Dealing with salinity in Wheatbelt Valleys - Department of Water

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years) in order to collate a long-term comprehensive suite of data on drainage performance. At this relatively early stage in the project only preliminary data and limited evaluation are available; however, Water Level (AHD) 272.25 272.00 271.75 271.50 271.25 27/03/00 27/05/00 27/07/00 27/09/00 27/11/00 27/01/01 Time (date) (a) Town T1S T2S T3S T4S T1D T2D T3D T4D – 5 – Ali and Coles trends in shallow and deep piezometers at various transects and sites, quality of water flowing in various drains, and water and salt outflow rate from the subcatchment will be discussed. Figure 2: Temporal variation of water levels in shallow and deep piezometers at (a) town, (b) Latham and (c) Deluise sites (Wakeman sub-catchment, Narembeen). Figures 2(a), (b) and (c) illustrate the temporal variation of shallow and deep water levels in piezometers at various sites with a water table decline evident at all sites except Deluise. The decline, although significant, may be related to a natural balancing of the system following an extreme episodic recharge event that occurred in January 2000. Continued monitoring over a longer time period will enable the impact of drainage on the system to be evaluated. Preferential flow, through lenses of porous material, was observed at various sites through visual observation and dye tests (Figure 3). This may explain the ability of seemingly low conductivity soils being able to transmit larger quantities of water than theory would suggest as summarised by Nulsen et al. (1986) and Berhane (1999) and may have contributed to the lowering of the water tables. There were rising trends in both shallow and deep water levels at the Deluise site (Figure 2(c)). Figure 3: Lenses of porous material in clayey soil at Deluise site (Narembeen) The drain at this site is not connected to the local natural creek line and therefore acts as an evaporation ditch. Rising water tables over time are
Ali and Coles expected under these conditions. The quality of water flowing in the drains declined as it moved towards the downstream end of the sub-catchment. The quality of water flowing in the drain at Pini was relatively fresher as compared to that flowing through the town of Narembeen. This is not an unexpected trend (Figure 4). The deterioration in the drain water quality at the Deluise site was considered to occur as a result of evaporation of water in the drain due to its isolation and role as a Drain Water Quality (EC, mS/cm) 140 120 100 80 60 40 Pini Latham Deluise Town 1/05/00 1/06/00 1/07/00 1/08/00 1/09/00 1/10/00 1/11/00 1/12/00 Time (Date) Figure 4: Temporal variation of water quality during 2000 in selected drains (Narembeen) Drainage Design, Construction and Maintenance The design, placement and maintenance of drains are critical issues that should be considered in conjunction with environmental impacts. In general, the majority of deep drains constructed in the Wheatbelt are designed on the basis that they do not allow the entry of surface runoff. That is why only base flow is usually considered in the design of these drains. But due to poor protection against its entry, the surface runoff usually enters into these drains as a result of significant rainfall events. Velocities generated within these drains during heavy rains result in the undercutting of the drain slopes and washing of eroded material into the drains. This causes sedimentation and a drastic reduction in their effectiveness. Additionally, at locations where drains cross roads, the culverts are usually required. These are designed on the basis that the drains are for groundwater or baseflow only and, therefore, are incapable of managing excess surface runoff. This often causes extensive damage to both the drain and the road. Spoil bank slumping into the drains is another major cause of sedimentation (Figure 6). – 6 – containment structure. Water flow and salt loads discharged from the main drain passing through the town of Narembeen varied between 10 and 15 ML/day and between 400 and 600 Tons/day respectively for the period of record (Figure 5). The rate of discharge and salt load changed drastically during and after the occurrence of significant rainfall events. The contributing area surrounding the drain is yet to be determined, and no valid conclusions can be drawn from these initial data as yet. Figure 5: Temporal variation of flow and salt outflow from a main drain in the town of Narembeen (Wakeman sub-catchment) Appropriate design and placement of the drain and spoil banks can minimise the amount of runoff entering the drain and reduce erosion. Drain embankments/spoil banks, shape, landscape location, compaction, angle of repose, soil type, gradient, velocity and carrying capacity are some of the factors that must be considered at the planning and design phase. The drain slope is another important design parameter as it determines the drain's stability and is likely to vary according to soil type based on light (sandy) to heavy (clayey) soils and it is considered best practice to determine the natural angle of rest for each location. FUTURE DIRECTIONS While there are a myriad of views about drainage and its effectiveness, there remains a limited amount of scientific research directed at the long-term effectiveness of such drains at local and catchment scales. Study sites like those at Narembeen and Dumbleyung are being designed and managed to answer the long-term questions about drainage efficiency; however, it may be some time (5-10 years) before there are adequate data to make
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: Ali and Coles erosion, maintenance
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 and 54: George and Coleman two to four fold
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Page 59 and 60: George and Coleman current trends c
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George and Coleman While not as div
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George and Coleman SPECIES Table 5:
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George and Coleman advantages of so
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George and Coleman this volume). In
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George and Coleman Venture Economy
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George and Coleman Lawrence, C. (19
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Hatton and Ruprecht WATCHING THE RI
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Since the mid 1970s annual rainfall
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Effect of clearing on runoff The ot
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Salinity Monthly streamflow (ML) 10
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The ratio of the salt outputs to in
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- 11 - Hatton and Ruprecht Table 4:
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THE FUTURE In looking at the future
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McFarlane, D.J., George, R.J. & Far
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Keighery, Halse and McKenzie Terres
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Keighery, Halse and McKenzie Wetlan
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Keighery, Halse and McKenzie specie
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Keighery, Halse and McKenzie enviro
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Lloyd number of legal cases pending
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Lloyd 0 -500 -1000 -1500 -2000 -250
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Lloyd Table 3. Sheep grazing days i
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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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