FINAL REPORT: Wimmera River environmental flows study July 2013 Document history Revision: Revision no. 03 Author/s P. Clark P. Boon N. Marsh N. Bond T. Doeg A. Wealands D. Blackham Checked A. Wealands Approved A. Wealands Distribution: Revision no. 03 Issue date 19 July 2013 Issued to M. Toomey (WCMA) Description: Final Report Revision no. 02 Issue date 3 July 2013 Issued to M. Toomey (WCMA) Description: Final Report Revision no. 01 Issue date 06 May 2013 Issued to M. Toomey (WCMA) Description: Draft for comment Citation: Please cite this document as: Alluvium (2013). Wimmera River environmental flows study. Report by Alluvium Consulting Australia for Wimmera Catchment Management Authority, Horsham, Victoria Acknowledgements: We would like to acknowledge and thank the following people for their input in this study: Greg Fletcher Mark Toomey Bryce Morden Stephen Ryan Ref: R:\Projects\2012\049_Wimmera Glenelg FLOWS Review\1_Deliverables\03_Wimmera FLOWS\P112049_Wimmera_R02_v03.docx Contents 1 Introduction 1 1.1 Project scope 1 1.2 Study reaches 1 1.3 Study limitations 3 1.4 Purpose of this report 4 2 Water resource development in the Wimmera catchment 5 2.1 Surface water hydrology 6 Available data 6 Seasonality of the flow regime 7 Summary of flow characteristics 9 2.2 Groundwater 11 3 Environmental objectives 15 3.1 Catchment environmental values 15 3.2 Catchment influences 15 3.3 Environmental flow objectives 16 3.4 Self-sustaining fish populations 16 Description 17 Relevant reaches 18 Flow objectives 19 System limitations to achieving environmental objective for fish 21 3.5 Healthy and diverse water dependent vegetation 21 Water dependent vegetation of the Wimmera system 22 Relevant reaches 26 Flow objectives 26 System limitations 30 Notes on salinity thresholds 31 3.6 Diverse and abundant macroinvertebrates 32 Description 32 Relevant reaches 33 Flow objectives 33 System limitations 34 3.7 Healthy platypus communities 35 Description 35 Relevant reaches 35 Flow objectives 35 System limitations 36 3.8 Geomorphic processes 37 Geomorphology of the Wimmera system 37 Relevant reaches 38 Flow objectives 38 System limitations 39 3.9 Water quality 40 Description 40 Relevant reaches 41 Flow objectives 41 System limitations 41 Notes on salinity units 42 Wimmera River environmental flows study i 4 Approach to environmental flow determination 43 4.1 Hydraulic modelling 43 4.2 Seasonal frequency and durations 44 4.3 Rates of rise and fall 45 4.4 The ‘or natural’ recommendation 47 5 Wimmera River - environmental flow recommendations 48 5.1 Reach 2 & 3 Wimmera River Huddleston’s Weir to MacKenzie River 48 Summary Reach 2 & 3 characteristics 48 Environmental objectives 49 Environmental flow recommendations 50 Notes on environmental flow recommendations 52 Compliance point 52 Performance assessment 53 Comparison to 2003 study 56 5.2 Reach 4 Wimmera River MacKenzie River to Lake Hindmarsh 60 Summary Reach 4 characteristics 60 Environmental objectives 61 Environmental flow recommendations 61 Notes on environmental flow recommendations 64 Compliance point 65 Performance assessment 66 Comparison to 2003 study 68 6 Tributaries of the Wimmera River – environmental flow recommendations 72 6.1 Reach 1&2 Mackenzie River - Lake Wartook to Distribution Heads Weir 72 Reach 1 Lake Wartook to Dad and Dave Weir 72 Reach 2 Dad and Dave Weir to Distribution Heads Weir 72 Environmental objectives 72 Environmental flow recommendations 73 Notes on environmental flow recommendations 75 Compliance point 75 Performance assessment 76 Comparison to 2003 study 78 6.2 Reach 3 Mackenzie River – Distribution Heads Weir to Wimmera River 81 Environmental objectives 81 Environmental flow recommendations 81 Notes on environmental flow recommendations 84 Compliance point 84 Performance assessment 85 Comparison to 2003 study 87 6.3 Mt William Creek 90 Lake Lonsdale to Wimmera River 90 Environmental objectives 90 Environmental flow recommendations 90 Notes on environmental flow recommendations 92 Compliance point 92 Performance assessment 93 Comparison to 2003 study 93 6.4 Bungalally Creek - Toolondo Channel to MacKenzie River 93 Environmental objectives 93 Environmental flow recommendations 93 Notes on environmental flow recommendations 94 Compliance point 95 Wimmera River environmental flows study ii Performance assessment 95 Comparison to 2003 study 95 6.5 Upper Burnt Creek - Distribution Heads Weir to Toolondo Channel 96 Environmental objectives 96 Environmental flow recommendations 96 Notes on environmental flow recommendations 99 Compliance point 99 Performance assessment 100 Comparison to 2003 study 103 6.6 Lower Burnt Creek - Toolondo Channel to Wimmera River 105 Environmental objectives 106 Environmental flow recommendations 106 Notes on environmental flow recommendations 106 Compliance point 107 Performance assessment 107 Comparison to 2003 study 107 6.7 Yarriambiack Creek - Downstream of the Wimmera River 108 Environmental objectives 108 Environmental flow recommendations 108 Notes on environmental flow recommendations 109 Compliance point 109 Performance assessment 111 Comparison to 2003 study 113 7 Conclusions and recommendations 115 8 References 117 Attachment A Summary of hydrologic gauge data 124 Attachment B Environmental flow objectives 128 Figures Figure 1. Study reaches for the Wimmera catchment 2 Figure 2. Proportions of daily flows in the lower, mid and upper third percentiles in each month (Wimmera 2) 7 Figure 3. Proportions of daily flows in the lower, mid and upper third percentiles in each month (Mt William) 8 Figure 4. Proportions of daily flows in the lower, mid and upper third percentiles in each month (MacKenzie) 8 Figure 5. Median monthly flows under different seasonal conditions (unimpacted modelled daily data at Glenorchy) – Wimmera 2/3 9 Figure 6. Median monthly flows under different seasonal conditions (unimpacted modelled daily data at Wartook)- MacKenzie River 1/2 10 Figure 7. Median monthly flows under different seasonal conditions (unimpacted modelled daily data at Lake Lonsdale) – Mt William Creek 10 Figure 8. Illustrative guide to flow components (source: VEWH 2013). 11 Figure 9. Depth to water table – Wimmera catchment 12 Figure 10. Estimated baseflow at two Wimmera sites (calculated using the Lyne-Hollick filter) 13 Figure 11. Key water-dependent environmental values in the Wimmera River catchment. 15 Figure 12. Burnt Creek illustrating the small channel with insufficient depths to sustain permanent refuges (March 2013) 18 Figure 13. Large permanent refuges on upper MacKenzie River (left) and the reach 2 on the Wimmera (March 2013) 19 Figure 14. Example of vegetation mapping that can be used when devising environmental flow recommendations: vegetation of the Wimmera River near Dimboola (left shows modelled 1750 EVCs, right shows EVCs mapped in 2005). Source: DSE biodiversity interactive mapsite. 23 Figure 15. Wimmera River at Tarranyurk. The red arrows indicate salt scalds at the toe of the bank.(March 2013) 26 Wimmera River environmental flows study iii Figure 16. Percentage change in AUSRIVAS at Wimmera River at Riverside (WR32) compared to data collected pre- drought in 1994 (Brooks and Butcher 2012). 33 Figure 17. Median, 10th and 90th percentile salinity levels recorded at Lochiel Railway Bridge (right) and Glenorchy (left) 41 Figure 18. Climatic conditions – wet, average, dry and drought years 44 Figure 19. Wimmera River at Faux’s Bridge (W2&3) (July 2012) 48 Figure 20. Modelled inundation extents for Gross Bridge (Wimmera Reach 2/3) 52 Figure 21. Location of active flow gauges in Wimmera 2 & 3 53 Figure 22. Total Annual Shortfall across year types for Wimmera 2/3 (1=Drought, 2=Dry, 3=Average, 4=Wet) 55 Figure 23. Wimmera reach W2&3 shortfall summary by Climatic Condition (median values shown) 55 Figure 24. Percentage of years compliant under different environmental water delivery – Wimmera Reach 2/3 56 Figure 25. Comparison of total environmental water recommendations for two studies 58 Figure 26. Total environmental water recommendations by year type (note logarithmic Y axis makes values appear more similar) 59 Figure 27. Annual shortfall comparison – Wimmera 2/3 (1=Drought, 2=Dry, 3=Average, 4=Wet) 59 Figure 28. Reach 4: Lake Hindmarsh (left) and Horseshoe Bend Dimboola (right). (July 2012) 60 Figure 29. Reach 4 at Jeparit (left) and Tarranyurk gauge (right). (July 2012) 61 Figure 30. Modelled inundations on Wimmera Reach 4 64 Figure 31. Location of active flow gauges in Wimmera 4 65 Figure 32. Total Annual Shortfall across year types (1=Drought, 2=Dry, 3=Average, 4=Wet) (W4) 67 Figure 33. Wimmera Reach 4 shortfall summary by climatic condition 67 Figure 34. Percentage of years compliant under different environmental water delivery (W4) 68 Figure 35. Comparison of total environmental water recommendations for two studies (W4) 70 Figure 36. Total environmental water recommendations by year type (note logarithmic Y axis makes values appear more similar). 71 Figure 37. Annual shortfall comparison – Wimmera 4 (1=Drought, 2=Dry, 3=Average, 4=Wet) 71 Figure 38. Location of active flow gauges and hydraulic models in MacKenzie River 1 & 2 75 Figure 39. Total annual shortfall across year types (1=Drought, 2=Dry, 3=Average, 4=Wet) – MacKenzie River Reach 1&2 77 Figure 40. MacKenzie River Reach 1&2 shortfall summary by seasonal condition (median values shown) 77 Figure 41. Percentage of years compliant under different environmental water delivery – MacKenzie River Reach 1&2 78 Figure 42. Comparison of total environmental water