Effects of vegetation on hydrology in Australia

Characteristics of Oz veg n 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’ n Widespread …

Effects of vegetation on hydrology/hydraulics

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

Dryland salinity

Note: break-of-slope salinity + regional water tables (low slope) Infiltration: 0.5 – 5mm/a15 – 150 mm/a

State/Territory2050 New South Wales Victoria Queensland South Australia Western Australia Tasmania Total $A250m/a $R1.2 Bn/a

Prognosis? n “Parachute” n Response time? n 50 – 1500 years

Effects of vegetation on runoff

Variability of annual peak discharge vrs. Catchment Area

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

Deciduous Rain Runoff

Evergreen Runoff Rain

Surface-cover

Effects of landuse (vegetation) on stream flows?

Eucalypt Woodland Pasture Mean annual rainfall (mm) Mean annual yield (mm) Eucalypt Forest Pine Forest from Vertessy and Bessard (1999) The impact of afforestation on mean annual yield (the MAYA model)

The impact of afforestation on daily flows (Tumut, NSW) Pasture Percent of time that daily flow is exceeded Daily flow (mm) Pines (5-10 years) from Tumut experiment, NSWSF

Reduction in annual yield (mm) reduction (mm) % planted area Estimated annual yield reduction

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 *** In summary, after afforestation:

The dilution effect: a plausible afforestation scenario upland afforestation commences lowland groundwater relaxation may start flow salt concentration years

Runoff and water supply + fires

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

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

Before After

Echidna Creek - Maximum temperature summer 2001/2002 Forested stream Cleared streams

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

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

Next lecture n Other controls on the hydrograph n Regionalisation n Begin on geomorphology!