Nowcasting Beach Advisories at Ohio Lake Erie Beaches

Data were collected during the recreational season of 2007 to test and refine predictive models at three Ohio Lake Erie beaches. In addition to Escherichia coli (E. coli) concentrations, field personnel collected or compiled data for environmental and water-quality variables expected to affect E. coli concentrations including turbidity, wave height, water temperature, lake level, rainfall, and antecedent dry days and wet days. At Huntington (Bay Village) and Edgewater (Cleveland) during 2007, the models gave correct responses 82.7 and 82.1 percent of the time; these percentages were greater than percentages obtained by use of the previous day’s E. coli concentrations (current method). In contrast, at Villa Angela during 2007, the model gave correct responses only 61.3 percent of the days monitored; this percentage was lower than that achieved by use of the current method (74.6 percent). To refine the Huntington and Edgewater models, data from 2007 were added to existing datasets, and the larger datasets were split into two or three segments by date. Models were developed for dated segments and for combined datasets. At Huntington, the summed responses for separate best models for dated segments resulted in a greater percentage of correct responses (85.6 percent) than the one combined best model (83.1 percent). Similar results were found for Edgewater. Water-resource managers will determine how to apply these models to the Internet-based “nowcast” system for issuing water-quality advisories during 2008.