Effects of vegetation on hydrology in

Australia

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 …

Effects of vegetation on hydrology/hydraulics

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

Dryland salinity

Note: break-of-slope salinity + regional water tables (low slope)

Infiltration: 0.5 – 5mm/a 15 – 150 mm/a

State/Territory 2050

New South Wales 1 300 000

Victoria 3 110 000

Queensland 3 100 000

South Australia 600 000

Western Australia 8 800 000

Tasmania 90 000

Total 17 000 000

$A250m/a

$R1.2 Bn/a

Prognosis?

“Parachute” Response time?

50 – 1500 years

Effects of vegetation on runoff

Variability of annual peak discharge vrs. Catchment Area

More variable precipitation? El Nino? Evergreen vegetation?

(Evapotranspiration ???) (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

0

200

400

600

800

1000

400 600 800 1000 1200 1400 1600

Pasture

Mean annual rainfall (mm)

Mean annualyield (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)

0.01

0.001

0.1

1

10

0 20 40 60 80 100

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)

0

50

100

150

250

450

0

100

200

300

400

0 20 40 60 80 100

red

uct

ion

(m

m)

% 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 afforestationcommences

lowland groundwaterrelaxation may start

flow

salt concentration

years

0 1005 40 80

Runoff and water supply + fires

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!

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

18

20

22

24

26

28

30

32

34

36

25/1

1/01

30/1

1/01

05/1

2/01

10/1

2/01

15/1

2/01

20/1

2/01

25/1

2/01

30/1

2/01

04/0

1/02

09/0

1/02

14/0

1/02

19/0

1/02

24/0

1/02

29/0

1/02

03/0

2/02

08/0

2/02

13/0

2/02

18/0

2/02

23/0

2/02

28/0

2/02

05/0

3/02

Tem

pera

ture

(D

eg C

) EC1

EC2

EC3

EC4

D1

P1

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 after96 hrs at 23oC.

• 50% shade from riparian vegetation will ensure survival

Summary

Sclerophyllous vegetation affects all aspects of hydrograph

Clearing, fire = rising water table and salinity Reforestation = decreasing runoff Shade = decreased water temperatures

Next lecture

Other controls on the hydrograph Regionalisation Begin on geomorphology!