Annual Variation of Stream Water Temperature

An empirical equation has been found that appears to closely fit the annual variation of temperature in a stress. This equation is a modified sine curve and gives the temperature of the stream water as a function of the day of the water year and the average annual temperature of the stream. The applicability of the equation was verified using field data for 37 different stream stations. This data was analyzed by the method of least squares, and the average index of correlation obtained was 0.979. It was observed that the annual average temperature of the streams studied did not vary appreciably from year to year. In addition, the empirical coefficients of the temperature sine curve also did not change materially from year to year. Analysis of only 12 monthly average temperatures was observed to yield almost identical results as an analysis of 365 daily temperature readings. Although all of the calculations were performed on an IBM 650 computer, this means that the required calculations can be made by hand within a reasonable time.