Stream gauge monitoring

Tony Bernardi (Hydrologist) and James Diack (Science Officer) have been busy visiting and maintaining the five stream gauges which are stationed at strategic points along Mulloon Creek as part of our ongoing scientific monitoring program in the Mulloon Rehydration Initiative (MRI).

The MRI aims to improve stream water quantity and quality and to reduce extreme fluctuations to more consistent and moderated levels. This improves the health and viability for flora and fauna to survive especially during extreme climatic events. We monitor various parameters to understand the overall health of the system and observe where changes are occurring.

Each of the five telemetered stream gauge stations have four key components:

  • stilling well – secures the instrument in the creek

  • logger box – houses the data logger which stores information

  • telemetry system – sends data via mobile network to data management system 

  • solar panel & battery – supplies power to instrument & telemetry.

The stream gauges monitor water level, water temperature, electrical conductivity (salinity), turbidity (cloudiness), pH (acidity), dissolved oxygen and oxygen reduction potential.  

Logger box for the stream gauge at Peter’s Pond sited 50 meters uphill to protect it from floods.

Logger box for the stream gauge at Peter’s Pond sited 50 meters uphill to protect it from floods.

Monitoring water levels is necessary to determine water quantity in the creek by using survey data of the stream profile to calculate volume. The implementation of leaky weirs slows water flow and helps moderate water levels during low flows (low rainfall periods), providing the necessary water levels for flora and fauna to continue thriving. Having good flora and fauna, including microbial and aquatic invertebrates, helps maintain good water quality, and this improved water quality further improves the productivity and health of the waterway.

Water temperature can affect the amount of dissolved oxygen in the water. Dissolved oxygen is also positively affected by aquatic plants and riffle zones (including the leaky weirs), and is important for water quality for creatures such as frogs, fish and insects. Water temperature also affects the rate of aquatic photosynthesis and the metabolic rates of all flora and fauna. Managing stream water to maintain good levels of dissolved oxygen and moderated temperatures provides an indication of health for flora and fauna. This helps maintain a healthy ecosystem and good water quality for downstream users. 

Measuring for electrical conductivity (EC) shows us how much dissolved salt is in the creek. While all natural waters contain some dissolved salts including sodium, magnesium and calcium, high levels of EC can cause health issues for flora and fauna, and issues for human use whether for drinking or for farm animals or irrigation for plants. 

Turbidity measures concentrations of particulates in the water which impact light penetration, ecological productivity and habitat quality. In streams, increased sedimentation and siltation can occur, harming habitat areas for fish and other aquatic life. Particles also provide attachment places for pollutants such as metals and bacteria. For this reason, turbidity readings can be used as an indicator of potential pollution in a body of water. During a rainstorm, particles from the surrounding land are washed into the river making the water a muddy brown colour, indicating water that has higher turbidity values. Also, during high flows, water velocities are faster and water volumes are higher, which can more easily stir up and suspend material from the stream bed, causing higher turbidity. Turbidity can tell us a lot about possible erosion upstream. When rain fell after the bushfires this summer during February to March 2020, turbidity spiked in the creek due to the lack of effective groundcover in upper parts of the catchment. 

Monitoring instruments taking readings in Mulloon Creek. The white cable on the right connects the instruments, which are sitting in the stilling well, to the logger box further upslope.

Monitoring instruments taking readings in Mulloon Creek. The white cable on the right connects the instruments, which are sitting in the stilling well, to the logger box further upslope.

Most Australian streams have a neutral to slightly basic pH that ranges between 6.5 to 8, where pH can range from 0 to 14, with 7 being neutral. The pH is influenced by the types of rock and vegetation that it flows through in the catchment before reaching the waterway. The pH of water determines the solubility (amount that can be dissolved in the water) and biological availability (amount that can be utilised by aquatic life) of chemical constituents such as nutrients (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, cadmium, etc.). For example, in addition to affecting how much and what form of phosphorus is most abundant in the water, pH also determines whether aquatic life can use it. In the case of heavy metals, the degree to which they are soluble determines their toxicity. Metals tend to be more toxic at lower pH because they are more soluble.

With amazing riparian vegetation occurring along the creek as a result of our rehydration work, we’ve had to relocate some of the solar panels to sunnier spots.

With amazing riparian vegetation occurring along the creek as a result of our rehydration work, we’ve had to relocate some of the solar panels to sunnier spots.

Oxygen reduction potential (ORP) measures how well the creek or waterway can clean itself by breaking down waste products such as dead plants and fish. High readings mean a higher level of oxygen which allows for more efficient breakdown of waste products and a healthier waterway. Its ability to do this is decreased or increased in relation to the other water chemistry variables: pH, total alkalinity, total dissolved solids, temperature, etc. ORP is measured in addition to dissolved oxygen because ORP can provide additional information on the water quality and degree of pollution, if present.

Monitoring how these water quality parameters change over time allows us to assess water quantity and quality, keeping in mind that some of these parameters interact with and influence each other, which influences the overall health of the waterway as an integrated system. When combined with the monitoring of flora and fauna, it helps us build up a bigger more integrated picture of how our revegetation and rehydration works are affecting the creek’s water quantity and quality and the health of the ecosystem.

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.

Kelly Thorburn