Trapping sediment in stormwater wetlands


View story in H20 Thinking

Constructed wetlands and ponds are now widely used for the treatment of urban stormwater contamination, but the better they are understood the better they may work.

“Given the financial cost and amount of land taken up in constructing stormwater ponds and wetlands, it is highly desirable that we can reliably predict their performance in trapping sediment,” says Yong Li, a PhD candidate at Monash University in Melbourne, and eWater CRC.

An efficient system collects sediments and reduces the concentrations of suspended solids, total phosphorus, total nitrogen and heavy metals in stormwater, to protect the condition of creeks and other receiving waters downstream. It often consists of a ‘train’ of structures combined in series or parallel to suit the sources of contaminants.

While there are already computer models, such as MUSIC*, that help stormwater managers predict and assess the performance and cost-effectiveness of potential stormwater management strategies, Yong decided to try a different approach.

She has undertaken a comprehensive series of laboratory, field and modelling studies to investigate two key physical processes - sediment deposition and re-suspension - both within and between individual storm events, in wetlands and ponds.

The model that Li has developed can deal with variable flow conditions in real wetlands, in both wet and dry periods.

When she compared her modelling results with those generated by the widely-used k-C* model, she concluded that the new Nf model, when combined with the CSTR (continuously stirred tank reactors) flow hydrodynamic model, was better suited to simulating different flow conditions in constructed stormwater wetlands, without the need for complex calibration.