THE EFFECT OF REGULATING THE LACHLAN RIVER ON THE BOOLIGAL WETLANDS – THE FLOODPLAIN RED GUM SWAMPS February 2009 Jessica L. Armstrong, Richard T. Kingsford & Kim M. Jenkins Wetlands & Rivers, School of Earth & Environmental Sciences, University of New South Wales, NSW 2052 Table of Contents List Of Tables ............................................................................................................................... i List Of Figures ............................................................................................................................. ii Executive Summary .................................................................................................................... 1 Introduction ................................................................................................................................. 3 Study Area ................................................................................................................................... 7 2.1. The Lachlan River ............................................................................................................. 7 2.2. The Booligal Wetlands ...................................................................................................... 9 Methodology ............................................................................................................................... 11 3.1. Rainfall ............................................................................................................................ 11 3.2. Hydrological Analysis ..................................................................................................... 12 3.2.1. Daily flow duration curves ....................................................................................... 12 3.2.2. Flow-spell analysis ................................................................................................... 13 3.2.3. Monthly flow analysis .............................................................................................. 14 3.2.4. Percentage flow analysis .......................................................................................... 14 3.3. Vegetation Analysis ........................................................................................................ 15 3.3.1 Experimental Design ................................................................................................ 15 3.3.2. Aerial photography ................................................................................................... 16 3.3.3. Image processing ...................................................................................................... 16 3.3.4. Image interpretation ................................................................................................ 17 3.3.4. Field assessment ...................................................................................................... 18 3.4. Statistical analyses ......................................................................................................... 22 Results ........................................................................................................................................ 26 4.1 Climate ............................................................................................................................. 26 4.2. Volumetric Changes .................................................................................................... 27 4.2.1. Changes in daily flow duration................................................................................ 33 4.2.2. Changes to seasonality............................................................................................. 38 4.2.3. Changes in flow thresholds ...................................................................................... 40 4.3. Vegetation Change ...................................................................................................... 42 4.3.1. Aerial photo interpretation ...................................................................................... 42 4.3.2. Comparison of field data and API ........................................................................... 47 4.3.3. Current red gum condition ...................................................................................... 49 Discussion .................................................................................................................................. 56 5.1 Changes to flow volume ............................................................................................... 56 5.2. Ecological effect on the Booligal Wetlands ................................................................ 59 5.3. Other hydrological changes to flow ............................................................................ 62 5.4. Management implications .......................................................................................... 64 5.5. Summary ..................................................................................................................... 67 Acknowledgements .................................................................................................................... 69 References ............................................................................................................................... 70 LIST OF TABLES Table 1. Two-way analysis of variance (ANOVA) design for aerial photo visual estimates of canopy cover Table 2. Three-way ANOVA design for assessing current condition of river red gum vegetation Table 3. Results of simple linear regression analyses for the annual proportion of flow reaching downstream gauges from upstream gauges Table 4. Descriptive statistics for the annual proportion of flow reaching downstream gauges from upstream gauges Table 5. Two-way ANOVA results for API visual estimates Table 6. Comparison of accuracy for two aerial photo methods (visual and point count) Table 7. One-way ANOVA results for field survey Table 8. Three-way ANOVA results for assessing current condition of river red gum vegetation i LIST OF FIGURES Figure 1. Map of study site Figure 2. Experimental design for API visual estimates of cover Figure 3. Experimental Design for field assessment Figure 4. Diagram of 25m2 quadrat used in the field Figure 5. Annual rainfall index cumulative deviation from the mean Figure 6. Annual flow at Forbes and Booligal Figure 7. Proportion of flow reaching downstream gauges from upstream gauges Figure 8. Daily flow duration curve for Booligal Figure 9. Daily flow duration curve for Condobolin Figure 10. Daily flow duration curve for Boorowa Figure 11. Seasonal monthly flow comparison at Booligal Figure 12. Daily spells analysis at Booligal Figure 13. Aerial photo interpretation results – visual method Figure 14. Aerial photo interpretation results – point count method Figure 15. Comparison of ground truth data and aerial photo estimates Figure 16. Current condition of river red gums ii Plate 1. Current images of Murrumbidgil Swamp (2008) Plate 2. Current images of Lower Gum Swamp (2008) Plate 3. Current Images of Top Gum Swamp (2008) Plate 4. Current Images of Lachlan River Gums (2008) iii EXECUTIVE SUMMARY River gums Eucalyptus camaldulensis are increasingly signifying the significant decline in the ecological health of rivers and their floodplains. This long-lived species, sometimes living up to hundreds of years has survived long periods of drought in Australia’s history but the impacts of river regulation and diversion and the current drought has caused high mortality of river red gums along the rivers of the Murray-Darling Basin. Extensive river red gum areas have died along the River Murray, Lowbidgee floodplain on the Murrumbidgee River and also in the Macquarie Marshes. Little is known of the health of river red gums on other river systems in the Murray-Darling Basin. We focused our research on the relatively poorly studied Lachlan River in southern New South Wales and investigated the ecological health of river red gums within in a group of its more significant wetlands, the Booligal Wetlands. These wetlands are extensive covering about 15,000 ha. They are nationally important and are recognised for the large waterbird colonies they can sustain. They form a part of the extensive lower Lachlan river wetlands and rely on river flows from the upper Lachlan, with the tributaries of the Belabula and Abercrombie Rivers. These wetlands integrate long-term changes to the river system. We investigated more than one hundred years of rainfall patterns and hydrological changes to the Lachlan River and the supply of water and the impacts of the changes to the river red gum swamp communities within the Booligal Wetlands. We analysed the available sequence of aerial photographs, spanning 35 years (1973-2008) to determine trends in river red gum health backed up with ground truthing. There are 10 large dams and 323 weirs within the Lachlan Catchment, an extensive system of canals, regulators, pumps and off-river storages that allow for the diversion of water from the river. We found no long-term decline in catchment rainfall where most flows for the Booligal Swamps are generated but there were significant declines in the Lachlan River’s flow have profoundly affected the ecology of the Booligal red gum swamps and these changes have coincided with the increasing impacts of major river regulation and diversion 1 of water for irrigation. The proportion of annual