Abstract
In this work, the turbulent flow dynamics and mass transport mechanisms in a natural SSZis analyzed. The study site is a river reach of the Lluta River, located in northern Chile in a high-altitude Andean environment known as the Altiplano (~ 4,000 masl) The large-scale turbulent coherent structures are characterized using field measurements and 3D numerical simulations. The detailed topography was measured through DGPS and digital image processing while the surface velocity field, through the LSPIV technique. Regarding the field data, numerical simulations were performed using a DES turbulence model coupled with a 3D passive scalar transport model for Re = 45,800. The coherent structure dynamics in the shear layer was identified as the main mechanism that drives the mass and momentum transport processes between the SSZ and the main channel. Also, the 2D vortical structures of the mean flow are analyzed within the lateral cavity, since they have a strong influence in mass transport, increasing mean residence times due to their lower velocities and longer exchange timescales. Finally, the performance of two simplified transport models is analyzed to represent the mass transport dynamics at larger scales.
Highlights
Stream channels can be separated into advective and non-advective zones [5]
Transient or surface storage zones (SSZ) are characterized by low velocities compared to the flow in the main channel, and long residence times that favor the deposition of contaminants, nutrient uptake and interactions with reactive sediments
A complex surface flow was observed in the field, characterized by a large recirculation area and the presence of a sink point located in the leftbank downstream the narrowing section, where the flow is divided in opposite directions: one part enters the cavity and the other one moves onto the main channel in streamwise direction
Summary
Stream channels can be separated into advective (main channel) and non-advective (transient storage) zones [5]. Transient or surface storage zones (SSZ) are characterized by low velocities compared to the flow in the main channel, and long residence times that favor the deposition of contaminants, nutrient uptake and interactions with reactive sediments. Limited works have determined and analyzed the turbulent flow features of natural SSZ with high Reynolds numbers [4], where the interaction between turbulent flow, solute transport and intricate stream bathymetry represent a very complex problem [13]
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