In September 2018, the Strathbogie Groundwater Project began monitoring water levels in eleven groundwater bores on the Tableland, to develop an understanding of the regional groundwater resource. Most of these bores are monitored manually every few months to measure depth of the water table, whilst the water level in one bore (soon two) is monitored automatically and continuously. Half the bores have no water pumped from them, the other half are regularly pumped either by submersible pumps or jet pumps. Pumping regimes vary, but volumes pumped from the five ‘active’ bores are relatively small < 1ML/year. The bores range in depth from 4 m to 38 m.

Depth to the water table in ten private bores on the Strathbogie Tableland. Inactive bores – solid lines; active/pumped bores – dashed lines.

The graph above shows that, predictably, the water level in all bores declined steadily between September 2018 and May 2019. The biggest drop over the seven months was 3 m, whilst a number of bores remained fairly steady and dropped by less than 1 m. It appears that active bores (where water was pumped) behaved similarly to inactive bores, suggesting that pumping rates had minimal impact on water levels in these bores.

What’s a bit more alarming is that water table depths this season are similar to those at the end of the Millenium Drought. This is despite the district having had good annual rainfall for the last few years.

Depth to the water table varies considerably across the landscape, but is generally within about 4 to 10 m of the surface.

Location of the eleven groundwater bores being monitored on the granitic Strathbogie Tableland.

The bore being automatically monitored is providing a detailed picture of how groundwater in a local area is responding to both season and to pumping from the bore (for stock and domestic). The graph below shows daily variation in ground water level during 2019. This bore has a submersible solar powered pump installed to deliver stock water and is about 25 m deep. The water level is usually between 5 and 6 m below the surface. On sunny days in summer and autumn, the pump runs almost continuously and water level in the bore drops by about 3 m. On cloudy days there is very little pumping and the water level drops less. The expected trend of a gradual lowering of the water table during summer and autumn can be clearly seen, as can the reversal of that trend – the water table becoming shallower – once regular rainfall commenced in May. The recovery of the water table may also have been helped by significantly less pumping (with increased cloudy weather).

Daily variation in depth of water table near Strathbogie, from an ‘active’, 25 m deep bore, measured with automated bore monitoring equipment.

The prompt influence of rainfall on the water table can clearly be seen by comparing the rainfall graph (below), with the water level change, over the same period, above. The impact of summer rainfall (at this scale graph) is discernible, though minor, but the onset of regular rain in May is clearly seen, as the water table rises in response to successive rainfall events.

The aquifer this bore is tapping clearly has a plentiful supply of water. Even with regular, daily pumping, the water level in the bore recovers quickly, within minutes, when the pump stops. This can be seen in the graph below, during an intermittently cloudy 21 June.

Water level fluctuation in an active bore during intermittent pumping.

Though still in it’s early stages, the Strathbogie Groundwater Project is already providing interesting results. In the next months we will continue monitoring these eleven bores and we hope to add more automatically monitored bores to the project. Anyone interested in taking part in the project is welcome to get in touch by leaving a comment, or contacting bertram.lobert@activ8.net.au.

This project is funded by the Victorian Government and the Goulburn Broken Catchment Management Authority. Farm Monitoring Solutions provided and installed the automated bore monitoring equipment.