Constraining mechanistic models of indicator bacteria at recreational beaches in lake Michigan using easily-measurable environmental variables

Beach closures have significant economic and human health implications. The ability to create and use near-real time hydrodynamic and transport models that simulate fecal indicator bacteria (FIB) levels at our nation's recreational beaches is important to effectively managing coastal resources. Described herein is the development and application of an unsteady, threedimensional hydrodynamic fate and transport model constrained using easily measurable environmental variables such as electrical conductivity (EC) and turbidity. The model was able to simulate observed Escherichi coli (E. coli) concentrations at three beaches in close proximity to the Burns Waterway along the Indiana Dunes National Lakeshore. This model utilized an unstructured grid that has the ability to accurately represent local features in the area, including the complex shoreline and breakwaters that influence hydrodynamics and mixing. This allows for the better prediction of FIB at local beaches, reducing human health risks and decreasing the number of unnecessary beach closures.