Plants have an in-built ability to find water, which is great for their survival, but can sometimes cause problems for human installed infrastructure like groundwater monitoring bores .
In 2021, PHCC implemented a monthly monitoring program to measure ground water levels at bores installed in and around Lake McLarty as part of the “Saving Lake McLarty – Phase 1” project. We do this using a specialised measuring tape that is embedded with conductors with a battery powered probe on the end. The probe, commonly known as a ‘plopper’ consists of electrodes with an insulating gap between them. The plopper is lowered down the bore and when it touches the surface of the groundwater the circuit is completed and a buzzer sounds. This distance to groundwater is then read from the measuring tape at the top of the bore casing, which were surveyed against the Australian Height Datum when we installed them. This allows us to compare groundwater levels in each of the monitoring bores across the lake bed and to determine seasonal variation in ground water levels.
Over the last few months it has been increasingly difficult to get the probe all the way to the bottom of one of the bores and so last month we took a waterproof camera that we lowered down the borehole to see what the blockage was and some ‘fishing gear’ to retrieve it from the bore. We retrieved a mass of roots that were growing inside the bore casing.
The bore casing has thin slots cut into it that allow ground water from the aquifer to enter the casing while keeping sand and dirt out. When this slotted section, or the screen, is installed at relatively shallow depth in heavily vegetated areas the plants take advantage of the easy path to water offered by the casing screen. As a result of our fishing trip the screen is now in great condition but we will need to keep an eye on it through our monitoring program.
The Saving Lake McLarty project is supported by funding from the Western Australian Government’s State NRM Program.