Field experiments to determine gas transfer at gated sills

Field experiments were conducted to determine the oxygenation potential of gated sill structures in the Ohio River Valley. The objective was to determ ine operational procedures for water quality improvement. Oxygenation poten tial is typically characterized by gas transfer efficiency, with high trans fer efficiency indicating a greater input of oxygen into the water. Direct oxygen measurement can be unreliable in determining transfer efficiency, an d this is due to upstream stratification, relatively high background concen trations, and changes in saturation concentration when the bubbles are expo sed to hydrostatic pressures within the stilling basin. As a result, in sit u methane was used as an independent dissolved gas tracer. Methane is natur ally present in measurable quantities with little stratification, and it do es not experience an appreciable increase in saturation concentration with bubble depth. Therefore, methane measurements better reflect the true trans fer efficiency of a structure. This paper focuses on the factors that influ ence transfer efficiency and how to achieve high quality field data through the use of methane and oxygen measurements. In addition, results from six- gated sill structures in the Ohio River Valley are presented.