Review of the Operation of the Cap : Ecological Sustainability of Rivers of the Murray-Darling Basin.

river health | Murray Darling Basin

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Title: Review of the Operation of the Cap : Ecological Sustainability of Rivers of the Murray-Darling Basin.
Creator: Whittington, John
Creator: Cottingham, Peter
Creator: Gawne, Ben
Creator: Hillman, Terry J.
Creator: Thoms, Martin
Creator: Walker, Keith
Subject: 270000 Biological Sciences
Subject: flow regimes
Subject: Cap
Subject: ecological sustainability
Subject: river health
Subject: Murray Darling Basin
Date: 2000
Publisher: Murray-Darling Freshwater Research Centre
Description: "February 2000".
Project no.: MDBC Project R10004 Ecological Sustainability of Rivers - Cap Review M/FOLDER/203
Publication no.: CRCFE Client Report
Description: MDFRC item.
Description: The Ministerial Council introduced the Cap on diversions from the Murray Darling Basin river system in June 1995, which in 1997 was confirmed as a permanent Cap. Two primary objectives for implementing the Cap were: -the need to maintain and, where appropriate, improve existing flow regimes in the waterways of the Murray-Darling Basin to protect and enhance the riverine environment; and, -to achieve sustainable consumptive use by developing and managing Basin water resources to meet ecological, commercial and social needs. With the introduction of the Cap, the Ministerial Council undertook to review its operation in the year 2000. The Ecological Sustainability of the Rivers component of the Review was undertaken by the Cooperative Research Centre for Freshwater Ecology, with input from submissions received from partner governments, the Community Advisory Committee and directly from stakeholders. The main conclusions of the Review are as follows: -Sustainability in the Murray-Darling Basin should be defined as the indefinite preservation of: - a functional and diverse ecosystem which, as well as meeting aesthetic and ethical requirements, provides a natural resource suitable for (all) human uses and production; and - a socio-economic system capable of using the natural resource productively to the maximum good of the current and future communities. -The development of the Basin's water resources, and in particular the reduced flows associated with these developments, has had a major impact on the riverine ecosystem. Impacts related to reduced flows include; - reduced areas of wetlands; - degradation of floodplain forests; - less diverse and reduced populations of native plants and animals; - exacerbation of problems of salinity, pest species, eutrophication and blue-green algal blooms; and - alteration of the shape of the Basin's rivers. -Because of water resource development, the Basin ecosystem is moving to a new and different state. This transition will require many decades to complete – with the full impacts of the current level of abstraction yet to be realised. -The Cap is set at a level of diversions that contributed to the current degradation of the riverine environment, and while the Cap is an essential step in slowing on-going decline, there should be no expectation that the Cap, at its current level, will improve the riverine environment. -However, without the Cap it is most probable that the health of the Basin's river system would be significantly poorer, as extractions approached the Full Development Scenario level. -Determining an appropriate level for the Cap requires science to identify ecological impacts of the current level of diversions and describe the long-term consequences of these impacts on sustainability. It is the role of the community, using this understanding, to strike the balance between the economic benefits and ecological costs of diversions. The level of the Cap needs to reflect this balance. However, the ecosystem itself will decide if the level of diversions is sustainable. -For the main part, the environmental benefits of the Cap, and hence its contribution to sustainability of the system, will depend on the skill with which the environment's allocation is managed. Provision of effective environmental flows are constrained by a lack of ecological knowledge, limitations of infrastructure, state boundaries, the wish to protect floodplain developments and timing and volume constraints imposed by the need to deliver water for consumptive use. -Indications of continued decline in river health suggest that current land and water management practise will require that the Cap allow significantly less extraction if the Cap alone is expected to achieve environmental sustainability. -Increasing the level of diversions in upstream rivers will further exacerbate environmental degradation downstream. These effects must be recognised when determining the level of the Cap in upstream jurisdictions. -The Cap has contributed (or will when fully implemented) to the sustainability of the river system by: - Restricting further diversions in all rivers, regardless of their current level of water resource development, thus protecting all riverine environments to the benefit of the whole Basin; - Protecting important high flow events – through limitations on access to off allocation that have been introduced to ensure Cap compliance; - Providing an incentive for more accountable water resource management, including conversion to volumetric allocations; and - In conjunction with other water reforms, provided a framework for water trading to develop. -The Cap's contribution to ecological sustainability would be enhanced by: - Reducing transmission losses across the Basin; - Returning all government funded water savings to the environment; - More efficient management of the environments allocation; - Basin-wide adoption of diversions models for evaluating compliance; - Rapid development of Computer Simulation Models to replace Demand Models for determining the Cap; - Defining the Cap so as to protect the proportion allocated to the environment from the effects of reduced catchment water yield; - Adopting the principle that all water in excess of the Cap is considered the environment's entitlement; and, - Integrating management of groundwater and surface water. -There is a need for an annual Ecological Audit of the Basin's river system. An Ecological Audit would assess the Basin-wide coordination, effectiveness and ecological outcomes of environmental flow management undertaken by the State's and the ACT. The Ecological Audit would also comment on the health of the Basin's river system by reporting the condition of a number of performance sites across the Basin. In terms of the specific questions raised in the project brief, the responses are: 1. Collate and assess relevant scientific and policy reports and submissions of the partner Governments and the CAC addressing the ecological sustainability of the river system of the Basin. A considerable body of scientific and management literature indicates that the health of the Murray-Darling Basin's river system has declined as a result of water abstraction, and that this decline is likely to continue as the full effects of past management practise occur. Scientific evidence indicates that further extractions from the river system are not ecologically sustainable, and that the existing level of extraction may not be sustainable. Much of this information is synthesised in the book, "Rivers as Ecological Systems – the Murray-Darling Basin". Relevant reports include the Stressed Rivers Assessments, Water Allocation Management Planning Reports, Scientific Panel Reports for the Murray, Barwon-Darling and the River Murray Barrages, and the NSW Wales Rivers Survey. Submissions to the Review were received from the partner governments to the Murray-Darling Basin Initiative, The Community Advisory Committee of the Murray-Darling Basin Ministerial Council (CAC), industry groups and directly from other stakeholders throughout the Basin. A number of issues relating to the ecological sustainability of the Basin's rivers emerged from the submissions including: - no consistent definition of ecological sustainability; - widespread support for a Cap to protect the ecological health of the river system; - disagreement over existing levels of environmental degradation and its causes; - difficulties in striking the balance between environmental impact and economic benefit; - insufficient scientific input into setting and evaluating the Cap; - no agreement on a sustainable level for the Cap; - greater accountability for management of environmental allocations; - the Cap alone will not ensure sustainability – other water management policies will be required; - the Cap needs to be supported by an integrated approach to catchment management; - confusion between impacts of the Cap and other water reforms; and - confusion about what the Cap is intended to achieve. 2. Address the impact of the operation of the Cap in achieving its objectives to ensure ecological sustainability of the Murray-Darling Basin river system by examining the following questions: 2.1. How Should Sustainability be defined for the purposes of the Cap? The Cap aims to make increases in production sustainable by fostering development, through more efficient use of diversions, without allowing growth in diversions. Production will only be sustained if both the ecosystem and the socio-economic system are sustained in the long-term. Recognising that sustaining the ecosystem that maintains the resource is the key component to the future of the Murray-Darling Basin, sustainability should be defined as the indefinite preservation of: - a functional and diverse ecosystem which, as well as meeting aesthetic and ethical requirements, provides a natural resource suitable for (all) human uses and production; and - a socio-economic system capable of using the natural resource productively to the maximum good of the current and future communities. In terms of its operation, the Cap must seek to apportion water between the riverine ecosystem and consumptive human uses such as to: - reserve sufficient water to maintain the ecosystem in line with ESD principles; and - preserve a supply of water suitable for human use. Leaving aside the socio-economic component, sustainability should address three fundamental ecological values: biodiversity, ecosystem function and ecosystem integrity. The appropriate spatial scale for assessing the Cap's contribution to sutainability is basin-wide and over a temporal scale of decades. The long-term decline in the Basin's natural capital (soil and water resources) indicates that we are failing the test of intergenerational equity, a fundamental tenet of sustainability. 2.2. What does science tell us about the suitability of the level at which the Cap is set? Determining an appropriate level for the Cap is a three-stage process – science addresses the first two stages: -The effects of the current level of diversions on the ecology of the river system have to be determined, -The long-term consequences of these ecological effects have to be clearly understood, and -With this understanding, the community has to make an assessment of the benefits and costs of diversions to determine an appropriate level for the Cap. Current levels of water abstraction are having a significant impact on the ecological sustainability of the Basin's river system. Throughout the Basin, Scientific Panel Assessments, Stressed Rivers Assessments and state water management planning reports have documented environmental impacts associated with reduced flows. These impacts include reduced areas of wetlands, less diverse plant and animal populations, and reduced populations of native fish, birds, macroinvertebrates and aquatic and floodplain plants. Reduced flows will continue to exacerbate problems of salinity, pest species, eutrophication and blue-green algal blooms. Reduced flows are altering the shape of the major rivers. In summary, reduced flows are a major cause of reduced river health in the Murray-Darling Basin. However, the full impacts of the current level of abstraction and other changes to the Basin's land and water resources are yet to be realised. The various ecological and geomorphic responses to the altered conditions that have been imposed will require many decades to complete. Assessing the suitability at which the Cap is set is complicated by the long-term natural variability in stream-flow of the Basin's river system and the long time-period over which changes occur. Also, there are few pre-Cap data against which to assess the environmental impact of the Cap. The focus should be on determining whether the current (capped) levels of diversions will conserve ecosystem function, integrity and biodiversity. This will require the continued development of ecological tools and techniques for assessing whether this has been achieved. It is clear from submissions to the Review that there is community disquiet over the state of the Basin's rivers. There is a strong desire to see an improvement in river health. It is also clear that further abstractions, anywhere in the basin, will decrease the health of the river ecosystem. 2.3. What aspects of the operation of the Cap constrain or support the sustainability of the river system? The Cap contributes to the sustainability of the Murray-Darling Basin river system by protecting end-of-system flows through limiting the growth in diversions, regardless of a river's current level of diversions. This protects the few remaining relatively undeveloped rivers from exploitation. The Cap has protected ecologically important medium and high flow events through limitations on access to off-allocation that have been introduced to ensure Cap compliance. In conjunction with other water reforms, the Cap has provided incentive for conversion to volumetric allocations and provided a framework for water trading to develop. Reducing transmission losses on water diverted to agriculture would enhance the Cap's contribution to sustainability of the Murray-Darling Basin river system. Information supplied by the Commission indicates that basin-wide at least 25% of diverted water is lost in transmission. Evidence from rehabilitation of South Australian irrigation schemes indicates much of this water can be reclaimed. At the Basin-scale river health will be improved by increasing the environment's share of water. Water saved from government-funded programs to reduce transmission losses should be removed from the Cap and be allocated to the environment. Water currently outside of the Cap (in-stream and environment's share) should not be traded into consumptive use. The volume of water needed to achieve sustainability will depend upon the provision of effective environmental flows. The delivery of these is constrained by a lack of ecological knowledge, limitations of infrastructure, the wish to protect floodplain developments, state boundaries and timing and volume constraints imposed by the need to satisfy consumptive users. Diversion models provide a more robust method of supporting the Cap than end-of valley flow regimes, which have clear technical problems with accurate measurement. Climate adjustment of diversions in the southern parts of the Basin ensures that a greater proportion of total stream-flow is diverted in dry years. Over time, the Cap should be defined so that it both limits diversions and guarantees a minimum proportion of stream-flow for the environment. 3. At a Basin scale, assess the potential hazards and level of risk to the health of the riverine environment (including algal blooms and salinity), and comment on the role of the Cap in containing these hazards and reducing the level of risk to riverine health. Export of salt from dryland sources to the aquatic environment is a major threat to water quality in the Basin and will impact on both water users and the riverine environment. Additional diversions from the Basin's rivers will increase the salinity of the remainder of the river downstream. The availability of dilution flows, the volume of which is protected by the Cap, will be an increasingly important constraint on salinity management in the future. Warm, slow moving, nutrient rich waters promote the development of blue-green algal blooms. Increasing flow can dissipate existing blooms. Further diversions from the Basin's rivers will increase the likelihood of conditions favouring the development of blooms. Also, increased diversions will reduce the capacity to provide flushing flows for diluting nutrient or dissipating developing blooms. The introduction of the Cap has not led to a reduced frequency and intensity of blue-green algal blooms however, it is likely that without the Cap, the frequency and intensity of blue-green algal blooms would be greater than it currently is. Predicted long-term changes in climate and land use in the catchment will significantly reduce catchment water yield, and consequently the volume of water in the Basin's rivers. This will have the effect of increasing the long-term proportion of stream-flow diverted from the Basin's rivers. Reductions in water yield from a catchment disproportionately impact on the environment's share. 4. Using two river valleys as the basis for case studies, assess the impact of the Cap to the sustainability of these valleys. 4.1. Lower Murray Regulation has significantly reduced the annual flow to the Lower Murray and the variability of mid-range flows so that the present regime is dominated by low flows with occasional high flows. As regulation has increased there have been declines in the range and abundance of many species of native plants and animals, including fish, crayfish, turtles, frogs, birds and mammals. In their place, species like carp and willows predominate. Modelling of the effects of Full Development Scenario have shown that the Cap has protected against further reductions in short-term variations in flow and the magnitude, duration and frequency of floods. Expansion to Full Development Scenario would exacerbate the loss of habitat diversity, reduce the frequency and duration of exchanges between the channel and the floodplain and change the metabolic functioning of the Lower Murray aquatic system. Due to the variability of the system, and the long lag times between the imposition of a stress and the ecological response, it is not possible to say whether the Cap has halted the decline in the integrity of the Lower Murray. It is possible to say that if the Cap had not been imposed, the move toward a Full Development Scenario would have resulted in further dramatic declines in the condition of the river. This decline would have affected areas such as the Coorong and Lake Victoria far more severely than other ecological components. 4.2. Condamine Balonne Large-scale intensive irrigation and flow regulation began relatively recently in the Condamine Balonne system. Diversions in the late 1990's from the Condamine Balonne system were nearly double the diversions reported in the 1995 Water Audit. Flow regulation now has a significant impact on the hydrology of the river, which has impacted on the fish and macroinvertebrate fauna. Further development in the Condamine Balonne catchment is likely to have a dramatic impact on ecological functions and eventually the sustainability of the river system downstream of Bourke. There is a serious risk that a Cap implemented in the Condamine Balonne (based on the WAMP) will fail to recognise the relative importance and potential impact of water resource development in this sub catchment on the ecological sustainability of the entire Basin.
Funding: MDFRC funding agency: Murray-Darling Basin Commission
Funding: MDFRC client: Murray-Darling Basin Commission (Now Murray-Darling Basin Authority)

Language: en
Rights: Open Access. This report has been reproduced with the publisher's permission.
Rights: Permission to reproduce this report must be sought from the publisher.
Type: report

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