Scientific Investigations Report 2006-5192

Models for Predicting Recreational Water Quality at Lake Erie Beaches

By Donna S. Francy, Robert A. Darner, and Erin E. Bertke

 

Abstract

Data collected from four Lake Erie beaches during the recreational seasons of 2004—05 and from one Lake Erie beach during 2000–2005 were used to develop predictive models for recreational water quality by means of multiple linear regression. The best model for each beach was based on a unique combination of environmental and water–quality explanatory variables including turbidity, rainfall, wave height, water temperature, day of the year, wind direction, and lake level. Two types of outputs were produced from the models—the predicted Escherichia coli concentration and the probability that the bathing–water standard will be exceeded. The model for one of beaches, Huntington Reservation (Huntington), was validated in 2005. For 2005, the Huntington model yielded more correct responses and better predicted exceedance of the standard than did current methods for assessing recreational water quality, which are based on the previous day's E. coli concentration. Predictions based on the Huntington model have been available to the public through an Internet–based "nowcasting" system since May 30, 2006. The other beach models are being validated for the first time in 2006. The methods used in this study to develop and test predictive models can be applied at other similar coastal beaches.

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Contents

Abstract

Introduction

Methods

Data Collection

Quality Assurance and Quality Control

Data Analysis and Development and Testing of Predictive Models

Relations Between Escherichia coli Concentrations and Environmental or Water–Quality Variables

Development and Validation of Beach-Specific Predictive Models

Determination of Model Output Values

Model Validation

Future Work

Summary and Conclusions

Acknowledgments

References Cited

Figures

  1. Map showing locations of the five Lake Erie beaches used for studies of predictive modeling
  2. Graphs showing Escherichia coli concentrations in water by wave height and 24–hour wind direction, Villa Angela, 2004—2005
  3. Graph showing establishment of the threshold probability for Huntington 2000—2004 model

Tables

  1. Summary statistics of Escherichia coli (E. coli) concentrations at five Lake Erie beaches, 2000—2005
  2. Pearson's r correlations between log10 Escherichia coli (E. coli) concentrations and explanatory variables at five Lake Erie beaches, 2000—2005
  3. Variables and regression statistics for beach models
  4. Numbers of correct responses and the sensitivities and specificities of model responses with indicated thresholds and predicted Escherichia coli (E. coli) concentrations compared to previous day's E. coli concentrations (current method for assessing recreational water quality)
  5. Responses of the Huntington model 2000—2004 in 2005 and comparison to responses obtained with previous day's Escherichia coli (E. coli) concentrations (current method for assessing recreational water quality)

Send questions or comments about this report to the author, Donna S. Francy, at dsfrancy@usgs.gov, 641-430-7769.

For more information about USGS activities in Ohio, visit the USGS Ohio Water Science Center home page.

Printed copies can be obtained from OWSC or contact the author.


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