Evaluating stormwater treatment alternatives

Maroochy Shire on the Sunshine Coast has an extensive waterway network that adds much to the area’s splendour and makes it a desirable place to live. However, the more people migrate to the area, the greater the threat grows to its catchments and waterways. Today, stormwater and agricultural run-off as well as nutrients from treated sewage discharge pose major risks to the health of the Maroochy River estuary.

Water sensitive urban design (WSUD) is a major part of the solution. A key planning component for many new developments, specialists increasingly recognise that retrofitting WSUD into existing urban areas can help solve urban water quality problems, such as capturing stormwater run-off, removing its contaminants and lessening its amount.

As there are many treatment alternatives, the challenge is to evaluate those many choices to achieve the great possible hydrology and water quality improvements at the lowest possible costs.

Engineering and environmental consultants BMT WBM did just that in an existing area close to Maroochydore Library, where the firm worked with the Sunshine Coast Regional Council to retrofit multiple WSUD elements. Using eWater’s urban stormwater modelling software called music (model for urban software improvements conceptualisation), the project team was able to fully assess the full range of possible stormwater management devices.

music, developed by eWater CRC, let the team evaluate and coordinate stormwater treatment measures from a network of related urban catchments and subcatchments simultaneously. They were able to rapidly assess different scenarios then examine the results both for particular rainfall events and for the long term.

They then ranked all the measures according to the software’s estimates of their treatment effectiveness and life cycle costing. This showed the best choices for stormwater were an integrated system of swales, bioretention systems and porous pavements.

The team also installed several types of rainwater tank, for water harvesting for use in toilets, directing overflow from the tanks into a rain-garden which promotes infiltration.

By examining alternatives using the modelling software, and looking at their costs, BMT WBM could see the minimum requirements for retrofitting a suburb or a subcatchment. Indeed the modelling software allowed them to showcase much more than the minimum WSUD elements, with aesthetic benefits to the area as well as environmental benefits to the river considered.

The Maroochydore Library project highlights both the ease of integrating WSUD into existing urban areas and the success of partnerships of industry and government in delivering such projects. As a measure of its success, this project was nominated as a finalist in the 2009 Healthy Waterway Awards WSUD Category.

Environmental and engineering consultants around Australia use the stormwater modelling software, music, to design urban development proposals that meet water-sensitive urban design standards.

Not a detailed design tool in itself, music rather aims to set out the alternatives for improving stormwater quality. The software is allowing planners to assess the pros and cons of various engineering systems for improving stormwater quality - biofilters, swales, wetlands and the like.

The latest version of the software, music v4, improves realism and increases choices. It includes major advances to the science and enhances the ability to model new stormwater technologies like porous pavements. It also includes raw rainfall data for 50 major population centres in Australia. Users who take up the ‘support’ option have access to more than 1000 pluviometer stations across Australia.

The new version offers features that improve flexibility and usability. These include more accurate modelling of bioretention and infiltration systems and better re-use options. Users can model parameters such as total suspended solids, total phosphorus and total nitrogen. The new version also offers many other refinements.