With the surface water monitoring program for the Yalgorup Lakes now up-and-running it’s time to look under the surface. Groundwater, as the name suggests, is water that is found under the surface of the ground. In landscapes formed of limestone, rainwater seeping into the ground can dissolve the limestone forming underground channels through which water flows. In sandy country, rainwater seeps into the sand which acts like a giant sponge from which the water can leak out over time, for example as surface springs. The Thrombolites of Lake Clifton have formed in an area where groundwater seeps into the lake foreshore and nearshore lake bed from adjacent limestone and sandy country. This fresh groundwater, rich in calcium dissolved from the limestone, has the flow duration and chemistry that the Thrombolites need to develop. Without this fresh water flow, the Thrombolites would not survive in the salty water at Lake Clifton: it’s their Life Blood!
Groundwater levels and chemistry can be assessed using tubes with a slotted or screened section, known as piezometers. These tubes are placed into boreholes drilled into the ground with the slotted or screened section buried at a pre-determined depth to allow groundwater to flow through them. By regularly measuring the depth to the groundwater table at various locations in the vicinity of Lake Clifton, and comparing with the levels of the surface water in the lake, we can determine the direction of groundwater flow and also estimate its ebbs and flows of groundwater into the lake during the year.
Piezometers are typically installed in groups (or nests) with the slotted or screened section of each tube placed at a different depth so that differences in chemistry, in particular salinity, through the groundwater profile can be measured.
Over coming months, the groundwater chemistry and flow will be checked along the north-east side of Lake Clifton with a view to installing long-term monitoring piezometers to keep an eye on the flow of water to the Thrombolites. This work forms part of a comprehensive program of assessments being carried out to help inform better management in the future and is part of PHCC’s National Landcare Program Wetlands and People project funded by the Australian Government.