Silverleaf Weir Upgrade

QLD
Sunwater
2020
34m

long retaining wall constructed

200L/s

expected flow

45t

excavator used to complete works

1,500

species safely relocated

Abergeldie collaborated with Sunwater to successfully deliver the Silverleaf Weir Upgrade, a complex project requiring meticulous safety and environmental planning with works occurring in and near the water.

The completion of tasks before the year-end holiday period was crucial to mitigate site risks during the peak wet season and potential impacts on irrigators. Abergeldie efficiently dewatered the creek and safely relocated over 1,500 species during the project. The collaborative approach with Sunwater and key stakeholders enabled the project to be delivered within budget, five weeks ahead of schedule, and with no recordable injuries or environmental incidents. 

Scope of works

The works included: 

  • Construction planning, documentation, and site mobilisation. 
  • Provision of safety, quality, and environmental measures. 
  • Provision of site access and temporary works facilities. 
  • Hydrographic survey of the seabed during cofferdam construction. 
  • Geotechnical investigations. 
  • Decommissioning of existing weir, piles, and concrete structures. 
  • Design, certification, installation, and removal of temporary cofferdam. 
  • Dewatering and installation of permanent sheet piles to weir structure.
  • Upgrades to weir outlet pipe and inlet structure.
  • Weir concrete encapsulation and structural steel installations. 
  • Installation of structural steel access, safety rails, trash screens, bulkhead gates, sliding gates, and valves. 
  • Excavation, backfilling, and erosion protection.
  • Site cleanup, demobilisation, and as-built drawings provision. 

Complexity with construction of the cofferdam

The multi-stage project comprised a hydrographic survey of the seabed, conducted both before and during the construction of the cofferdam. This approach was essential to maintain environmental compliance while dewatering and decommissioning the pre-existing weir, piles, and concrete structures. The cofferdam itself was equipped with a 34m-long sheet pile retaining wall, expertly installed using a 45T excavator fitted with a Movax attachment. This method efficiently minimised both the load on the cofferdam during construction and the impact on the existing weir throughout the upgrade. 


Managing the wet season 

The works were carried out during the wet season within an active waterway, where the water flow often surpassed the weir’s 100% capacity. The project team prioritised the creation and execution of an emergency plan specifically designed for high-water events. This plan proved critical when storms hit in late October, causing water levels to rise, and overtopping the cofferdam, resulting in work delays.  

Due to the meticulous preparation, no materials, equipment, or project progress were lost during the high-water event. The project team efficiently addressed the washout caused by the overflowing water, enabling them to complete the project ahead of the practical completion date.


Enhanced infrastructure to support agriculture in the region

The Silverleaf Weir plays a critical role in regulating the water supply for a diverse agricultural region. This water supply supports the cultivation of olives and grapes, cattle grazing, pig production, and a variety of crops such as peanuts, lucerne, and cotton. Further, a recent addition of duboisia bio-crop plantations dedicated to pharmaceutical product development.