Abstract Introduction Study Area Aquifer Framework and Definitions Transmissivity, Hydraulic Conductivity and Storage Coefficient Hydrogeology - Sediment Hydraulic Conductivity   -  W. Broward Co.   -  Central and E. Broward Co. - Aquifer Delineation > Transmissivity Distribution Ground-Water Flow System Summary References Cited PDF Version

The generalized distribution of transmissivity on the surficial aquifer system of Broward County is shown in figure 38. The lines represent approximate boundaries that separate areas of general ranges of transmissivity. Transmissivity may vary by an order of magnitude within a mapped area and locally may be either less or greater than the range indicated. Therefore, site-specific investigations of transmissivity and the hydrogeology may often be necessary for various potential local uses of the water resource. Values taken into consideration for mapping, selected from those listed in table 2, table 3, and table 4 are shown and are subject to the limitations previously discussed. The mapping emphasized the higher transmissivity values because they are believed to be close to the true transmissivity in that all values may be lower than natural due to well construction or partial penetration. Other information used as mapping guides include the hydrogeologic test drilling results particularly in west and north Broward County, drawdown around well fields, and an attempted aquifer test of the Hallandale well field. Hydraulic data within about 2 miles of the coast are lacking because supply wells are not drilled in the area threatened by saltwater intrusion.

In general, the surficial aquifer system increases in transmissivity from less than 75,000 ft²/ d in north and west Broward County to probably greater than 1,000,000 ft²/d in coastal southeast Broward County. The transition from relatively low to high transmissivity occurs across a narrow east-west trending zone in central Broward County and is more gradual elsewhere. The transmissivity in coastal areas usually exceeds transmissivity in those areas several miles directly inland. In much of east and south-central Broward County, the transmissivity of the surficial aquifer system is about 300,000 ft²/d or more. Most of the transmissivity in that area occurs within the very highly permeable zone of the Biscayne aquifer. In west Broward County, the gray limestone, like the Biscayne aquifer, has significant transmissivity and accounts for most of the transmissivity of the surficial aquifer system along the westernmost and northernmost part of that area.

In southeast Broward County, the high specific capacities from partially penetrating wells at the Hallandale well field (fig. 9), as much as 4,500 (gal/min)/ft, suggest that the transmissivity there may exceed 1,000,000 ft²/d. This is supported by observation of drawdowns of only a few hundredths of a foot in nearby wells for a pumping rate of 2,400 gal/min during an aquifer test (Bearden, 1972, p. 15) that was unsuccessful because of the nominal drawdown, and by the very shallow cone of depression for the well field. High specific capacities and low hydraulic gradients (Bearden, 1974, fig. 11, fig. 12, fig. 13) at the Hollywood and Dania well fields suggest that transmissivity in these areas may also exceed 1,000,000 ft² d. Also, the Hollywood area has at least two highly permeable zones (Bearden, 1974, fig. 7 and p. 10, 30, and 31), and the supply wells are partially penetrating. This area of very high transmissivity may extend as far north as the Snyder Park test drilling site (G-2347, fig. 17 and fig. 22) where thick, extremely porous, and permeable Key Largo Limestone and other permeable lithologies were found.

In northeast Broward County, the transmissivity is less than that in the southeast because the surficial aquifer system contains more sand and less limestone having large cavities. The lowest transmissivities in east or south-central Broward County occur in the northwestern part of east Broward County, west of the Cypress Creek Canal east site and Hillsboro Canal east site (G-2342 and G-2323, respectively). Most of the sediments in that area are sand and shell, commonly with clay or lime mud (fig. 15 and fig. 16).

Available data indicate that transmissivity of the surficial aquifer system may be extremely variable in west Broward County, primarily because of variations within the Biscayne aquifer. Because few tests are available on the Biscayne aquifer in west Broward County (three test sites lie outside the Biscayne aquifer), the mapped pattern (fig. 38) should be used with caution in that area. Very high transmissivity occurs where the Biscayne aquifer has significant open solution-cavity zones. Otherwise, transmissivity on the gray limestone aquifer in the Tamiami Formation may equal or exceed that of the Biscayne aquifer. The Alligator Alley central site (G-2320, fig. 17), cavity zones are either poorly developed or mostly filled with sand, shell, and lime mud. At site G (fig. 11, table 3), a test by the U.S. Army Corps of Engineers in the Biscayne aquifer indicated a comparatively low transmissivity of 110,000 ft²/day. At the Twenty-Six Mile Bend site (G-2312, fig. 20), very little rock with open solution holes exists, and the site is not included in the Biscayne aquifer. The boundary between the area of less than 75,000 ft²/d and that of 75,000 to 150,000 ft²/ d should be regarded as a general trend. It closely approximates the western limit of the Biscayne aquifer shown in figure 36. North and west of that boundary, the limestones of the Fort Thompson Formation are thinner and denser with fewer cavities; therefore, the gray limestone aquifer is likely to have greater transmissivity than the Fort Thompson Formation in that area. The transmissivity of the gray limestone aquifer throughout most of west Broward County probably ranges from 20,000 to 88,000 ft²/d. It is less where the aquifer thins or is absent along the eastern edge of west Broward County.