Can higher flow rates improve performanceof border-check irrigation

in the Murray Dairy Region?

Mike Morris, Amjed Hussain, Malcolm Gillies

The Murray Dairy Region

Image: Murray Dairy

Why fast flow irrigation?• Millennium drought (1997-2009)

• ↓ dairy irrigators• ↑ dairy farm system complexity• ↓ time

• System modernisation• ↓ outlets• ↑ flow

• On-Farm Irrigation Efficiency Program • ↑ ↑ redevelopment

What were the issues?

• Industry• Does faster flow save water?• Does it improve productivity?

• Catchment managers• Are there catchment scale

implications?

What is fast flow?

• We have no standard definition• “Fast” is getting faster..• Our working definition has been

{conventional best practice} x 2

Field measurements• Paired irrigation bays • Managed by the farmer• Monitored for the full irrigation season

• Inflow hydrograph• Depth hydrographs • Soil profile water content• Surface drainage• Watertable depth• Productivity

ModellingSurface irrigation models applied to assure process understanding

Light soil site

Soil: Cobram loamBay length: 243 mBay width: 60 mSlope 1:750 Crop: lucerne (alfalfa)Irrigation flow rates:

High flow bay: 0.36 ML/d/m bay width Low flow bay: 0.18 ML/d/m bay width

Cumulative infiltration

0

40

80

120

0 50 100 150 200

t (min)

Z (

mm

)

Heavy soil siteSoil: Moira loamBay length: 200 mBay width: 40 mSlope 1:650 Crop: perennial pastureIrrigation flow rates:

High flow bay = 0.33 ML/d/m bay width Low flow bay = 0.17 ML/d/m bay width

Cumulative infiltration

0

10

20

30

40

0 20 40 60 80 100

t (min)

Z (

mm

)

• High flow provided limited control of infiltrated depth

• High flow had greatest runoff variation and losses

• Excess water applied can cause substantial deep drainage at both high and low flow rates

• Precision of irrigation management was insufficient to capture any potential savings

Light soil, lucerne site

Heavy soil, pasture site• Very low permeability subsoil

• Very slow drainage (~10 hr)

• All irrigations replenished soil profile moisture

• Minimal impact on soil moisture in subsoil

• Advantage of high flow limited to reductions in the duration of irrigations, reducing labour costs

Generalising these results• Analytical Irrigation Model (Austin and Prendergast, 1998)

– Kinematic wave assumptions

– Linear infiltration function

• Monte Carlo analysis (100,000 model realisations)– Flow rate = 0.1 - 0.5 ML/d/m bay width

– Cut-off = 20 - 400 mins

• Keep “reasonable” irrigations (22,000 model realisations)– Runoff > 0 and < 10% inflow

Bay attributesLength 400 mWidth 50 mSlope 1:750Roughness 0.25Crack fill 37.5 mmFinal infiltration 2 mm/hr

Bay attributesLength 400 mWidth 50 mSlope 1:750Roughness 0.25Crack fill 37.5 mmFinal infiltration 2 mm/hr

76 min

154 min

Bay attributesLength 400 mWidth 50 mSlope 1:750Roughness 0.25Crack fill 37.5 mmFinal infiltration 2 mm/hr

76 ± 5 min

154 ±10 min

Flow rate and irrigation performance

Average infiltrated depth vs Flow rate

Low quarter uniformity vs Flow rate

for final infiltration from 0.1 to 20 mm/hr

for bay length from 200 to 1000 m

Bay attributesLength 400 mWidth 50 mSlope 1:750Roughness 0.25Crack fill 37.5 mmFinal infiltration 0.1 - 20 mm/hr

Bay attributesLength 400 mWidth 50 mSlope 1:750Roughness 0.25Crack fill 37.5 mmFinal infiltration 0.1 - 20 mm/hr

Bay attributesLength 200 - 1000 mWidth 50 mSlope 1:750Roughness 0.25Crack fill 37.5 mmFinal infiltration 2 mm/hr

Bay attributesLength 200 - 1000 mWidth 50 mSlope 1:750Roughness 0.25Crack fill 37.5 mmFinal infiltration 2 mm/hr

Conclusions• Water savings with high flow rates are not supported

by our data or modeling• Were there savings, the irrigation practice on farms

measured was not precise enough to capture them• Outcomes were more variable at higher flow rates• We need airbags, not turbo-chargers!