Lenthall Dam Crest Gate Modification Project

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GHD was engaged to modify the crest gates of the Lenthall Dam located in Queensland’s Hervey Bay Area.

The five spillway gates installed for the raising of Lenthall dam used buoyancy to automatically raise or lower depending on the dam level. Since their installation, the gates had not operated as intended. A Computational Fluid Dynamics (CFD) study conducted by GHD identified uplift of the gate as the root cause. This increased the risk of malfunction of the gates during floods and had to be addressed to maintain satisfactory levels of reliability for safe operation of the dam.

GHD’s involvement in the rectification project was to determine the cause of the gate closure and provide solutions to prevent this from occurring.

The CFD modelling undertaken analysed the behaviour of the gates during overflow conditions and quantified the forces involved. It was also used to develop a solution to the operational challenges being experienced.

Our team developed a solution comprising conventional engineering analysis and Finite Element Methods. It consists of a precast concrete deflector wall with steel wing plates to modify flow behaviour over the gates. Hydraulic cylinders connected to the gates with cables were used to lock the gates in the lowered position.

As a result of our work, the gates can now open fully during floods, thereby reducing risk to the dam and lowering upstream flood levels.



We recognise our clients’ needs for solutions that harness in-depth knowledge with forward thinking to produce innovative, safe and cost-effective outcomes. We have successfully delivered through all methods of project delivery, from the conventional approach to design and construct, alliances and Engineering Procurement and Construction Management (EPCM). 

GHD provides services for the following dam types and appurtenant structures:

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