Characterisation of the Yarragadee aquifer - Northern Perth Basin, Western Australia

Schafer, D; Kern, A; Meredith, KT

Characterisation of the Yarragadee aquifer - Northern Perth Basin, Western Australia

Date

2013-09-19

Authors

Schafer, D

Kern, A

Meredith, KT

Publisher

International Association of Hydrogeologists

Abstract

The Yarragadee aquifer in the Northern Perth Basin near Geraldton in Western Australia has been characterised using a variety of groundwater investigation techniques to enable better aquifer management for town water supply, industrial and agricultural usages. New structural contour surfaces and sand percentage maps for aquifer layers have been generated using borehole gamma and lithology data from over 200 bores (including 27 new bores). 3-D salinity distribution maps have been developed using correlations with borehole resistivity, airborne transient electromagnetic (TEM) data and borehole salinity measurements. Groundwater chemistry, stable isotopes (δ18/16O and δ2H0) and radiocarbon (14CDIC) data collected from 45 bores was used to characterise localised shallow and sub-regional groundwater-flow systems. Detailed hydrographs were prepared using data-loggers that recorded water level at hourly intervals to understand groundwater recharge dynamics. Localised shallow groundwater in the study area was found to be fresh (<1000 mg/L TDS) and relatively young (~1.5 to 7.0 ka) and in contrast, the deeper sub-regional groundwater was more saline (~ 2000 to 7000 mg/L TDS) and older (>9 ka). Recharge rates for the localised shallow groundwater were found to be much higher than sub-regional groundwater. The influence of faults on groundwater flow is demonstrated by conductivity contrasts observed across faults along TEM flight lines. Stable isotope data indicates that all groundwater is meteoric in origin and Na-Cl type waters dominate the area. Water level rises of around 10 m have been observed in upland areas since a major period of land clearing took place in the 1960s and 1970s. Post-clearing recharge rates have been estimated to be approximately double those of pre-clearing recharge rates. Significant salt input has been inferred to be incorporated during recharge of the sub-regional groundwater which occurs further inland and higher in the landscape. The localised shallow groundwater is fresher, likely because higher recharge and groundwater-ow rates dilute the salt input from rainfall. The improve understanding of recharge, groundwater flow and the source of groundwater salinity will enable the reassessment of available groundwater in the Yarragadee aquifer near Geraldton to be undertaken.

Keywords

Aquifers, Western Australia, Australia, Agriculture, Water supply, Well logging, Transmission electron microscopy, Groundwater recharge

Citation

Schafer, D., Kern, A., & Meredith, K. (2013). Characterisation of the Yarragadee aquifer - Northern Perth Basin, Western Australia. Paper presented to the IAH 2013, Perth, Australia : "Solving the groundwater challenges of the 21st century", International Association of Hydrogeologists 40th International Conference, Perth, Western Australia, 15-20 September 2013, (pp. 181-182).