Sharing the hydrological story at Mulloon
At the recent Mulloon Institute Rehydration Conference, we presented a small but robust sub-set of the hydrological data collected as part of the Mulloon Rehydration Initiative monitoring program.
We presented this data in the context of the Mulloon Interactive Web Map (Figure 1.) which can be viewed by anyone at this link.
Figure 1. Screenshot of interactive web map showing the Mulloon catchment boundary.
To keep the conversation going with those who are interested, here is a brief overview of the presentation.
Pictured below (Figure 2.) is a Digital Elevation Model of the section of Mulloon Creek in which in-stream structures have been installed between 2006 – 2020.
Figure 2: Digital Elevation Model (DEM) showing the approximate extent of the two floodplains outlined in black and the location of the Mid and Lower Mulloon stream guages.
Pictured below (Figures 3 and 4) are two slides showing the volume of water flowing through the Mulloon Creek catchment between two streamflow gauges that are 10km apart. The upstream gauge is called Mid Mulloon, the downstream gauge is called Lower Mulloon.
The Mid Mulloon stream gauge is immediately downstream of the original 2006 Home Farm 'Natural Sequence Farming' demonstration completed in 2006. This demonstration installed 14 in-stream structures and many more gully structures built along a 2.5-km stretch of creek and several tributary gullies within the 100 ha Mid Mulloon floodplain pocket.
The Lower Mulloon stream gauge is downstream of 35 in-stream structures installed between 2018 and 2020.
Figure 3: Median daily flows at both Mid Mulloon stream gauge and Lower Mulloon stream gauge between 2006 – 2018.
Figure 3 provides the median daily streamflow at each stream gauge between 2006 and 2018. This corresponds to a relatively dry period, after the Home Farm 'Natural Sequence Farming' demonstration structures were installed into the Mid Mulloon floodplain pocket but before any leaky weirs were built further downstream along the Lower Mulloon floodplain. During this period, the stream gauges show us that a median flow of 27.3 megalitres of water per day left the Mulloon Home Farm Mid Mulloon floodplain pocket whereas a median of 7.5 megalitres per day flowed from the Lower Mulloon floodplain.
Therefore, plenty of water (27.3 megalitres a day) left the Mid Mulloon floodplain pocket between 2006 – 2018, but only 7.5 megalitres a day reached the Lower Mulloon stream gauge 10km downstream.
What happened to the 20 megaliters of water per day lost between the two gauges? Most likely, it infiltrated into the aquifers of the Lower Mulloon floodplain. A reasonable amount would have evaporated as well.
Figure 4. Median daily stream flow 2018-2024.
Figure 4 covers a much wetter period on the east coast of Australia. This slide covers the period after 35 leaky weirs were installed along the 10km of Mulloon Creek between the Home Farm Mid Mulloon gauge and the Lower Mulloon gauge.
The median daily flow at the Mid Mulloon gauge immediately downstream of the Mid Mulloon floodplain during this period was 40.4 megalitres a day (an increase of 48% from the previous dry period – which would be expected during a wet period). The median daily flow at the Lower Mulloon gauge was 53.3 megalitres – an increase of 610% from the previous dry period median of 7.5 megalitres per day.
The data shown in Figures 3 and 4 proves that the installation of structures in the Mulloon Catchment has not reduced streamflows. Rather, the increased median flows recorded at the Lower Mulloon gauge potentially represent a net increase of surface water moving through the system.
We look forward to sharing more data stories soon.
To learn more about the Mulloon Rehydration Initiative’s history and monitoring framework, please read the following article: https://onlinelibrary.wiley.com/doi/full/10.1111/emr.12549
The Mulloon Interactive Web Map has been supported by the Australian Government through Citizen Science Grant funding.
The Mulloon Rehydration Initiative is jointly funded through the Mulloon Institute and the Australian Government’s National Landcare Program, with assistance from the NSW Government’s Environmental Trust.