June 29, 2017

Leonards Reserve GPT


As part of the Sydney Water Corporations “Stormwater Environment Improvement Program” (SEIP) there was a proposal to construct a large Gross Pollutant Trap (GPT) on a large concrete channel.

The aim was to deflect the water out of the channel and into an offline device to remove the pollutants from the stream flow. However it was discovered that the channel flow regime was supercritical and the initial concept of a diversion weir would result in a change of flow regime, a hydraulic jump and localised flooding.

As such an alternate had to be devised. BALANCE RnD were engaged to provide a solution. The solution consisted of a methodology whereby a “Hump” in conjunction with a channel widening were employed to create a deflection mound at low flows but maintained the same supercritical flow regime at high flows thereby avoiding the flooding problem.

The concept was tested in the hydraulics lab and then also confirmed with 2-D hydrodynamic modelling. The concept is fully constructed and is succesfully fully operational.

The Concept utilises MINIMUM ENERGY principles which were tested in the flume and confirmed with a 2D model, prior to construction. This project was the subject of a Conference Paper presented at NOVATECH in Lyon in 2007. A copy of the paper can be downloaded here.

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