Improving Connectivity of Flows in the Lower Ovens Floodplain

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Many of the floodplains and wetlands within the Murray-Darling Basin have been subject to anthropogenic changes that have negatively affected the condition of these environmental assets. The lower Ovens River and its floodplain wetlands are in much better condition than many other rivers in the basin due to the absence of major water storages and abstractions from the upper catchment, with less impact on flooding. However, it still has a number of issues to manage including:

  • vegetation clearance,
  • pest species,
  • the operation of the Murray River and backwatering from Lake Mulwala, and
  • the construction of levees, channel banks and roads that have disconnected wetlands from the river.

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Water Technology were engaged by the North East Catchment Management Authority to investigate the issue of wetland and waterway connectivity but also addressed some of the other issues. The project developed hydrodynamic models that gave us an understanding of the flood behaviour to inform management decisions and environmental initiatives in the future. The project undertook extensive condition assessment of the significant ecological assets within the lower Ovens River floodplain. The project also established a database linking the flood behaviour to barriers to connectivity and ecological assets.

O1The objectives of this study included:

  • Improved understanding of floodplain flow dynamics and the connectivity between the channel, overbank areas, and environmental assets;
  • Improved understanding of the extent and locality of barriers to flow on the floodplain; and,
  • Improved understanding of the ecological condition of the lower Ovens River floodplain and how enhanced connectivity would benefit water dependant assets.

The Ovens River

The Ovens River flows from the heights of the Victorian snow fields, down through the Ovens River valley past towns such as Bright and Myrtleford where it meets the Buffalo River, then on to Wangaratta where it meets the King River. The Ovens River then flows on through the lower valley entering the Murray River at Lake Mulwala. In total, the Ovens River is approximately 150 km long from its headwaters to its confluence with the Murray River.

The upper catchment is steep and dominated by native forest with some pine plantations, while the lower catchment is reasonably flat with a wide floodplain, anabranching waterways and characterised by extensive agriculture (pasture, grapes and orchards). Within the study area, the Ovens River is a sinuous stream and the floodplain features numerous wetlands created by meander cut-offs, with relatively frequent flooding of these floodplain features.

O2The total Ovens River catchment area is just over 7,500 km². Rainfall varies dramatically across the catchment, with average annual rainfalls ranging from 2,000 mm at Mount Hotham to just 400 mm at Yarrawonga.

The lower section of the Ovens River downstream of Wangaratta has been declared a Heritage River due to its unique habitat and its importance for endangered fish species. The assessment of barriers to connectivity focused on this area, but the wider study area is the Ovens River downstream of Myrtleford, the Buffalo River downstream of Lake Buffalo and King River downstream of Lake William Hovell.

Outcomes

The study resulted in a number of specific barriers and issues being identified which underwent an assessment of risk and restoration potential. Risk profiles were developed based on the perceived value of a wetland/floodplain feature and the likelihood of this value being affected. Assessments of restoration potential were made based on judgement of the realistic potential for management actions to improve hydrologic connection, vegetation condition and/or fish passage at each identified site. Management actions were then proposed for each of the specific issues. Water Technology produced a report for each of the individual stages. A report was also produced summarising the five stages of the project.

This project has clearly demonstrated why the lower Ovens River floodplain is in such a good condition. It provides the link between floodplain wetland condition, hydrology, ecology, and river/floodplain/wetland connectivity. The study showed that 96% of wetlands are inundated on average every 3 years.

The lower Ovens River could be used as the benchmark for how a healthy river and floodplain can be achieved within the Murray-Darling Basin. Although the lower Ovens River, floodplain and wetlands are in great condition, a number of issues/threats were identified and prioritised and management actions developed. These issues/threats should be considered further with a view to protecting and enhancing a magnificent environmental asset that is the lower Ovens River.

O3

Project Collaborators

North East Catchment Management Authority

About Water Technology

As these projects demonstrate, Water Technology is a specialist consultancy offering high-level services in the fields of coastal/estuary dynamics, surface water hydrology/hydraulics, floodplain management, geomorphology, waterway management and ecology. The company was formed in 2000 with a commitment to providing technical excellence in the delivery of investigations in coastal, water resources and natural resource management fields.  Please get in touch with us if we can assist you in your wetland and river work.

WTB


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