The role of turbulence and internal waves in the structure and evolution of a near-field river plume

Abstract

Abstract. An along-channel momentum budget is quantified in the near-field plume region of a controlled river flow entering Doubtful Sound, New Zealand. Observations include highly resolved density, velocity and turbulence, enabling a momentum budget to be constructed over a control volume. Estimates of internal stress (τ) were made from direct measurements of turbulence dissipation rates (ε) using vertical microstructure profiles. High flow speeds of the surface plume over 2 m s−1 and strong stratification (N2 ~ 10−1 s−2) resulted in enhanced turbulence dissipation rates (ε > 10−3 W kg−1) and internal stress (τ > 10−2 m2 s−2) at the base of surface layer. An observed transition from a supercritical to sub-critical flow regime in the initial 1 km indicates the presence of an internal hydraulic jump and the subsequent release of internal gravity waves. The momentum flux divergence of these internal waves suggests that almost 15 % of the total plume momentum can be transported out of the system by wave radiation, therefore playing a crucial role in the redistribution of momentum within the near-field plume. Observations illustrate that the evolution of the momentum budget components vary between the distinct surface plume layer and the turbulent, shear-stratified interfacial layer. Within the surface plume, a momentum balance was achieved. The dynamical balance demonstrates that the deceleration of the plume, driven by along-channel advection, is controlled by turbulence stress from the plume discharge point to as far as 3 km downstream. In the interfacial layer however, the momentum equation was dominated by the turbulence stress term and the balance was not closed. The redistribution of momentum within the shear-stratified layer by the observed hydraulic jump and internal wave radiation could account for the discrepancy in the budget.

Turbulent Scales Observed in a River Plume Entering a Fjord

“…The spatial variability in the thickness of the plume can be attributed to changes in tidal stage and tailrace discharge rate (Figure ), the heterogeneous nature of the turbulent field (Figure ), or high‐frequency internal waves generated by the fast surface plume discharged into the deep, stationary ambient. However, the generation and impact of internal waves on plume structure is beyond the scope of this study and is instead examined in (McPherson et al, ).…”

The pressure characteristics analysis of oil pulsation flow based on VMD

“…Subsequently, Mizusgina et al 9 reported a comprehensive study of pulsating flow and obtained the phase mean velocity and turbulence intensity of the fluid from the information measured by an electrochemical method, which only covers 20 cycles for the difficulty concerned in the experiment, which limits the convergence of the results. McPherson et al 10 regarded as the momentum flux divergence of those internal waves suggest that just about 15% of the whole plume momentum are often transported out of the system by wave radiation, thus playing a vital role within the redistribution of momentum among the near-field plume.…”