Figure 1 Above. Location of USGS Monitoring Stations and Water Control Structures. Inset of Joe Bay during Tropical Storm Harvey and Hurricane Irene. [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 Nino 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. Daily Mean Values of Stage for Trout Creek. [larger image]

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Hurricane Irene Storm Track [larger image]	Hurricane Irene Color IR Image [larger image]
above Hurricane Irene images courtesy of NOAA
Hurricane Irene Time Series Discharge Data at Trout Creek During Hurricane Irene [larger image]	Aerial Photo of Trout Creek [larger image]

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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 3. Unit Values of Stage for Trout and McCormick Creek During Tropical Storm Harvey and Hurricane Irene. [larger image]	Figure 4. Unit Values of Salinity for Trout and McCormick 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.

FOR MORE INFORMATION: CLINTON HITTLE MARK ZUCKER cdhittle@usgs.gov mzucker@usgs.gov U.S. Geological Survey 9100 NW 36th St. Suite 107 Miami, FL 33178 305-717-5815

http://sofia.er.usgs.gov

Related information:

SOFIA Project: Freshwater Flows into Northeastern Florida Bay

SOFIA Project: Hydrologic Monitoring in Joe Bay