Groundwater flow modelling of the Bulimba Formation and Wyaaba Beds aquifers - Karumba Basin, Queensland. A technical report to the Australian Government from the CSIRO Northern Australia Water Resource Assessment, part of the National Water Infrastructure Development Fund: Water Resource Assessment

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Doble, Rebecca; Taylor, Andrew; Davies, Phil; Smolanko, Nick; Turnadge, Chris


2018-06-29


Report


58


This report describes groundwater modelling using an updated conceptual model that aims to improve estimates of the availability of groundwater resources in the Karumba Basin aquifers in the Mitchell catchment and to complement the hydrogeological assessment described in Taylor et al. (2018). The groundwater model is the first to include the Bulimba and Wyaaba aquifers and was designed to be simple, yet flexible enough to incorporate new data as they become available. The model is a Class 1 model according to the Australian Groundwater Modelling Guidelines, with low confidence associated with predictions due to insufficient data to support model calibration. Analysis of lithological logs indicated that while the aquifers are highly heterogenous, the Wyaaba Aquifer thickness comprises around 11% (range 0 to 79%) of the Wyaaba Beds, and the Bulimba Aquifer thickness is around 15% (range 2 to 51%) of the Bulimba Formation. While the Wyaaba Aquifer is predominantly limestone deposits within 40 km of the coast and the Bulimba Aquifer consists of layered sand to sandstone palaeochannels, both aquifers are often present as multiple layers within their respective formations. FloPy, a Python-based MODFLOW model that allows for model transparency and reproducibility, was used to develop the cross-sectional groundwater model for the Kurumba Basin aquifers in the Mitchell catchment. The model was calibrated in steady state and run in transient mode to determine the effects of groundwater pumping for 20 years at three hypothetical extraction locations. Estimates of the water balance and aquifer properties estimates were constrained using heuristic, sensitivity and uncertainty analyses. The key outcomes from the numerical modelling include that: (i) potential extraction volumes of between 1 and 5 GL/year may be possible from the catchment, depending on the location of groundwater pumping and improved confidence in current recharge estimates; (ii) localised impacts are likely to be reduced when the extraction is dispersed over multiple bores, rather than from a single location; (iii) extraction in excess of 2.5 GL/year near the aquifer outcrop area is likely to lead to localised aquifer depletion; and (iv) it is unclear if extraction of >5 GL/year or extraction closer than 40 km to the coast has the potential to induce seawater intrusion. Groundwater recharge flux estimates predicted using the numerical model and heuristic water balance (2.5 to 25 GL/year) are likely to be at the low end of the range of recharge rates suggested by the chloride mass balance (CMB) analysis described in Taylor et al. (2018). The greatest sources of uncertainty in the modelling were the vertical hydraulic conductivity of the aquitards between the Wyaaba and Bulimba aquifers, the hydraulic connectivity between the Bulimba Formation recharge beds and the Bulimba Aquifer, as well as the heterogeneity of the aquifers. Recommendations for future work include: (i) airborne geophysics over the Mitchell River Fan Aggregation to better characterise the aquifer heterogeneity and to identify the freshwater–seawater interface, (ii) additional drilling of observation bores in the Bulimba Formation outcrop to better estimate hydraulic connectivity and improve groundwater recharge estimates, and (iii) core sample testing to improve estimates of vertical hydraulic conductivity between the Wyaaba and Bulimba aquifers to improve predictions of the behaviour of the groundwater system during extraction as well as constraining the water balance.


CSIRO


Australia


Northern Australia Water Resource Assessment; NAWRA


Hydrogeology


Published Version (pdf) (31.11MB)


https://doi.org/10.25919/5b86ed975a298


This report has been placed on the CSIRO repository and may be made available to persons outside of CSIRO for non commercial purposes, in its entirety and without deletion of disclaimers and copyright information.


EP182526


Client Report (Author)


English


Doble, Rebecca; Taylor, Andrew; Davies, Phil; Smolanko, Nick; Turnadge, Chris. Groundwater flow modelling of the Bulimba Formation and Wyaaba Beds aquifers - Karumba Basin, Queensland. A technical report to the Australian Government from the CSIRO Northern Australia Water Resource Assessment, part of the National Water Infrastructure Development Fund: Water Resource Assessment. Australia: CSIRO; 2018. csiro:EP182526. https://doi.org/10.25919/5b86ed975a298



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