Brisbane CBD Backflow Prevention Devices for Flood Water Isolation

Up to 40 backflow prevention devices have been installed across 12 Brisbane stormwater systems benefiting about 1500 properties.

AWMA were approached to deliver reliable, high head, customised infrastructure to protect Brisbane’s CBD from flooding.

Working in conjunction with the Brisbane City Council (BCC), AWMA developed critical infrastructure to address backflow issues in key city stormwater drains.

The Milton gate alone is designed to protect approximately 452 local properties across Milton, Rosalie and Auchenflower, including the Milton State School. Installing flood-prevention devices on drains and pipes is generally straight forward. The Milton Drain however, proved to be quite a challenge. The very popular bikeway and pedestrian access required isolation, as did the large trapezoidal shaped drain that extended all the way up to the bridge above.A concept report by Cardino Group proposed twin sector gates with secondary flap gates. AWMA went forth and designed:

• a 6m wide x 4m high duplex /316/2507 stainless steel dual leaf top sealing isolation penstock;
• two 2200mm duplex non return (flap) gates; and
• one 2200mm 316 pedestrian gate.

The structure is subject to 7.5m bi-direction head pressure. The prepared design was subjected to third party RPEQ structural certification by GHD and designed in accordance with AS4100-1998, AS3990-1993, AS1170.0 & AS1170.2.

Creek Street, one of the busiest streets in Brisbane, was found to be the most suitable location for the CBD install. BCC contractors undertook a series of night works in an effort to construct a suitable chamber and complete the AWMA installation with minimal disruption to city traffic.

AWMA’s Creek Street solution involved custom designing a grade 316 stainless steel dual leaf TLF penstock to isolate the existing 2700mm diameter brick stormwater pipe. The 3 tonne multi-leaf penstock has a clear span of 3m x 3m and is designed to withstand 5.5m of water pressure.

A risk management review conducted by AWMA resulted in an integrated flap gate to prevent excess pressure on the gate and the pipe itself. Customised low profile headstocks were engineered to meet restrictions under the roadway.

In June 2014 officials unveiled the 6m wide x 4m high Dual Leaf Penstock installed in Milton. The specialised penstock is operated via a powered actuation system, and designed to withstand 7.4m water pressure.

AWMA are an approved supplier to the Brisbane City Council for their Backflow Program.

Many Brisbane suburbs are vulnerable to water inundation. Stormwater systems have been identified as high priority sites for backflow device installation across many flood prone areas.

Backflow prevention devices stop flooding caused by river water rising up out of drains.

For further information visit our  back flow prevention devices or flood mitigation pages or View Brisbane Times article.

Photos by Brisbane Times and BCC.

“The Milton Backflow Prevention Device (MBPD) was one of the most difficult Projects McIlwain’s have completed; working in a live creek, adjacent arguably Brisbane’s busiest road (Coronation Dr), preventing tidal influences, and with extremely tight access constraints. As such, the design and construction programming coordination was one of the most critical elements in ensuring the success of the Project. Whilst AWMA were not directly sub-contracted by McIlwain, it was imperative that this coordination and planning ran smoothly to ensure “best for Project” outcomes were achieved. The relationships built throughout the course of the Project between McIlwain Civil, Brisbane City Council and AWMA Pty Ltd, ensured that this success was achieved.” Matt Scully Project Manager McIlwain Civil.