A Flood impact (afflux) practice note: Floodplain development impact assessment has been developed in collaboration with state government stakeholders, industry and key planning associations.

This will assist developers, their advisers and the community with the preparation of development applications in flood-prone areas. The guidelines are also intended for use by Melbourne Water and other authorities to assess whether applications for development in these areas are acceptable.

The guidelines were tested on selected urban developments and state projects to gain critical insights and identify practical limitations before a broader roll-out.

Access the guidelines: Flood impact (afflux) practice note: Floodplain development impact assessment (PDF, 797KB)

Risk-based approach to assessments

Melbourne Water has developed the practice note to provide clear and practical guidance on managing offsite flood level impacts for proposed developments, where zero-afflux cannot be achieved, by using a risk-based flood impact assessment framework.

Where it can be demonstrated that a zero afflux can’t be reasonably achieved, the new best-practice guidelines help to further assess the application to:

• better understand the flood risk profile of a development
• provide general advice on flood-risk management
• recommend a procedure to evaluate flood impact
• assess factors including, but not necessarily limited to, flood levels, flood hazard category, level of service (degree of flood protection) and duration of inundation
• determine acceptable flood impact tolerances.

This Practice Note sits alongside DEECA’s 2019 Guidelines for Development in Flood Affected Areas and maintains the policy that ‘there should be no detrimental impacts to nearby properties, particularly properties downstream’.

Developments must not compromise the natural function of the floodplain and avoid:

• Flow diversion 

• Increased flood velocity 

• Increased flood levels 

• Loss of flood storage.

Developers are required to provide evidence of their compliance to flood management deliverables for their application to be approved.

Next steps

Melbourne Water will review these guidelines again within 12 months to ensure that their risk-based approach is effective and progressively improved. Feedback from industry and other stakeholders will help us identify any gaps, inconsistencies, or unintended consequences.

The updated guidelines will come into effect from 4 February 2026.

Send your questions or feedback on the updated guidelines to [email protected] or phone 131 722.