Stormwater Management Strategy – Merrimu Precinct Development

Rain Consulting has worked closely with Bacchus Marsh Developments over several years to deliver the Merrimu Stormwater Management Strategy and supported the developer throughout the evolving Precinct Structure Plan (PSP) approval process. This comprehensive plan addresses drainage, flood risk, water quality, and integrated water management (IWM) for a major new community north-west of Melbourne, spread across 530 hectares of predominantly rural land. Our work continues as the project develops.

Above & Beyond Strategies

The Merrimu project is a large, sensitive site with complex soils and significant erosion risks. Rain was engaged to develop a practical and robust stormwater strategy that balanced the requirements of Melbourne Water with future community needs and technical constraints. The strategy required careful planning, specialist soil assessments, and close collaboration with multiple stakeholders.

Rain delivered the following solutions.

• Detailed hydrologic and hydraulic modelling (TUFLOW and RORB) to map all drainage and flood risks.
• Soil investigations and erosion risk assessments to identify suitable outfall locations and asset design.
• Staged concept designs for wetlands, retarding basins, and stormwater assets across six major catchments.
• MUSIC water quality modelling to ensure all treatment assets exceed best practice standards.
• Integration of open space, urban cooling, conservation zones, and future water reuse into the drainage layout.
• Resolution of complex outfall and catchment boundary issues (including piping, land take, and stable outfalls).
• Ongoing consultation and negotiation with Melbourne Water and other stakeholders.
• Incorporation of Integrated Water Management (IWM) and water harvesting opportunities for long-term community benefit.
• Facilitated fortnightly project meetings with Melbourne Water.
• Design of twelve separate wetland and retarding basin assets.

Rain delivered a robust, adaptable stormwater strategy that meets PSP and Melbourne Water requirements, with clear pathways for staged approvals and future refinement. All major drainage, water quality, and open space assets have been planned in detail, with mitigation strategies for challenging soils and outfall constraints. The solution future-proofs the development while balancing environmental and community needs.

Creating a robust stormwater strategy for Merrimu that balances technical constraints, environmental sensitivity, and future community needs—supporting a 530-hectare development with resilient, sustainable water management from planning through to delivery.