Report of the Ovens Scientific Panel on the Environmental Condition and Flows of the Ovens River

"December 2001".

Project Number: Bulk Entitlement conversion process for the Ovens Basin.

MDFRC item.

The Department of Natural Resources and Environment (DNRE) is overseeing a Bulk Entitlement conversion process for the Ovens Basin, with the aim of converting current water authority rights to water to Bulk Entitlements under the provisions of the Water Act (1989). A key feature of this process involves an assessment of current environmental conditions and identification of any current or potential impacts on environmental values associated with the regulation of flow within the river system. The broad environmental objective of the Bulk Entitlement conversion process is to ensure that current environmental values are protected and, where possible, enhanced. The Ovens Basin Bulk Entitlement Project Group appointed a Scientific Panel (convened by the Cooperative Research Centre for Freshwater Ecology) to consider environmental issues and to provide independent advice on the opportunities that exist through the Bulk Entitlement Conversion Process to better protect and enhance existing environmental values associated with regulated waterways in the Ovens Basin. The Scientific Panel had two objectives: 1. To specify a regulated flow regime that will sustain and where possible improve the current environmental values, dependent on water flows in the Ovens Basin; and 2. Provide advice to the Project Group on the environmental benefits of a variety of management options and operational scenarios. The representative reaches considered by the Scientific Panel were: 1. Buffalo River: Lake Buffalo to the Ovens River; 2. Ovens River: From the confluence with the Buffalo River to the confluence of the King River; 3. King River: Lake William Hovell to Edi; 4. King River: Edi to the Ovens River confluence; 5. Ovens River: from the confluence with the King River to the Murray River. Some of the major tasks completed by the Ovens Scientific Panel while undertaking this project included: - Integration of existing knowledge of the environmental condition of streams in the study area (including the considerable experience and knowledge of the Ovens system held by Panel members); - Consultation with Goulburn Murray Water to clarify the operation of the system; - An intensive field trip, used to assess environmental conditions at 22 sites across the study area; - Consultation with local landholders to gain their perspective of the river system; - Analysis of hydrological data to identify changes to stream hydrology that have occurred since the regulation and diversion of water for agriculture and urban supply; - A series of workshops to develop a common understanding of the river system, important environmental values to be protected, and how these values may have been affected by regulation and other catchment activities; - The development of recommendations for a flow regime that will protect or enhance the environmental values identified for the river system. Flow Regulation Flow in the Ovens, King and Buffalo Rivers is modified by three processes: 1. The presence and operation of Lake Buffalo and Lake William Hovell; 2. Progressive extraction of water for irrigation and town water supply; and 3. Changes to the form of the channel due to channelisation, anabranching, substrate and snag extraction and flood levees. Examination of hydrological data indicated that regulation associated with the operation of the Buffalo and William-Hovell Dams does not affect the magnitude of floods in the Ovens and King Rivers, other than causing a slight delay of the flood peak if it arrives when the dams are empty. The effects of current regulation on river flow are limited to the summer-autumn period in years with 'average' and ‘below average' flows, a time when the natural flow regime is already low. This effect is less evident during wet years when summer-autumn flows are relatively high. Within this summer-early autumn timeframe, regulation results in an overall flow reversal in the Buffalo and King Rivers; early in the low-flow period, regulated flows are lower than natural and then switch to being much higher. The flow reversal is often exacerbated by the release of supplementary flows to the Murray River to relieve capacity restraints when supplying downstream irrigators. While regulation has seen an increase in the summer-autumn low-flows in the Buffalo and King Rivers, the extraction of water for agriculture and urban supply has reduced the low flow volumes in the Ovens River below Wangaratta. Overall, the effect of regulation and diversions on the flow regime across the study area is mainly confined to low flow periods, resulting in changes to the depth of in-channel flows in the order of tens of centimetres. Summary of environmental values associated with the Ovens River system The Scientific Panel identified the following environmental values associated with the Ovens River system, recommending that they should be protected in the future: - The Ovens River is one of the last largely unregulated rivers in the Murray Darling Basin and is particularly important as a reference against which to assess the state of other lowland rivers in the region; - The natural flow regime (including both high and low flows) as it maintains geomorphological, biological and ecological processes; - Habitat diversity that includes instream features such as abundant large woody debris, cobbles, riffles, pools, bars, anabranches, flood runners and the littoral fringe, and floodplain and wetland/billabong features in the nearby landscape; - Threatened species (flora and fauna), including up to ten native fish species of State and national conservation significance and icon species such as Murray cod; - Riparian vegetation, especially in the upper King River and the lower Ovens River, which may serve as a template for future restoration or rehabilitation efforts. The remnant riparian and floodplain vegetation also provides important habitat for threatened species (fish, birds, amphibians) whose natural habitat in the region has been greatly reduced since European settlement. This includes river redgum forest and box woodlands, and herb wetlands such as those occurring adjacent to the lower section of the Ovens River. In particular, lowland riparian habitat is an important refuge for threatened native fish species such as Trout cod and Murray cod; - Generally good water quality conditions, especially above Wangaratta, that supports river and wetland biota and increases the likelihood of success of river rehabilitation via habitat reinstatement; - Connectivity between the river channel and its floodplain that maintains floodplain function; - Links with the Murray River, with the Ovens being important for water yield, water quality and fish migration. The protection of the above environmental values is consistent with the objectives of the Heritage Rivers Plan for the Ovens River and the priorities of the Northeast Catchment Management Authority (Northeast Catchment & Land Protection Board 1997). Protection of these values can, therefore, be used as a guide for setting environmental management plans at the local and regional level. Summary of threats to environmental values A large number of activities and processes pose threats of varying degrees to the environmental condition of the Ovens River system. This is not surprising given the broad range of activities and land use that occur across the study area. The threats to environmental values include those associated with flow and river management, agricultural and industrial practices and activity, natural ecological processes, and invasion by pest plant and animal species. Environmental threats may be summarised as: --Rapid changes to water releases from the two dams that rapidly reduces the habitat available for biota; --The potential for cold water releases from the dams in summer that may limit the biological activity or distribution of river biota; --The potential for low or zero flows in lower river reaches due to concentrated pumping by diverters at weekends (this needs to be confirmed) or from water releases failing to meet irrigation demand; --The release of supplementary flows to the Murray, which may send unseasonable biological cues to native biota; --The removal of snags and the clearance of riparian vegetation that helps to stabilise stream bed and banks and provides instream habitat; --The encroachment of willows that affect channel geomorphology and result in increased erosion, altered habitat, reduced biodiversity, and altered food quality for instream biota; --Bed and bank works by local landholders and previous gravel extraction that has reduced stream habitat diversity and mobilised sediments in the river system; --Natural bed and bank erosion (exacerbated by bed and bank works undertaken over many decades) that results in increased sediment loads in the river system; --The infilling of pools by transported sediments, for example in the Ovens River below Myrtleford and the lower King River, that may smother instream habitat; --Management of Tea Garden Creek, its weir and nearby levees, in a manner that disconnects the creek from its floodplain, reduces the variability of flow entering from the Ovens River and serves as a barrier to fish movement; --The presence of the Lake Buffalo and Lake William Hovell that serve as barriers to fish movement; --The presence of carp, trout and other introduced species that compete with, or reduce habitat condition, for native fish species; --The dominance of weeds such as blackberry and willows over large areas that reduce riparian habitat quality; --Grazing and watering of livestock in floodplain wetlands and billabongs that reduce water quality and habitat conditions; --Minor eutrophication and pollutants from urban areas (e.g. Wangaratta) and industrial discharges that may result in less than expected macroinvertebrate families pre