Groundwater flow and solute transport modelling of the unconfined Broome aquifer: Broome peninsula, Western Australia

Deirdre Cathleen Kelly

    Research output: ThesisMaster's Thesis

    392 Downloads (Pure)

    Abstract

    This study focused on how the Broome aquifer operates hydrogeologically, as a basis for developing best management practices in the surrounding catchment to minimise impacts associated with nutrient pollution from waste water disposal. The importance of these works resides in the need to better understand the environmental triggers for growth of the Cyanobacteria, Lyngbya Majuscula (Oscillatoriaceace) on the north shore of Roebuck Bay.

    In general the key determinants of the flux of nitrogen through aquifers to coastal waters are: the supply rate of the contaminant from the soil surface medium via deep drainage; redox conditions in subsurface environment; the residence time of groundwater within aquifers, the extent of contact with rich clay sediments; and the availability of dissolved organic carbon(DOC). All of which have either been discussed or evaluated (where possible) during this study. Using finite element modelling in FEFLOW it has been possible to evaluate rudimentary groundwater flow and solute transport processes governing Broome’s unconfined aquifer. The model can successfully simulate observed (regional) flow dynamics, map primary extents of nitrate transport through the aquifer and uncover vital knowledge gaps.

    Current information combined and with transient transport modelling suggests that the nutrient migration from the wastewater irrigated sites and the Broome South Wastewater Treatment Plant (BSWWTP) do impact the groundwater beneath these sites. Under varying recharge and nutrient concentration scenarios modelling results show, under best and worst case scenarios, the observed Lyngbya blooms in the intertidal zones of Roebuck Bay, can likely be attributed to the migration of nitrogen from the Golf Course and BSWWTP. At this stage initial best estimates extracted from FEFLOW suggest nutrient loads from the BSWWTP and Golf Course into Roebuck Bay are likely to range between 500 kg/year –1000 kg/year, assuming denitrification is taking place at the source. At the inland irrigated sites (BRAC, St Mary’s and Peter Haynes Oval) nitrogen migration is localised and does not discharge into Roebuck Bay, however infiltration into the Broome aquifer is taking place and will remain for extended periods if wastewater disposal activities are continued unchanged.

    Ultimately this study showed the fate of these contaminants is site specific and difficult to measure or predict due to the heterogeneous nature of aquifer sediments (namely the Broome Sandstone), the complex contaminant dynamics within Roebuck Bay’s subterranean estuary and the many factors relating to density-coupled groundwater flow. Nevertheless, the available evidence does suggest that under a range of point source loads and climatic conditions that significant groundwater fluxes of these contaminants are taking place. The works here also highlight the need for improved waste water holding and disposal practices and monitoring at all wastewater sites across the peninsula.
    Original languageEnglish
    QualificationMasters
    Publication statusUnpublished - 2015

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