Distribution of Flows in Northeastern Florida
Topical Area: Water Circulation and Currents
Eduardo Patino and Clinton D. Hittle, Hydrologists, U.S. Geological Survey, Miami, Florida
During the last decade, Florida Bay has experienced ecological deterioration that has been partly attributed to an increase in salinity. Salinity is directly related to the amount of water that enters Florida Bay from the mainland and to flow patterns within the bay. Restoration of the Florida Bay ecosystem requires a better understanding of the linkage between the amount of water flowing into the bay and the salinity and quality of the bay environment. As sheetflow is reestablished by flow management in the wetlands of the Everglades, it is expected that these changes will be reflected in the amount of water exiting the mainland through the principal streams or as sheetflow into Florida Bay. Several agencies, including the U.S. Geological Survey, U.S. Army Corps of Engineers, and the South Florida Water Management District, are now developing and calibrating models to simulate and predict the movement of water in the mainland, flows into Florida Bay, and circulation patterns within the bay.
The U.S. Geological Survey is conducting a study, which began in October 1995, to determine the distribution of flows in northeastern Florida Bay. This study will provide essential flow and salinity data for models along the mangrove zone, where data have not been previously available. Flow through the mangrove zone in northeastern Florida Bay is naturally controlled by the wet and dry conditions of the Everglades wetlands, regional wind patterns, and, to a lesser extent, by tidal action in the Gulf of Mexico toward the western part of the bay. The flow of water from the mainland into northeastern Florida Bay is confined to several streams or creeks, except during extreme high-water conditions, when significant sheetflow can be observed through low-lying mangrove areas between the streams. Acoustic technology is being used to determine the flows in streams that discharge water into Florida Bay.
Five sites are being studied in northeastern Florida Bay in Dade and Monroe Counties, Florida. These sites are: McCormick Creek, Taylor River, Mud Creek, Trout Creek, and West Highway Creek. Activities at these sites include the collection of continuous water-level and velocity data with periodic field measurements of discharge. Data-collection activities include the use of acoustic velocity meters (AVM's) to record water velocities at predetermined elevations within the water column, water-level recorders for the calculation of stage dependent cross-sectional areas, temperature and specific conductance sensors, and data-collection platforms for the transmission of all data to the U.S. Geological Survey office in Miami for processing and storage. Velocities and specific conductance are being recorded at three different elevations with temperature only recorded at top and bottom elevations. All discharge measurements are being performed using an Acoustic Doppler Current Profiler (ADCP). Discharge records for all instrumented sites are being calculated by using stage dependent cross-sectional areas and relations established between recorded velocities (AVM) and mean measured velocities (ADCP).
Mean stream discharge for all gaged sites from April 1996 to March 1998 indicates that about 66 percent of flow is discharged into northeastern Florida Bay through Trout Creek. The variation of flow between the wet season (May-October) and the dry season (November-April) indicates that about 90 percent of gaged flow enters northeastern Florida Bay during the wet season. Velocity and water-level data collected from the sites indicate that flows through creeks draining into northeastern Florida Bay are greatly affected by regional wind patterns and do not present tidal signatures typical of most estuarine streams. Salinity data indicate that, at times, there is a vertical stratification; however, this does not occur frequently nor does it last for extended periods of time. The analysis of discharge data suggests that low-pass filters, commonly used to calculate "net flows" by smoothing the tidal effects, are not suitable for use at these sites, given the "noisy" flow patterns. Further study of the effects of wind and the "storage factor" of uplands is needed to better understand the flow system along the mangrove zone of northeastern Florida Bay.