River and Cooling Water Temperature Fluctuations

Cooling water discharged from a power plant changes the fluctuating water temperature characteristics of a receiving river in a clearly detectable way. Daily and hourly water temperature data from two power plant sites on the Upper Mississippi River were used to compute for illustration the magnitude of such differences. Extreme value analysis, autocovariance and spectral analysis, and nonlinear curve fitting methods were applied alternatively. Amplitudes of seasonal periodicities, of diurnal periodicities, and of random components were determined. The results indicate that time series analysis of water temperatures measured downstream from an existing cooling water outfall may provide equally or even more realistic and useful information on the size of a cooling water plume than quasi-instantaneous surveys of spatial water temperature distributions.