US Department of the Interior
US Geological Survey
WRI 87-4034

>Abstract Introduction Study Area Aquifer Framework and Definitions Transmissivity, Hydraulic Conductivity and Storage Coefficient Hydrogeology Ground-Water Flow System Summary References Cited PDF Version

An investigation of the surficial aquifer system in Broward County, begun in 1981, is part of a regional study of the aquifer system in southeast Florida. Test drilling for lithologic samples, flow measurements taken during drilling, aquifer testing, and analyses of previously available data permitted delineation of the permeability framework (on geologic sections), the aquifers in the system and the generalized transmissivity distribution, and interpretation of the ground-water flow system.

The surficial aquifer system, in which an unconfined ground-water flow system exists, comprises the sediments from land surface to the top of a regionally persistent zone of low permeability called the intermediate confining unit. The aquifer system materials vary from clays to cavernous limestone in composition. These sediments are grouped as the Biscayne aquifer at the top; an intervening semiconfining unit primarily of clayey sand; a gray limestone aquifer in the Tamiami Formation (west Broward County); and sand or clayey sand near the base of the surficial aquifer system. The depth of the base of the aquifer system ranges from about 160 feet below land surface in westernmost Broward County to more than 350 feet near the coast. These drilling and aquifer- test data indicate a complex permeability framework. Hydraulic conductivities of the very highly permeable zone of the Biscayne aquifer exceed 10,000 feet per day in places; in the gray limestone aquifer, they range from 590 to 930 feet per day, except in a less-permeable upper zone of the aquifer that occurs primarily in northwesternmost Broward County.

Transmissivities of the surficial aquifer system vary locally but have a definite areal trend. Estimated values are generally about 300,000 square feet per day or more in the southeast, south- central, and part of coastal northeast Broward County. Transmissivity is lower to the north and west, decreasing to less than 75,000 square feet per day over a large area in northwest and north- central Broward County. High transmissivity generally is associated with the Biscayne aquifer. The gray limestone aquifer has transmissivities that range from about 20,000 to 88,000 square feet per day in west Broward County. The transition from high transmissivity to relatively low transmissivity is often only a few miles wide and coincides with the decrease of cavernous porosity and associated permeability in the Fort Thompson Formation or the Anastasia formation.

Ground-water circulation in Broward County must be considered in either predevelopment or development conditions because of changes in hydrologic factors that control flow. Effective canal drainage and large-scale pumping from municipal well fields have greatly altered the predevelopment flow system in east Broward County by: (1) eliminating a coastal ground-water ridge; (2) reducing deep circulation and reducing or eliminating seasonal westward movement of ground water; and (3) causing accelerated stormwater runoff and short ground-water flow paths, generally lowering the water table, and inducing saltwater intrusion. In west Broward County, hydrologic and permeability framework evidence suggests that water entered the gray limestone aquifer by lateral movement from Hendry, Collier, and Palm Beach Counties, and by downward seepage from the Everglades and the Biscayne aquifer during predevelopment times, and moved southward into Dade County to coastal discharge areas. Depth profiles of specific conductance and chloride support the interpreted movement in west Broward County. Circulation in the Biscayne aquifer inland was also primarily to the south. Little change in the predevelopment ground-water flow system has occurred in west Broward County compared to east Broward County.

Chemical concentrations and water temperature are given in metric units. Chemical concentration is given in milligrams per liter (mg/L) or micrograms (µg/L). Milligrams per liter is a unit expressing the concentration of chemical constituents in solution as weight (milligrams) of solute per unit volume (liter) of water. One thousand micrograms per liter is equivalent to one milligram per liter. For concentrations less than 7,000 mg/L, the numerical value is the same as for concentrations in parts per million.

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD 1929) -- a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called "Mean Sea Level of 1929."

The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

Related links:

Hydrogeology of the Surficial Aquifer System, Dade County, Florida (Water Resources Investigations Report 90-4108)