Urban salinity scoping study for Greater Launceston area: Part 2 Investigation work

J. W. Griffioen and B. McDowell

The investigation of a pilot study area in the suburban Greater Launceston Area (GLA) has confirmed that soils at a number of sites in the study area have high levels of salinity, much of the salts being readily soluble. The investigation also found medium to extremely saline groundwater conditions throughout the study area. The types of salt in the soil and groundwater are broadly related to two groupings based on the mapped surface geology: (i) Tertiary and undifferentiated sediments; and (ii) dolerite and dolerite derived sediments. Groundwater levels in unconfined and semi confined aquifers generally parallel the local topography, with localised upward and downward flows possible anywhere on the gentle slopes of the pilot study area. Areas of observed salinity impact at the Casino Golf Course and St Patrick’s School sports grounds are related to intense irrigation, construction of water storage ponds (Casino) and cut and fill slope modification (School).

The study concludes that groundwater recharge and seepage in response to rainfall and irrigation contributed to creating artesian conditions in the Tertiary sediments which mobilize in situ salts in areas with upward flow conditions. Specific geological confining conditions probably have less of an impact.

The study has no temporal data to allow an assessment of the effect of changing land use on groundwater levels and quality, and therefore any predictions of areas at risk from future salinity outbreaks have no ‘calibration’ at this stage.