deep drainge under irrigated cotton in central queensland
TRANSCRIPT
Jack McHugh, Lance Pendergast,
Peter Evans and Jerome Arunakumaren
Deep drainage under irrigated cotton on the
Central Highlands
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HistorySome say they don’t “leak” but science has always said they will
Deep drainage was generally presumed to be minimal on heavy clay soils “the soils don’t leak” paradigm
Substantial leaching of Chloride and considerable drainage (Shaw & Yule ‘78).
Closely matching inputs of rainfall and irrigation water with crop water use and high climatic demand will save the day.
Yet under typical irrigations of 7.2 ML/ha in the EIA drainage was as high as 246mm (Carroll et al., ‘95, Connolly et al., ‘98 & ‘99).
Deep drainage is typically 100-200mm/year and can vary from 50 – 260mm, although 900 mm has been observed. (Silburn and Montgomery 2003).
Deep drainage represents an economic loss to farmers (Vervoort & Silburn, 02).
Salts must be stored somewhere. If mobilised, they pose a risk to groundwater, riverine systems and the sustainability of the irrigation area.
Aims of RWUE II project:
1. Characterise / quantify deep drainage for selected irrigated cotton soils.
2. Use this knowledge to identify land and management parameters contributing to deep drainage e.g. down furrow distance.
3. Map the soils of selected cotton growing areas in terms of soil inherent properties, linked to risk of accelerated deep drainage, and the aquifers beneath in terms of their ability to hold these excess waters.
4. Develop a hydrogeological conceptualisation of the EIA and possibly a calibrated groundwater model.
5. Communicate the results…
Two parts – Drainage & GW impacts
Modelling
Deep Drainage- SALF
- SODICS
- SIRMOD
- FAO56 Evapotranspiration
Part 1
Comet River
Sites
Nogoa River
MacKenzie River
Emerald Irrigation Area
0
100
200
300
400
500
600
700
Nyang (500m) Arcturus (1000m) Denliza (1200m)Farms and furrow length
De
ep
dra
ina
ge
(m
m)
SaLFSirmodFAO56Sodics
Furrow SaLF SIRMOD FAO56 SODICS
Head Mid Tail Head Mid Tail Head Mid Tail Head Mid Tail
500 25 10 9 123 85 30 180 135 60 262 1152 552
1000 27 15 15 496 427 161 337 257 0 83 491 240
1200 10 18 4 204 153 61 188 138 75 153 217 440
Field Length (m)
Note: DD originating from rainfall not included in SIRMOD estimates
0
20
40
60
80
100
120
140
160
180
0 200 400 600 800 1000 1200 1400
Distance Down Furrow (m)
Infi
ltra
ted
De
pth
(m
m)
2nd Irrigation (1.48 ML/ha)2nd Irrigation deep drainage6th Irrigation (0.97 ML/ha)6th Irrigation deep drainage
Head Mid Field
Tail
3.35 L/s for 30.3 hours
3.77 L/s for 17.7 hours
2nd Irrigation Soil Water Deficit: 110 mm
6th Irrigation Soil Water Deficit: 67 mm
0
20
40
60
80
100
1 2 3 7 10 15 18 25 32 36 50 56 92 100
Deficit (mm)
Rainfall DD
0
2040
6080
100
120140
160
34 60 67 70 87 87 88 89 92 93 110119128
Deficit (mm)
mm
Irrigation DD
A prescriptive approach to irrigation management.
Water end-users and advisers – an appreciation of the intricacies of irrigation management.
But farms utilise very sophisticated instruments!!!!→when to irrigate,
→but not necessarily how much to apply and→when to stop.
Farmers need to measure the volume and adjust the application rate to field conditions.
Simple field indication of wetting front at the bottom of the root zone.
Conclusions & Recommendations….Part 1
Companion Study
“Preliminary investigation of ground water impact of the Emerald Irrigation Scheme”
This large volume of deep drainage and the probable contaminates it carries, is a threat to local groundwater resources
and downstream users, and a considerable economic loss to the farmers.
Considerable drainage for >20years
Why haven’t we seen rising groundwater levels on a broader scale?
Part 2
3.5kmWeathered basaltHard basalt
Black soils – brown clays Observation bores
Groundwater level & flow gradient 2004 – Western EIA (Emerald Hill)
Retreat creek & overflowSelma Channel 3
45m
Sand Multi-coloured clays
Field waterlogging & discharge
5km
Nogoa River
20m
Tertiary BasaltQuaternary Alluvium
BillabongBlack soils – brown claysObservation bores
Groundwater level & flow gradient 2004 – Eastern EIA
7km
Nogoa River
70m
Tertiary BasaltQuaternary Alluvium
Winston Creek
Black soils – brown claysObservation bores
Groundwater level & flow gradient 2004 – Eastern EIA
Weemah ChannelCapricorn Hwy
0
100
200
300
400
500
600
700
Nyang (500m) Arcturus (1000m) Denliza (1200m)Farms and furrow length
De
ep
dra
ina
ge
(m
m)
SaLFSirmodFAO56Sodics
So where is the rest of the water? 100-200 mm/season
Bores• Not serviceable – not accessible.• Position – not on farms.• Key NR&M historical aquifer pump test data could not be located.
Other key limitations• DEMs – Eastern EIA – inadequate.• Gauging stations – Data.• Infrastructure characteristics. • Water course incision data.• Information sharing (Institutional
and public)Recommendations• Conduct slug permeability testing.• Produce depth to groundwater plan for the EIA.• Carefully monitor bores that show rising ground water
trends at variance with the recent rainfall trend.• Data custodians need to be approached formerly.
To find out you need to do a lot more……