Quantifying Internal Canal Flows in South Florida
Mitch Murray, and Rick Solis
U.S. Geological Survey, Center for Water and Restoration Studies, Miami,
FL.,USA
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, L28U 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 flowweighted 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.
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.
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.