Melbourne Water STORM Help


What is STORM?

Melbourne Water has developed the Stormwater Treatment Objective- Relative Measure (STORM) Calculator as a method of simplifying the analysis of stormwater treatment methods. The STORM Calculator is designed for the general public to easily assess Water Sensitive Urban Design (WSUD) measures on their property.

The tool has been developed specifically for small residential and industrial developments to rate how well different properties treat stormwater and to compare them against a common measurement system.

The STORM Calculator displays the amount of treatment that is required to meet best practice targets, using WSUD treatment measures. The tool is capable of calculating the performance of a range of commonly implemented treatment measures including:

The STORM Calculator can uses rainfall data from any region in Victoria, Australia, by looking at the municipality in which the development is located.


The STORM Calculator has been developed from the stormwater assessment tool created by the Association of Bayside Municipalities (ABM) and published in the Delivering Water Sensitive Urban Design: Clean Stormwater - A Planning Framework (2004) (PDF, 4.36MB).

The data used for calculating the STORM rating has been taken from the Model for Stormwater Improvement Conceptualisation (MUSIC) (PDF, 414kb) version 3, developed by the Cooperative Research Centre for Catchment Hydrology. (CRCCH, 2005).

How STORM works

The STORM Calculator rates the performance of treatment measures relative to the percentage of best practice targets that have been achieved by those treatment measures.

Inputs to the model include impervious areas and a selected treatment measure.

An adjustment factor adjusts for different hydrologic regions and then a series of tables provide treatment performance. A weighted average is calculated, providing a final STORM rating. A rating of 100 means that objectives have been met.

Achieving best practice

The best practice standards have been set out in the Urban Stormwater Best Practice Environmental Management Guidelines (Victoria Stormwater Committee, 1999) for reduction in total suspended solids (TSS), total phosphorus (TP) and total nitrogen (TN) loads.

The Best Practice Environmental Guidelines (BPEG), published by the Victorian Stormwater Committee, establishes specific stormwater quality objectives to assist in determining the level of stormwater management necessary to meet the State Environment Protection Policy (SEPP) requirements. These guidelines are now a referenced document in the State Planning Policy Framework. The best practice performance objective from the BPEG, from which the STORM Calculator rates treatment performance, is : TN: 45% retention of the typical annual load.

The reduction in TP and TSS load have not been included in the STORM calculator as the reduction in TN is usually limiting, making the reduction in TP and TSS mostly irrelevant to STORM calculations.

How accurate is STORM?

The calculator can be used across Victoria, Australia. The tool is limited to the assessment of discrete treatment measures ie it does not model accurately a treatment train where several treatments are designed in series. The tool is also limited to sites where the coverage of impervious surfaces is greater than 40%.

For large complex sites more sophisticated modelling should be undertaken (eg MUSIC).


This calculator and website may be of assistance to you but the State of Victoria and its employees do not guarantee that the calculator and/or website is without flaw of any kind, or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence that may arise from you relying on any information on this website.

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