Yarra River Focus Catchment


eWater CRC worked on local water management issues in partnership with organisations in Victoria.

Focusing on the middle and lower reaches of the Yarra River, the project team looked at ‘hypoxia’ (too little dissolved oxygen) in relation to flow and fish-kills, and applying new software that could help the region’s river managers prevent hypoxia occurring.

Catchment context

The middle and lower reaches of the Yarra River, from Yering Gorge (near Yarra Glen) to Dights Falls (Kew), run through the Yarra Valley district and Melbourne’s eastern suburbs. The river catchment as a whole (from its source to Port Phillip Bay) is home to nearly 2 million people (around 1/3 of Victoria’s population), and about 200,000 of them live and work in this region at the eastern edge of the urban area.

At the urban fringe the catchment supports agriculture and hobby farms, while through the eastern suburbs the river is edged by parklands extensively replanted with native vegetation. These reaches are popular for a range of recreation activities, including boating and fishing.
The water is fresh, if silty. Contamination by runoff from agriculture, stormwater and septic tanks can occur, but the river supports diverse species of native fish (including Murray Cod, Macquarie Perch and eels), frogs and native birds.

There have been several instances of low concentrations of dissolved oxygen (DO) in these middle and lower reaches and in the Yarra River estuary in recent years. Because low-oxygen conditions have been implicated in fish-kills and other negative ecological impacts in rivers elsewhere, hypoxia is a potential major risk to the ecological health of the Yarra River. Fish and other aquatic animals depend on DO to breathe and are at risk of dying when the concentration falls too low.

Application

eWater and partner organisations investigated the relationships between flow regime, DO and water temperature in the Yarra, and how native fish respond to changing DO conditions. One objective was to find trigger levels that could initiate management actions, such as augmenting river flow to refresh the water in zones with poor DO concentration.

Two of eWater CRC’s next-generation software tools were used in this application for: (i) generating time-series of river flow characteristics under varying catchment conditions; and (ii) applying information about such factors as flow conditions, contaminant loads, and flow routing, to model hypoxia and responses of native fish over time.

eWater’s input

The team aimed to understand the circumstances in which hypoxia events can develop in the Yarra River, and to develop software tools that river managers could use to explore possible ways of reducing that risk, including by releases of water from upstream storages.

Base data was collected both by collating existing data and by conducting new studies. The work includes monitoring of water quality and DO, and radio-tracking of native fish movements in relation to water quality and flow.

The resulting relationships, together with local rainfall and hydrological data, were imported into eWater’s catchment modelling software and ecological response-modelling software. Once calibrated, the team used the models to simulate the river and its flow conditions for a range of catchment, climatic and land-use scenarios. The outputs will be forecasts of frequencies, durations and geographical extent of hypoxia events in the lower-middle Yarra River, and predicted ecological outcomes with respect to fish.


Click on the button below to download a copy of the Yarra River Application Project: Source for Catchments Hydrology Calibration Report. (4.5mb)

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Yarra River Application Project Final Report (1.1mb)

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Outcomes

This application of eWater’s software helped to build an ongoing capability to determine how water levels and conditions in the Yarra River affect dissolved oxygen concentrations and fish, and how river flows can be managed to reduce the risk of hypoxia under a range of scenarios related to current and future climate conditions and land use.

The models were developed in such a way that the general approach and information requirements may be applied to similar river situations elsewhere.

All eWater tools demonstrated in focus catchments are part of our integrated water modelling suite.

Partners involved