Reaeration at Low-Head Hydraulic Structures

Abstract : The physics of gas transfer is presented as a basis for describing the physical processes that contribute to the oxygen transfer (reaeration) characteristics of a hydraulic structure. A mathematical description of the gas transfer process is presented and the effects of the physical processes on the variables in the equation are described. Measurement techniques and uncertainties are discussed. Guidance is presented on the conduct of field studies. Based on the uncertainty in direct measurement of dissolved oxygen, guidance is presented to help determine the need for alternative measurement techniques, i.e., use of tracer gases. Oxygen transfer for several types of low- head structures is characterized on the basis of the theory and mathematical description with an empirical coefficient derived from field measurements. The uncertainty in predictions made with these descriptions is quantified. Enhancement techniques, including operational strategies, mechanical alternatives, and structural modifications, are discussed.