This paper is being presented at the WSUD 2013 Conference

The Magical 72 Hours – Does it Exist in Practice?


Thomas Cousland, Water Technology, Melbourne, Australia
David Reginato, Melbourne Water, Melbourne, Australia
Sarah Law, Water Technology, Melbourne, Australia
David Carew, Melbourne Water, Melbourne, Australia
Chris Beardshaw, Water Technology, Melbourne, Australia


Wetlands across Melbourne and Australia have generally been designed with a notional 72 hour detention time in line with the practice notes presented in the WSUD Engineering Procedures (CSIRO, 2005). Melbourne Water operates over 160 urban wetland systems as part of its role as drainage and stormwater manager within the greater Melbourne metropolitan area. Whilst many of these systems are preferentially offline systems a variety of catchment setup and flow regimes can be seen. Whilst all are notionally designed for a 72 hour detention time, this paper explores whether this occurs in practice across a monitored wetland.
Continuous simulation of a recently constructed wetland has been undertaken to assess the flow characteristics of the constructed outlet structures. This has been undertaken using long term flow simulations in a 1D hydraulic model. Bathymetric survey of Melbourne Water’s Brushy Creek wetland in Croydon was utilized, and the system was monitored over a number of events to determine water levels and hydraulic influences. This calibrated data set allows comparison to the results determined through the best practice design standards. Final recommendations for the practicality of outlet structures and the 72 hour notional detention time are then drawn.

You can download the full paper here

About The Author

Warwick Bishop
Warwick is a Director of Water Technology and has over 20 years of experience in surface water management. He has led a wide variety of projects covering areas such as flood risk management, water quality, sediment transport, coastal hazard, WSUD and environmental flows. Warwick has an Honours Degree in Civil Engineering from the University of Melbourne and a Masters of Engineering Science Degree from Monash University, investigating the detailed hydraulics of stormwater treatment wetlands. Warwick has experience throughout Australia in both rural and urban contexts. Since 2011 he has provided specialist input to the Flood Intelligence Unit of SES during both catchment and coastal flood emergencies. He is actively involved in Engineers Australia and is the current chair of the Victorian Water Engineering Branch Committee. Warwick has also contributed to the revision of Australian Rainfall and Runoff, with a particular focus on the application of flood models in urban areas.

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