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T. K. Al-Hosni 1,2 and T. R. Weaver 2 1 2

Estimating groundwater recharge in arid to semi-arid areas: An example from the southeast Murray Basin, Australia. T. K. Al-Hosni 1,2 and T. R. Weaver 2 1 2. Introduction.

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T. K. Al-Hosni 1,2 and T. R. Weaver 2 1 2

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  1. Estimating groundwater recharge in arid to semi-arid areas: An example from the southeast Murray Basin, Australia T.K.Al-Hosni 1,2 and T. R. Weaver 2 1 2

  2. Introduction • In Australia, the removal of native vegetation, which efficiently consumed most of the rainfall in semi-arid areas, over the last 200 years following European settlement has increased groundwater recharge, causing regional water tables to rise. This allows evaporation of groundwater near the surface and mobility of soluble salts leading to stalinizations of soil and water resources.

  3. Objectives • This approach, combing WTF, CMBand14C,is to… • assess • the timescales over which different methods constrain the spatial variability of recharge. • and provide • order of magnitude estimates of both present day and pre-land clearing recharge rates. • These results have • significant implications for the management of recharge and determining future trends in salinity the sustainability of groundwater in the region.

  4. E W 200 200 40 41 60 29 30 31 4 50 3 2 56 55 0 0 200 200 The Murray Valley

  5. Hydraulic Conditions L. h/l <10-4 L. h/l up to 10-3 V. gradients 10-4 to 0.31 m/m

  6. 52000 48000 44000 40000 EC S/cm 36000 32000 28000 24000 20000 16000 12000 8000 4000 0 Hydraulic Conditions

  7. Rainfall vs. Potential Evaporation

  8. Corowa rainfall in winter (June to August) is typically higher than evaporation, while around Swan Hill only once every 2-4 years do episodic events occur.

  9. Quantifying Recharge (using CMB) • In semi arid areas, chloride mass balance may be used to determine recharge rates: where P is annual precipitation and Clppt and Clgw are the chlorideconcentrations in precipitation and groundwater, respectively.

  10. Quantifying Recharge (using CMB) A4 A3 A2 A1

  11. Quantifying Recharge(using 14C contents) • The recharge (R) to the top unit (Shepparton Formation) can also be calculated using 14C velocity (v) and effective porosity (ne) : R = v ne • Generally, the vertical groundwater velocity based of 14C data in the Murray Valley is 1.1 to 5.4 mm/year and the effective porosity for the Shepparton Fm is assumed to be 5 to 20%. • The estimated recharge rates are ~ 1 mm (<0.2 % of modern rainfall). These recharge rates reflect long-term pre-land clearing recharge rates.

  12. Quantifying Recharge (using WTF) • Healy and Cook (2002) Recharge (R) is related to specific yield (Sy) and the fluctuation in the water table height over time (h/t) via

  13. Quantifying Recharge (using WTF) A4 A3 A2 A1

  14. Quantifying Recharge (using WTF) B D F C

  15. Quantifying Recharge (using WTF) Corowa and Finley bores show a seasonalresponseto rainfall. Deniliquin and Barham bores (westward) show lessresponse to rainfall. Rainfall at Finley (1985 to 2002, with 6 month moving average)

  16. Quantifying Recharge (Findings)

  17. Conclusions

  18. Conclusions sporadic recharge consistent seasonal recharge NW SE young gw ~ modern to 7.3 ka modern recharge rates 10-75 mm/yr long-term recharge rates 20 mm/yr old gw > 33 ka modern recharge rates 3-11 mm/yr long-term recharge rates 0.04 mm/yr

  19. THANK YOU

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