Prediction of Effective Saturation Concentration at Spillway Plunge Pools

Abstract

Bubbles entrained in spillway plunge pools are subject to the hydrostatic force of the water column, increasing the pressure within the entrained bubbles. This phenomenon is important for the exchange of atmospheric gases such as nitrogen and oxygen, often causing dissolved gas supersaturation downstream of the plunge pool. A weighted average or effective bubble depth is introduced to predict more accurately gas transfer at spillways. A theory is developed for estimating the effective bubble depth given the spillway angle of inclination, velocity, and depth of flow at jet impact and tailwater depth. The relationship is fitted to dissolved oxygen and methane data previously reported by the authors and is successfully applied to four Bureau of Reclamation spillways for which both oxygen and nitrogen measurements were available.