Geology topics

Research about Miami-Dade County, Florida

Source-linked reports with geographic coverage including Miami-Dade County, Florida.

23 records · Page 2Linked to original sources

USGS1990

Vegetative changes in a wetland in the vicinity of a well field, Dade County, Florida

Plant communities present in 1978 and 1986 were analyzed at 250 random points on stereoscopic pairs of aerial photographs for four study sites in the vicinity of the Northwest Well Field in Dade County, Florida. Sites NW and NE lie northwest of the well field beyond the cone of depression. Site SW lies in the outer part of the cone, and site SE lies within the cone of depression. Relative frequency values for several plant types including herbs, shrubs-small trees, and trees were analyzed by the Heterogeneity G-test to determine heterogeneity among sites in 1978 and 1986. In 1978, all four sites were dominated by plant communities having herbs, shrubs, or a mixture thereof. The communities at sites NW and NE were similar, and those at SE and SW were somewhat similar. In 1986, sites NW, NE, and SE were dominated by a mixture of shrubs and trees. Only at site SW was the relative frequency of occurrence of herbaceous plants still high. At each site, there was a decrease in herbaceous vegetation and an increase in woody vegetation during this period, with the increase in trees being greatest at site SE. Time between the start of the well-field operation in May 1983 and the January 1986 photographs was insufficient to allow determination of any direct effects of the well field on the vegetation. Ground-level observations in 1987 and 1988 indicate a trend toward continued increase in dominance of woody plants and a decrease in herbaceous wetland vegetation. Development of a forest of the exotic pest tree melaleuca is occurring at all four sites, but especially at site SE. Vegetative changes between 1978 and 1986 are attributed to an invasion of the exotic species melaleuca, a shortened hydroperiod, and natural succession within the plant communities.

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USGS1988

Effects of two stormwater management methods on the quality of water in the upper Biscayne aquifer at two commercial areas in Dade County, Florida

This study is part of a continued effort to assess the effects of urban stormwater recharge on the water quality of the Biscayne aquifer in southeast Florida. In this report, the water-quality effects on shallow ground water resulting from stormwater disposal by exfiltration trench and grassy swale were investigated at two small commercial areas in Dade County, Florida. One study area (airport) was located near the Miami International Airport and had a drainage area of about 10 acres overlying a sandy soil; the other study area (free zone) was located at the Miami International Free Trade Zone and had a drainage area of about 20 acres overlying limestone. The monitoring design for each study area consisted of seven sites and included water-quality sampling of the stormwater in the catch basin of the exfiltration trench, ground water from two wells 1 foot from the trench (trench wells), two wells 20 feet from the trench, and ground water from two wells at the swale from April 1985 through May 1986. Eleven water-quality variables (target variables) commonly found in high levels in urban stormwater runoff were used as tracers to estimate possible changes in ground-water quality that may have been caused by stormwater recharge. Comparison of the distribution of target variables indicated that the concentrations tended to be greater in the stormwater in the exfiltration trench than in water from the two wells 1 foot from the trench at both study areas. The concentration difference for several target variables was statistically significant at the 5-percent level. Lead, for example, had median concentrations of 23 and 4 micrograms per liter, respectively, in stormwater and water from the two trench wells at the airport study area, and 38 and 2 micrograms per liter, respectively, in stormwater and groundwater at the free zone. Similar reductions in concentrations between stormwater and water from the two trench wells were indicated for zinc at both study areas and also for nitrogen, phosphorus, and organic content at the free zone. This trend suggested that the exfiltration trench at both study areas may function as a partial trap for some chemical substances present in stormwater. A comparison of the distribution of the 11 target variables and major ionic composition in water from the two trench wells and the two wells 20 feet from the trench did not indicate a notable horizontal stratification at either study area. A vertical difference between 10 and 15 feet, however, was indicated at the free zone with major ions in greater concentrations at 15 feet. The vertical variability in groundwater near the trench at the free zone may have been the result of stormwater dilution in the upper (10-foot) zone. The ground-water quality at the swale was quite dissimilar to that near the exfiltration trench at both the airport and free zone study areas. Data indicated that the groundwater environment at both sales was anaerobic as evidenced by abundant ammonia nitrogen and iron and trace levels of sulfate. Anaerobic conditions at the swale may have been the result of poor drainage and high organic content of soils. Significant biochemical cycling in the ground water at the swales precluded any assessment of quality effects that may result from storm-water infiltration.

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USGS1978

Quality of the water in Borrow Ponds near a major highway interchange, Dade County, Florida, October-November 1977

Water, bottom sediment, and aquatic plants were sampled from ponds near a major south Florida highway interchange to document concentrations of selected constituents in an aquatic environment near heavy vehicular traffic. Generally, concentrations of constituents were within the range expected in an uncontaminated environment in south Florida. However, concentrations did exceed south Florida background levels or Environmental Protection Agency criteria in a few cases. Two trace elements--chromium (20 micrograms per liter) in ponded surface water and lead (500 micrograms per gram) in bottom sediment--exceeded background levels. Concentrations of dieldrin (22 micrograms per kilogram) and polychlorinated biphenyls (53 micrograms per kilogram) also exceed background levels in bottom sediment. The concentration of phenol (23 micrograms per liter) in ground water exceeded Environmental Protection Agency quality criteria by 22 micrograms per liter, but was within the background range for south Florida. Ten metals were detected in the cattail or algal samples, but only iron, manganese, and zinc were in higher concentrations than those in the bottom sediment. (Woodard-USGS)

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USGS1976

Simulations of water-level drawdowns in proposed well-field areas, Dade County, Florida

Electrical analog model simulations of hydraulic conditions in the Biscayne aquifer were made at proposed inland well-field sites in Dade County, Florida. Simulated drawdowns of water levels after 7 months of continuous pumping at 50, 100, and 150 million gallons per day were obtained at each site. Simultaneous pumping of each of the sites at 50 million gallons per day showed that after 7 months pumping there would be interference between proposed well fields. (Woodard-USGS)

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USGS1976

Analog-model simulations for secondary canal controls and forward pumping water-management schemes in southeast Florida

The analog model of the Biscayne aquifer of southeast Florida was used to approximate the effects of two proposed water-management schemes. One involved adding a secondary control structure in a major canal which is controlled near the coast. In the model the controls were operated in accordance with canal water level both above and below the secondary control. Although the model could not differentiate between control openings of 1 foot or 5 feet, it showed that the secondary control is a viable method of conserving ground water. The second scheme involved pumping ground water ('forward pumping') from the Biscayne aquifer in inland areas during the dry season to: (1) augment canal flows toward the coast to sustain ground-water levels there, and (2) generate additional ground-water storage space for recharge in the wet season. Several sites on the model were programmed for forward pumping wells and the storage change was noted as a percentage of the ground-water withdrawal. (Woodard-USGS)

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