Continuous and discontinuous gravity currents in open-channel embayments.

Area of Science:

• Environmental Fluid Dynamics
• Riverine Ecosystems
• Pollutant Transport

Background:

• Embayments act as significant storage zones in rivers but are vulnerable to pollution from industrial sources and sewage via gravity currents.
• Accumulated contaminants in embayments degrade aquatic habitats and negatively affect ecosystem functions.

Purpose of the Study:

• To investigate the three-dimensional vortical structures of continuous and discontinuous gravity currents within channels connected to embayments.
• To simulate different lateral embayment configurations to understand dense fluid exchange processes between the embayment and the main river channel.

Main Methods:

• Utilized unsteady Reynolds-averaged Navier-Stokes equations with an algebraic Reynolds stress model (ASM) enhanced for buoyancy effects.
• Simulated lateral embayments with varying configurations to analyze fluid and mass exchange dynamics.
• Validated the model using experimental data for continuous and discontinuous gravity currents in straight channels and embayment mass exchange.

Main Results:

• The model demonstrated reasonable agreement between simulated and measured flow and concentration fields.
• Both continuous and discontinuous gravity currents exhibited similar head propagation patterns within the embayment.
• Continuous gravity currents promoted rapid concentration diffusion in both the embayment and downstream main channel early on.
• In discontinuous currents (aspect ratio 1.0), dense fluid initially filled the embayment before flushing into the main channel.
• The embayment's geometric aspect ratio had a minor influence on the exchange coefficient, which averaged 0.33 for continuous gravity currents.

Conclusions:

• The developed numerical model accurately captures the complex dynamics of gravity currents interacting with river embayments.
• Understanding these flow dynamics is crucial for managing pollutant transport and mitigating habitat degradation in riverine systems.
• Embayment geometry plays a subtle role in modulating pollutant exchange, highlighting the need for site-specific assessments.