Sand body connectivity Leederville Aquifer Perth Basin

Author: Rick Jones

Jones, Rick, 2021 Sand body connectivity Leederville Aquifer Perth Basin, Flinders University, College of Science and Engineering

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With demand on the water resources of the Perth Basin increasing due to impacts from population growth and climate change, groundwater resource management practices such as aquifer storage and recovery schemes will increasingly become an important component of the management of this resource. Within aquifers such as the Leederville, the heterogeneity of sediment grain size distribution can have an impact on the movement of groundwater within the aquifer body. This variation in grain size distribution can be imparted by depositional processes resulting in variable sand body connectivity which can impose an anisotropic flow field within the aquifer. To investigate sand body connectivity within the Leederville aquifer, downhole geology logs from 19 bore holes drilled through the Wanneroo Member at the site of the Water Corporations Beenyup Groundwater Recharge Trial were collected. From this downhole geology data, four hydrofacies classes were derived based on the logged sand to silt ratios. Using these hydrofacies, a geostatistical model was developed of the Wanneroo hydrostratigraphy at the Beenyup recharge site. This modelling utilised the markovian transitional probabilities approach as implemented in the TPROGS software (Carle 1999). To account for the broadly westerly direction of sediment flux during deposition, the TPROGS model contained a preferential orientation of the sand bodies on a west to east orientation. The stochastic FloPy modelling in MODFLOW 6 conducted with these TPROGS hydrofacies realisations show that there is anisotropic flow between depositional dip and depositional strike directions due to the preferential orientation of these sand bodies. This anisotropic flow within the conceptual hydrofacies model highlights the potential control that aquifer geologic heterogeneity can have on site scale groundwater movement within the Leederville aquifer. Consequently, a site scale in the Leederville aquifer groundwater flow driven laterally and vertically away from the orientation of preferential permeability (dip direction), by induced head gradients (such as from aquifer injection and abstraction induced localised groundwater gradients), will likely be impeded by permeability contrasts on a local scale. These flow retardant zones are a result of the juxtaposition of textural fabrics running parallel to the primary orientation of deposition within the aquifer. This highlights the need for further high-resolution geological investigations with the Leederville aquifer to accurately identify the higher conductivity zones, as it is these higher conductivity zones such as the coarse grained sands that will dominate the localised groundwater flow on a site scale.

Keywords: Leederville Aquifer, Beenyup, texture contrast, TPROGS, hydrofacies, flow field

Subject: Hydrology thesis

Thesis type: Masters
Completed: 2021
School: College of Science and Engineering
Supervisor: Craig Simmons