ANALYSIS OF REAERATION EQUATIONS USING MEAN MULTIPLICATIVE ERROR

Numerous equations employing depth, velocity, and slope have been deve loped to estimate the stream reaeration coefficient. These have been e valuated previously using statistics based on differential errors, whi ch are shown to be biased toward underprediction. A new metric, the me an multiplicative error (MME), overcomes this defect and offers other advantages, including identical results for both reaeration and gas tr ansfer coefficients and less sensitivity to extreme errors. It is equa l to the geometric mean of the factors, greater than unity, by which t he estimates would have to be multiplied or divided to equal the corre sponding measurements. With the use of the MME to test 10 selected equ ations, against a compilation of field measurements based on gas trace rs, current equations are shown to be of little value at low slopes, w hereas some frequently used equations are shown to have little general value. Slope is found to be an essential component of reaeration equa tions. Recommendations are made for estimating the reaeration coeffici ent.