Advantages and Disadvantages of Irrigation ... - Riversymposium

Advantages and Disadvantages of Irrigation
Mosaics as an Alternative to Traditional forms of
Irrigation in Northern Australia
Freeman Cook
Senior Principal Research Scientist
3 rd September 2007

What are Irrigation Mosaics
Rainfall
Surface
water
ET
Rainfall
Surface
water
ET
“Contiguous”
“Patchiness”
Coast
River
Unsaturated zone
Bores
Rootzone
Unsaturated zone
Coast
River
Unsaturated zone
Bores
Rootzone
Unsaturated zone
Groundwater system
Groundwater system
• Traditional irrigation systems
consist of
• One large patch
• Source from dams, bores and offtakes
often from existing river
systems supplemented by dams
• Canals and other delivery
infrastructure
• Irrigation of total area within
scheme
• Can result in undesirable
environmental effects
• Irrigation mosaics
• Numerous small patches
• Source from small dams, bores or
existing river systems
• Delivery infrastructure localised
• Possibility to avoid irrigation of
unsuitable areas
• It may be possible to minimise
some adverse effects of irrigation
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

Why Irrigation Mosaics
Rainfall
Surface
water
ET
Rainfall
Surface
water
ET
“Contiguous”
“Patchiness”
Coast
River
Unsaturated zone
Bores
Rootzone
Unsaturated zone
Coast
River
Unsaturated zone
Bores
Rootzone
Unsaturated zone
Groundwater system
• Irrigation often not suitable
for all areas within scheme
• Water-table rise and
salinisation often problems
• Lack of flexibility to respond
to climatic changes
• System less adaptable as
large ‘sunken’ cost
Groundwater system
• Irrigation can avoid
unsuitable areas
• Water-table rise and
salinisation can be
controlled
• More flexibility to respond to
climatic changes
• Can use an adaptive
management
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

Why Consider Irrigation Mosaics for Northern
Australia
• Climate is very different from Southern Australia
• Opportunity to design more sustainable and environmentally sensitive
developments
Monthly Water Balance (mm)
400
200
0
-200
Kununurra
90% rain, 10% ETO
Mean rain & ETO
10% rain, 90% ETO
Katherine
Burdekin
400
200
0
-200
Monthly Water Balance (mm)
Jan Feb Mar Apr MayJun Jul AugSep Oct NovDec
Jan Feb Mar Apr MayJun Jul AugSep Oct NovDec
Jan Feb Mar Apr MayJun Jul AugSep Oct NovDec
Month
Month
Month
100
Loxton
Griffith
Tatura
100
Monthly Water Balance (mm)
50
0
-50
-100
-150
-200
90% rain, 10% ETO
Mean rain & ETO
10% rain, 90% ETO
50
0
-50
-100
-150
-200
Monthly Water Balance (mm)
-250
Jan Feb Mar Apr MayJun Jul AugSep Oct NovDec
Jan Feb Mar Apr MayJun Jul AugSep Oct NovDec
Jan Feb Mar Apr MayJun Jul AugSep Oct NovDec
-250
Month
Month
Month
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

Bio-Physical Aspects
• Investigation of Biophysical Properties as Related to Irrigation Patch
Size
• Water-table rise
• Water-table spreading
• Solute spreading
• Evaporative demand
• Can learn about all irrigation systems
R
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

Water-Table Rise
• The rise in the water-table above the initial level with years of irrigation.
• I = 1 mm/day recharge
• No sinks
• No slope on aquifer
400
h m
- h 0
(m)
300
200
100
R = 100 m
R = 500 m
R = 1000 m
R = 2000 m
R = 5000 m
R = 10000 m
R = 100000 m
Ks = 1 m/day
Sy = 0.1 m 3 m -3
h m
R
0
0 20 40 60 80 100 120
t (years)
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

Water-Table Rise
• Spacing of the irrigation patches is critical as well as size
Array of Patches
1000
H(ρ = 0)/H o
100
10
τ = 0.1
τ = 1
τ = 10
τ = 100
L
1
0.1
0 20 40 60 80 100 120
n = L/R
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

Water-Table Spreading
H
H
1e+0
1e-1
1e-2
1e-3
1e-4
1e-5
1e-6
1e-7
1e-8
1e-9
1e-10
10
1
0.1
0.01
0.001
0.0001
• For single patches the area affect by water- table spreading
increases as R increases.
• For an array of patches the impact is increased due to overlap
of the water-tables
• Spacing of patches is important
Single Patch
Array of Patches
ρ
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
τ = 1x10 -8
τ = 1x10 -5
τ = 1x10 -2
0 10 20 30 40 50 60
ρ
τ = 10
τ = 50
τ = 100
a
c
ρ
0 2 4 6 8 10 12
τ = 0.1
τ = 1
τ = 5
0 100 200 300 400 500 600
ρ
τ = 500
τ = 1000
τ = 5000
τ = 10000
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia
b
d
H(τ,ρ)
H(τ,ρ)
0.12
0.10
0.08
0.06
0.04
0.02
0.00
1e+3
1e+2
1e+1
1e+0
1e-1
1e-2
1e-3
1e-4
1e-5
ρ
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
L = infinity
L = 2
L = 2.2
L = 2.5
L = 5
a
ρ
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
1.0
b
ρ
L = infinity
L = 2
L = 2.5
L = 3
L = 5
0.01 0.1 1 10 100 10000.001 0.01 0.1 1 10 100 1000
ρ
L = infinity
L = 2
L = 2.5
L = 5
L = 10
L = 20
c
L = infinity
L = 2
L = 5
L = 10
L = 20
L = 50
d
0.8
0.6
0.4
0.2
0.0
1e+3
1e+2
1e+1
1e+0
1e-1
1e-2
1e-3
1e-4
H(τ,ρ)
H(τ,ρ)

Solute Spreading
• For single patches
• Δr = Rs – R, Rs = radius of solute spread
• Solutes spread further under large patches
• With correct spacing irrigation mosaics could reduce ‘pollution’ of areas outside of the
irrigated region
1e+5
1e+4
Δr (m)
1e+3
S1
Regression S1
S2
Regression S2
1e+2
1e+1 1e+2 1e+3 1e+4 1e+5
R (m)
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

Evaporative Demand
• Advection – hot air from outside can lead to increased water loss for wet
patches
• Not a lot of data on irrigation systems but quite extensive for water bodies
1
f(u)/A e
is the
wind factor for
evaporation
f(u)/A e
f(u)/A
Regression
0.1
1e+1 1e+2 1e+3 1e+4 1e+5 1e+6
R (m)
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

Conclusions - Specifics
• Irrigation Mosaics provide an alternative to traditional irrigation
schemes
• Advantages of irrigation mosaics for bio-physical properties could
be reduced water-table height, water-table spreading and solute
spreading
• These advantages are dependent on the spacing between, and
size of the individual patches.
• We have designed some tools which give insight into design of
such mosaic systems
• Increased evaporation is a biophysical disadvantage that has been
determined
• The social and economic advantages and disadvantages will need
to be determined if such systems are to be adopted.
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

Conclusions - General
• The principles determined in this work are applicable to existing
irrigation systems as well as mosaics
• They give insight into the performance of the biophysical
system
• For a specific area the localised conditions would have to be
taken into account and other tools used in conjunction with
those so far developed
• There is still a lot more to do with development of analytical
tools for this and related problems.
CSIRO. Advantages and Disadvantages of Irrigation Mosaics as an Alternative to Traditional forms of Irrigation in Northern Australia

CSIRO Land and Water
Freeman Cook
Senior Principal Research
Scientist
Phone: 07 3214 2840
Email: freeman.cook@csiro.au
Web: www.csiro.au/group
Thank you
Contact Us
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