; 1993) and contributed further to the regional decline in cultivated lands.

Estimated agricultural water use in the tri-county area increased from about 355 to 979 Mgal/d between 1953 and 1988, respectively, but decreased to about 632 Mgal/d in 1995 (tables 2-5). The greatest increase in consumptive water use occurred in Palm Beach County, paralleling construction of the Everglades Agricultural Area during the latter half of the 1950s and an increase in sugar production in the United States during the 1960s.

Table 2. Estimated agricultural water use in Miami-Dade, Broward, and Palm Beach Counties in 1953 [Click on image for entire table (#2)]

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Table 3. Estimated agricultural water use in Miami-Dade, Broward, and Palm Beach Counties in 1977 [Click on image for entire table (#3)]

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Table 4. Estimated agricultural water use in Miami-Dade, Broward, and Palm Beach Counties in 1988 [Click on image for entire table (#4)]

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Table 5. Estimated agricultural water use in Miami-Dade, Broward, and Palm Beach Counties in 1995 [Click on image for entire table (#5)]

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Mining

Limestone and sand and gravel have been mined in southeastern Florida for construction and road material since the early 1920s (Gunter, 1927). Limestone extraction has played an important role in the westward expansion of urban areas, representing an inexpensive source of building material. The Venetian Pool, listed on the National Register for Historic Places and located in residential Coral Gables (fig. 15), was built in 1924. The public pool is the site of a former quarry used for construction materials during the early development of Coral Gables. By 1953, five companies extracted about 5.9 million tons of limestone in Broward, Miami-Dade, and Palm Beach Counties (Calver, 1957), increasing to 21.3 million tons by 1971.

As early as 1974, the U.S. Bureau of Mines recognized that limited land availability and mineral resource statutory restrictions place mining activities in conflict with urban development. Urban sprawl merely increased demand for crushed rock and construction aggregate at the same time as residential developers competed for the same land resource (Edgerton, 1974). The 89-mi² Lake Belt area in Miami-Dade County has become an area of intense resource competition (figs. 23A and 23B). Located on the eastern margin of the Everglades Shark River Slough historic flow-way, the underlying limestone bedrock is characterized by high transmissivity and location of the largest well field in Florida - the Northwest Well Field (fig. 20). The same area represents the largest source of high-quality construction aggregate used for cement, building, and road material in Florida (Dade County Lake Belt Plan Implementation Committee, 1997). By the close of the 20th century, 35 to 40 million tons of limestone were extracted in northwestern Miami-Dade County on an annual basis (Northwest Dade County Freshwater Lake Plan Implementation Committee, 1997).

Figure 23A. Extent of limestone borrow pit mines in the Lake Belt area in 1963 and 1975. Courtesy of E.A. Swayon, EAS Enginnering, Inc. (written commun., 2003). [larger image]

 

Figure 23B. Extent of limestone borrow pit mines in the Lake Belt area in 1984 and 1992. Courtesy of E.A. Swayon, EAS Enginnering, Inc. (written commun., 2003). [larger image]

Figure 24. Lake Belt limestone borrow-pit mine in Miami-Dade County. Photographs courtesy of the South Florida Water Management District archives. [larger image]

Mining operations in northwestern Miami-Dade County have been active since the 1950s, but their size and extent were comparatively limited until the 1980s (figs. 23A, 23B, and 24). Florida’s 1984 Henderson Wetlands Act recognized that there was substantial economic value in the limestone mineral reserves in Miami-Dade County; although this legislative act was designed to mitigate wetland destruction, it exempted mining in wetland areas bordering Everglades National Park heavily infested with exotic melaleuca trees. Borrow-pit mining is transforming wetland areas into deep quarry lakes, 30 to 80 ft in depth. Proposed expansion of mining operations and the conversion of abandoned quarries to in-ground reservoirs as part of the Everglades restoration have created unresolved public health concerns regarding increased well-field vulnerability to surface-water pathogen contamination, and environmental concerns associated with the potential increase in seepage from water-conservation areas and the nearby Pennsuco wetlands area (figs. 23A and 23B).

During the 1980s and 1990s, limestone extraction methods increased the available urban residential waterfront property through excavation of artificial lakes in western and central Palm Beach and Broward Counties (fig. 25). Residential artificial lakes are largely multipurpose in nature, having served to: (1) provide construction fill for roads, (2) elevate low-lying lands for development in former marginal wetland areas, (3) reduce urban flooding, and (4) help increase land values due to their aesthetic appearance (Frederick and others, 1997). In Palm Beach County, water is pumped from the Hillsboro Canal into Lake Worth Drainage District canals near Boca Raton, in part, to maintain water levels within local community artificial lakes.

Figure 25. Artificial lakes along the Sawgrass Expressway in reclaimed wetland areas adjoining water-conservation areas in Broward County. These artificial lakes have served as a source of artificial fill for residential construction and to capture stormwater runoff. Photographs courtesy of the South Florida Water Management District archives. [larger image]

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