Periodic stream-temperature data have been collected at 280 different sites in Indiana by the U.S. Geological Survey and the Indiana State Board of Health. These data have been analyzed using a simple-harmonic curve-fitting procedure.
When the equation coefficients are known, calculations can be made for a given stream to estimate the maximum and minimum temperatures, the temperature on a given day, the day a given temperature is expected, or the length of time temperatures will exceed, or be less than, a specific.
The calculated harmonic coefficients were related to 23 topographic, basin, and climatic characteristics, and were analyzed by multiple-regression analysis techniques. The regional regression analysis for the harmonic- mean stream temperature, M, resulted in the following arithmetic function of station latitude (LAT).
M = 41.36 - 0.7166 (LAT)
The multiple correlation coefficient (r) was .72. Poor correlations were found for the harmonic phase-angle and amplitude coefficients, C and A, respectively. Constants of 4.32 radians for C and 11.27° Celsius for A are suggested as average statewide values in Indiana streams. The mean temperature of the White River at Indianapolis was raised 3.5° Celsius above expected ambient levels caused by climatic conditions alone, primarily as a result of discharges from powerplants.
In general, the harmonic coefficients depicting annual variability in stream temperatures, generated from the Indiana State board of Health data collected every 2 weeks, are the same as coefficients generated from the U.S. Geological Survey date collected every 4-6 weeks.