1. Jack McHugh, Lance Pendergast, Peter Evans and Jerome Arunakumaren Deep drainage under irrigated cotton on the Central Highlands

3. History Some say they don’t “leak” but science has always said they will D eep 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.

5. Modelling Deep Drainage - SALF - SODICS - SIRMOD - FAO56 Evapotranspiration Part 1

6. Comet River Sites Nogoa River MacKenzie River Emerald Irrigation Area

8. Note: DD originating from rainfall not included in SIRMOD estimates 440 217 153 75 138 188 61 153 204 4 18 10 1200 240 491 83 0 257 337 161 427 496 15 15 27 1000 552 1152 262 60 135 180 30 85 123 9 10 25 500 Tail Mid Head Tail Mid Head Tail Mid Head Tail Mid Head SODICS FAO56 SIRMOD SaLF Furrow Field Length (m)

12. 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

19. 3.5km Weathered basalt Hard basalt Black soils – brown clays Observation bores Groundwater level & flow gradient 2004 – Western EIA (Emerald Hill) Retreat creek & overflow Selma Channel 3 45m Sand Multi-coloured clays Field waterlogging & discharge

21. 5km Nogoa River 20m Tertiary Basalt Quaternary Alluvium Billabong Black soils – brown clays Observation bores Groundwater level & flow gradient 2004 – Eastern EIA

22. 7km Nogoa River 70m Tertiary Basalt Quaternary Alluvium Winston Creek Black soils – brown clays Observation bores Groundwater level & flow gradient 2004 – Eastern EIA Weemah Channel Capricorn Hwy

25. So where is the rest of the water? 100-200 mm/season