July 23, 2017

North St. Balmain GPT

BALANCE_Banner_Hyd_North St

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 underground Box Culvert system in North Street Leichardt in Sydney.

The original design consultant wanted to utilise a Collapsible weir system inside the box culvert to divert flow out of the culvert and into the Gross Pollutant Trap (GPT) or Pollutant Capture Device (PCD). Sydney water required indisbutable evidence that the concept would not compromise system capacity.

As a result BALANCE RnD were engaged to test the concept using a physical hydraulic model. The model showed that the treatable flow rate claimed was unacheivable and that there was a localised presurisation of the system where the diversion rejoined the original system due to an internal hydraulic jump forming.

This meant that pits locally had to be bolted down to avoid surcharge and flooding of the street. The tests resulted in several recommendations and these were implemented during construction.

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.

Brokers Rd Basin Labyrinth Weir

Physical Hydraulic Model of the Brokers Rd Basin

This project was undertaken by Rudy whilst working for Wollongong City Council. However it represents an excellent example of utilising the cost effectiveness of the hydraulics laboratory to undertake design, and design refinement.

Previous consultants had prepared a Labyrinth weir concept for the PMF spillway, that was on a straight alignment.

The structure was very large, and did not make it easy to convey flow back to the watercourse. The redesign of a labyrinth on a radius conceptually produced a far more cost effective solution.

Two models 1:50 and 1:100 scale were constructed to review the labyrinth performance.

Further the 1:50 scale model was used to investigate the impact of a foot bridge over the structure on flow behaviour. Several special features were aded as part of the design refinement. Including a stepped weir inlet on the low flow, and energy dissipation at the outlet.

Further enhancement was also discussed but to date not implemented. This included a self opening gate structure on the medium flow inlet to enhance the performance of the storage in the basin.