Introduction (SS of Dade, Florida)

By Chris V. Noble, Robert W. Drew, and James D. Slabaugh, Natural Resources Conservation Service

United States Department of Agriculture, Natural Resources Conservation Service,
in cooperation with
University of Florida, Institute of Food and Agricultural Sciences, Agricultural Experiment Stations, and Soil Science Department; Florida Department of Agriculture and Consumer Services; and Florida Department of Transportation

 

This survey area is in the extreme southeast part of Florida. It is bordered on the north by Broward County, on the west mainly by the Everglades National Park, on the east by the Atlantic Ocean, and on the south by Biscayne Bay.

Figure 1.—Location of Dade County area in Florida.

The survey area makes up 621,080 acres, or about 970 square miles. Miami, the county seat, is in the north-eastern part of the survey area, on the west shore of Biscayne Bay.

The economy of the survey area is fairly well diversified. Because of the money generated by tourism and retirement living, the Miami area and adjacent coastal areas are known as the "Gold Coast." The leading industries or economic activities include construction, real state, housing, recreation, the service trades, sports events, motion picture and television filming, transportation, manufacturing, limestone mining, and cement production.

Miami is one of Florida's principal deep-water ports. Commercial and sport fishing and agricultural crops, including such major cash crops as citrus, vegetables, and special tropical fruits and vegetables, are important to the economy. Ornamental nursery plants, for indoor and outdoor landscaping, have surpassed citrus and surgarcane as the major cash crops in Florida.

General Nature of the Survey Area

This section describes the environmental and cultural factors that affect the use and management of soils in the survey area. These factors are climate, history and development, geomorphology, geology, hydrogeology, and transportation facilities.

Climate

This survey area has a subtropical marine climate characterized by long, warm, rainy summers and mild, dry winters. Temperatures are moderated by the Atlantic Ocean and Gulf Stream, but the moderating effects quickly diminish inland. Table 1 gives data on temperature and precipitation for the survey area as recorded at the Miami International Airport. In winter, the average temperature is 68 degrees F and the average daily minimum temperature is 60 degrees. The lowest temperature on record, which occurred in December 1934, is 26 degrees. In summer, the average temperature is 82 degrees and the average daily maximum temperature is 89 degrees. The highest recorded temperature, which occurred in July 1942, is 100 degrees.

Frosts occur about once a year. Killing frosts occurred in February 1917, December and January 1917 and 1918, January 1928, December 1934, January 1940, January and February 1958, December 1962, and January 1970, 1977, and 1981 (23).

Rainfall varies greatly from place to place during the year and on a yearly basis. The total annual precipitation is approximately 57.6 inches. Of this, 10.6 inches, or about 18 percent, usually falls in the period November through March. The growing season for most vegetable crops is included in this period. The heaviest one-day rainfall during the period of record was 16 inches in April 1979. Thunderstorms occur about 74 days each year, and most occur in late afternoon (22).

Hurricanes occasionally strike the survey area, especially in September and October. Damaging hurricanes occurred in October 1906, September 1926, November 1935, September 1945 and 1947, October 1950, September 1960, August 1964, and September 1965 (22).

The average relative humidity in midafternoon is about 74 percent. Humidity is higher at dawn, when the average is about 84 percent. The sun shines 78 percent of the time possible in summer and 66 percent in winter. The prevailing wind is from the east-southeast.

History and Development

Tekesta Indians were the first known permanent settlers in the survey area. They were encountered by Ponce de Leon in 1513. They were nonagricultural and lived by hunting, fishing, and trading with other tribes and later with the Spanish. Their numbers were greatly reduced by disease and by warfare with the Creek Indians. The final 80 families moved to Cuba with the Spanish in 1763. The survey area evidently was completely depopulated (9). It came under the control of England in 1763. In that year, Spain again was given control of Florida. The Creek Indians, who later became the Seminoles of north Florida, were known to hunt in the Everglades and make raids as far south as Key West, but they were not permanent settlers until after the Tekesta Indians moved to Cuba. By 1830, the Seminoles had taken over and absorbed any remaining tribes. Florida became part of the United States in 1821.

In 1808, the Spanish Government granted John Egan 100 acres of land along the Miami River, in an where Miami is now located. Richard Fitzpatrick established a cotton plantation along the Miami River. Early settlers grew oranges, lemons, limes, bananas, coconuts, and grapes (4).

On July 2, 1838, Congress granted one township near present-day Cutler to Dr. Henry Perrine for the purpose of introducing purely tropical plants and trees to south Florida. In 1847, Dr. Perrine was killed by Seminole Indians before his project was implemented (4).

Dade County was established on February 4, 1836. The present boundaries were established after the formation of Palm Beach County in 1909 and Broward County in 1915. The first county seat was on Indian Key, which was the most important settlement. In 1844, the county seat was moved to Miami. In 1889, it was moved to June. In 1900, it was moved back to Miami. The county was named in honor of Major Francis L. Dade, who along with his troops was killed by Seminoles near what is now Bushnell, Florida, in 1835 (4).

The population of the county began to grow after the Homestead Act of 1866. By 1870, small settlements were established in Biscayne, Lemon City, Ft. Dallas (Miami), Coconut Grove, and Cutler. The settlers supported themselves through hunting, fishing, farming, and making starch from Florida arrowroot. Development was hindered because the only way in or out was by boat. In 1896, Henry Flagler extended a railroad into Miami. By 1900, the population had grown to 5,000. In 1915, Dixie Highway, which linked Miami with the rest of the country, was completed.

Construction of water-control structures, which began in 1906 and continues to the present, has allowed farming and urban development in areas in the Everglades that originally were too wet for these uses. A period of large-scale land development and increasing population occurred in the county from 1920 through 1926. The takeover of Cuba by Fidel Castro in 1959 triggered the migration of 500,000 people to the county. The addition of the Mariel Refugees in 1980 also increased the population of the county.

Geomorphology

Richard A. Johnson, Florida Geological Survey, Bureau of Geology, Department of Natural Resources, helped prepare this section and the sections "Geology" and "Hydrogeology".

This survey area is on the southeastern peninsula of Florida, in the southern or distal zone. The area is divided into the Everglades Trough, the Atlantic Coastal Ridge (Miami Ridge), the Southern Slope, and the Gulf Coastal Lagoons (fig. 2).

Figure 2.—Geomorphological areas of Dade County. (gif, 23 KB)

Most of the northern and western parts of the survey area are made up of the Everglades Trough. This trough formed when dissolution of the underlying limestone lowered the land surface to below the water table.

The Miami Ridge is the southern extension of the Atlantic Coastal Ridge, which extends along the eastern Atlantic shore of Florida south from the vicinity of Jacksonville. The Miami Ridge is along most of the eastern coast of the survey area. In this area, it is made up of oolitic limestone, which formed as a broad, low shoal under warm, shallow marine water during a period of higher Pleistocene sea level, beginning about 2 million years ago. Because of tidal action, swales cut into the top of the ridge generally have a northwest-southwest orientation. A wave-cut cliff, or scarp, formed along the southeast edge of the ridge during a period of higher sea level. This cliff has been called the Silver Bluff Scarp (12).

On aerial photographs the Southern Slope shows a parallel pattern of drainage within an area that generally is covered by water. The apparent parallelism is caused by the coalescence of small islands of trees into linear strings of vegetation. Two small areas of Gulf Coastal Lagoons are between the Southern Slope and Florida Bay to the south. These lagoons are more typical of the southwest coast of Florida and barely extend into the survey area at this location.

Geology

The sediments of south Florida are dominated by limestone and dolostone. The survey area is underlain by at least 11,800 feet of these carbonate sediments (3). Only the section of rocks normally encountered when water wells are drilled, generally to a depth of less than 200 feet, is considered in the following discussion of geology. A geological cross section of the survey area is shown in figure 3.

Figure 3.—A geological cross section of Dade County area. (gif, 27 KB)

The Hawthorn Group (undifferentiated) consists of interbedded sand, silt, clay, dolostone, and limestone. All of the lithological components are interbedded and intermixed. This group is intermixed throughout with phosphate, generally in the form of sand-sized grains. In this survey area the top of the group consists of sand and clay (13) and forms the base of the Biscayne aquifer. The lower part of the group consists of soft or hard, sandy, phosphatic dolostone or limestone. The group attains a thickness of more than 900 feet in the survey area (14). The upper part of the group acts as a confining unit for the Floridan aquifer system, which yields water to flowing wells in the survey area but is not used because the water is saline.

In some areas the Hawthorn Group is overlain by a thin layer of limy sand containing scattered phosphate grains and small quantities of shell material. This bed is probably equivalent to the Tamiami Formation, but not much information is available concerning this formation in this survey area. Where it occurs in the survey area, it probably forms the base of the Biscayne aquifer.

The Caloosahatchee Formation may occur as scattered remnants as much as 25 feet thick in the survey area, but little definite information is available concerning the occurrence of this formation in the area. The formation consists of shells, sand, and some limestone and sandstone.

The Fort Thompson Formation, which consists of interbedded limestone, sand, and shells, is one of the most productive units within the Biscayne aquifer. It averages 50 to 70 feet in thickness and thickens to the east, as shown in figure 3 (13). It typically consists of alternating freshwater and marine sediments, which generally are permeable. The limestone beds in the Fort Thompson Formation can be cavernous and interconnected, thus providing channels through which water can flow.

The Anastasia Formation, a sandy, shelly limestone unit, extends along the Atlantic coast more 150 miles to the north of this survey area. Although it does not occur at the surface anywhere in the survey area, it forms a major part of the Biscayne aquifer in coastal areas, where it is much as 120 feet thick (13). This unit typically has beds of marine limestone, consisting mainly of cemented whole and broken shells (coquina). These beds are extremely permeable. Because they are relatively close to the surface and in close proximity to the ocean, however, the water contained in them can be saline (10).

Key Largo Limestone merges laterally with the Anastasia Formation and with Miami Limestone in the southern and east-central parts of the survey area (13). This formation is at the surface throughout the upper keys, but in this survey area it is generally below the surface. It consists of hard limestone derived from coral, algae, and some shells. It is as much as 60 feet thick in the survey area (13). It is essentially a fossil reef, which formed during a period of higher Pleistocene sea level. It typically is very porous and is a very prolific water-producing part of the Biscayne aquifer (13).

Miami Limestone is at or near the surface in almost all of the survey area. This formation is a soft, oolitic limestone that is generally less than 40 feet thick (12). It characteristically contains large quantities of ooliths, which are small, spherical particles formed when calcite or aragonite was deposited in concentric layers around a nucleus of some type. Miami Limestone is considered to be a part of the Biscayne aquifer. It is a good source of water, although it yields less water than the underlying formations and does so less easily.

Limestone is the primary mineral resource in the survey area. It is mined from below water level by draglines in at least 31 pits (5). Most of the pits are mined for Miami Limestone. Some of the pits in the north-central part of the survey area, however, are mined for material similar to Tamiami Limestone, which is at the surface in Collier County, along the Tamiami Trail. The limestone is used as a source of base material for roads, in the manufacture of cement products, and in a variety of other ways.

Hydrogeology

The Biscayne aquifer of the surficial aquifer system provides copious quantities of water to wells in the survey area. It extends from the surficial material near or at the surface to a depth of almost 200 feet in the northeast corner of the county (13). The base of the aquifer is generally considered to be the deepest porous limestone bed in the section above the relatively impermeable sand, silt, and clay of the Hawthorn Group or "tight" sand in the Tamiami Formation (13). The water in the aquifer begins as rainfall, which percolates into the sand or limestone at the surface and flows by gravity below the water table, where it can be tapped by wells. Most wells that are not municipal or commercial are less than 100 feet deep and have casing that extends from the surface to below the water table. Many commercial or municipal wells are 100 to 200 feet deep. The lower part of all the wells is left uncased in the limestone or shell beds. The water is derived from these beds. The formations that make up the Biscayne aquifer are identified in the section "Geology."

Because of relatively low elevations throughout the survey area and a close proximity to the ocean, salty ocean water moving into canals toward the west can infiltrate the Biscayne aquifer during dry periods, when the amount of rainfall is low. The upward flow of saline water toward the surface and evaporation at the surface can cause contamination of the soil by salt in agricultural areas and elsewhere (10).

Transportation Facilities

This survey area is served by several major highways. U.S. Highway 1 runs in a north-south direction in the eastern part of the survey area. It is the only highway that runs the entire length of the county. Highway A1A connects the barrier islands. U.S. Interstate 95 runs in a north-south direction, merging with U.S. Highway 1 in Miami. The Homestead Extension of the Florida Turnpike runs in a north-south direction near the center of the survey area. It connects with U.S. Highway 1 near Florida City. Okeechobee Road (U.S. Highway 27) runs in a northwest-southeast direction, connecting Miami with the Homestead Extension and with Krome Avenue (County Road 997). Krome Avenue runs in a north-south direction from the Homestead Extension to near the north end of the county. It is the westernmost through road. Tamiami Trail (U.S. Highway 41) runs in an east-west direction. It is the only road that runs across the entire width of the county. State Road 9 extends from U.S. Highway 1 north into Broward County. U.S. Highway 441 parallels U.S. Interstate 95 north into Broward County.

Miami is served by a complex urban loop highway system, a commuter rail, and a bus system. Seven bridges connect the barrier islands with the mainland. The Port of Miami receives goods from and ships them to areas throughout the world. The port also serves as a point of departure for many cruise ships.

Two railroad lines serve the survey area. Amtrack service is available from Miami. Access to the Intracoastal Waterway and the Atlantic Ocean is readily available. Miami International Airport is a major metropolitan airport. It provides direct flights to many parts of the world. Other commercial airports include Homestead General Aviation Airport, New Tamiami Airport, Opa-Locka Airport, and Opa-Locka West Airport. The survey area has many private landing fields.

How This Survey Was Made

This soil survey updates the survey of Dade County published in 1958 (18). It describes the soils to a greater depth than the previous survey. Many of the soil and map unit names have been changed because of new information. Though some soil boundaries have been readjusted, most are essentially the same as those in the original survey.

Soil scientists made this survey to learn what soils are in the survey area, where they are, and how they can be used. They observed the steepness, length, and shape of slopes; the size of streams and the general pattern of drainage; and the kinds of native plants or crops. They dug many holes to study the soil profile, which is the sequence of natural layers, or horizons, in a soil. The profile extends from the surface down into the parent material, which has been changed very little by leaching or by plant roots.

The soil scientists recorded the characteristics of the profiles that they studied and compared those profiles with others in nearby counties and in more distant places. They classified and named the soils according to uniform nationwide procedures. They drew the boundaries of the soils on aerial photographs. These photographs show trees, buildings, fields, roads, and other details that help in drawing boundaries accurately. The soil maps at the back of this publication were prepared from aerial photographs.

The areas shown on a soil map are called map units. Most map units are made up of one kind of soil. Some are made up of two or more kinds. The map units in this survey area are described under the headings "General Soil Map Units" and "Detailed Soil Map Units."

While a soil survey is in progress, samples of some soils are taken for laboratory measurements and for engineering tests. The characteristics of all the soils are determined through field tests. Interpretations of those characteristics may be modified during the survey. Data are assembled from other sources, such as test results, records, field experience, and State and local specialists. For example, data on crop yields under defined management are assembled from farm records and from field or plot experiments on the same kinds of soil.

Only part of a soil survey is done when the soils have been named, described, interpreted, and delineated on aerial photographs and when the laboratory data and other data have been assembled. The mass of detailed information then should be organized so that it can be used by farmers, woodland managers, engineers, planners, developers and builders, home buyers, and others.

Soil Classification and Soil Mapping

After describing the soils in a survey area and measuring or characterizing their properties, soil scientists systematically classify the soils into taxonomic classes that have a specified range of characteristics. The system of taxonomic classification used for soils in the United States, described in "Soil Taxonomy" (19), has categories that are based mainly on the kind and character of soil properties and the arrangement of soil horizons within the profile. Once the individual soils in a survey area are classified, they can be compared and correlated with similar soils in the same taxonomic class that have been recognized in other areas.

Soils occur on the landscape in an orderly pattern that is related to the geology, the landforms, and the vegetation. Each kind of soil is associated with a particular kind of landscape or with a segment of the landscape. By observing the soils in the survey area and relating their position to specific segments of the landscape, the soil scientists can evolve a concept, or model, of how the soils formed. During mapping, this model enables the soil scientists to predict with a considerable degree of accuracy the location of specific soils on the landscape.

Individual soils on the landscape commonly merge into one another as their characteristics gradually change. To construct an accurate soil map, the soil scientists must determine the boundaries between the soils. They can observe only a limited number of soil profiles. Compared to the whole three-dimensional soil volume, the areas examined are little more than points. These few observations, however, supplemented by an understanding of the soil-landscape relationship, are sufficient to verify predictions of the kinds of soil in an area and to determine the boundaries. The delineated map units are based on inferences derived from this small sample.

A ground-penetrating radar (GPR) system and hand transects were used to document the type and variability of the soils occurring in the map units (7, 8, 11, 15). The GPR system was used successfully on all soils to measure the depth to and determine the variability of major soil horizons or other soil features. In this survey area 133 random transects were made by GPR or by hand. Information from notes and ground-truth observations made in the field were as used, along with radar data, to classify the soils and to determine the composition of map units. The map units described in the section "Detailed Soil Map Units" are based on these data and on data in the survey published in 1958.

Soil Variability and Map Unit Composition

A map unit delineation on a soil map represents an area dominated by one major kind of soil or an area dominated by two or three kinds of soil. A map unit is identified and named according to the taxonomic classification of the dominant soil or soils. Within a taxonomic class there are precisely defined limits for the properties of the soils. On the landscape, however, the soils are natural objects. In common with other natural objects, they have a characteristic variability in their properties. Thus, the range of some observed properties may extend beyond the limits defined for a taxonomic class. Areas of soils of a single taxonomic class rarely, if ever, can be mapped without including areas of soils of other taxonomic classes. These areas of differing soils are called inclusions.

Most inclusions have properties and behavioral patterns similar to those of the dominant soil or soils in the map unit, and thus they do not affect use and management. These are referred to as similar inclusions. Their properties are noted in the description of the dominant soil or soils. Some inclusions have properties and behavior different enough to affect use or require different management. They genarally occupy small areas and cannot be shown separately on the soil maps because of the scale used in mapping. The dissimilar inclusions are mentioned in the map unit descriptions. A few inclusions may not have been observed and consequently are not mentioned in the descriptions, especially where the soil pattern was so complex that it was impractical to make enough observations to identify all of the kinds of soil on the landscape.

The presence of inclusions in a map unit in no way diminishes the usefulness or accuracy of the soil data. The objective of soil mapping is not to delineate pure taxonomic classes of soils but rather to separate the landscape into segments that have similar use and management requirements. The delineation of such landscape segments on the map provides sufficient information for the development of resource plans, but onsite investigation is needed to plan for intensive uses in small areas.

Confidence Limits of Soil Survey Information

Predictions about soil behavior are based not only on soil properties but also on such variables as climate and biological activity. Soil conditions are predictable over long periods, but they are not so predictable from year to year. For example, soil scientists can predict with a fairy high degree of accuracy that a given soil will have a high water table within certain depths in most years, but they cannot assure that a high water table will always be at a specific level in the soil on a specific date.

Confidence limits in soil surveys are statistical expressions of the probability that a soil property or the composition of a map unit will vary within prescribed limits. These limits can be assigned numerical values based on a random sample. In the absence of specific data for determining confidence limits, the natural variability of soils and the way soil surveys are made must be considered. The composition of map units and other information are derived largely from extrapolations made from a small sample. Also, information about the soils does not extend below a depth of about 6 feet. The information in the soil survey is not meant to be used as a substitute for onsite investigation. Soil survey information can be used to select from among alternative practices or general designs that may be needed to minimize the possibility of soil-related failures. It cannot be used to interpret specific points on the landscape.

Specific confidence limits for the composition of map units in this survey area were determined by random transects made by ground-penetrating radar or by hand across mapped areas. The data are given in the description of each soil under the heading "Detailed Soil Map Units." Soil scientists made enough transects and took enough samples to characterize each map unit at a specific confidence level. For example, map unit 40 was characterized at a 95 percent confidence level based on transect data. The composition is described as follows: "On 95 percent of the acreage mapped as Pomello sand, Pomello and similar soils make up 98 to 99 percent of the mapped areas." On the other 5 percent of the acreage, the percentage of Pomello and similar soils may be higher than 99 percent or lower than 98 percent.

The composition of some map of the units in this survey area, such as Urban land and other miscellaneous areas, was determined on the basis of the judgment of the soil scientist rather than by a statistical procedure.

< Back to Table of Contents