A modelling study was carried out using separate 3-dimensional circulation model and flushing model components of WQMAP to investigate the residence times of Oyster Cove, an artificial canal system connected to the adjacent Saltwater Creek estuary, Gold Coast, Australia. The flow between the canal system and estuary is controlled via a system of uni-directional and bi-directional structures. To validate the circulation model and the influence of the flow structures, a detailed field experiment was carried out using flow meters, tide gauges and fluorescent dye. Following the validation process, the model was used to examine the existing mixing dynamics and residence time of the canal estate. Finally, the model was used to compare a hypothetical design alternative to the existing layout and quantify the effect on the canal's residence time by changing the position of the flow structures and using different combinations of flow structures.