Reaeration of Oxygen in Shallow, Macrophyte Rich Streams: II. Relationship between the Reaeration Rate Coefficient and Hydraulic Properties

The rate coefficient K 2 of the physical exchange of oxygen between flowing water and the atmosphere is dependent on water temperature and the hydraulic variables: mean velocity of flow U , mean depth H , and slope S of the stream channel. 36 equations from the literature predicting K 2 on basis of combinations of U, H and S have been tested against 144 corresponding measurements of K 2 and hydraulic variables taken in 10 reaches in 6 Danish streams with different development of the submerged macrophyte community. A statistical analysis showed that all equations except one had to be rejected. To improve predictive accuracy an equation K 2 (20 °C) = 8784 U 0.734 H −0.420 S 0.930 was developed applying multiple linear regression. This equation allows K 2 ‐predictions for streams where the hydraulic variables U range from 0.06 to 0.52 m s −1 , H from 0.12 to 1.37 m and S from 0.3 to 7.4 × 10 −3 m m −1 , respectively. Using this equation the lower and upper 95 % limit of confidence for a given K 2 ‐prediction ( K 2 p ) are K 2p /1.95 and K 2p × 1.95, indicating that such equations at best approximate the real K 2 . Therefore K 2 should preferably be measured.