Modeling Dissolved Gas Supersaturation Below Spillway Plunge Pools

Excessive supersaturation of dissolved gases, primarily nitrogen and oxygen, can cause gas bubble disease, and eventual mortality, in fish. This potential threat is currently a concern in efforts to aid anadromous fish survival in the northwestern United States. In an effort to better understand dissolved gas supersaturation and assist in its mitigation, physically based relationships have been expanded and developed to predict dissolved gas supersaturation below spillways. This paper discusses the predictive technique as applied to the dissolved gas supersaturation that occurs because of the stilling basin and the river reaches immediately downstream of the structure. Gas transfer across both the water surface and the bubble interface are considered. Extensive field data from three spillways on the Columbia and Snake Rivers is used to fit coefficients that the predictive relationships require. The inclusion of more physically based parameters will allow for the evaluation of the operation and design of the structures and may provide insight for efforts to mitigate high dissolved gas concentrations downstream of such structures.