Estimation of Water Temperature Exceedance Probabilities Using Thermo - Hydrodynamic Modeling

A continuous simulation approach is proposed for estimating water temperature exceedance probabilities using thermo-hydrodynamic modeling. The approach uses (1) a deterministic unsteady ow and heat transport model, (2) continuous hydrological and meteorological data for a long historical period, and (3) synthetic records of tributary water temperatures and other model inputs. Representative historical records of stream ow, air temperatures, and other hydrometeorological variables are obtained from nearby gages. Stochastic modeling methods are used to construct synthetic records for other model inputs, including in ow water temperatures. An application of this deterministic-stochastic approach is presented for a complex waterway in northeastern Illinois with heat discharges from several power plants and wastewater treatment plants. Statistical results from the continuous simulations are compared to results obtained from traditional event simulations. The application illustrates the information that engineers and biologists can obtain for (1) evaluating compliance with water temperature standards, and (2) assessing the e ect of water temperatures on aquatic habitat. [Key Terms: Aquatic ecosystems, Hydraulics, Modeling/Statistics, Simulation, Temperature standards, Time series analysis, Stochastic analysis, Upper Illinois Waterway.] Respectively, Assistant Professor and Professor, Iowa Institute of Hydraulic Research and Department of Civil and Environmental Engineering, The University of Iowa, Iowa City, Iowa, 52242; Engineer, Espey, Huston & Associates, 11838 Rock Landing Drive, Newport News, Virginia 23606; and Engineer, Philip Williams & Associates, Pier 35, The Embarcadero, San Francisco, California,