Dealing with salinity in Wheatbelt Valleys - Department of Water

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(1997) later refined the relationship between aquifers and salinity into ten models. They concluded that local-scaled regolith or saprock aquifers were dominant, although intermediate-scaled sedimentary systems were common in valleys. Clarke et al. (2000) showed that the K sat of the saprock aquifer and intensely weathered aquitard was similar in western areas (Woolbelt). Clarke also found that in palaeo-valleys in the western areas, the lower sandrich palaeochannel aquifer has a K sat ~300 times higher (~3 m/d) than the lacustrine aquiclude (Clarke et al, 2000). These are similar to those found by Salama (1997; 3–6 m/d) in the Avon palaeochannel and George & Dogramaci (2000; 5 m/d) in the Toolibin palaeochannel. Groundwater velocities are typically very low. Given typical hydraulic conductivities (0.5–5 m/day) and gradients (1:1000–1:10,000) for wheatbelt valley sediments, flow velocities in the deeper saprolite and sedimentary aquifers of about 0.1 m per year are considered likely. Under exceptional circumstances, in surface sediments, where there is a high permeability (> 1.0 m/day), and gradient (0.005), velocities may increase to 5 m/yr. For velocities of greater than this either the permeability must be very high (soil macropores) or the gradient increased by intervention (drainage or pumping). Hydrology and salinity of wheatbelt valleys The magnitude of recharge to wheatbelt valleys is not known with precision although several authors have attempted to estimate it. McFarlane et al. (1989) used hydrograph analysis to determine that recharge in valley sediments was at least as significant as that on hillslopes, recording rates of 35 mm/yr at Toolibin. George et al. (1991) in reviewing recharge processes from a range of wheatbelt sites agreed, and concluded that recharge occurred everywhere that discharge did not and that even in these areas, it could alternate between seasons. They further showed that episodic recharge is critical, a subject Lewis (2001) has comprehensively reviewed. A range of techniques (chloride, water balance and hydrograph) was used to estimate the relative magnitude of recharge between catchments and landforms in wheatbelt valleys (George 1992b). He concluded that recharge from uncleared catchments was typically of the order of 0.05 mm/yr, while for the same catchments, recharge increased to be between 6 and 10 mm/yr. after clearing. Recharge was highest in upland (e.g. Danberrin and Ulva soil associations) and sandy surface valley soils (e.g. – 3 – George and Coleman Colgar, Belka) and least in clay-rich soils (e.g. Merredin and Booraan surfaces). Recharge to valley sediments also takes place laterally, either directly from connected fluvial sequences of sediments or from depth, where groundwater from adjoining saprock and potentially fractured rock systems enters sedimentary aquifers (Salama et al. 1993; Salama 1997). The degree of interconnectedness has not been assessed in detail; however modelling at Toolibin (George & Dogramaci 2000) suggests saprock and palaeochannel aquifers, and at Merredin (Matta 2000) saprock and overlying sediments are both well connected and respond to pumping. Groundwater discharge from valley sediments has also never been measured directly. In only one experiment known to the authors, Greenwood & Beresford (1980) used ventilated chambers to document the 'water use' (discharge) of bare soil near Kellerberrin. They measured rates of the order of 0.4 mm/d in summer (equated to 80 mm/yr) at a site where saltbush was growing. George (1992a) calculated potential discharge rates from piezometers (calculated vertical flux), concluding rates of between 50 and 230 mm/yr. Using a water balance approach, George (1992b) indicated that if the effective discharge rates were 80 mm/yr (~3% of pan evaporation rates), the entire recharge to the Wallatin Creek catchment (i.e. water added annually to the groundwater) could be lost from 12% (2880 ha) of the catchment. Furthermore, from first principles, at equilibrium recharge will equal discharge and as catchment average recharge is about 20 mm/yr, and the potential discharge area is 20–30% of the landscape, average discharge rates will be no more than 100 mm, a number similar to that estimated above. This low flux rate has significant implications for salinity management, as we will discuss later. The effect of the imbalance between recharge and discharge can be measured by monitoring trends in groundwater levels. In wheatbelt valleys, landholder groups and government, typically using shallow piezometers or observation wells, are monitoring trends in water levels. Short & McConnell (2001) documented trends in deep bores across the entire agricultural area. They concluded that where the watertable was within 2 m of the soil surface, there was often no trend (water levels neither rose nor fell from their 1–2 m position). However, where watertables were greater than 2–5 m below the soil
George and Coleman surface, the vast majority of bores showed a rising trend. At Toolibin and Merredin, typical of wheatbelt valley systems, watertables in saline areas have been relatively stable for some years (McFarlane et al. 1989; George 1999) although pressures may SWL (m relative to ground level) SWL (m relative to ground level) 0 -2 -4 -6 -8 -10 -12 0 -1 -2 -3 Mar-86 Apr-78 Mar-87 Mar-88 Mar-82 Mar-89 Apr-90 Apr-91 Mar-86 Apr-92 Apr-93 Date Feb-90 Date continue to rise if located near a palaeochannel (Figure 1). By contrast, valley bores located within tributaries with deep watertables are rising at about 0.15 to 0.3 m/yr, despite lower than average rainfalls during the past twenty years (Figure 1). This rate of rise is similar to that recorded in bores on hillslopes (Short & McConnell 2001). Figure 1: Two bores from wheatbelt valleys. Bore MD01 is a deep bore located in cleared farmland in the upper reaches of the Merredin valley. It has a typically deep watertable and shows a 2.5 m rise over the last 15 years (0.15 m/yr).By contrast, Bore 77 is located in valley sediments in the lower Toolibin catchment, within a 1000 ha remnant. This bore shows a small rise over the past 23 years (0.05 m/yr), despite a shallow watertable. – 4 – Apr-94 Apr-95 Apr-96 Jan-94 Apr-97 Apr-98 Jan-98 Apr-99 Apr-00 Apr-01 Dec-01
Page 1 and 2:
Foreword Dealing with Salinity in W
Page 3 and 4: 1Day one: Monday 30th July. Field t
Page 5 and 6: Papers Dealing with Salinity in Whe
Page 7 and 8: Ali and Coles biggest challenges fa
Page 9 and 10: Ali and Coles erosion, maintenance
Page 11 and 12: Ali and Coles expected under these
Page 13 and 14: Ali and Coles Coles, N.A. & Ali, M.
Page 15 and 16: Commander, Schoknecht, Verboom and
Page 41 and 42: APPRECIATING AND CREATING OUR HISTO
Page 43 and 44: services. The Government responded
Page 45 and 46: WHEATBELT VALLEYS IN DIFFICULTIES T
Page 47 and 48: argue that they were really abnorma
Page 49 and 50: 1990s, the wheatbelt valleys in par
Page 51 and 52: REFERENCES Agstats (1997). Agricult
Page 53: George and Coleman two to four fold
Page 57 and 58: George and Coleman for example in t
Page 59 and 60: George and Coleman current trends c
Page 61 and 62: George and Coleman While not as div
Page 63 and 64: George and Coleman SPECIES Table 5:
Page 65 and 66: George and Coleman advantages of so
Page 67 and 68: George and Coleman this volume). In
Page 69 and 70: George and Coleman Venture Economy
Page 71 and 72: George and Coleman Lawrence, C. (19
Page 73 and 74: Hatton and Ruprecht WATCHING THE RI
Page 75 and 76: Since the mid 1970s annual rainfall
Page 77 and 78: Effect of clearing on runoff The ot
Page 79 and 80: Salinity Monthly streamflow (ML) 10
Page 81 and 82: The ratio of the salt outputs to in
Page 83 and 84: - 11 - Hatton and Ruprecht Table 4:
Page 85 and 86: THE FUTURE In looking at the future
Page 87 and 88: McFarlane, D.J., George, R.J. & Far
Page 89 and 90: Keighery, Halse and McKenzie Terres
Page 91 and 92: Keighery, Halse and McKenzie Wetlan
Page 93 and 94: Keighery, Halse and McKenzie specie
Page 95 and 96: Keighery, Halse and McKenzie enviro
Page 97 and 98: Lloyd number of legal cases pending
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Page 101 and 102: Lloyd Table 3. Sheep grazing days i
Page 103 and 104: Lloyd Hectares project to provide w
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INTRODUCTION The Lake Chinocup Catc
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agriculture) in various stages, the
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- 3,477 ha of remnant vegetation or
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Scientists talk of up to 30% of the
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6320000 6300000 6280000 6260000 624
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Although the waterlogged area under
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eliminates drainage through the nex
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REFERENCES Dawes, W.R., Stauffacher
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Pannell ECONOMICS, SOCIETY AND ENVI
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Pannell • the area of land protec
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Pannell Proposals to construct majo
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Pannell been conducted for the Cent
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Pannell investments in long-term la
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Pannell Pannell, D.J. (2001). Dryla
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Porter, Bartle and Cooper Table 1:
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Porter, Bartle and Cooper operation
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Porter, Bartle and Cooper Increase
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Porter, Bartle and Cooper support i
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Porter, Bartle and Cooper that is a
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CASE STUDY - TOOLIBIN LAKE AND CATC
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• The distribution, storage and m
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Secondly, there is a set of practic
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within three categories: relationsh
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CONCLUSIONS Actions to protect and
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FIELD TOUR LOCATIONS FIELD TOUR NOT
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COLES FARM “Avon River Basin Over
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Conference Outcomes Dealing with Sa
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with Salinity in Wheatbelt Valleys:
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with Salinity in Wheatbelt Valleys
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Photo Gallery 2 Dealing with Salini
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APPENDIX 1 BACKGROUND HYDROLOGY AND
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WHEATBELT HYDROLOGY Flow in the Yil
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Flow (ML) STREAM SALINITY Salt Rive
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APPENDIX 2 WATER MANAGEMENT OPTIONS
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APPENDIX 3 MANAGING WATER AND SALIN
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SUMMARY- TIMELINE OF RECENT SIGNIFI
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RECENT HISTORY OF WATER AND SALINIT
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Figure 1. Hydrological cross-sectio
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Depth (m) 316 315 314 313 312 311 M
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FURTHER INVESTIGATIONS AND MANAGEME
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Dealing with salinity in Wheatbelt Valleys - Department of Water

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