Resistivity

A resistivity survey maps differences in the electrical resistance of the ground. These differences can indicate buried features whose materials or moisture content contrast with the surrounding soil.

It can help locate wall foundations, rubble spreads, yards, paths and metalled roads. Moisture-retaining features such as pits, ditches, drains and gullies can also produce detectable contrasts.

Our usual twin-probe arrangement uses one fixed pair of electrodes and one mobile pair. The surveyor moves the mobile probes across a grid to record changes in resistance and build a picture of the site.

The twin-probe method described on this page generally investigates to around one metre. This is an approximate working depth, not a guarantee: the ground conditions, probe spacing and nature of the feature affect detection.

Stone foundations and rubble can retain less moisture than the soil around them, making it harder for electrical current to pass. They may therefore appear as high-resistance anomalies, although the local conditions influence the response.

The fills of ditches and pits may hold more water than the surrounding ground. Where that moisture contrast exists, they can conduct current more readily and appear as low-resistance anomalies.

No excavation is normally needed to collect the readings. Small probes are inserted into the ground to make electrical contact, allowing the area to be investigated with minimal surface disturbance.

Yes. The technique relies partly on moisture contrasts, so very dry ground, saturation and seasonal changes can influence the readings. Site conditions should be considered when choosing the survey timing and interpreting the results.

Yes. The methods measure different physical properties, so they can provide complementary evidence. Resistivity is particularly useful when structural remains are suspected, while gradiometry can help investigate magnetic contrasts across the site.

Please provide a site location, a plan of the survey area, the approximate size and details of any suspected remains or previous investigations. Information about access, vegetation and ground conditions will also help us discuss the scope with you.