1. Can higher flow rates improve performance of border-check irrigation in the Murray Dairy Region? Mike Morris, Amjed Hussain, Malcolm Gillies

2. The Murray Dairy Region Image: Murray Dairy

3. 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

4. What were the issues? Industry Does faster flow save water? Does it improve productivity? Catchment managers Are there catchment scale implications?

5. What is fast flow? We have no standard definition “Fast” is getting faster.. Our working definition has been {conventional best practice} x 2

6. 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

7. Modelling Surface irrigation models applied to assure process understanding

8. Light soil site Soil: Cobram loam Bay length: 243 m Bay width: 60 m Slope 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

9. Heavy soil site Soil: Moira loam Bay length: 200 m Bay width: 40 m Slope 1:650 Crop: perennial pasture Irrigation flow rates: High flow bay = 0.33 ML/d/m bay width Low flow bay = 0.17 ML/d/m bay width

10. 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

11. 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

12. 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

13. Bay attributes Length400 m Width50 m Slope1:750 Roughness0.25 Crack fill37.5 mm Final infiltration2 mm/hr

14. Bay attributes Length400 m Width50 m Slope1:750 Roughness0.25 Crack fill37.5 mm Final infiltration2 mm/hr 76 min 154 min

15. Bay attributes Length400 m Width50 m Slope1:750 Roughness0.25 Crack fill37.5 mm Final infiltration2 mm/hr 76 ± 5 min 154 ±10 min

16. 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

17. Bay attributes Length400 m Width50 m Slope1:750 Roughness0.25 Crack fill37.5 mm Final infiltration0.1 - 20 mm/hr

18. Bay attributes Length400 m Width50 m Slope1:750 Roughness0.25 Crack fill37.5 mm Final infiltration0.1 - 20 mm/hr

19. Bay attributes Length200 - 1000 m Width50 m Slope1:750 Roughness0.25 Crack fill37.5 mm Final infiltration2 mm/hr

20. Bay attributes Length200 - 1000 m Width50 m Slope1:750 Roughness0.25 Crack fill37.5 mm Final infiltration2 mm/hr

21. Bay attributes Length200 - 1000 m Width50 m Slope1:750 Roughness0.25 Crack fill37.5 mm Final infiltration12 mm/hr

22. Bay attributes Length200 - 1000 m Width50 m Slope1:750 Roughness0.25 Crack fill37.5 mm Final infiltration12 mm/hr

23. 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!