A major Everglades restoration goal is to provide the wetland and Florida Bay with the right amount of water at the right time. The need for accurate information on the quantity, timing, and distribution of water flows through the Everglades into Florida Bay is necessary for successful water management as it relates to restoration efforts. Hydrologic models and biological research are dependent upon accurate outflow data to calibrate and verify boundary conditions, and establish flux parameters. With this information, water management practices can be monitored and decisions made on the distribution and amount of flow required to restore the Everglades to a more natural system.

In October 1994, the U.S. Geological Survey (USGS), as part of the South Florida Place Based Studies Program, began a study to measure freshwater discharge into northeastern Florida Bay. Water flow, stage, and salinity data were collected at five instrumented sites, and water flow data were collected at four noninstrumented sites. The five instrumented sites from east to west are West Highway Creek, Trout Creek, Mud Creek, Taylor River, and McCormick Creek. The four noninstrumented sites from east to west are East Highway Creek, Oregon Creek, Stillwater Creek and East Creek (fig. 1). Data at the instrumented sites are collected every 15 minutes and transmitted via satellite every 4 hours to the USGS Miami office. Data from the noninstrumented sites are collected on a monthly and storm event basis. The study was expanded in 1999 to determine flow distribution into Joe Bay and upstream flow characteristics for Taylor River. Four salinity probes were installed at creeks along the northern coast of Joe Bay, and additional instrumented sites were installed along upstream Taylor River and Stillwater Creek (fig. 1).

Figure 1. Location of Florida Bay Monitoring Stations. Click for larger image.

The quantity of water flowing through Taylor Slough and the C-111 Basin, including rainfall and evaporative losses, can be defined as total cumulative outflow volume in acre-feet from the creeks. The USGS water year (October through September) annual summaries for 1996- 99 of outflow volume for the five instrumented and four noninstrumented sites are presented in table 1. Sheetflow over the Buttonwood embankment into northeastern Florida Bay is considered negligible due to the higher elevation of the embankment. Water levels in the area drop rapidly after storm surges (such as those associated with Hurricane Irene in 1999) and flow into the bay is mainly constrained within the creeks. Trout Creek stage, discharge, and salinity data indicate that the highest water levels correspond to negative flows during storms, and positive "freshwater" outflows return after winds subside and water levels decline.

The timing of flows is directly related to the wet/dry season variations with more than 80 percent of annual freshwater flow entering northeastern Florida Bay between June and November. Negative flows predominate the dry season and lower water levels in the wetland along with southerly winds cause saltwater to intrude upstream and into the inland subembayments, such as Joe Bay and upstream Taylor River.

Due to the complex drainage basin of the southeastern Everglades and the flat topography, small changes in water level can cause changes in flow distribution that would not be observed without directly computing discharge at the creeks. Discharge computation and salinity observations at the creeks and subembayments have yielded the following: (1) Trout Creek carries approximately 50 percent of the freshwater outflow to northeastern Florida Bay including the gaged and ungaged creeks; (2) West Highway Creek rarely has net negative flow on a monthly basis; (3) McCormick Creek had net negative flow for water year 1998 following the El Nino event; (4) flow exchange between Joe Bay and Long Sound does occur, and direction of flow is dependent upon water levels in the Taylor Slough and C-111 Basins; and (5) northeastern Joe Bay shows a direct connection with outflows from S-18C.

The accurate measurement of quantity, timing, and distribution of freshwater flows to northeastern Florida Bay can be used to establish goals for restoring the Everglades. Direct field observations accompanied by model predictions will invariably facilitate a better understanding of the diverse Everglades ecosystem.

(This abstract was taken from "Programs and Abstracts - 2001 Florida Bay Science Conference". (PDF, 6.8 MB))

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