Effects of vegetation on hydrology in Australia

1. Effects of vegetation on hydrology in Australia

3. Characteristics of Oz veg • Sclerophyllous (Eucalypts, acacia) • “hard leaves" - small, tough evergreen leaves. The hard cells within the leaves maintain a rigid structure at low water potentials, instead of collapsing. • Fire ‘loving’ • Widespread …

9. Effects of vegetation on hydrology/hydraulics

10. Issues associated with vegetation and hydrology/hydraulics • Input to water tables = Salinity • Proportion of water to Runoff • Salinity revegetation • Fire and water supply • Water quality = Temperature

11. Dryland salinity

12. Infiltration: 0.5 – 5mm/a 15 – 150 mm/a Note: break-of-slope salinity + regional water tables (low slope)

13. $A250m/a $R1.2 Bn/a

14. Prognosis? • “Parachute” • Response time? • 50 – 1500 years

15. Effects of vegetation on runoff

17. Variability of annual peak discharge vrs. Catchment Area

19. Why is Australian RO more variable? • More variable precipitation? • El Nino? • Evergreen vegetation? (Evapotranspiration ???) • (ET) = 100 to 200 mm > per year than deciduous

20. Deciduous Rain Runoff

21. Rain Runoff Evergreen

22. Surface-cover

23. Effects of landuse (vegetation) on stream flows?

24. 1000 Pasture Eucalypt Woodland 800 Eucalypt Forest Pine Forest 600 Mean annual yield (mm) 400 200 0 400 600 800 1000 1200 1400 1600 Mean annual rainfall (mm) The impact of afforestation on mean annual yield(the MAYA model) from Vertessy and Bessard (1999)

25. 10 Pasture Pines (5-10 years) 1 Daily flow (mm) 0.1 0.01 0.001 0 20 40 60 80 100 Percent of time that daily flow is exceeded The impact of afforestation on daily flows(Tumut, NSW) from Tumut experiment, NSWSF

26. Estimated annual yield reduction 400 300 200 reduction (mm) 100 0 0 20 40 60 80 100 % planted area 0 100 250 50 150 450 Reduction in annual yield (mm)

27. In summary, after afforestation: • Evapotranspiration will increase • Groundwater recharge will reduce • Water yields will reduce • Low flows will reduce • Peak flows will reduce • *** We can predict these changes reasonably well ***

28. 0 5 40 100 80 The dilution effect: a plausible afforestation scenario years salt concentration flow upland afforestation commences lowland groundwater relaxation may start

29. Runoff and water supply + fires

30. Limits to effects of cover on hydrology? • Urban extremes? • Above 20 year floods, landuse is irrelevant • Catchment is saturated and all catchments behave like concrete!

31. Study Site: Echidna Creek, SEQ • Riparian Rehabilitation project: • Commenced March 2001 • Whole sub-catchment • ~4km stream frontage • Stock exclusion • Off-stream solar powered stock watering • Concrete crossings • Revegetated with native riparian species (rainforest) • 2m plant spacing • Funded by: South East Qld Water Quality Monitoring Strategy • Managed by: Maroochy River Catchment Coordinating Committee

32. Before After

33. Echidna Creek - Maximumtemperature summer 2001/2002 Cleared streams Forested stream

34. Mayflies PREDICTED WATER TEMPERATURE INCREASES IN A NZ PASTURE STREAM (Rutherford et al. 1997) Water temperature in small streams • 50% of Mayflies die after • 96 hrs at 23oC. • 50% shade from riparian • vegetation will ensure • survival About 3km length of riparian vegetation is required to restore a Natural’ water temp.

35. Summary • Sclerophyllous vegetation affects all aspects of hydrograph • Clearing, fire = rising water table and salinity • Reforestation = decreasing runoff • Shade = decreased water temperatures

36. Next lecture • Other controls on the hydrograph • Regionalisation • Begin on geomorphology!