Dissolved Oxygen Transfer by Convective Cooling in Lakes and Rivers

Summary

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Gaseous Oxygen is dissolved into the surface waters of rivers, lakes oceans and then mixed by turbulence within the water column. The turbulent mixing which controls this transfer rate is poorly understood in conditions of low wind and strong thermal stratification where convective cooling and other mechanisms are important. This project will investigate these effects through both experimental and numerical approaches.

Supervisor

Associate Professor Nicholas Williamson.

Research location

Aerospace, Mechanical and Mechatronic Engineering

Synopsis

Large scale fish kill events are an increasingly common occurrence in inland Australian rivers as a result of low dissolved oxygen (DO) levels. Rivers have significant DO demand for fish respiration and biological activity in the sediments and water column. Under normal conditions this DO demand is met by the continual transfer of gaseous oxygen from the atmosphere into the water surface, where it is then mixed through the water column by turbulence. When river flow is low however the water column can become thermally stratified and buoyancy effects damp out turbulent mixing thereby reducing DO transport from the surface. These conditions lead to DO depletion and fish kills. The gas transport process is very complex. Studies across a wide range of flows (lakes, oceans, rivers) have shown that gas transfer from the surface is usually controlled by small scale mixing at the surface driven by larger scale turbulence within the water column. However, the dynamics of the turbulence, including how the turbulence is generated have a strong influence on the process and require separate parameterisations. The strongly stratified flow regimes seen leading up to fish kill events in Australian rivers are very different from conditions examined in most early investigations, so we are unable to predict DO supply into a water body before, during or after a fish kill event.

This project comprised of two main lines of investigation:

Numerical research program which will use highly resolved direct numerical simulations to investigate the near surface mixing in strongly stratified river/lake flow under light wind forcing. The dynamics of convective cooling on gas transfer and the dynamics of non-breaking surface waves will investigated.
A field program which will involve deploying high accuracy eddy covariance instruments to capture the turbulent oxygen and heat flux near the surface. Our well equipment fluid mechanics laboratory will be used for testing and development of instrumentation.

PhD projects are available on both topics.

Additional information

The research will be conducted within a large multi-disciplinary team including engineers and freshwater ecologists.

Successful candidates must:

Have a strong interest in fundamental fluid mechanics, heat and mass transfer and numerical or experimental methods for fluid mechanics.

How to Apply:

To apply, please email nicholas.williamson@sydney.edu.au the following:

CV
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Opportunity ID

The opportunity ID for this research opportunity is 3426