Rockhampton sits on the alluvial plains of the Fitzroy River, with elevation around 11 m above sea level. The underlying geology varies from Tertiary basalts to Quaternary sands and clays. Understanding the subsurface in this region demands more than standard boreholes. Electrical resistivity and VES surveys provide continuous profiles through conductive floodplain deposits and resistive basalt edges. Before drilling a single test pit, a resistivity line can map the boundary between the shallow clay cap and the deeper gravel beds. This method drastically reduces the need for costly exploratory holes. It also complements data from a calicatas exploratorias program when the target depth exceeds 3 metres.
A single VES profile can detect a buried paleochannel at 12 m depth that three boreholes spaced 20 m apart would miss entirely.
Scope of work
- Schlumberger array with AB/2 spacing up to 200 m for deep penetration
- Real-time GPS logging of electrode positions (±0.1 m accuracy)
- Correlation with nearby ensayo SPT results for ground truth
Area-specific notes
The most common error contractors make in Rockhampton is assuming the shallow clay layer is uniform across the entire site. After heavy rain, the clay can mask deeper variations in resistivity. Without a VES survey, a developer once poured continuous footings over a buried sand lens that liquefied during wet-season loading. The fix cost three times the original geotechnical budget. Electrical resistivity surveys catch these anomalies early. They also reveal saline groundwater intrusion, a real hazard near the Fitzroy River estuary. Skipping this step leaves the foundation vulnerable to differential settlement that no amount of structural reinforcement can fully correct.
Standards used
AS 1726 – Geotechnical site investigations (2017), AS 1289 – Standard test method for field measurement of soil resistivity, SEG – Society of Exploration Geophysicists guidelines for resistivity surveys
Linked services
2D Electrical Resistivity Tomography (ERT)
Multielectrode cable with 48 or 72 electrodes. Covers up to 400 m per line. Ideal for detecting buried channels, fault zones, and groundwater tables in the Rockhampton floodplain. Data processed and interpreted within 5 working days.
Vertical Electrical Sounding (VES)
Single-point sounding with expanding electrode spacing. Best for depth-to-bedrock or layer thickness mapping at discrete locations. Cost-effective for small subdivisions or single-lot residential sites. Results in 3 working days.
Typical parameters
Watch how it works
FAQ
What is the difference between 2D ERT and VES?
2D ERT uses a multi-electrode cable to produce a continuous cross-section of resistivity along a line. VES uses expanding electrodes at a single point to measure vertical layering. ERT is better for lateral variability like buried channels; VES is faster and cheaper for simple depth-to-rock estimates.
How much does an electrical resistivity survey cost in Rockhampton?
A standard VES survey for a residential block typically ranges between AU$890 and AU$1,590 depending on line length and access conditions. 2D ERT lines covering 200–400 m cost more due to equipment and processing time. Contact us for a fixed quote based on your site plan.
Can resistivity surveys detect groundwater in Rockhampton?
Yes. Freshwater has high resistivity (50–500 ohm·m), while saline groundwater is very conductive (1–10 ohm·m). In the Fitzroy River floodplain, saline intrusion is a known issue. A VES or ERT profile can map the freshwater/saline interface and help design dewatering or foundation strategies.