SA Road Stormwater Drainage Inlets: Hydraulic Study

The Australian Flow Management Group operates a specialist facility with a range of infrastructure for testing water related equipment and technologies.

A Comprehensive Study of SA's Drainage Inlet Systems

The Urban Water Resources Centre (UWRC) at the University of South Australia conducted a comprehensive set of hydraulic studies, examining the performance of the most common stormwater drainage inlets in use on South Australia’s roads.

This extensive study was carried out using the centre's full-scale road surface drainage test rig (see below). The majority of South Australian metropolitan councils and Transport SA provided support for this study which was then matched by the Catchment Management Subsidy Scheme. Outcomes of this work have provided much needed information to assist governments and councils in understanding and resolving flooding, and public safety issues associated with stormwater drainage systems.

The Centre has conducted similar studies for governments and councils in Queensland, ACT and WA.

Background

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.