Hydrological & groundwater observations

Research Coordinator Luke Peel has been watching the recent floodwaters closely as he and Hydrologist Tony Bernardi and their team are part way through the detailed installation of monitoring equipment throughout the Mulloon Rehydration Initiative (MRI). 

Reedy Creek logger box - note the flood debris hanging from the solar panels

With most of our hydrological monitoring equipment installed within the floodplain, much of it was directly impacted by the rising floodwaters but overall not too much damage was sustained. There certainly was a decent volume of water moving through the system though, with the Reedy Creek stream gauge recording a water depth of at least 3.8m before the flood peaked and the modem sputtered out. The floodwaters went on to leave a debris line a further 50cm above that.

Partially submerged set of piezometers at Duralla,
downstream of the Sandhills Creek confluence with Mulloon Creek.

Groundwater observations

One of the most rewarding and validating things following the flood is knowing that the stream and groundwater aquifers are now fully recharged. But one of the most exciting things was discovering that the floodplain was so well recharged that one of our piezometer wells has been acting like an artesian bore with water flowing out of the top of 40cm above ground level!

You can view a video of the artesian piezometer here: https://vimeo.com/459188600

We currently have 76 piezometer wells installed within the Mulloon catchment to give us access to the groundwater aquifers to measure changes in water level, temperature, and salt (EC) as the MRI rolls out across the catchment. 

Half of these sites will be paired with a soil moisture monitoring system (31 Sentek soil moisture sensors) with six sensors distributed from 10cm sub-surface through to 1.5m, i.e. 10cm, 30cm, 50cm, 80cm, 110cm, and 150cm.

Series of piezometers at varying depths shallow, medium and deep (aiming for underlying base rock).

Interestingly, during their installation more than one aquifer was discovered at some piezometer sites, usually separated by an impervious layer such as heavy clay. 

TMI has invested in multiple piezometers at these locations to sample the individual aquifers and hopes to identify which aquifers are connected to each other (across or along the floodplain) and which are connected to the stream by analysing data from the piezometer array. Tracers inserted into the groundwater will also help to assess where this groundwater comes from and goes to.

University of Canberra students testing water quality and depth in piezometers

Collecting this data helps informs us about how water moves through the landscape and helps us develop a conceptual hydro-geological model, particularly for sub-surface water movement. It also generates more questions. Where is the groundwater recharge coming from? Where does it go? How long does it last? Can floodplain pasture roots access this water? Is the recharged groundwater prolonged due to the leaky weirs installed in the creek? 

This is a great example of the value of the instrumentation and science being conducted to gain better knowledge of the quantity and quality of water stored or moving through the landscape, and how it benefits local landholders and downstream users, including Sydney residents who eventually drink the water that has passed through the Mulloon catchment.

The Mulloon Rehydration Initiative is jointly funded through the Mulloon Institute and the Australian Government’s National Landcare Program and is supported by various affiliates.

Newly fenced piezeometers to protect their pole and logger box from damage