Bulk Entitlement conversion process for the Ovens Basin
CRCFE Technical Report No. 09/2001
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 present or contribute to eutrophication downstream in Lake Mulwala. --Ill-coordinated construction of levees throughout the system – particularly where other responses to high flow may be more ecologically sound. Summary of the environmental effects of flow regulation The effects of flow regulation on the ecological components of the river system may be summarised as: --River hydrology has been altered, with changes mainly restricted to low-flow periods in average or dry years. This has resulted in increased summer-autumn flows in the Buffalo and King Rivers and reduced summer-autumn flows in the lower Ovens River (the latter increases the potential for reducing instream habitat during critical low— flow periods). A ‘flow reversal' also occurs in the summer-autumn period, with lower than normal flows in early summer switching to higher than normal flows in late summer-autumn; --River geomorphology remains largely unaffected by flow regulation; --Water quality remains largely unaffected by flow regulation but has been affected by inputs of nutrients and organic pollution, presumably in runoff form agricultural and urban areas; --The effect of flow regulation on aquatic vegetation is largely unknown and will prove hard to disentangle from other factors without a targeted study. Floodplain wetlands are likely to have been affected by isolation from the river channels (due to levees) and land management practices (e.g. livestock access); --Macroinvertebrates are unaffected by river regulation in upstream areas. The decline in macroinvertebrate communities in downstream areas is probably due to multiple catchment impacts; --Native fish populations, including threatened species, have been affected by dams and weirs that act as barriers to migration. The extent of reduced habitat availability due to lower than natural flows in the lower Ovens reach needs to be confirmed. The extent of cold water releases from Lake Buffalo and the potential for cold water releases from Lake William Hovell also requires confirmation, as does the potential risk of dispersing fish larvae by flows such as supplementary releases to the Murray River; --The connection between the river channel and its floodplain has been largely unaffected by flow regulation by the dams. However, river-floodplain connections have been altered by the presence of levees in mid Ovens and lower King River reaches. Flow and other management recommendations were, therefore, developed to ensure sufficient low-flows to maintain existing instream habitat, particularly for threatened fish species and other management actions that reinstate or improve habitat available for river and wetland biota. Flow and associated management recommendations Flow and river management recommendations were developed to maintain the current high environmental or ecological value of the Ovens system and to address a number of the threats to environmental values. In particular, the recommendations aim to protect: --The natural attributes of the Ovens River, including the largely natural flow regime and the connection of river flows with surrounding floodplain. Given that the Ovens River is one of the few remaining lowland rivers in Victoria with a relatively natural flow regime, its protection must be considered as a high priority; --Both the natural high flow and low flow events that are recognised as important attributes of the Ovens River. As no specific flow recommendations are required for the high flow season (June through to October), other than to continue with current dam operations in a fashion that causes as little disruption to natural flows in the Buffalo and King Rivers as possible, flow recommendations have been based on low-flow exceedance data. In particular, the 95% exceedance flows were adopted to set low-flow limits that are likely to maintain habitat for native fish. Given the need for additional work to confirm the low-flow requirements of native fish, the flow recommendations should be considered as interim values only. In changing current regulation practices to meet environmental flow recommendations, priority should be given to the protection of the Ovens River below Wangaratta. Higher flows in the upper Buffalo and King Rivers in summer (especially if releases are colder than natural) increases the potential habitat available for introduced brown trout, which competes with native species. However, the opinion of the Scientific Panel is that increased summer flows in the upper reaches are likely to be less detrimental to the Ovens system as a whole, than the loss of habitat that might result from very low flows in the Ovens River below Wangaratta, which is known to support many threatened species. The generally good condition of the Ovens River system could be improved further by actions that complement the safeguard of the largely natural flow regime. These include habitat rehabilitation works, implementation of existing catchment management and water quality strategies and a review of levees required to protect key infrastructure. The ongoing maintenance or improvement to environmental conditions in the Ovens River system will be bolstered by: --Giving the lower Ovens River greater status and protection as a natural reference site and a site for scientific merit and study, and in light of its Heritage River status; --Listing the lower Ovens River as a critical habitat for Murray cod in Victoria; --Supporting ongoing attempts to re-establish Trout cod populations in the Ovens River; --Removal of the weir on the Ovens River at Tea Garden Creek and pumping water to users; --Removing the barrier on the Maloney's Creek; --Taking care to avoid significant reductions in flow associated with weekend pumping by diverters; --Undertaking instream habitat work, especially in reaches 2 and 3, to improve habitat for fish; --Implementing the Ovens Basin Water Quality Strategy; --Implementing the national carp management strategy within the Ovens River basin; --Reviewing the status, policy, and criteria for levee construction, maintenance and removal. The Scientific Panel was asked to consider the diversion of 5 GL as a contingency to supply water to irrigators near the Warby Range. This raises a number of potential environmental concerns. For example, to meet the extra demand without impacting on the security of supply of existing diverters may require an increase in the storage capacity of one or both dams. This will mean that a greater proportion of annual flow will be captured, which in turn can reduce the frequency of ecologically important flows (e.g. small to medium flow pulses important for maintaining instream habitat diversity and water quality). Extra demand and a further increase in summer flows also increase the likelihood of ‘flow inversion' effects in the river system (higher than natural summer flows, lower than natural winter flows). Increased summer releases may also increase the severity or extent of any cold water releases from the dams and reduce the natural variability in the flow regime that is considered to play an important part in maintaining generally good stream conditions. The Scientific Panel, as a first preference, recommends that the ‘ecological icon' status of the present flow regime be recognised and that no further diversions be made from the Ovens system. If this is deemed unattainable, then the Panel recommends that any further water extraction from the Ovens River should be taken from high flow events (preferably at Wangaratta where the 5 GL diversion is a relatively small component of total flow) and pumped to an off stream storage, rather than by expansion of existing storages and increased discharge during the irrigation season. In this way, the flow regime will be protected by minimising the increased summer flows that already exist, and taking the 5 GL at a time when this volume is a relatively small part of the discharge in the river. Any diversions should only occur after possible impacts on flows in the Murray and associated wetlands (e.g. Barmah forest) are first considered. Knowledge Gaps Further investigations to fill key knowledge gaps are recommended to confirm the low-flow recommendations and to improve our understanding of the environmental condition of the river system. These include: --Additional fish habitat surveys at very low flows to update environmental flow requirements in the Ovens Bulk Entitlements; --Further investigation of cold water releases from the dams that have the potential to confound the effect of environmental flows, especially for fish. --Investigation of changes to river flow, if any, that occur with concentrated pumping by diverters on weekends and at night; --Further investigation to determine the factors that are affecting macroinvertebrate communities in the lower Ovens River, with particular attention to pollutants; --A survey to provide information on the distribution or ecology of in-channel macrophytes and riparian vegetation. This will help to identify the recruitment requirements of woody riparian species, and assess the seasonal responses of in-channel macrophytes. An important future consideration will be the establishment of a performance monitoring and assessment program to ensure that environmental values are protected and to assess the response of the river system to future management actions (e.g. riparian rehabilitation, additional winter diversion should this occur). While important components of the river system are already monitored (e.g. hydrology, water quality, biological health using macroinvertebrates), there is no routine monitoring for components such as geomorphological changes, fish, and aquatic or riparian vegetation communities. Responsibility for undertaking the various management actions and for assessing their effect will require negotiation between stakeholders such as the NECMA, DNRE, GMW, EPA and local communities.
MDFRC funding agency: Department of Natural Resources and Environment, VIC
MDFRC client: Cooperative Research Centre for Freshwater Ecology
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Copyright (2001) Murray-Darling Freshwater Research Centre.