Measurement of air-water oxygen transfer at hydraulic structures

There is a significant oxygen transfer associated with most hydraulic structures because the air entrained into the flow is split into small bubbles, which greatly increases the surface area for transfer. In spite of the importance of oxygen transfer at hydraulic structures, there has been a lack of literature articles that specifically discuss the measurement technique and analysis. This paper seeks to rectify that oversight. The relationship for a transfer efficiency from the mass transport equation is developed, and the adjustment of measurements for water temperature and unit discharge are discussed. Accurate oxygen-transfer measurements require that oxygen stratification upstream of the structure is minimal or nonexistent. A winter technique for oxygen-transfer measurement that takes advantage of ice-cover formation in the upstream reservoir is described. This technique takes advantage of a high dissolved-oxygen (DO) deficit, and no oxygen stratification in the upstream reservoir. Thus, the measurement uncertainty (to the 95% confidence interval) was generally to be below 0.1 in transfer efficiency units. This is generally considered to be an excellent measurement accuracy for oxygen transfer at hydraulic structures.