Instream flow assessment in New Zealand

1. Instream flow assessment in New Zealand

2. Flow assessment framework Evaluate for changes in flow Morphology Velocity/depth Water quality Methods and parameters Hydraulic geometry 2d models Stage/Discharge Water surface profile DO Temperature NH3 Biological evaluation Water quality suitability Habitat suitability Flow assessment based on flow response curves of biological indicators Flow regime requirements Methods Flushing flow analysis (shear stress) Fluctuating flow habitat analysis Sediment deposition

3. Instream habitat • Habitat suitability is a widely used concept e.g., angling and hunting • No suitable habitat - no fishSuitable habitat - maybe..

4. Three basic life requirements for fish and benthic invertebrates that live in flowing water • Velocity • Depth • Cover

5. New Zealand adult brown trout (Hayes & Jowett 1994) 1.0 1.0 0.8 0.8 0.6 0.6 Suitability Suitability 0.4 0.4 0.2 0.2 0.0 0.0 0.0 0.3 0.6 0.9 1.2 1.5 0.0 0.4 0.8 1.2 1.6 2.0 Depth (m) Velocity(m/s) Adult brown trout (Raleigh et al. 1984) 1.0 1.0 0.8 0.8 0.6 0.6 Suitability Suitability 0.4 0.4 0.2 0.2 0.0 0.0 0.0 0.3 0.6 0.9 1.2 1.5 0.0 0.4 0.8 1.2 1.6 2.0 Depth (m) Velocity(m/s)

6. Predicted water level and depth Predicted velocity Prediction of depth and velocity Level at 11 m3/s 1.00 0.25 -0.50 Depth (m) Level at 5.3 m3/s -1.25 2.0 -2.00 1.6 11 m3/s 1.2 Velocity (m/s) 5.3 m3/s 0.8 0.4 0.0 0 4 8 12 16 20 Offset (m)

7. 11 m3/s 6 m3/s 1 m3/s Habitat quality across river

8. Maximum Point where habitat begins to reduce sharply Usable habitat summed over reach for each flow 10 8 Weighted usable area (m2/m) 6 4 2 0 0 5 10 15 20 25 Discharge (m3/s)

9. NZ case studies 5 6 4 3 1 2

10. River flows are affected by : • Hydroelectric diversion, • Hydroelectric flow control, or • Irrigation diversion • Studies between 1979 and 2001 • Trout, benthic invertebrate, and native fish goals

11. For each project: • Description of river and flows • Habitat analysis and flow recommendation • Before and after photographs • Biological response

12. Waiau RiverHydroelectric diversion • Lake fed river - natural mean flow 450 m3/s • River diverted for hydropower generation in 1976 • Minimum flow of 0.3 m3/s since dam construction

13. Goal: Trout and food production Winter flow Summer flow 30 Adult brown trout 25 20 Food production WUA (m2/m) 15 10 5 0 0 5 10 15 20 25 30 Discharge (m3/s) • Maximum habitat at >15 m3/s • Sharp drop as flow goes below 10 m3/s

14. Minimum flow of 12-16 m3/s since August 1997 Before: flow about 1 m3/s After: flow about 16 m3/s

15. Waiau River Before After minimum flow 1000 100 Flow (m3/s) 10 1 1 year

16. Numbers of trout (>20 cm) 250 Before After minimum flow 200 150 Brown and rainbow trout per km 100 50 0 1996 1997 1998 1999 2000 2001

17. Brown and rainbow trout densities ranked nationally 350 300 Waiau River 250 After 200 Trout (> 20 cm) per km Before 150 100 50 0 River (300+ reaches in descending order)

18. Monowai RiverControlled flow to hydroelectric plant • Lake fed river - mean flow 13.8 m3/s • Dam at lake controls flow to downstream power station • Minimum flow of near zero, usually each night

19. Goal: Invertebrate abundance and diversity Maximum Sharp drop 15 Food production 10 WUA (m2/m) 5 0 0 2 4 6 8 10 Discharge (m3/s) • Maximum habitat at 5-7 m3/s • Sharp drop as flow go below 3 m3/s

20. Minimum flow since July 1994 Before After minimum flow 20 15 10 Flow (m3/s) 5 0 1-JAN-95 1-JUL-95 1-JAN-92 1-JUL-92

21. Invertebrate abundance and diversity After minimum flow increased to 6 m3 s-1 Before 25 1000 20 800 Taxon richness 15 Density (no m-2) 600 Taxon richness (no per sample) 10 400 Density 5 200 0 0 1991 1992 1993 1994 1995 1996 1997 1998 • Invertebrate abundance doubled • Number of species doubled

22. Ohau RiverHydroelectric diversion • Lake fed river - mean flow 80 m3/s • Flow diverted for hydropower in 1979 • Minimum flow of near zero

23. Goal: High quality brown trout fishery Maximum 20 Food production 15 WUA (m2/m) 10 Adult brown trout 5 0 0 5 10 15 Discharge (m3/s) Habitat analysis indicated excellent adult trout and food producing habitat at 10 m3/s

24. Minimum flow of 10-14 m3/s since 1994 Before: Flow < 1 m3/s After: Flow 10 m3/s

25. Failed to meet expectations • Trout present, but not many • Reasons unknown • Food ? • Recruitment? • Flow too high?

26. Tekapo RiverHydroelectric diversion • Lake fed river - mean flow 90 m3/s • Lake flow diverted in 1978 leaving 10 m3/s from tributaries

27. Goal: High quality trout fishery Habitat begins to drop sharply 30 Food production • Excellent adult trout spawning and food producing habitat at >10 m3/s /m) 20 2 WUA (m 10 Trout spawning 0 0 5 10 15 20 3 Discharge (m /s)

28. Just below dam Zero flow 45 km downstream Flow 10 m3/s

29. Tekapo River • Before diversion (flow 90 m3/s) • Not mentioned in angling surveys • Some trout spawning • After diversion (flow c. 10 m3/s) • Up to 240 brown and rainbow trout (> 20 cm) per km • More than 200 juvenile brown and rainbow trout per km

30. Brown and rainbow trout densities ranked nationally 350 300 250 After 200 Before? Brown and rainbow trout (> 20 cm) per km 150 100 50 0 River (300+ reaches)

31. Moawhango RiverHydroelectric diversion • Natural mean flow 9.3 m3/s • In 1991, all water was diverted to another river system

32. Deleatidium Zelandoperla decorata Aoteapsyche Hydrobiosis parumbripennis Maoridiamesa Orthocladinae Tanytarsus vespertinus Goal: benthic invertebrate community composition Sharp drop Maximum 15 12 WUA (m2/m) 9 6 3 0 0 1 2 3 4 5 Discharge (m3/s) • Sharp reduction at flows < 0.8 m3/s

33. Minimum flow of 0.6 m3/s since June 2000 Before 0.06 m3/s After 0.52 m3/s

34. Desirable species Undesirable species 40 Before (1997) 30 After (2002) Percentage of total 20 10 0 Elmidae Lymnaea Tanytarsus Ostracods Deleatidium Oligochaeta Zelandoperla Aoteapsyche Maoridiamesa Orthocladiinae Potamopyrgus Pycnocentrodes

35. Waipara RiverDiversion for irrigation • Small gravel-bed river • Mean flow 2.5 m3/s

36. Goal: maintain native fish population Sharp drop 8 Common river galaxias 6 Longfin eel (<300 mm) Upland bully WUA (m2/m) 4 Torrentfish Bluegill bully Common bully 2 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Discharge (m3/s) Habitat for a species with “intermediate” velocity preference begins to decline sharply at 0.12 m3/s

37. Dec 1998-May 1998 Dec 1999-May 2000 • Dry summer • Less than recommended minimum (0.12 m3/s) for 36% of time • Wet summer • Less than recommended minimum ( 0.12 m3/s) for 11% of time

38. Dry 1998/99 summer Wet 1999/00 summer Beginning of summer End of summer 1000 1000 100 Fish per 100 m 100 Fish per 100 m 10 10 1 1 Torrentfish Upland bullies Bluegill bullies Canterbury galaxias Torrentfish Upland bullies Bluegill bullies Canterbury galaxias Effect on Fish Population

39. Conclusion • This is all the NZ data on biological response to flow changes • Flow assessments were based on habitat requirements • 5 out of 6 were successful • The outcomes don’t support commonly held views that more flow is better and that all aspects of a natural flow regime are important

40. Thank you