Continuous Hydrologic Data in Florida Bay Channels

Clinton Hittle and Grant Poole U.S. Geological Survey, Center for Water and Restoration Studies, Miami, FL

Hydrologic data from six channels within Florida Bay (fig. 1) are being collected by the U.S. Geological Survey (USGS) to help understand flow characteristics and better define the transport of post-larval Pink Shrimp into and out of the bay. The data will improve hydrodynamic and biological models being developed for use with the Comprehensive Everglades Restoration Plan (CERP), a goal of which is to improve the quantity, quality, timing, and distribution of flows within the Everglades ecosystem. Continuous water velocity, stage, salinity, and temperature data have been collected at 15-minute intervals since January 2002. Monitoring stations are co-located with post larval pink shrimp nets managed by the USGS, National Oceanographic and Atmospheric Administration (NOAA), and the University of Miami Rosenstiel School of Marine and Atmospheric Science (RSMAS).

Figure 1. Location of Florida Bay monitoring stations.

All stations have salinity/temperature probes installed at about mid depth in the channel; probes are cleaned and calibrated during routine site visits. Elevations were established on each station in 2002 by the USGS and are referenced to the North American Vertical Datum of 1988 (NAVD 88). Elevation data was computed using a helicopter-based differential global positioning system coupled with a mechanical height finder (fig 2). The elevation data established at each monitoring station allows for comparisons of water level between the sites.

Figure 2. Helicopter based survey method.

Acoustic Doppler Velocity Meters (ADVM) continuously monitor flow conditions and water levels within the channels. The ADVM measures an average water velocity within a fixed sample volume. Continuous channel discharge is computed using velocity data collected from the ADVM and a boat mounted Acoustic Doppler Current Profiler (ADCP). Regression analysis is used to relate the ADVM velocity to mean measured velocity calculated during ADCP discharge measurements. The resulting equation, known as an index velocity rating, converts all ADVM index velocities into approximate mean channel velocities. These corrected velocities are multiplied by the channel area to produce continuous discharge record. Acquiring ADCP discharge measurements over the entire range of flow conditions expected to occur at the site improves this computation method. Figure 3 shows the relation between index velocities and ADCP mean measured velocities at Whale Harbor Channel. 3.00

EXPLANATION 2.50 C a l i b r a t i o n r a t i n g 2.00 M e a s u r e d V i I n d e x v e l o c i t y 1.50 V A D C P m e a n m e a s u r e d v e l o c i t y

2 R C o e f f i c i e n t o f d e t e r m i n a t i o n 1.00 A D C P A c o u s t i c D o p p l e r C u r r e n t P r o f i l e r 0.50

0.00 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 2.50 -0.50

-1.00 V = 1.13Vi - 0.03 -1.50 R2 = 0.99 -2.00

ADVM INDEX VELOCITY, IN FEET PER SECOND

Figure 3. Velocity relation for the Whale Harbor monitoring station

The continuous discharge data from these sites will benefit studies that require estimates of total hydraulic transport into and out of the bay, while the continuous data for all parameters will be valuable for verifying future simulations of Florida Bay hydrodynamics.

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, [email protected]