Figure 1. Location of Florida Bay monitoring stations. [larger image]

Understanding salinity and circulation dynamics along the boundary between the Everglades and Florida Bay is an important component of Everglades restoration. Hydrodynamic models that simulate flows, water levels, and salinity within Florida Bay and the interior wetlands are considered valuable tools for assessing proposed management practices in the Comprehensive Everglades Restoration Plan (CERP) and for evaluating water control structural modifications. Detailed information on how estuarine creeks respond to extreme hydrologic conditions along the boundaries between estuaries and wetlands will improve model verification.

Data on water velocity, water level, salinity, and temperature are currently being collected continuously at 14 U.S. Geological Survey (USGS) monitoring stations in northeastern Florida Bay (fig. 1). Data from the monitoring stations are available from 1996 to present.

These data allow a detailed examination of estuarine creek response to extreme hydrologic events. Two creeks (McCormick and Trout) are presented here for comparison. Daily mean values of stage for Trout Creek (fig. 2) identify most of the major storms that affected northeastern Florida Bay since 1996, including five hurricanes, two tropical storms, and an El Niño related winter storm.

A comparison of storm surges between McCormick Creek and Trout Creek for Tropical Storm Harvey and Hurricane Irene indicates how storm strength and path can affect water levels and salinities across central and eastern Florida Bay. Tropical Storm Harvey made landfall near Everglades City on September 21, 1999 and moved east-northeast across Florida. Water levels between the two creeks were similar in magnitude during Harvey (fig. 3).

Figure 2. (above) Daily mean values of stage for Trout Creek, 1996 - 2002. [larger image]

Figure 3. (above) 15-minute interval stage values for McCormick and Trout Creek during Tropical Storm Harvey and Hurricane Irene. [larger image]

Hurricane Irene made landfall near Cape Sable on October 15, 1999 and moved to the northeast across Florida. Storm surge from Irene increased water levels at McCormick Creek about one foot more than at Trout Creek.

Increases in salinity at McCormick Creek and Trout Creek were observed during storm surges for both Harvey and Irene. During Harvey, McCormick Creek experienced an increase in salinity from about 20 to 30 parts per thousand (ppt) in 20 hours, with a subsequent decrease back to 20 ppt in only four hours (fig. 4).

Figure 4. 15-minute interval salinity values for McCormick and Trout Creek during Tropical Storm Harvey and Hurricane Irene. [larger image]

At Trout Creek, salinity increased from about 7 ppt to 24 ppt in 24 hours, but took another 24 hours to drop back to 7 ppt (pre-surge conditions). During Hurricane Irene, McCormick Creek salinity increased from about 5 ppt to 17 ppt in 6 hours with a subsequent decrease to 5 ppt in 13 hours. Trout Creek salinity during Irene's passage increased from about 1 ppt to 20 ppt in 10 hours, decreasing back to 5 ppt over the next 24 hours. After an additional 42 hours, salinity returned to the pre-storm level of about 1 ppt. Both creeks experienced a greater salinity increase from Irene than Harvey. Residence time was also greater because more saline water associated with the surge was pushed upstream.

A detailed evaluation of estuarine creek responses to extreme hydrologic conditions and subsequent comparison to hydrodynamic model output will help verify model capabilities in simulating natural systems. The evaluation also will support a science-based approach for CERP activities.

Contact: Clinton D. Hittle, U.S. Geological Survey, 9100 N.W. 36th Street, Suite 107, Miami, FL 33178. Phone: 305-717-5815, Fax: 305-717-5801, cdhittle@usgs.gov.

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

Back to Project Homepage (Freshwater Flows into Northeastern Florida Bay or Hydrologic Monitoring in Joe Bay)