River loses Blues
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A UQ PhD student is investigating why the Brisbane river changed from blue to brown.
Luis Neumann has been researching the sediment processes in the river responsible for the turbidity or "dirtiness" of the water.
Mr Neumann's innovative thesis is unusual in that his research methods span the fields of both chemical and environmental engineering.
Using equations known as population balances to calculate changes to the population of cohesive sediments in the river, he demonstrated the sediment did not have enough time to settle, giving the river a dirty appearance.
"Today's large tidal intrusion means tidal velocities are much higher than in the past. The larger the tidal velocity, the higher the bottom shear stress that erodes the river bottom and the higher the turbulence that keeps the particles in suspension," he said.
Mr Neumann is examining the process known as flocculation through which suspended solids in the river collide and stick together to form flocs.
He said in the past, researchers had assumed values for parameters affecting flocculation whereas he had been able to quantify the influence of different parameters.
Mr Neumann said the size and shape of the flocs affected sediment transport and light penetration, factors largely responsible for the river's colour.
