Scoping Study for the Narran Lakes and Lower Balonne Floodplain Management Study

"August 2002".

Project Number: Strategic Investigation Program — Rivers — Project R2011.

MDFRC item.

124 pages. ISBN 1 87681024 6.

Large floodplain ecosystems are a feature of Australia's dryland rivers. They are associated with extensive wetlands and numerous lakes and their ecological integrity is maintained by hydrological connections between the floodplain and adjacent river channels. The Lower Balonne floodplain complex straddles the New South Wales (NSW) and Queensland (Queensland) border. The complex contains a series of dryland rivers, two wetlands listed in the directory of important Australian wetlands (the Lower Balonne River floodplain and the Culgoa River floodplain park) and the Narran Lakes, a Ramsar-listed wetland. Hence, this is a region of diverse physical habitats and wetland 'styles', and of potentially high biodiversity. The Lower Balonne floodplain complex has been subjected to large-scale water resource and floodplain development. As a result, the flow regime of the Lower Balonne complex, and the Narran Lakes system in particular, has been substantially modified. Future developments along the Narran River, which flows into Narran Lakes, can occur in both NSW and Queensland. The Condamine- Balonne Water Allocation Management Plan (WAMP) acknowledges a likely expansion of water abstraction and diversion on the Queensland side. Under WAMP-modelled scenarios of different levels of water resource development, inflows to Narran Lakes would be less than 50% of natural. Without the WAMP in action, inflows could decline to 28% of natural. This report provides the results of a scoping study into the Lower Balonne floodplain complex, with particular reference to the Narran Lakes ecosystem. The study had four main outputs: • a review of the hydrology, ecology and cultural issues of the system; • a discussion of the implications of draft management plans on the system; • an ecological monitoring framework for the system; and • identification of the main knowledge requirements for the area. This study found a surprisingly large amount of information on the Narran River and its terminal lakes. Over 140 documents or reports were sourced. Many other documents exist but were not provided by the relevant agencies. Our review and synthesis of these documents showed that there has been little coordination of work on the Narran River and the Narran Lakes. This is probably not only because several different agencies have responsibilities for the area, but also because the lakes are subject to several different management frameworks. For example, the Narran Lakes Nature Reserve only includes a relatively small part of the whole terminal system and does not include the largest lake, and the Ramsar-listed component overlaps the Nature Reserve boundaries. The whole Narran Lakes terminal wetland complex should be considered as a single ecosystem and should be managed as such, not in bits and parts.

Overall, the quality of information and data contained within the cited reports is poor and cannot provide a basis for management of the Narran Lakes. Little of the available information directly addresses the effects of water resource development in the Condamine-Balonne catchment on the ecological condition or character of the Narran River and its terminal lakes. The only exceptions are recent studies emerging from the CRC for Freshwater Ecology and the Condamine-Balonne WAMP, although raw data backing the latter document have not been formally analysed. In general, studies that collect quantitative information on hydrology, geomorphology, water quality or biota have not been well designed. They generally are locationspecific and do not measure spatial or temporal variability. The most useful data are those on waterbirds. Waterbird records have been collected since 1971, although the sampling has been sporadic and the methods varied. There are also some valuable vegetation data. However, the emphasis has not been on connecting the vegetation communities with flooding regimes, but rather on mapping the terrestrial components. Other biotic data exist, some valuable, some limited, all of which would benefit from collation into a single data base/GIS system that would be available to help target future research and monitoring efforts. From the studies that have been undertaken in the region it is evident that: Water resource development has reduced the frequency of flows downstream of St George in excess of 31% (e.g. Average Recurrence Interval of 1.5 year floods increased by 48%); Combined with the impact of large-scale floodplain development, water abstractions have significantly reduced hydrological connections between the river channels and associated floodplains; Reduced hydrological connections have the potential to significantly alter ecological processes in the region; Hydrological connections are a key driver in maintaining the ecological integrity of the Lower Balonne floodplain and Narran Lakes; Rates of sedimentation on the Lower Balonne floodplain have increased by an order of magnitude (1.63 to 11.06 cm year-1) because of increases in sediment supply resulting from upstream land use changes; The texture and geochemistry of sediments being deposited in the Lower Balonne region have also changed — some of the sediment cores taken from the floodplain have high salinity levels at relatively shallow depths (mean salinity values range from 0.17 to 1.56 mS — plant growth can be inhibited by some of these salinity levels); Changes to the flow regime and increased sediment loads in the Narran River will lead to significant alterations to the extent and quality of available habitat, and hence will affect a range of biota and ecological processes in the Narran Lakes ecosystem; and Current and proposed development in the region can only lead to a deterioration in the ecological character of this Ramsar-listed wetland. It is clear that the information available does not provide enough detail to establish the current ecological character of the Narran Lakes nor to reliably predict the effects of increased water resource development.

For the Narran Lakes ecosystem and the Lower Balonne floodplain there are four areas of interest under the Commonwealth’s Environmental Protection and Biodiversity Conservation (EPBC) Act: the part of the catchment listed as a Wetland of International Importance; the two nationally, and possibly internationally, important wetlands: Culgoa Floodplain Wetlands and the Lower Balonne River Floodplain wetlands; and the presence of several listed migratory waterbird species and the presence of two nationally listed plant species. Under the Ramsar Convention, Australia has an obligation to ensure that the ecological character of the Narran Lakes is retained — failure to do so will contravene Australia’s obligation to the Convention. In the absence of a clear understanding of the ecological character of a listed site, it is recommended that presence, abundance, and activities of certain species and ecological communities, especially waterbirds, act as the expression of the ecological character until such time as it can be adequately described. Under the EPBC Act the expectation is that the Minister would seek to prevent or modify any action deemed likely to cause the loss of these attributes. In so determining, the Act expects the Minister to take the precautionary principle into account. We recommend a monitoring framework to assess the current ecological character of the Narran Lakes and floodplain and to determine changes in ecological character using on-going monitoring that incorporates appropriate control or reference ecosystems. It is important that a number of comparable systems (e.g. Paroo, Culgoa etc.) be evaluated as possible control or reference sites. Our monitoring framework includes four components: First, there needs to be a conceptual model that drives the choice of variables and processes on which monitoring is focused; Second, there should be a rigorous and thorough limnological survey that establishes current ecological character. All available data should be used to optimise the design of this survey, although only data on fish and vegetation are likely to be adequate for this purpose. This survey should measure most components of the biota of the Narran Lakes and floodplain, as well as variables such as sedimentation rates and components of water quality. The survey should also build on existing programs, such as the NSW National Parks and Wildlife Service waterbird monitoring; Third, the assessment of current ecological character should feed into an on-going ecological monitoring program, and into specific research projects that address important knowledge gaps. The on-going monitoring should use the results of the baseline survey to choose key variables that seem important to ecological character, are sensitive to changes in water regime, are statistically reliable to sample and have power to detect changes. The on-going monitoring needs to have a time component and should compare the Narran system to suitable control or reference systems; Fourth, it is also very important that functioning gauges be installed in all three lakes and be linked to a gauge in the Narran River, possibly at Wilby Wilby. The data from these gauges will be a major component of an input response model that links flow, habitat and ecological response. The Narran Lakes wetlands are regarded as significant within the Murray-Darling Basin, hence the declaration of the Nature Reserve and the Ramsar listing for part of the site. Sixty-five species of waterbirds have been recorded in the Narran Lakes in the past decade, forty-six of which breed in the wetland system. These numbers are comparable to the Macquarie Marshes and suggest that the Narran system is potentially one of the most important breeding and feeding habitats for waterbirds within the Basin. The Narran