STORM vs MUSIC | Which Assessment Does Your Project Need?

In Brief

A STORM-style assessment is generally suited to smaller developments with straightforward runoff catchments and relatively simple treatment measures.

MUSIC modelling is generally used where a project contains larger or multiple catchments, connected treatment trains, more complex runoff pathways or subdivision-scale stormwater infrastructure.

The original Melbourne Water STORM Calculator has now been replaced by BlueFactor for suitable small developments. However, the term “STORM assessment” remains common in existing planning permits, council correspondence and project discussions.

The choice should not be based solely on which method is faster or simpler. The accepted assessment depends on the development, the proposed treatment system and the requirements of the relevant council or drainage authority.

Understanding the Two Assessment Methods

STORM and MUSIC occupy the same broad technical territory: both can be used to demonstrate how a development treats stormwater runoff and performs against applicable water-quality objectives.

The main difference is the level of detail each method can represent.

• STORM or BlueFactor provides a simplified assessment for suitable smaller developments.
• MUSIC provides more detailed modelling of runoff, treatment nodes and connected treatment systems.

A simple townhouse development may be capable of being represented using roof catchments, rainwater tanks, a driveway treatment and a small number of untreated areas.

A larger subdivision may involve multiple sub-catchments, roads, sediment ponds, wetlands, raingardens, harvesting systems and staged drainage infrastructure. That type of project is more likely to require MUSIC modelling.

For a broader overview of STORM reports and treatment assessments, visit the Certified Energy STORM Knowledge Hub.

What Is a STORM Assessment?

A STORM assessment is a simplified method of evaluating the stormwater-quality performance of a development proposal.

It commonly considers:

• total site area;
• roof catchments;
• driveways and paved surfaces;
• landscaped or permeable areas;
• rainwater tank capacity;
• roof area connected to tanks;
• rainwater reuse demands;
• raingardens or biofiltration areas;
• permeable paving;
• untreated impervious areas; and
• the overall stormwater treatment result.

The original STORM Calculator produced a relative score indicating how the proposed treatment strategy performed against the relevant best-practice objective.

Victorian planning guidance historically described STORM as most appropriate for small-scale subdivisions, typically below one hectare, while recognising that more sophisticated modelling may be preferable for larger developments.

What Is MUSIC Modelling?

MUSIC stands for Model for Urban Stormwater Improvement Conceptualisation.

It is a more detailed modelling platform used to represent how rainfall, runoff, pollutant loads and stormwater treatment measures interact over time.

A MUSIC model can represent:

• multiple source catchments;
• different land-use and surface characteristics;
• connected drainage pathways;
• sequential treatment measures;
• high-flow bypasses and overflows;
• rainwater or stormwater harvesting;
• raingardens and biofiltration systems;
• sediment ponds;
• constructed wetlands;
• infiltration systems; and
• complex treatment trains.

MUSIC is therefore better suited to projects where the order, connection and performance of several stormwater measures need to be modelled explicitly.

The Main Difference: Simplicity Versus Detailed Modelling

The distinction is not simply that STORM is used for residential projects and MUSIC is used for commercial projects.

The more useful dividing line is stormwater system complexity.

A smaller project may be suitable for a simplified assessment where:

• the assessment boundary is clear;
• the number of runoff catchments is limited;
• the treatment measures are straightforward;
• the runoff connections can be explained simply; and
• the responsible authority accepts a simplified tool.

MUSIC may be more appropriate where:

• the site contains numerous sub-catchments;
• runoff passes through several connected treatments;
• the project is staged;
• different land uses need separate modelling;
• the development contains subdivision-scale drainage assets;
• overflows and bypasses need to be represented;
• stormwater harvesting forms part of the strategy; or
• council or Melbourne Water specifically requires MUSIC.

When a STORM-Style Assessment May Be Suitable

A simplified treatment assessment may suit a relatively small and uncomplicated development.

Examples may include:

• a townhouse development on a conventional residential site;
• a small multi-dwelling development;
• a modest apartment project;
• a residential extension with a specific treatment requirement;
• a small commercial building;
• a small industrial development; or
• another project with a limited number of clearly defined catchments.

The treatment strategy may include a small number of elements such as:

• rainwater tanks connected to dwelling roofs;
• toilet flushing or landscape irrigation reuse;
• a raingarden receiving driveway runoff;
• permeable paving in selected areas; and
• a limited quantity of untreated runoff.

Even where a project appears simple, the relevant council should confirm that the proposed assessment method is acceptable.

When MUSIC Modelling May Be Needed

MUSIC becomes more relevant as the stormwater system grows in scale or complexity.

It may be required for:

• larger residential subdivisions;
• neighbourhood or precinct-scale developments;
• major commercial or industrial sites;
• large car parks and extensive road networks;
• multiple buildings draining to shared treatment assets;
• developments with several linked treatment measures;
• wetlands and sediment ponds;
• complex stormwater harvesting systems;
• staged developments;
• projects referred to Melbourne Water; or
• projects where the responsible authority specifically requests a MUSIC model.

Melbourne Water maintains dedicated MUSIC modelling guidelines for models submitted to it. The current guidance addresses matters such as rainfall data, model inputs, high-flow bypasses, overflows and treatment-node configuration.

How Treatment Trains Affect the Choice

A treatment train is a sequence of stormwater treatment measures through which runoff passes.

For example, runoff may travel through:

1. a gross-pollutant treatment;
2. a sediment pond;
3. a raingarden or wetland; and
4. a harvesting or discharge system.

The order of these measures can affect their operation and treatment performance.

MUSIC can model the connection between individual treatment nodes and show how runoff and pollutant loads move through the system.

A simplified STORM-style assessment is less suitable where the project depends on a detailed sequence of pre-treatment, primary treatment, bypasses, overflows and downstream assets.

Melbourne Water describes a treatment train as a sequence of treatments selected and ordered to maximise performance and protect downstream assets from pollutants such as litter and coarse sediment. :contentReference[oaicite:1]{index=1}

Does Project Area Determine the Required Tool?

Project area is an important indicator, but it is not the only consideration.

Victorian planning guidance has historically described STORM as most appropriate for small subdivisions, typically below one hectare, and MUSIC as suitable for more complex subdivision, neighbourhood or regional-scale projects. :contentReference[oaicite:2]{index=2}

However, a small site can still require MUSIC where it has:

• complex drainage arrangements;
• several connected treatment systems;
• sensitive receiving conditions;
• major harvesting infrastructure;
• significant external catchments; or
• a direct council or authority requirement.

Conversely, the suitability of a simplified method for any larger site should not be assumed merely because the proposed treatments appear simple.

The assessment method should reflect both scale and complexity.

STORM Has Been Replaced by BlueFactor

Melbourne Water replaced its original STORM Calculator with BlueFactor in December 2025.

BlueFactor now occupies the simplified-assessment role for suitable small developments, while MUSIC remains available for projects requiring more detailed modelling. :contentReference[oaicite:3]{index=3}

This means that a new project may be described as requiring:

• a BlueFactor assessment;
• a stormwater treatment assessment;
• a best-practice stormwater result; or
• a MUSIC model.

Older planning permits and council correspondence may still request:

• a STORM report;
• a STORM certificate;
• a STORM score; or
• a 100% STORM rating.

Where the wording refers to the former tool, the project team should confirm whether the responsible authority will accept the current BlueFactor output or requires another assessment method.

Can You Choose STORM Instead of MUSIC?

Not necessarily.

The assessment method may be nominated by:

• the relevant planning scheme;
• a council application checklist;
• a request for further information;
• a planning permit condition;
• a drainage authority;
• Melbourne Water;
• a Stormwater Management Strategy requirement; or
• the technical complexity of the proposed system.

A project should not use a simplified method merely to avoid the additional work associated with MUSIC where the stormwater system cannot be represented adequately.

Likewise, a relatively simple project should not automatically be burdened with detailed MUSIC modelling where an accepted simplified assessment can answer the relevant planning question.

How the Assessment Outputs Differ

A STORM-style report generally provides a concise account of:

• site and impervious areas;
• runoff catchments;
• rainwater tanks and reuse;
• other treatment measures;
• untreated runoff;
• key assumptions; and
• the resulting treatment score or benchmark outcome.

A MUSIC submission may provide substantially more technical detail, including:

• source-node and catchment configuration;
• rainfall and evapotranspiration data;
• runoff parameters;
• pollutant-generation parameters;
• treatment-node properties;
• node-to-node connections;
• bypasses and overflows;
• treatment-train performance;
• annual flow and pollutant results;
• model files;
• input justifications; and
• an auditor report where required.

For Melbourne Water submissions, the model itself and justification of key inputs may be required rather than screenshots or a short summary alone. :contentReference[oaicite:4]{index=4}

Example: A Small Townhouse Development

Consider a three-townhouse proposal with:

• three principal roof catchments;
• three rainwater tanks;
• toilet and garden reuse;
• one shared driveway;
• a small raingarden; and
• several minor untreated paths.

The catchments and treatment measures are limited and can be described clearly.

Subject to council acceptance, this type of project may be suitable for a simplified BlueFactor or STORM-style assessment.

The assessment can test whether the tanks, reuse demands, raingarden and untreated areas collectively achieve the required stormwater treatment result.

Example: A Residential Subdivision

Now consider a larger subdivision containing:

• multiple residential catchments;
• new roads and footpaths;
• public open space;
• several raingardens;
• sediment ponds;
• a constructed wetland;
• a stormwater harvesting system;
• high-flow bypasses;
• staged development; and
• shared downstream drainage infrastructure.

This system depends on the connections between several catchments and treatment assets.

MUSIC is more likely to be appropriate because it can model the treatment train and the movement of runoff and pollutant loads through the connected system.

Do Either of These Assessments Replace Drainage Design?

No. STORM, BlueFactor and MUSIC primarily assess stormwater treatment performance.

They do not automatically provide:

• pit and pipe sizing;
• minor drainage design;
• major overland flow design;
• on-site detention calculations;
• peak discharge assessment;
• legal point of discharge information;
• flood-level assessment;
• finished surface levels;
• structural treatment details; or
• civil construction drawings.

A project may require a stormwater treatment model and separate civil, hydraulic or flood-related documentation.

Victorian planning guidance distinguishes stormwater-quality treatment from the minor and major drainage systems needed to convey runoff and manage larger storm events. :contentReference[oaicite:5]{index=5}

Does MUSIC Automatically Produce a Better Result?

Not necessarily.

MUSIC provides a more sophisticated representation of the system, but the quality of the result still depends on:

• accurate catchment areas;
• appropriate rainfall data;
• justified runoff parameters;
• realistic treatment-node inputs;
• correct treatment connections;
• appropriate bypass and overflow settings;
• coordination with the physical design; and
• compliance with applicable modelling guidelines.

A detailed model using unrealistic inputs is not inherently more reliable than a well-prepared simplified assessment for an appropriately simple project.

Melbourne Water’s MUSIC guidance requires current modelling approaches and input parameters, and it no longer accepts new models based on its superseded 2018 templates or guidance. :contentReference[oaicite:6]{index=6}

Why Choosing the Correct Method Matters

Selecting the wrong assessment method can delay a planning submission or create unnecessary redesign.

A simplified assessment may be inadequate where:

• the treatment train cannot be represented properly;
• external catchments affect the site;
• the authority needs detailed modelling files;
• the development relies on major shared assets; or
• MUSIC has been specifically requested.

Detailed modelling may be unnecessarily complex where:

• the development is small;
• the catchments are straightforward;
• only a few treatment measures are proposed;
• a simplified tool is accepted; and
• the council only needs a concise treatment result.

Early confirmation of the required method helps the project team prepare the correct information and reserve suitable space for the treatment measures.

Practical Considerations for Victorian Projects

Check the Council Request

Determine whether the council has asked for a STORM report, BlueFactor result, MUSIC model, WSUD response or Stormwater Management Strategy.

Review the Project Scale

Consider the overall development area, number of catchments and extent of roads, roofs and other impervious surfaces.

Map the Treatment Connections

Identify whether runoff passes through one treatment or several connected measures.

Identify Shared Infrastructure

Shared wetlands, sediment ponds, harvesting systems and downstream assets often indicate the need for more detailed modelling.

Confirm Authority Requirements

A project referred to Melbourne Water or another drainage authority may need to follow specific modelling guidelines and submission requirements.

Separate Treatment From Drainage

Confirm whether civil drainage plans, detention calculations or flood assessment are required in addition to the water-quality model.

Use the Current Tool and Guidance

New small-development assessments should reflect the transition from STORM to BlueFactor, while MUSIC models should use the applicable current modelling guidance.

Which Assessment Does Your Project Need?

A STORM-style or BlueFactor assessment may be appropriate where:

• the project is relatively small;
• the catchment layout is simple;
• the treatment measures are limited in number;
• the runoff routing is straightforward;
• there is no complex treatment train; and
• the relevant council accepts the simplified method.

MUSIC modelling may be appropriate where:

• the project is larger or subdivision-scale;
• there are multiple source catchments;
• several treatments are connected in sequence;
• the project includes wetlands, sediment ponds or harvesting;
• bypasses and overflows need to be modelled;
• the development is staged;
• Melbourne Water is reviewing the model; or
• the responsible authority specifically requires MUSIC.

Where the requirement is unclear, the available plans and council correspondence should be reviewed before the assessment scope is confirmed.

How Certified Energy Can Help

Certified Energy can review the proposed development and help determine whether a focused STORM-style or BlueFactor assessment is appropriate.

For suitable projects, this may include:

• reviewing the council request or permit condition;
• measuring site and impervious areas;
• identifying runoff catchments;
• reviewing rainwater tanks and reuse demands;
• assessing raingardens and permeable surfaces;
• testing the overall treatment performance;
• documenting the assessment assumptions;
• coordinating treatment measures with the project drawings; and
• identifying when more detailed MUSIC, civil or hydraulic input may be required.

A simplified STORM assessment should not be presented as an alternative to MUSIC where the scale, treatment system or authority requirements call for detailed modelling.

Explore the STORM Assessment Knowledge Hub or send through the current plans and council correspondence for an initial review.

Frequently Asked Questions

What is the main difference between STORM and MUSIC?

STORM is a simplified stormwater treatment assessment for suitable smaller projects. MUSIC provides more detailed modelling of runoff catchments and connected treatment systems.

Is STORM still used in Victoria?

The original STORM Calculator has been replaced by BlueFactor for suitable small developments. The STORM term remains common in existing reports, permits and council requests.

When is a simplified assessment suitable?

It may suit a relatively small project with a limited number of clearly defined catchments and treatment measures, subject to council acceptance.

When is MUSIC required?

MUSIC may be needed for larger developments, multiple catchments, treatment trains, subdivision infrastructure or where the relevant authority specifically requests it.

Is MUSIC only used for subdivisions?

No. It may also be used for complex commercial, industrial, institutional or mixed-use developments where detailed catchment and treatment modelling is needed.

Can a townhouse development require MUSIC?

Yes. Although many townhouse projects are relatively straightforward, MUSIC may be required where the site, drainage arrangement or treatment system is unusually complex or council specifically requests it.

Can a large site use BlueFactor?

Suitability should not be assumed. Larger developments are more likely to require detailed modelling, particularly where they contain multiple catchments or treatment trains.

Does MUSIC replace a Stormwater Management Plan?

No. A MUSIC model may form part of a broader Stormwater Management Plan, but the plan may also address drainage, detention, discharge, maintenance and implementation.

Do STORM and MUSIC assess flooding?

They primarily address stormwater treatment performance. Flooding, drainage capacity and overland flow may require separate assessment.

Who decides which assessment is required?

The appropriate method is influenced by the planning controls, project complexity and the requirements of the relevant council, Melbourne Water or drainage authority.

Suggested Internal Links

• STORM Assessments and Reports Knowledge Hub
• What Is a STORM Assessment?
• When Is a STORM Assessment Required in Victoria?
• What Does a STORM Report Include?
• How Is a STORM Score Calculated?
• What Does a 100% STORM Rating Mean?
• STORM vs WSUD: What Is the Difference?
• STORM Report vs Stormwater Management Plan
• STORM Assessment vs Drainage Design
• What Information Is Needed for a STORM Assessment?