South Australian Road Stormwater Drainage Inlets: Hydraulic Study


Links to inlet data for each participating organisation are provided below:


The Urban Water Resources Centre (UWRC) at the University of South Australia conducted a comprehensive set of hydraulic studies, examining performance of the most common roads’ stormwater drainage inlets in use in South Australia. The study was carried out using the Centre's unique full-scale road surface drainage test rig (see below). The majority of South Australian metropolitan councils and Transport SA have provided support for this study which has been matched by the Catchment Management Subsidy Scheme. The outcomes of this programme now provide much needed information, which will assist in understanding and resolving flooding, and public safety issues associated with existing and future stormwater drainage systems. A comprehensive data base of road inlet hydraulic data has been created that describes the performance of most inlets systems utilised in South Australia.

The Centre has conducted similar programmes for Queensland, ACT and WA. Much of the information generated from these studies have been adopted in their local drainage manuals.

diagram of South Australian Road Stormwater Drainage Inlets: Hydraulic Study

University of South Australia’s Full Size Road Test Rig


Road stormwater drainage inlets are the one point in the drainage system subject to increased risk of failure where knowledge of hydraulic behaviour is limited. Stormwater drainage, including road inlets, represents a significant component of council infrastructure, ongoing maintenance and liability and is designed to meet a certain level of flood protection. However, uncertainties surround the hydraulic data of road stormwater inlets used throughout South Australia.

Inadequate knowledge of road inlet capacities raises a number of issues in relation to flood protection:

  • Inadequate capacity may cause flooding on the roadway and possibly properties
  • Inadequate capacity may result in the below surface system not operating at design
  • Lack of accurate information can lead to an over-conservative design, increasing cost and maintenance
  • Over spacing of inlets will lead to excessive flow width on the road pavements

Historically, the majority of hydraulic performance data has been derived from results of scale model testing. A study comparing capture curves derived using both full-size and scale model test facilities (Argue and Pezzaniti, 1995a) revealed deficiencies associated with scale model testing where it involved triangular cross-section gutter flow. Another study (Argue and Pezzaniti, 1996) for the Institute of Municipal Engineers Australia (Queensland) demonstrated that scale model theory is not suitable for hydraulic simulation of road surface drainage.

It has been shown through studies conducted at the University of South Australia by members of the UWRC that full size testing can provide accurate data on inlet capture performance despite the complex nature of the hydraulic behaviour. This has lead other states in Australia to adopt design data derived from full-size hydraulic testing.

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