Coastal sands of Northeastern Tasmania: geomorphology and groundwater hydrology

A regional study of the Quaternary geomorphology of coastal northeastern Tasmania defined landforms and deposits which offer good groundwater development potential, and also pointed to geomorphic problems worthy of more detailed research. Marine transgression and regression appear to have been a main feature of landform development in coastal northeastern Tasmania since Late Tertiary times. The present landscape is dominated by low, sandy plains created during the Last Interglacial marine transgression and by aeolian landforms which were formed during the succeeding glacial stage. The immediate coastal areas are backed by marine and aeolian landforms deposited during and since the marine transgression. The regional study revealed that deposits of possible marine origin and interglacial age, occur to an elevation of approximately 32 m. This is ‚ÄövÑvÆ 10 m above the upper limits of similar deposits elsewhere in Tasmania and is ‚ÄövÑvÆ 26 in higher than equivalent features in stable areas of mainland Australia. These relationships indicated that tectonic uplift in Tasmania may have occurred during the late Quaternary. Further research indicated that the sea level in northeastern Tasmania most likely attained an elevation of ‚ÄövÑvÆ 32 in during the Last Interglacial Stage, and that the area has experienced a moderate uplift rate of approximately 0.2 m/ka. The stratigraphic relationships between Quaternary marine deposits also indicate that older, probably of Oxygen Isotope Stages 7 and 9 age, marine deposits occur to 49 and 71 in respectively, thus indicating that uplift in Tasmania has been occurring over at least 300,000 years. Mapping and examination of the extensive longitudinal dunes and lunettes during initial stages of the programme indicated that they are products of environmental conditions substantially different from those of today. Dune morphology and grainsize characteristics suggest that zonal westerly air flows appear to have been stronger and from a slightly more northerly direction during the Last Glacial Stage than air flows which occur today. Stratigraphic studies infer that the temperature was markedly lower during formation of the longitudinal dunes. Evidence from fossil groundwater podzols indicates that precipitation during the Last Glacial Stage may have been only approximately one half of the present rainfall. Lunette stratigraphy and morphology reveal shifts in the relative importance of key components to the hydrologic cycle, such as precipitation, evapotranspiration and surface run-off, both during and since the late Last Glacial Stage. The coastal plains of interglacial marine sand form extensive unconfined aquifers and contain Abundant and accessible groundwater supplies. Computer and graphical simulations are applied to pumping test and drilling results, water table maps and continuous water level records to assess the groundwater system. Groundwater dynamics are controlled principally by precipitation and evapotranspiration. The system is renewable and moderate rates of groundwater withdrawal may even be beneficial.