Measurements of Oxygen Methane and Sulfur Hexaflouride Transfer at the Anoke Dam Gated Control Structure

Abstract

Hydraulic structures have an impact on the amount of dissolved gases in a river system, even though the water is in contact with the structure for a short time. While water is flowing over a spillway bubbles become entrained into the water thus creating more surface area for gas transfer. Because of this, the same gas transfer that normally would require several miles in a river can occur at a hydraulic structure (Rindels and Gulliver, 1986). Many times interest lies in the transfer of oxygen from the atmosphere to the water. Therefore it seems logical to use oxygen for measurement. However there are some problems associated with dissolved oxygen measurements. If the dissolved oxygen level is close to saturation the uncertainty associated with the measurements affects the overall uncertainty of gas transfer. Also, if the reservoir is stratified it is difficult to predict withdrawal from the various layers with the required precision. In light of these problems associated with measuring dissolved oxygen another method, known as the tracer technique, has been developed. The basis of the tracer technique is that the absorption of oxygen into the water and the desorption of the tracer are equivalent. The tracer gas transfer is related to oxygen transfer through results of laboratory experiments.