The hydraulic habitat of the river describes the forces exerted upon living things by the water running through the channel. It is often a useful way to think about how ecological responses are affected by flows.

While river flow in the Lower Goulburn/Kaiela River is expressed as volumes (ML/day), the living things in this environment experience properties of the flow such as depth, velocity and shear stress. We believe that these hydraulic variables may often be better predictors of environmental responses to changing flows than the flows themselves.

In the Long-Term Intervention Monitoring (LTIM) Project, we developed hydraulic models for four sites along the Lower Goulburn/Kaiela River. These allow us to calculate changes in hydraulic variables using the hydrology data from the river. We’ve used these models to calculate the duration of inundation for plants on the riverbank, the velocity of water during spawning season of Golden perch, and the peak height of flow events as a predictor of erosion or deposition of sediments on riverbanks.

Bank condition

The banks of the Lower Goulburn/Kaiela River support a range of plants that in turn form habitat for waterbugs and small bodied fish. At the beginning of the Long-Term Intervention Monitoring (LTIM) Project, there was community concern that environmental flows were causing an increase in riverbank erosion. We started monitoring erosion and deposition of sediments on the banks using erosion pins and were able to demonstrate that, while environmental flows did increase the amounts of both erosion and deposition, these increases were small relative to the normal processes of change in the river channel. Riverbanks are naturally dynamic environments and we expect them to change over time.

In more recent years, renewed concerns have arisen about the potential effects of summer Inter Valley Transfers (IVT). Early results show that the sustained high flows of IVTs during the warm, dry summer months, can have considerable impacts on erosion.

We have updated our methods from the original monitoring program and are now monitoring bank condition at three sites on the Lower Goulburn/Kaiela River using drone-based photogrammetry (taking high-resolution pictures of the banks and comparing them over time). This provides much richer data than was possible with the original erosion pin method, and has already demonstrated substantial erosion and deposition around major natural and regulated flow events.

Drone captured data before and after flows shows riverbank erosion and deposition caused by the often subtle changes in bank form, as emphasised by the major erosion seen on a more susceptible bank at Loch Garry on the Lower Goulburn/Kaiela River.

Ecosystem metabolism

Ecosystem metabolism refers to the production of food for fish and water bugs through photosynthesis (gross primary production) and the breakdown of that food to release the energy it contains (ecosystem respiration). These processes are the basis for the food web that links all animals and plants in the river system.

We measure ecosystem metabolism by monitoring dissolved oxygen levels in the river water at high frequency (a reading every 10 minutes). These data are then put through a statistical model to produce daily estimates of gross primary production and ecosystem respiration: increases in dissolved oxygen over time provides a measure of the rates of primary production and decreases in dissolved oxygen over time provides a measure of the rates of ecosystem respiration. We have four oxygen loggers deployed along the length of the Lower Goulburn River. These are being maintained by the consulting company ALS, as part of its monitoring work for the Victorian Government. We have used the data to explore how the rate and total amount of primary production and respiration changes with changing flows in the system.

Macroinvertebrates are used as indicators of stream health across the world. In our program, a more important consideration is how macroinvertebrates can be a food source for the large-bodied fish that are the target of environmental flows. Any management actions that can increase the number of macroinvertebrates should be of benefit to fish populations.

We are measuring the abundance and biomass of large-bodied crustaceans (prawns and shrimps) that are the largest macroinvertebrate species in the Lower Goulburn River and are food items for fish like Murray cod, Golden perch and Trout cod. At eight sites spread along the river, we set bait traps regularly through the year to see how crustacean biomass changes along the river and with major flow events. We also take samples along the river’s edge to gain a basic picture of macroinvertebrate biodiversity using what are known as ‘rapid bioassessment’ methods.

Vegetation on riverbanks helps to stabilise those banks and reduce erosion. It also provides habitat for aquatic animals when the river rises. During the Millennium drought, the semi-aquatic vegetation on the banks of the Lower Goulburn/Kaiela River was gradually replaced by terrestrial species during years of extreme low flows. When the drought broke in 2010, the high flows killed off much of this vegetation leaving the banks bare and susceptible to erosion. One of the focuses of environmental flows has been to improve the amount and diversity of riverbank vegetation.

In recent years, the advent of high summer Inter Valley Transfers (IVT) has posed a new threat to the recovering vegetation on the banks of the Lower Goulburn/Kaiela River. Sustained high flows during the warmer months of year is bad for young plants that germinate in spring.

Our monitoring is using surveys up and down the riverbanks at two sites on the Lower Goulburn/Kaiela River to track the abundance of key species over time and around major flow events. We are assessing vegetation in Spring, Summer and early Autumn to better understand how patterns of vegetation abundance over the growing season are shaped by environmental flows, natural flows and IVTs.

The focus of this component is Golden perch and Silver perch. They are thought to be the only two fish species in the Murray Darling Basin that rely on increased discharge (flow) to initiate spawning. Golden perch and Silver perch spawn during rises in streamflow in spring-summer once water temperatures have reached certain thresholds. Monitoring conducted under the Long-Term Intervention Monitoring (LTIM) Project demonstrated that flow velocities (~30 cm/s average flow velocity) and temperature (~18.5 °C) make Golden perch spawning extremely likely.

We are monitoring spawning at four sites along the Lower Goulburn River using drift nets that are deployed overnight once a week for 10 weeks over spring and into early summer. In addition to eggs and larvae of Golden and Silver perch, we have detected breeding by native fish species including Murray cod, Trout cod and Murray River rainbowfish. These species spawn under a range of flow conditions. Demonstrating that they are spawning in the Goulburn River is important for understanding the health of the whole fish assemblage.

One of the principal aims of The Basin Plan is to improve native fish communities throughout the Murray-Darling Basin. Native fish have declined dramatically since European settlement of Australia with many different stressors, flow regulation among them, to blame. An improving native fish assemblage would demonstrate that environmental flows and other management actions are putting in place the environmental processes that can lead to long-term improvements in the top portions of the food web.

We are monitoring the fish community with an annual intensive survey that uses electrofishing and fyke nets to sample fish from ten sites along the Lower Goulburn/Kaiela River in Autumn. Collected fish are counted, measured and weighed before being released back into the river. This is a continuation of sampling that began under the Long Term Intervention Monitoring (LTIM) Project and is primarily aimed at providing data for basin-scale analyses of fish assemblage changes over time, and whether these can be related to environmental flows.