Figure 1. Study area showing location of Tribal lands, data-collection sites, and major canals and levees. [larger image]

The need to determine future surface-water flow requirements in the interior canal system of south Florida is being met with the successful implementation of strategic placed stream-flow and water-quality gaging sites in the interior of southern Florida. The multi-agency effort involves four entities that collect, analyze, and distribute information for water managers. In 1995 the U.S. Geological Survey (USGS) established three monitoring sites south of Lake Okeechobee in an effort to accurately gage flows in canals entering and exiting Tribal lands, the Big Cypress National Preserve, and Water Conservation Area 3A in southern Florida. These flows are also being monitored to calculate nutrient loads in the canals that cross or border Tribal lands. Two of the gaging sites, L-28U and L-28IN, are located on the southern border of the Seminole Tribal lands along the L-28 canal and the L-28 Interceptor canal, respectively, west of Water Conservation Area 3A in Hendry County (fig. 1). The third gaging site, L-28IS, is located along the L-28 Interceptor canal where flows enter the western lands of the Miccosukee Indian Tribe from the Big Cypress National Preserve in Collier County and has been discontinued.

Acoustic instrumentation, in lieu of standard methods for field data collection and flow computations, is used to quantify flows in the canals. Using the acoustic velocity meter (AVM), Acoustic Doppler Velocity meter (ADV), and the Acoustic Doppler Current Profiler (ADCP), it is possible to more accurately gage flows in this type of environment because of new capabilities to quickly measure low or rapidly changing water velocities. Construction, instrumentation, and calibration of the flow gaging sites were completed by the USGS during 1996 and 1997. The South Florida Water Management District (SFWMD) installed flow-weighted samplers at the gaging sites for nutrient analysis in conjunction with the stream flow monitoring; the Seminole and Miccosukee Indian Tribes have serviced the flow-weighted samplers. Real-time telemetry instrumentation and programming assistance along with phosphorus and nitrogen load calculations have been provided by the SFWMD. ADCP calibration of the installed acoustic velocity meter indexes is ongoing and development of the "sum of least squares regression" has been provided for data processing at all sites and continues to be refined. Velocity data collected during the dry season has displayed a phenomenon known as acoustic refraction or ray bending produced by thermal stratification in the water column during extended periods of very slow vertical flow. Various installed electromagnetic and new Doppler mean velocity-indexing techniques have been tested and proven largely successful.

The L-28U site along the L-28 canal is used to monitor freshwater flows from the lands of the Seminole Tribe and to provide nutrient data load summaries. Average annual runoff of 63,930 acre-feet for the period from 1997 to 2001, represents about twice the inflow amount determined by the SFWMD at their upstream U.S. Sugar Outflow (USSO) site located on the northwestern border of the Seminole Tribal lands. The L-28IN site along the L-28 Interceptor canal is used to monitor flows from the lands of the Seminole Indian Tribe to the Big Cypress National Preserve and ultimately to Miccosukee Tribal lands as well as providing nutrient data for water-resources planning and management. Annual runoff averaged 53,140 acre-feet from 1997 through 2001. The L-28IS site along the L-28 Interceptor canal, discontinued September 1999, was used to monitor flows from the lands of the Seminole Indian Tribe and the Big Cypress National Preserve to the lands of the Miccosukee Indian Tribe. For the three years of operation this site also provided flows and associated nutrient load data for water managers, and was instrumental in bracketing and quality assuring the flow calibration conditions for the upstream L-28IN site. Average annual runoff at the site for the 1997-1999 periods was calculated to be 49,070 acre-feet.

Measuring flow-weighted nutrient loads requires extremely accurate flow-data collection combined with a highly coordinated nutrient collection and analysis procedure. A collaborative product that meets this need is provided as part of current efforts and has been documented in seven semi-annual progress reports presented to the SFWMD/Seminole Working Group. An ancillary report was produced from funding sources outside of the USGS Placed Based Studies (PBS) program budget during the 2002 water year (Lietz, 2002). The report examines the feasibility of estimating concentrations and loads based both on USGS acoustic backscatter data and Seminole Tribe nutrient water quality data.

REFERENCES

Lietz, A.C., 2002 (in press), Feasibility of estimating constituent concentrations and loads based on data recorded by acoustic instrumentation: U.S. Geological Survey Open File Report 02-285, 10 p.

Contact: Mitch Murray, mmurray@usgs.gov, Rick Solis, rsolis@usgs.gov, U.S. Geological Survey, 9100 NW 36 St., Ste. 107, Miami, FL, 33178. Phone: (305) 717-5827, Fax: (305) 717-5801. Question 1.

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

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