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| Florida Science Center |
OFR 2005-1394
Prepared in cooperation with
Palm Beach County Department of Environmental Resources Management
2005
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CONTENTS Abstract Introduction Purpose and Scope Description of Study Site and Canal System Previous Studies Acknowledgments Data Collection and Processing Methods Historical Data Collection at the C-51 Canal Discharge and Real-Time Turbidity Data Suspended-Sediment Sample Collection Cross-Sectional Water-Quality Surveys Laboratory Analytical Methods Quality Assurance Development of Rating Curve Estimators Using Surrogate Technology Relation of Suspended Sediment to Turbidity Relation of Suspended Sediment to Other Explanatory Variables Comparison of Data for Suspended-Sediment Concentration and Transport in the C-51 Canal Summary Selected References |
The Lake Worth Lagoon watershed encompasses about 450 square miles in Palm Beach County, and represents one of the most important estuarine areas in Florida. Anthropogenic activities beginning in the late 19th century and continuing through today have adversely affected the natural resources and aquatic biota of the lagoon. A major concern is the large deposition of muck sediment that has had a deleterious effect on seagrass growth. The major cause of these sediment deposits most likely is due to stormwater heavily laden with fluvial sediment, discharging through the S-155 control structure on the West Palm Beach (C-51) Canal.
To address this problem, the U.S. Geological Survey and the Palm Beach County Department of Environmental Resource Management engaged in a joint partnership utilizing surrogate technology to develop rating curve estimators based on the relation between suspended sediment and different explanatory variables, including turbidity and discharge. To fulfill this objective, a continuous, instream water-quality monitoring station that records turbidity data in real time was installed upstream of structure S-155. Point samples were collected near the probe, and depth- and width-integrated samples were collected along the stream cross section. The water samples were collected over a range of seasonal and hydrologic conditions (from 2- to 85-percent exceedance on the flow-duration curve) and analyzed at a U.S. Geological Survey sediment laboratory. Four rating curve estimators were developed based on simple linear and multiple linear regression analyses to estimate suspended-sediment concentrations upstream of structure S-155 using the logarithms of turbidity, turbidity and discharge, and discharge. The coefficients of determination (R2) ranged from 0.75 to 0.90.
Cross-sectional water-quality surveys were made at three verticals in the stream cross section during various seasonal and hydrologic conditions to assess water-quality homogeneity in the stream. Results indicated a range of concentration differences of 18 to 60, 11 to 62, 9 to 33, and 18 to 31 percent for the surveys made on December 4, 2003, March 15, 2004, September 14, 2004, and November 7, 2004, respectively.
Quality-assurance samples were collected as part of this study and included equipment blanks, field blanks, and duplicate samples. Relative percent differences between duplicate samples collected at the probe and cross section (4.6 and 0.0 percent, respectively) were within Florida Department of Environmental Protection standards.
The nonparametric Wilcoxon signed-rank test was used with hydrologic data to statistically compare: (1) measured and estimated suspended-sediment concentrations; (2) suspended-sediment concentrations estimated at the probe and at the cross section; (3) estimated suspended-sediment concentrations at the cross section using different explanatory variables; and (4) estimated suspended-sediment loads at the cross section using different explanatory variables. The suspended-sediment concentrations at the stream cross section were estimated from continuous turbidity and discharge data collected during the 2004 water year (October 2003 to September 2004). Statistically significant differences at the 95-percent confidence level (p-value less than 0.025) occurred for all suspended-sediment concentrations estimated at the cross section between turbidity and discharge, between turbidity and turbidity and discharge, and between discharge and turbidity and discharge. Estimated suspended-sediment loads at the cross section also were statistically significant between these same explanatory variables. Additionally, statistically significant differences occurred for suspended-sediment concentrations estimated from turbidity at the probe and at the cross section and for suspended-sediment concentrations estimated from turbidity at the probe and from turbidity and discharge at the cross section. In accordance with these results, the logarithm of both turbidity and discharge as explanatory variables is the best estimator for computing suspended-sediment concentrations and loads at the stream cross section.
Lietz, A.C., and Debiak, E.A., 2006, Development of Rating Curve Estimators for Suspended-Sediment Concentration and Transport in the C-51 Canal Based on Surrogate Technology, Palm Beach County, Florida, 2004-05: U.S. Geological Survey Open-File Report 2005-1394, 19 p.
U.S. Department of the Interior
U.S. Geological Survey
3110 SW 9th Avenue
Ft. Lauderdale, FL 33315
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