Hydrochemical assessment of a freshwater resource on Rottnest Island, Western Australia
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Date
2015-11-03
Journal Title
Journal ISSN
Volume Title
Publisher
National Centre for Groundwater Research and Training
Abstract
This project investigated the groundwater
hydrochemical processes within an Island aquifer system on Rottnest Island, located ~18 km west of Perth, WA. A freshwater lens on the Island supplies around 25% of the Island’s potable water requirements, however there is limited information regarding the dynamics of the lens and its resilience to ongoing abstraction and reduced recharge.
Understanding the hydrochemical processes and residence times of the groundwater is essential for making use of the system sustainable. Groundwater samples were collected quarterly from 12 production bores to obtain seasonal information and from 15 monitoring bores biannually to monitor the mixing zone. Rainfall samples were collected on a weekly basis. The chemical composition of water samples were analysed by ion chromatography and inductively coupled
plasma-mass spectrometry, while and stable water isotopes (SWIs) were analysed by
isotope ratio mass spectrometry. Tritium was analysed by liquid scintillation after being distilled and electrolytically enriched. hydrochemical analysis shows varied water types and suggests a mixing trend between a fresh and saline end-member. Samples range in composition from fresh Ca-Na-Mg-3-Cl to saline Na-Cl groundwaters with increasing electrical conductivity (EC). The mixing trend is also observed in the SWIs results, with the values becoming more enriched with
increasing EC. Fresh water within the lens was found to be ‘young’ and recharged within the last 10 to 30 years. While the fresh groundwater beneath Rottnest Island was found to be recently recharged and is arguably a sustainable resource, the hydrochemical results highlight the
importance of a long-term management strategy to ensure that the mixing zone below thefreshwater lens does not increase to a point where the freshwater source is no longer viable. The declining winter rainfall in the Perth region, resulting in reduced recharge to the lens, makes the management of this resource even more essential. ©The Authors.
Description
Keywords
Western Australia, Fresh water, Ground water, Aquifers, Tritium, Rain
Citation
Wells, E., Meredith, K., Baker, A., Post, P., & Andersen, M. (2015). Hydrochemical assessment of a freshwater resource on Rottnest Island, Western Australia. Paper presented at the Australian Groundwater Conference, 3-5 November 2015, The Shine Dome, Canberra, Australia, (pp. 101). Retrieved from:
https://www.iah.org.au/wp-content/uploads/2019/09/AGC2015-Book-of-Abstracts.pdf