Modelling philosophy

MUSIC is an aid to decision-making. It enables you to evaluate conceptual designs of stormwater management systems to ensure they are appropriate for their catchments.

By simulating the performance of stormwater improvement measures, MUSIC determines if proposed systems can meet specified objectives, both from a hydrologic and water quality perspective. MUSIC will simulate the performance of a group of stormwater management measures, configured in series or in parallel to form a "treatment train". MUSIC runs on an event or continuous basis, allowing rigorous analysis of the merit of proposed strategies over the short-term and long-term.

The adoption of a continuous simulation approach is recommended in modelling stormwater management systems. This stems from the fact that impacts of poor stormwater quality on aquatic ecosystem health are associated with cumulative pollutant loads and frequency of aquatic ecosystem "exposure" to poor water quality. Pollutant loads delivered to receiving waters from many of the small storm events (e.g. of magnitude less than the 3 month ARI peak discharge) can make up in excess of 90% of the annual loads discharged from the catchment. It also reflects the necessity of examining the hydrologic performance of treatment systems over a range of climatic conditions, not just design events, to ensure that the systems will be robust and not susceptible to high water levels, have sufficient storage capacity and have appropriate drawdown times.

The evaluation of the effectiveness of a stormwater management system is based on a risk-based approach associated with examination of:

1. the hydrologic effect of implementing the treatment system in terms of peak flow reduction, volumetric reduction and frequency of event flows;
2. the long-term frequency in which the receiving aquatic ecosystem is subjected to exposure of pollutant concentrations above a pre-specified threshold level; and/or
3. the long-term mean annual pollutant load delivered to the receiving waters.

MUSIC is designed to simulate stormwater systems in urban catchments and to operate at a range of temporal and spatial scales suitable for catchment areas from 0.01 km2 to 100 km2. Modelling time-steps can range from minutes to 24 hours to match the range of spatial scale.