Case Studies

Hillgrove Estate: Waterway, Sediment Basin and Retarding Basin Design



VS Fortune & Melbourne Water

Start Date:

March 2015

Completion Date:


Project Overview & Outcome


Hillgrove Estate is a 620 lot greenfield residential development located in Rockbank.


Engeny has delivered high quality outcomes for Melbourne Water and the developer from planning through design and into construction for water quality treatment works, a constructed waterway and retarding basin.

Project Details

The Problem

The Estate is within the Leakes Road Development Services Scheme and is positioned adjacent to a constructed waterway (Tributary of Kororoit Creek), two sediment basins, a wetland and a multi-cell retarding basin that are all Scheme assets

The Response

Engeny received a 5/5 rating from Melbourne Water for “User rating of work quality”, “User rating of ease to work with supplier” and “User rating of transfer effectiveness”.

The Details

The design of the constructed waterway and retarding basin presented an opportunity to preserve and enhance existing habitat values. This included preserving areas of Freshwater Lignum Shrubland (EVC 657) and Plains Grassy Wetland (EVC 125) by shaping the retarding basin to avoid these areas whilst still achieving the required flood storage. This was done by utilising proposed road alignments as retarding basin embankments. Culturally significant dry stone walls were also preserved by modifying the retarding basin embankment footprint.

The design of sediment basins and the wetland utilised water quality modelling software MUSIC together with various supporting calculations from the relevant industry and Melbourne Water guidelines. Erosion management for the constructed waterway was sized using results from a 1D/2D model of the floodplain and proposed retarding basin, a 1D HEC-RAS model of the constructed waterway and rock sizing estimates using CHUTE and RIPRAP software where appropriate.

The Result

Engeny initially undertook a functional design of the retarding basin, sediment basins and wetland and downstream waterway on behalf of Melbourne Water and has subsequently completed the following works on behalf of VS Fortune, the Hillgrove Estate developer:

  • Stormwater management plan.
  • ANCOLD consequence of retarding basin failure assessment.
  • Detailed design (drafting undertaken by GPR) of the retarding basin, constructed waterway and sediment basins.

Engeny is currently finalising our Quality Assurance for the retarding basin construction (a future Melbourne Water asset) that we have completed on behalf of the developer and Melbourne Water.

Project Relevance

The delivery of the Hillgrove Estate: waterway, sediment basin and retarding basin design demonstrates Engeny’s expertise in waterway and environmental management, including:

  • Investigation and design of Water Sensitive Urban Design initiatives to improve water quality, including MUSIC modelling.
  • Investigate stream bed stability to inform the design of the constructed waterway.
  • Review of environmental investigations, including flora and fauna, geotechnical, site surveys and cultural and heritage, all of which were used to inform the designs.

Project Innovation

Engeny worked closely with Melbourne Water to develop the functional design for the wetland and retarding basin. Innovations include:

  • The adoption of a shorter detention time on the wetland to achieve improved wetland health outcomes.
  • Sediment basin that includes a swale within the top part of the extended detention depth to improve plant survival within the swale.
  • Retarding basin that incorporates two (2) roads to form the embankment batters and includes two (2) sediment basins and a wetland within the basin.

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