Environmental Flows and Water Quality Objectives for the River Murray M/STR/1
CRCFE Technical Report
1.1 Setting the scene i. The health of a river is determined by its flow regime, the condition of its catchment & floodplain lands and in-channel habitats, and its water quality. These attributes must be considered holistically. Environmental flow allocations are an essential component of river management, but not sufficient alone to ensure a healthy river. Any decision to trade off flow requirements against other necessary management actions must be made with an understanding of the potential negative consequences. ii. From the outset, it was the unanimous and unequivocal opinion of this and previous expert panels that returning the River Murray System to a healthy working condition would require major improvements to river management – more environmental water, improved habitat condition, improved catchment & floodplain management, and better water quality. iii. A healthy working river is one that is managed to provide a sustainable compromise, agreed to by the community, between the condition of the river and the level of human use (see section 2.5). It was not the role of the ERP, or scientists in general, to decide upon the compromise between the competing values of production, ecosystem services and the natural environment. Rather, the ERP was asked to identify the level of work that will sustain indefinitely the ecological objectives first articulated by the Community Reference Panel and adopted by the Ministerial Council (see section 2.6). iv. The evolution of the degraded ecological condition of the River Murray is summarised. In the early 1900’s abstraction of water for consumptive use was low compared with modern levels, but water quality impacts would have commenced as a result of catchment clearing. The construction of Hume Dam and the locks and weirs on the lower Murray initiated an increased rate of degradation in ecological condition. This was accelerated by the rapid expansion in water abstraction for irrigation from the mid-1950s onwards. It is likely that during the 1960s or 1970s, ecological condition deteriorated to a point where the River Murray could no longer be considered as healthy. By 2001, the ecological condition of the River Murray is described as significantly impaired, and therefore unhealthy. v. The future condition of the River Murray System is clearly dependent on our actions now and over the coming years. Ecological condition continues to degrade under the present Cap and current river operations. Returning the River Murray System to a healthy condition will require major improvements to river management – significant environmental flow allocations, improved habitat condition, improved catchment & floodplain management, and better water quality. 1.2 Expert Reference Panel Assessment Process vi. The Expert Reference Panel (ERP) was appointed by the MDBC Environmental Flows and Water Quality Objectives Project Board. It has worked independently but has maintained extensive consultation with the Project Board, Project Team, and Community & Jurisdictional Reference Panels. vii. The ERP has adopted the Ministerial Council’s project objectives and has linked these to a suite of desired system level ecological outcomes and system level attributes for a healthy, working River Murray System. viii. The ERP has adopted a system level approach to assessing flow requirements and the potential ecological benefits offered by the flow management packages. This means that the net ecological benefits of any flow package or other management option (structural or operational) were considered across the entire length of the river system and its floodplain. Hence, the ecological assessments herein do not specifically address the management of individual river reaches, or floodplain wetlands and forests. Regional natural resource management agencies and river & catchment groups currently address issues at this scale. This report is designed to compliment their activities. ix. The system level approach adopted by the ERP led to a focus on five system level ecohydrological attributes for the River Murray System: -flow volume -flow distribution (pattern) -flow variability -connectivity (within and between the river channel and its floodplain) -water quality x. This report identifies the key threats to these attributes, and the Environmental Flow Requirements (EFRs) to address them. Key hydrological indicators used to assess short-term environmental benefits of the various options are described. 1.3 Performance Targets xi. Because of the lack of precise knowledge linking river flows to ecological condition it is extremely difficult to develop quantitative performance targets for improved management of river health. But, the river health concept does lend itself to a risk-based assessment framework, and it is this approach that the ERP has adopted in setting specific targets for river management actions. xii. The key outcome that the ERPs risk-based assessment has considered is: “Having a healthy, working River Murray System”. In this context, the key risk assessment is centred on the question: ”If we do x, what is the likelihood or probability of having a healthy working River Murray System?”. xiii. It is the considered opinion of the ERP that there is a substantial risk a working river will not be in a healthy state when key system level attributes of the flow regime are reduced below two/thirds of their natural level. xiv. Based on this ‘guidance value’ the ERP derived probability categories for successful environmental flows restoration. When key flow attributes are greater than two/thirds of their natural level, there is a high probability or likelihood of achieving a healthy river. When the same flow attributes are greater than half of their natural level, there is a moderate probability of achieving a healthy river. Below half natural, the probability of having a healthy river is low. xv. Caveat: The ‘two/thirds natural’ guidance level applies only to regulated and other impounded rivers. It is a target for river restoration, not a level for ‘acceptable degradation’ or ‘sustainable diversion’ of minimally impacted rivers. xvi. Caveat: These probability categories presume that the river offers suitable habitat and water quality for the growth and survival of native plants and animals. As already noted, the full benefits of environmental flow restoration will only be realised if river water quality, flood plain lands, and river habitat are also restored or protected. 1.4 Flow Option Packages assessment xvii. The risk categories described in xii. were used to analyse the likelihood that the flow option packages provided by the MDBC project team would deliver a healthy working River Murray System. The summary results of this analysis are outlined in the table below. xv. The key outcomes are that there would be a high probability of achieving a healthy working River Murray System if 4000 GL of new environmental flow allocations were combined with the operational improvements described in options package 57200. The same operational improvements combined with 1950 GL of new environmental flow allocations would lead to a moderate likelihood of achieving a healthy system. xvi. All other packages examined provide little confidence that a healthy river would be achieved in the future. Some localised ecological benefits are delivered by options A & B - for specific wetlands, floodplain forests or river reaches - but the overall system level impact was insufficient to improve the probability category. xvii. Further improvements in river operations beyond those described in options package 57200 may lead to better ecological outcomes for the same volumes of new environmental flows. Further modelling developments and work by the MDBC Project Team would be required to make this determination. This new work should include coupling of hydrological models for the major tributaries to the current River Murray hydrological simulation models, and consideration of environmental outcomes in those tributaries. xviii. None of the flow options packages considered herein provide significant ecological benefits for the Lower Darling River main channel and its adjacent floodplain (i.e. not enough to improve the river health probability category). xxii. No hydrological or hydrodynamic models for the Lower Lakes and Coorong were available to the ERP. This made it very difficult to assess ecological benefits of River Murray environmental flow allocations on these important wetland and estuarine regions. Further work is required to address this shortcoming in knowledge and predictive capability. xix. The full benefits of environmental flow allocations on the health of the river may not become apparent for many years – probably decades. Well designed monitoring programs will be essential to detect ecological response (both short and long term) to a change in the flow regime and the provision of environmental flows. xx. In the short to medium term, the benefits of river management actions are likely to be assessed by performance against hydrological outcomes and indicators. However, we emphasise that hydrological outcomes are only an interim performance indicator and that ecological outcomes and indicators must be used to measure the ultimate effectiveness of river management. xxi. Ecological outcomes of improved river management should be assessed using ecological indicators such as those developed in the Sustainable Rivers Audit, the National River Health Program and the National Land and Water Resources Audit. 1.5 Other river system requirements xxii. A range of structural and operational requirements must be addressed to ensure that the environmental flow option package benefits are realised. Failure to address these recommendations is likely to significantly reduce the ecological benefits delivered by environmental flow allocations. xxiii. Additional requirements addressed in this report are: Weir Management – permanent and seasonal removal Weir Management – partial draw-down Weir Management – fishways Thermal pollution – dam off-take design Dam releases – improved day to day variability in river height (flows) Barrage releases – fish passage and connection to the estuary Unseasonal flooding in Barmah-Millewa – increased capacity to deal with rain rejection flows Darling Anabranch Management – pipeline to supply water users Regulators – unseasonal wetting & drying Floodplain levees – improving natural floodplain inundation patterns and connectivity 1.6 Recommendations 1. Hydrological indicators are, at best, only surrogates for desired ecological outcomes. Ecological outcomes of improved river management should be assessed using ecological indicators such as those developed in the Sustainable Rivers Audit, the National River Health Program and the National Land and Water Resources Audit. 2. The health of a river is determined by its flow regime, the condition of its catchment, floodplain & in-channel habitats, and its water quality. These attributes must be considered holistically. Environmental flow allocations are an essential component of river management, but not sufficient alone to ensure a healthy river. Any decision to trade off flow requirements against other necessary management actions must be made with an understanding of the potential negative consequences. 3. Weir management - permanent and seasonal removal: -Non-essential locks and weirs should be removed; -Murray River lock and weir structures should be removed for two months each year, during periods of low irrigation demand (e.g. June-August); and -In the shorter term, Lock 8 should be decommissioned (empty weir pool and operate as a transparent structure) as an experimental trial with measurements of the positive (eg. Fish passage) and negative (eg. saline groundwater discharge) ecological outcomes being undertaken. 4. Weir management - partial draw-down: If recommendation 3 cannot be achieved in its entirety, then weir pools should be lowered by at least 1 metre for 3 months each winter-spring. 5. Weir management - fishways: If recommendation 4 cannot be achieved, then all locks and weirs should have fishways installed. 6. Weir management - raising height caveat: Undertake proper ecological assessment and cost-benefit analysis before any proposal to raise weir height proceeds. 7. Thermal pollutin - Dam off-take design: Undertake appropriate thermal mitigation works at Lake Hume and Dartmouth Dam, to provide release temperature close to natural. 8. Dam and weir release: Improve (promote towards natural) day-to-day variability in release patterns below all storages and weirs. 9. Barrage release: -Provide volume and timing of flows to promote significant fish recruitment in the Lower Lakes and Coorong; -Provide appropriate flows for the remainder of the year to maintain connectivity and fish passage between Coorong and ocean (i.e. keep the Murray mouth open); and -Undertake ecological and hydrodynamic studies to determine the volume and pattern of flows required to achieve the above. 10. Unseasonal flooding in Barmah-Millewa: -Reduce the frequency and volume of rain rejection events by improving management of water ordering, removing unnecessary structure, and clawing back operational airspace at Yarrawonga Weir. 11. Darling anabranch Management: -Implementation of pipelines to supply stock and domestic water to users along the Darling Anabranch; and -Removal of unnecessary structures (block banks, regulators and weirs) along Anabranch and associated Lakes. 12. Regulators: In cases where it is not possible in the short to medium term to modify weir heights or flow regime, consideration should be given to installing regulators on important wetlands and operating these structures to mimic natural wetting and drying regimes. 13. Floodplain levees: An audit should be undertaken of all floodplain levees and other structures (block banks, roads) that alter the natural movement of water across the floodplain. Unnecessary and illegal levees should be removed as a matter of priority.