Our part of the project involved the review of the barrage design to develop a cost effective and lower maintenance design.

The Mary River has a 5m tidal surges that bring salt water into the fresh water system of the Mary River, Northern Territory.  Approximately 25 years ago, the first barrage was constructed, however many of the barrages fail annually with water flowing around the barrages and eroding the in-situ materials.

Scope

The project involved the review of the barrage design to develop a cost effective and lower maintenance design.

Our Role

Ground Engineering attended the barrage sites to view the Mary River system and the existing barrages.  We also provided specialist geotechnical engineering in put into the design of the barrages and the maintenance strategy of the barrages to be undertaken during the dry season.

Key Challenges 

Complex environment: The Mary River Flood Plain is a dynamic environment with the river system changing (nearly) every wet season.  The Mary River has approximately 150 barrages throughout the River basin to limit the amount of salt water traversing upstream.

Designing for “failure”:  The existing barrage system was relatively “high strength” – The barrages remained intact however the water would flow around the barrages and erode the insitu soils.  The design involved establishing weak points of the barrage that would “fail” in a controlled manner to facilitate easy repair and maintenance of the barrages and not resulting in erosion of the insitu soils surrounding the barrages.

Communicating the Challenges: A key challenge of projects in complex settings is the communication of the risks and opportunities that exist; and how to mitigate the risks and realise the opportunities. 

We worked closely with Byrne Consultants to refine design solutions for the barrages and discussed the design intent and outcome with the NT Government.