A STORM assessment is a quantitative stormwater treatment assessment used to show how runoff from a proposed development will be managed and treated.
A STORM assessment evaluates stormwater runoff from the impervious areas of a development and measures the treatment performance of proposed measures such as rainwater tanks, raingardens and permeable surfaces.
It is commonly associated with Victorian planning applications where a council needs evidence that a project can achieve an appropriate stormwater-quality outcome.
The assessment is focused on runoff treatment and pollutant reduction. It is not a substitute for drainage design, on-site detention calculations, flood modelling or a civil engineering report.
Current terminology note: Melbourne Water has replaced its original STORM Calculator with BlueFactor. However, “STORM assessment” and “STORM report” remain familiar terms in existing council documentation, earlier planning permits and project discussions. The relevant council should confirm which assessment tool or reporting format it currently accepts.
When a site is developed, surfaces that once absorbed rainfall may be replaced by roofs, driveways, paths, paved areas and other impervious surfaces. Rainfall landing on these areas can become stormwater runoff and carry sediment, nutrients, litter and other pollutants into the drainage system and surrounding waterways.
A STORM assessment examines how much of this runoff is generated by the proposed development and how effectively the proposed treatment measures manage it before it leaves the site.
The assessment usually considers:
The resulting score or output helps demonstrate whether the proposed treatment strategy reaches the applicable best-practice stormwater-quality objective.
For a broader overview of STORM reports, treatment measures and Victorian project requirements, visit the Certified Energy STORM Knowledge Hub.
A STORM assessment is primarily concerned with the relationship between:
Each roof, driveway, path or paved surface should be accounted for. The assessor then identifies whether runoff from that surface is directed to a treatment measure or discharged without treatment.
For example, roof water may be directed to a rainwater tank that supplies toilets or landscape irrigation. Driveway runoff might be directed through a raingarden, while a small paved area may remain untreated.
The assessment combines these different catchments and treatment responses into an overall result for the development.
The purpose of a STORM assessment is to provide a clear, measurable response to stormwater treatment requirements.
Rather than simply stating that a project includes sustainable drainage features, the assessment tests whether the selected measures are appropriately sized and connected to the runoff-generating areas of the site.
This gives councils and project teams a practical way to review whether:
Urban development changes how rainfall moves through a site. An increase in impervious area can increase the volume and frequency of runoff entering drains and waterways.
Stormwater may also carry pollutants from roofs, driveways, paved surfaces and landscaped areas. Without suitable treatment, these pollutants can affect the health of creeks, rivers, bays and other receiving environments.
A STORM assessment matters because it turns the proposed treatment strategy into a measurable project outcome. It can help the project team identify whether the design needs:
Considering these matters early can reduce the risk of late redesign after architectural drawings, landscape plans and hydraulic services have already been developed.
Victorian planning provisions include stormwater management objectives for various forms of subdivision, buildings and works. Depending on the development type and applicable planning controls, an application may need to show how the proposed stormwater management system addresses runoff quality, retention, detention and discharge.
A STORM-style assessment may be used as supporting evidence where a council requires a quantitative stormwater treatment result for a relatively small or straightforward development.
Projects that may encounter stormwater treatment requirements include:
The exact requirement is not identical for every project. It can depend on the planning scheme, development type, project size, permit pathway, local policy and council expectations.
For that reason, a STORM assessment should not be described as automatically mandatory for every Victorian building project. The planning permit requirements and relevant council guidance should be checked for the particular site.
Melbourne Water’s original STORM Calculator has now been replaced by BlueFactor.
BlueFactor performs a similar planning role for small-scale developments by assessing stormwater runoff, pollutant generation and proposed treatment measures. It is intended for relatively small and straightforward residential or commercial developments rather than complex catchments or extensive treatment trains.
This means a new project described informally as requiring a “STORM assessment” may now be assessed through BlueFactor, depending on the council and the applicable submission requirements.
The distinction is important:
Existing reports and permits may still refer specifically to a STORM score. New applications should follow current council requirements rather than assuming that an older calculator output will always be accepted.
STORM and Water Sensitive Urban Design are closely connected, but they are not the same thing.
WSUD is the broader design approach. It considers how water is managed across a site through planning, architecture, landscaping, reuse, infiltration and stormwater treatment.
A STORM assessment is a quantitative assessment. It tests the stormwater treatment performance of selected measures and catchments.
A project may use WSUD measures such as:
The assessment then checks how those measures contribute to the required runoff treatment outcome.
Read the dedicated comparison in STORM vs WSUD: What Is the Difference?.
STORM and MUSIC can both be used to evaluate stormwater treatment, but they are suited to different levels of project complexity.
A STORM-style assessment is generally associated with smaller developments and relatively simple arrangements of catchments and treatment measures.
MUSIC can represent more complex catchments, drainage connections and treatment trains. It uses time-step simulation to model rainfall, runoff and the performance of connected stormwater treatment measures.
A larger or more complicated project may therefore require MUSIC rather than a basic STORM or BlueFactor assessment.
The relevant council or drainage authority should confirm which method is appropriate. See STORM vs MUSIC: Which Assessment Does Your Project Need? for a focused comparison.
A STORM assessment should not be treated as a complete stormwater engineering package.
It does not ordinarily replace:
The STORM assessment owns a narrower technical territory: quantifying stormwater treatment performance.
A project may need both a treatment assessment and separate drainage or civil engineering documentation. One does not automatically satisfy the purpose of the other.
Roof areas are only part of the assessment. Driveways, paths, patios, balconies and other sealed areas may also generate runoff and need to be included.
A treatment measure cannot simply be shown somewhere on the plan. The assessment needs a credible relationship between the runoff-generating catchment and the treatment receiving that runoff.
A tank generally performs more effectively when stored water is regularly reused. Tank volume, connected roof area and nominated end uses should therefore be coordinated rather than selected independently.
Raingardens, tanks and permeable systems require physical space and suitable connections. They should be considered before the site plan and landscape design become fixed.
Councils may differ in the information, drawings, annotations and assessment outputs they expect. Some may also have specific preferences for treatment measures or maintenance documentation.
The tank capacity, connected catchment, reuse connections and treatment areas shown in the assessment should match the architectural, landscape and hydraulic documents.
A preliminary STORM assessment can often begin using architectural plans, provided the site areas and proposed treatment strategy are sufficiently clear.
Common inputs include:
Read What Information Is Needed for a STORM Assessment? for a more detailed document checklist.
Certified Energy can review the available project drawings and identify the information needed to prepare a stormwater treatment assessment for a Victorian planning submission.
The assessment process may include:
The correct tool and reporting scope will depend on the project, its complexity and the requirements of the relevant council.
Explore the STORM Assessment Knowledge Hub or send through the available plans for an initial project review.
A STORM assessment is a quantitative assessment of how runoff from a proposed development will be treated. It considers impervious areas and treatment measures to determine whether the design achieves the required stormwater-quality outcome.
Melbourne Water has replaced the original STORM Calculator with BlueFactor. The STORM name remains widely recognised, but new projects may need to use BlueFactor or another assessment method accepted by the relevant council.
It measures the stormwater treatment performance associated with runoff from roofs, driveways, paths and other impervious surfaces, taking account of the treatment measures connected to those areas.
No. Its primary purpose is stormwater treatment and water-quality assessment. Flood behaviour, drainage capacity, detention and overland flow may require separate civil or hydraulic assessment.
No. WSUD is an integrated approach to water-sensitive planning and design. A STORM assessment quantifies the treatment performance of particular stormwater measures used within the design.
No. MUSIC provides more detailed modelling of catchments, drainage connections and treatment trains. A STORM-style assessment is generally suited to smaller, simpler developments.
Yes. A tank can improve the result when it captures runoff from an appropriate roof area and is connected to regular reuse demands such as toilet flushing or landscape irrigation.
No. The requirement depends on the development, planning controls, permit pathway and council expectations. Some projects need a different assessment method or may not require a quantitative treatment assessment.
A site plan and roof plan are commonly needed, together with dimensions or area information for roofs, driveways, paving, landscaping and proposed treatment measures.
It is best considered before the design is finalised. Early assessment leaves more opportunity to coordinate tank locations, catchment connections, landscaping and treatment areas without major redesign.