Using Electrical Resistance to Assess Groundwater

DBCA’s Gavan McGrath and Josephine Hyde setting up equipment to assess groundwater at Lake Clifton

The term “electrical resistance” is used when considering how well a substance conducts electricity (copper, for example, has very low resistance so that’s why it’s used in electrical wiring).  But can the relative electrical resistance of different layers in the ground be used to assess groundwater?  It turns out the answer is “yes”.

Using a technique called Electric Resistivity Tomography (ERT), a survey was recently conducted along the north-east margin of Lake Clifton.  A small electrical charge is created under the ground via a line of stainless steel pegs (see photo) and the monitoring equipment then measures how well, or not, the various underground layers conduct the charge.  From this a 2-D picture of what’s under the ground is created, in this case to a depth of about 20m.  Because fresh groundwater, saline groundwater and limestone all have different electrical resistance, the resulting picture can map these layers.  The recent work was a trial undertaken by DBCA and University of WA staff together with PHCC as part of our ongoing NLP2 Wetlands and People project. 

It is likely that this technique will be used along with other methods such as the use of PHCC’s recently acquired Spear Probe, to assess the flow of groundwater to the lake’s thrombolite community.

This project is a partnership between PHCC, DBCA and UWA and is part of the Australian Government funded National Landcare Program.