A crucial element of an impound dock system is the water-retaining gate located at the entrance. The type of gate chosen has most often been the mitre gate. Although the recent trend for new commercial docks has been for deep-water facilities, the use of mitre gates in established UK docks does continue and replacement gates are required as part of port maintenance systems. This paper examines the design assumptions and engineering survey methods adopted by the design/construction team and the associated consequences for the port operator.