MODELING DISSOLVED-GAS SUPERSATURATION BELOW SPILLWAY PLUNGE POOLS

Excessive supersaturation of dissolved gases, primarily nitrogen and o xygen, can cause gas bubble disease, and eventual mortality, in fish. This potential threat is currently a concern in efforts to aid anadrom ous fish survival in the northwestern United States. In an effort to b etter understand dissolved gas supersaturation and assist in its mitig ation, 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 sup ersaturation that occurs because of the stilling basin and the river r eaches immediately downstream of the structure. Gas transfer across bo th the water surface and the bubble interface are considered. Extensiv e field data from three spillways on the Columbia and Snake Rivers is used to fit coefficients that the predictive relationships require. Th e inclusion of more physically based parameters will allow for the eva luation of the operation and design of the structures and may provide insight for efforts to mitigate high dissolved gas concentrations down stream of such structures.