Amplified tides and surges in the Tamar Estuary, Tasmania

The convergent shape of many estuaries worldwide leads to amplification of tides and surges as they propagate inland. The kanamaluka/Tamar estuary at 41 degrees S is one such example, where sea level at high tide rises by 60 cm over the 70 km journey from the estuary mouth at Bass Strait to its head at the city of Launceston. A history of short-lived tide gauges and errors in level surveys means that few data are available to measure tidal heights and constituents, how they have changed with time and estuary morphology, and to inform predictions for the future. We filled a significant gap in observations of sea level in the Tamar estuary with the temporary deployment of five water level sensors over a period of six months from March to August 2018, with two upper estuary sensors extended to 2019. Here we provide a summary of these observations, describing the amplification of mean and spring tides. Two storm surges were recorded, a moderate 42 cm surge in July and a large 78 cm surge in August which caused minor flooding in Launceston. We provide justification for the installation of permanent gauges at key control points in the estuary channel, and their need to support further work exploring not only threats but also opportunities for the future. For example, these data were important for the calibration of a hydrodynamic model, a valued tool for a wide range of applications including; inundation mapping, sediment transport modelling, and water quality. The validity of such models depends on quality observations, informing decision-making for the critical challenges affecting environmental and economic assets concentrated in estuaries.