Elizabeth Street catchment integrated water cycle management plan

The Elizabeth Street Catchment Integrated Water Cycle Management (IWCM) Plan aims to mitigate the extreme flood risks present in the 308-hectare Elizabeth Street Catchment. The plan includes a suite of targets, projects and initiatives to be implemented over a five-year period. These actions will enable the City of Melbourne to reduce its flood risk and access alternative water sources for the sustainable irrigation of parks, open spaces, and street trees.

The catchment sits entirely within the municipality of Melbourne. It starts at College Crescent in Carlton and finishes where the Elizabeth Street drain joins the Yarra River below Flinders Street Station.

• Reduce flood risk: The Elizabeth Street Catchment is categorised by Melbourne Water as being at Extreme Flood Risk – the highest level. The plan aims to reduce this flood risk from ‘extreme’ to ‘high’.
• Develop alternative water supplies: To irrigate the municipality’s existing and future parks, gardens, trees and open spaces.

• Integrated water cycle management: The plan involves all the elements of the water cycle that the City of Melbourne can influence – water consumption, rainwater, stormwater, wastewater and groundwater management.
• Diverse solutions: A mixture of innovative interventions at a catchment scale were investigated for implementation. Interventions that acted to reduce runoff and downstream flood risk included permeable pavements, raingarden tree pits and stormwater harvesting using large tank storages. Green roofs were also explored as a method of reducing stormwater runoff.
• Top of catchment: The Carlton Squares, Royal Exhibition Building / Melbourne Museum, and Queen Victoria Market stormwater harvesting systems are key projects that will help to hold water in the top of the catchment and reduce flood risk at the bottom of the catchment.

• Recognise complexity: Complex problems require complex solutions, and patience and expertise are vital to develop them.
• Divide and conquer: Staging catchment scale plans and projects into manageable sections can be an effective method for achieving ambitious objectives.
• Identify the weakest link: Modelling the catchment’s drainage capacity identified that significant improvements could be achieved by increasing the pipe sizes in two key locations. This was an effective way for identifying drainage bottlenecks.
• Mimic nature: Increasing surface permeability can reduce hydraulic stress on drains and improve the replenishment of groundwater.
• Nuisance to resource: Stormwater harvesting can be used as a tool for addressing local drought and flood risks.
• Top of catchment: Increasing permeability and stormwater harvesting at the top of a catchment delivers greatest return for alleviating flood risks.
• Effective collaboration: Establishing a reference group that represents all internal and external stakeholders is an effective method for collaborating across a large area with a variety of land uses, owners and stakeholders.
• Hitch-hike opportunities: Timing projects with other works can be an effective way to explore additional possibilities and minimise disruption and construction costs.

The initiatives included in the plan are relevant and transferable to other urban areas with high imperviousness in the upper catchment and downstream flood risk.