The Hinze Dam is located on the Nerang River, 15km south-west of Nerang in South East Queensland and provides the major part of the Gold Coast region’s water supply. The Hinze Dam was built in 1976 and raised in 1989 up to a level of 93.5m. During the stage 3 upgrade the dam was raised once again, this time by 15m to 108.5m, thus doubling reservoir capacity and significantly elevating flood storage capacity. The project also provided greater flood mitigation potential for the riparian’s and properties downstream of the dam and adjusts the structures to current dam safety design guidelines and standards. The unfavorable geological formation influences the seepage through the structure, which causes increased leakage through the foundation, internal erosion and piping. The client’s design team, which was supported by Bauer, concluded that only a plastic concrete wall which stops seepage through the hard rock strata would meet all the requirements, providing a reliable and sustainable seepage barrier. The cut-off wall of 227m length, a depth of more than 50m and a thickness of 0.8m constructed by Bauer begins within the existing saddle dam, extends through a section of the central core and extends vertically into a 5,000m² hard bedrock area below the core where seepage is being decreased to a minimum.