Effect of atmospheric stability on water temperature predictions for a thermally loaded stream


  • David R. DeWalle


A steady state one-dimensional energy budget equation was numerically integrated to predict water temperatures in a 5.45-km-long thermally loaded stream reach for 131 five- or six-hour periods. Downstream water temperature prediction errors (measured minus predicted) using Jobson's Lake Hefner evaporation equation averaged −2.11°C and were well correlated (R2 = 46%) with an index to atmospheric stability. Use of a modified form of Shulyakovskiy's evaporation equation, which includes a term for evaporation by free convection, significantly reduced the average prediction error to 0.89°C and eliminated the effects of atmospheric stability (R2 < 1%). Correction of wind velocity data for the velocity of the air relative to the stream velocity also reduced prediction errors.