Lower Balonne Scoping Study Environment Theme

"January 2006".

Project Number: Environmental Review of the Lower Balonne Floodplain - M/BUS/93.

MDFRC item.

The Lower Balonne system extends from St George in Queensland to the Barwon River in northern NSW. The Lower Balonne system begins as a single channel of the Balonne River downstream of Beardmore Dam at St George in Queensland and extends to the Barwon River in New South Wales. Water is pumped from the rivers and distributary channels of the Lower Balonne during flood periods and flood overflows are diverted to storage for crop irrigation, mainly cotton. (Cullen et al. 2003). Consequently, modification of the natural flow regimes are likely to impact on the ecological communities of the rivers, floodplains and wetlands of the Lower Balonne system (McCosker 1996). The Queensland Water Resource (Condamine Balonne) Plan 2004 includes a strategy for event-based management to deliver flows to the Lower Balonne floodplain, especially to ensure that adequate flows reach the Ramsar-listed Narran Lake Nature Reserve to meet Australia’s international obligations under the Ramsar Convention. The Water Resource Plan proposes requires a comprehensive review five years after commencement, which must assess the effectiveness of the plan’s performance indicators, including event-based management rules, in delivering the desired outcomes of the plan. This Scoping Study is intended to assist in addressing the water needs of the Lower Balonne Floodplain as well as providing input to the upcoming five-year review. Cullen et al. (2003) identified important ecological assets in the Lower Balonne that need to be managed in terms of water resource planning. These assets are “the biota of the rivers, distributary channels and wetlands of the Lower Balonne, the internationally recognised Narran Lakes, the National Parks of the Culgoa floodplain, and the Darling River itself”. This review excludes examining the knowledge concerning the Narran Lakes as this has previously been reviewed by Thoms et al. (2003) and is currently under an extensive ecosystem study; and the Darling River itself, which is outside the scope of this brief. The floodplains of the Lower Balonne comprise a complex mosaic of vegetation communities. These include important native grassland, shrubland and woodland communities of riparian and floodplain habitats, with the floodplains of the Culgoa, Birrie and Narran rivers supporting the largest area of native grasslands in New South Wales (Dick, 1993). The plant communities in the Lower Balonne are reliant on intermittent flooding for recruitment and survival. Compared with River Red Gums, little data is available on the water requirements of key floodplain vegetation species found on the Lower Balonne floodplain, such as Coolibah, Black Box and Lignum, although the latter is a component of the Narran Lakes Project (Narran Lakes Newsletters http://mooki.canberra.edu.au/narran).

Vertebrate fauna surveys of the Coolibah floodplains of the Birrie and Culgoa (NSW reaches) record 19 species of native mammal, 112 birds, 23 reptiles and 6 frogs, while the trees themselves supply a habitat and refuge for a variety of mammals, birds and reptiles (Dick and Andrew 1993). The aquatic invertebrate and fish communities throughout the lowland catchment of the Darling River are considered threatened (NSW Fisheries Management Act 1994). One aquatic invertebrate, four fish and four water bird that have been listed under either federal (EPBC) or NSW legislation as threatened, vulnerable or endangered are recorded within the Lower Balonne system. A large amount of data about the Lower Balonne floodplain has been collected, although some of it is not readily accessible. It also varies widely in both temporal and spatial scales, as well as in quality and purpose of collection. These factors make it difficult to compare and relate the different sets of data in order to draw conclusions about the ecological condition of the Lower Balonne floodplain. There are some different conclusions drawn by the Technical Advisory Panel (TAP) to the WAMP, the Cullen report, and subsequent research regarding the ecological condition of the Lower Balonne system. The TAP report suggests that the biotic communities, particularly fish and invertebrates are moderately degraded in the lower sections of the Balonne systems and indicate that modification of the natural flow regime is a potential cause. The Cullen Report (Cullen et al. 2003) suggests that there is no scientific evidence to indicate that these communities are currently degraded to any extent but have not yet felt the impact of water resource development that occurred in the 1990’s. However, it is clear that flow dependent assets may suffer from the impacts of water resource development. Therefore it is recommended that: 1. All ecological assessments must take on a whole of catchment approach, therefore including the NSW portion of the Lower Balonne system; 2. The NSW portion of the Lower Balonne system must be assessed with the same rigour as QLD portion in terms of the number of sites monitored; 3. There should be an overarching continuity of the ecological assets assessed, even if it is to be divided amongst available expertise of various agencies i.e. riparian vegetation, macrophytes, fish, macroinvertebrates, water birds, frogs, turtles; and 4. Rigorous re-analysis of the annual monitoring data by SKM and EM in terms of indicators used and statistical significances of between-site variations.

Defining the environmental water requirements for the Lower Balonne is difficult due to the absence of published scientific work (Cullen et al. 2003) and there is limited specific knowledge of the water requirements of most flood dependent ecosystems and biota. To effectively manage flood dependent ecosystems, we need knowledge of: 1. How flooding and drying influence habitat availability 2. How flooding and drying influence the movement and dispersal of biota (fish, invertebrates, plants) within floodplain ecosystems 3. How flooding and drying trigger recruitment for a suite of biota (i.e. germination of plants) 4. What is the role of flooding and drying in maintaining biodiversity 5. How connectivity between riverine and floodplain environments influences carbon and nutrients dynamics 6. What extent of floodplain needs to be inundated to support viable riparian communities 7. What extent of wetland needs to be inundated to conserve “X” amount of biodiversity 8. What is the cost to the community as a consequence of lost productivity of flood plain ecosystems 9. What are the commence to flow values for flood-dependent wetlands In light of the considerable knowledge gaps and the lengthy time lag before the impacts of changes become apparent, it is critically important that the Precautionary Principle should be followed. There are many contradictions in the interpretation of the limited data available for the Lower Balonne system, with no direct link able to be made between modification to the hydrology due water extraction and water storages and possible degradation of the biotic communities. However both the TAP Report (QLD DNR 2000) and the Cullen Report (Cullen et al. 2003) both stress that if the current level of water extraction continues, in all likelihood there will be substantial impacts on the biota of the channels and floodplains that comprise the Lower Balonne system. It needs to be acknowledged that there will be a considerable time lag between changes in water extraction and biological responses and the impact of current water extraction may not be detectable for many years due to the inherent natural variation in flows (QLD DNR 2000; Cullen et al. 2003).

Research and monitoring recommendations Recommendation 1 - A joint taskforce of Qld and NSW natural resource agencies develop a cohesive monitoring program following the approach suggested by Scholz et al. (2005) in designing monitoring programs (Appendix 4). This program would require the full support of state agencies and community groups and developed within an adaptive management framework with clearly stated objectives and testable hypotheses. The monitoring program would eventually be able to describe the current condition and give an assessment of the biodiversity, abundance and community composition of instream and floodplain biota. The information gained from such surveys can then be used by managers to determine the extent of floodplain that needs to be inundated to preserve a proportion of the associated biodiversity (i.e. surveys might indicate that 20% of the floodplain area needs to be inundated for three months to preserve 90% of the current biodiversity). Recommendation 2 - A detail investigation is carried out to determine the watering requirements for Coolibah and Lignum plant communities. This investigation should use a combination of tradition plant survey methods combined with measurements of changes in plant vigour (or health) using remote sensing techniques. Recommendation 3 - A detailed investigation on the rates of sedimentation within the Lower Balonne under different flow regimes be undertaken. There is little knowledge of what the critical ecological processes in riverine and floodplain habitats are or how changes to the flooding regime may affect primary productivity and the exchange of material between components. Over the forthcoming years, the floodplain and riverine environments will experience a range of flood frequencies and intensities in response to increased water extraction and changing climatic conditions. Recommendation 4 - A detailed investigation be undertaken of the role of connectivity between the river channels of the Lower Balonne and associated floodplains and wetlands and three critical metabolic functions (primary production, nutrient cycling and decomposition).

The study would examine the response of each component to inundation to deter