3 Basin report
- 3.1 Morgan salinity
- 3.2 Murray River salinity profile
- 3.3 BSMS Salinity Registers
- 3.4 Rolling five-year reviews
- 3.5 Joint investment in salt interception works
- 3.6 Models and tools for assessment of Registers and end-of-valley targets reporting
- 3.7 Assessment of the salinity impacts of water trade
- 3.8 Flow and salinity relationships – The Living Murray
This chapter of the report is an overview of salinity management at the Basin level. Activities which have been implemented under the Basin Salinity Management Strategy and its predecessor (the Salinity and Drainage Strategy) have been undertaken by the Initiatives’ partners and by the Commission on their behalf. This chapter discusses those activities.
3.1 Morgan salinity
A Basin Salinity Target has been established at Morgan, South Australia, for the protection of key assets and values across the Basin and for the maintenance of the water quality in the Basin’s rivers. It is the key site for measuring the outcomes of Basin-wide salinity management activities.
Relatively low in-stream salt loads and EC levels were observed in 2005–06, with a measured daily salinity at Morgan of 484 EC or less for 95 per cent of the time. However, river salinity levels are highly dependent on the hydraulic conditions prevailing in the catchment over time. The current extended dry sequence has meant relatively little salt mobilisation and therefore low river salinities.
While the relatively low salinities at Morgan are welcome, the agreed Basin Salinity Target is to maintain the average daily salinity at Morgan at a level of less than 800 EC for at least 95 per cent of the time as modelled for the Benchmark Period.
The Benchmark Period is an established climatic and hydrological sequence from 1 May 1975 to 30 April 2000. It provides a stable measure against which the impacts of post-1988 development on salinity levels at Morgan are modelled.
The modelling shows that, if climatic conditions observed during the Benchmark Period returned, salinities at Morgan would be significantly higher. In that case, the simulated long-term salinity level at Morgan would have been 867 EC or less for 95 per cent of the time, compared with the 484 EC or less for 95 per cent of the time measured over the 2005–06 period.
As in previous years, there are a range of reasons for the current low salinity levels at Morgan:
- salt interception schemes prevented 1370 tonnes of salt from entering the river each day;
- the prevailing drought led to very low tributary inflows, some of which contribute high salt loads in wetter years;
- low river flows over the last decade have led to salt accumulation in the floodplains such as Chowilla (in wetter years, this salt is partially flushed to the river by flood waters);
- lower groundwater levels in many areas led to less groundwater (also usually highly saline) entering the rivers.
Reduced river salinity may also be a partial outcome of delayed benefits arising from some improvements in irrigation efficiencies in the Mallee. These efficiencies commenced a decade or more ago but there is a time lag between changed practices and a resulting reduction in groundwater discharge to the river.
Figure 2 demonstrates the recorded salinity levels at Morgan during the 2005–06 year. The red line shows the actual recorded salinity while the blue line shows what the salinity levels would have been without salt interception schemes or dilution flows. The red line describes what is commonly referred to as a ‘without intervention’ scenario.
Figure 2. The effect of salinity management in the Murray-Darling Basin – July 2005 to June 2006
‘Without intervention’ results are attained by using the accredited Murray River hydrological model, MSM-BIGMOD, to simulate the river flow and salinity that would exist if the salt interception works were not operating. During 2005–06, the effect of managing salinity (i.e. the difference between the red and blue lines in Figure 2) ranged from approximately 80 EC in late October 2005 to approximately 265 EC in June 2006.
Table 2 gives a summary of recorded salinity levels at Morgan in four time intervals: one, five, ten and 25 years. This comparison of historical data shows the improvement in salinity levels in the river over almost 30 years.
Table 2 also provides an indication of the net difference in the impacts of changed salt interception schemes, land use and salinity management on in-stream salinity between 1988 and 2006. The comparison shows that, over approximately 20 years, the 95th percentile salinity has declined by about 200 EC.
3.2 Murray River salinity profile
There are a number of sites along the Murray River at which flow and salinity data is recorded. Figure 3 is a profile of salinity in the River over the 2005–06 year. The chart shows salinity measured at Jingellic (headwaters), depicted on the left-hand end of the chart, through the recording sites along the Murray to Lake Alexandrina (Lower Lakes) at the right-hand end of the chart.
The 2005–06 median salinity (red line) is less than the modelled Baseline median (blue line), except at the Lower Lakes. The Baseline median is modelled using the Baseline Conditions. The difference at the Lower Lakes is due to the accumulation of very highly saline water in the Lakes over the course of the drought caused by negligible flushing and increased evaporation in the hotter, drier conditions. The figure also shows the median profile in 2004–05 (yellow line), which is similar to that in 2005–06.
Figure 3. River Murray salinity profile – Baseline medians for the Bench mark Period of 1975–2000 and 2005–06 medians
3.3 BSMS Salinity Registers
Overview
The BSMS Salinity Registers generate a consistent currency through which Basin-wide trade-offs and Accountable Actions can be managed transparently (BSMS 2001–2015). They have been established under Schedule C of the Murray-Darling Basin Agreement and are maintained by the Commission as the primary record of jurisdictional accountability for salinity management activities (in-valley actions). The Registers track the effect of these activities on salinity levels at Morgan, and as salinity benefits and costs along the River.
An Accountable Action is one where an activity (either on its own or cumulatively) is estimated to have an effect on daily average salinity at Morgan greater than 0.1 EC in the next 100 years (a Significant Effect). Accountable Actions are typically salt interception schemes, changes to river operation and water management including changes to water use efficiency, and new irrigation developments in the Mallee Region.
The credits and debits in the Registers reflect increases or decreases in average salinity costs to water users arising from the respective Accountable Actions.
The BSMS Salinity Registers are in two parts:
Register A maintains accountability for actions arising after the Baseline date, (1 January 1988 for New South Wales, Victoria and South Australia, and 1 January 2000 for Queensland). It is based on a 30-year rolling average and includes the EC effect at Morgan and cost outcomes for all entries. Actions in Register A that increase salinity at Morgan (and are thus a debit on the Register) include new irrigation developments, construction of irrigation drains, and wetland flushing. Credits on Register A are obtained by such activities as investment in salt interception schemes.
Register B accounts for actions that occurred before the Baseline date but the effects of which were not apparent until after 1 January 2000, when the Baseline Conditions were set. This reflects the time lag in salinity impacts, usually referred to as delayed salinity impacts. Register B also accounts for actions that offset these delayed salinity impacts (referred to as the ‘legacy of history’). In each year, Register B entries are based on one-fiftieth of the fifty-year prediction, which is commonly referred to as the ‘ticking clock’.
The 1999 Basin Salinity Audit predicted increases in salinity at Morgan for each tributary valley in the Basin, and these increases have been assigned as debits on Register B. The Register thus accounts for the EC impact at Morgan and for the cost effect. It also records actions taken after the Baseline date that will offset these ‘legacy of history’ impacts (credits). Credits can be generated on Register B by Programs of Actions which will help achieve the end-of-valley targets set by the States for each of their catchments.
Modelling for the Registers
The operation of the Registers is underpinned by a suite of models which determine both the salinity impacts downstream, and the economic costs to water users. Groundwater and hydrologic models for the tributary and main stem of the Murray are used along with economic modelling, which uses a salinity cost function. The primary purpose of the models is to estimate the impact of an Accountable Action on the salinity levels at Morgan and the economic costs to users downstream from where the impact occurs.
Establishing and improving the Registers
The Registers were initially established under the Salinity and Drainage Strategy (1988–2000) and have been adjusted to recognise both the effects of implementing the S&DS and the changes to salinity management implemented under the BSMS.
The S&DS Register was incorporated into Register A and adjusted to allow for improved assessment of salinity management activities, improved modelling techniques, a more extensive Benchmark Period, changed salinity cost functions and recalculated salinity impact`s.
Transition of the Registers from one strategy to the other was initiated during the 2003–04 year and completed in time to be incorporated into the November 2006 BSMS Salinity Registers. Key matters addressed in 2005–06 included improving the level of confidence for some entries, the process for approval of new entries, and the impacts of using a revised cost function.
Maintenance of the 2005–06 Registers
The Commission had agreed in 1999 that, in transition from the S&DS to the BSMS Strategy, recalculation of the Registers would include a transitional adjustment such that each State could still carry out the drainage works to which it would have been entitled had the S&DS Register remained in place. That is, a State would not be directly disadvantaged by transition to the BSMS Registers.
Following detailed work by the MDBC office and jurisdictions, the BSMS IWG recommended a methodology to manage this transitional adjustment. It has now been completed with a new Register entry, referred to as the S&DS Commitment Adjustment. This allows the States to maintain their rights to salt disposal held prior to changes to the Benchmark Period and the salinity cost functions.
Completion of the 2005–06 BSMS Registers has been supported by other activities:
- States have provided the improved data required to recalculate the Registers to a higher level of confidence;
- improved governance arrangements have been agreed for endorsement of the Registers and review by the auditors.
The Registers are produced using the best available data provided to the MDBC Office by the jurisdictions.
2005–06 BSMS Salinity Registers
The Registers show the individual entries for Accountable Actions as debits and credits expressed in EC impacts and cost effects. The BSMS Salinity Registers are at Appendix II, and a summary of the Registers is presented at Table 3.
‡ Black numbers indicate a credit entry.
Negative red numbers indicate a debit entry.
** to be determined
The level of confidence in the Register entries is reflected in the confidence column. A comparison of the confidence ratings in the 2004–05 Registers with those in the 2005–06 Registers demonstrates improvements in the confidence for many entries achieved over the last 12 months. Improvements in confidence levels are normally a result of improved data or improved modelling associated with that entry. Table 4 summarises an overall confidence rating for the data for each Basin State. Levels of confidence for individual actions, however, vary widely depending on the technical data available at the time of assessment, with salt interception schemes typically portraying the highest levels of confidence. Assessments of whether a jurisdiction is in net credit or debit should take into account the confidence levels for the data supporting the entries and the difference in methodology in calculating Register A and B. Appendix II includes the full list of confidence levels.
In considering the Salinity Registers themselves, there are several specific matters that should be mentioned:
- new modelling input salinity and flow data sequences were supplied by Victoria in line with the 25 year Benchmark Period. This improved data had a significant impact on the value of some Register entries.
- Register entries for Victoria will now reflect debits resulting from on-ground actions (based on the 30-year average) rather than bringing forward the impacts of expected actions.
- New South Wales has provided revised estimates on the impacts of some land and water management plans (LWMPs), salt load reductions for improved operation of the Buronga SIS, and ‘legacy of history’ data for the Darling and Murrumbidgee catchments.
- the salinity impacts of irrigation developments in the NSW Mallee from 1988 to 2003 have been included, however, final documentation and peer review is required.
- progress has been made on improvements in the application of IQQM to the Barwon-Darling River from Wilcannia to Menindee Lakes. Further work may be required over the next 12 months.
- South Australia provided updated modelling for four SIS and a number of agreed scenarios in an improved format.
- improved irrigation practice credits for South Australia currently on Register A may be required to be split between Registers A and B. A basis for this partitioning will be developed by November 2007.
Further matters relating to the update of Register entries are noted with respect to the rolling five-year reviews in Section 3.4.
Notification of new Accountable Actions by jurisdictions for 2005–06
Where any work or measure in the Basin could have a Significant Effect (i.e. a change of more than 0.1 EC in average daily salinity at Morgan within the next 100 years), the relevant jurisdiction should bring forward an assessment to determine whether the work constitutes an Accountable Action, to be entered onto the Registers.
New South Wales is currently working towards determining and documenting the salinity impact of post-2003 irrigation developments in the Mallee.
Victoria has provided early indication of an expected Accountable Action from the Mildura Marina.
South Australia has not currently notified any expected Accountable Actions, other than those specified in 2004–05 under their revised Accountability Statement.
Land-use change in Queensland is considered to have low risk of significant down-Basin salinity impacts over the medium to long term. Queensland therefore has no Accountable Actions that currently require notification. Rather, the focus for Queensland over the last few years has been towards improved monitoring networks, and land, water and vegetation management to mitigate local land and water salinity issues.
3.4 Rolling five-year reviews
Under the terms of the BSMS, each Register entry and each valley having an end-of-valley target require a regular review and audit. These are known as the rolling five-year reviews. The reviews assess the impact of actions implemented since the Baseline date (Register A) on river salinity. The impact assessed is the flow, salt load and salinity recorded at the nominated end-of-valley target site (and at the Morgan Target). The reviews also update the expected change in the future flow, salt load and salinity regime due to the ‘legacy of history’ (Register B).
Tables 5 and 6 show the timetable for these reviews for Register A and B respectively. Currently, the reviews examine a number of Register entries in any one year. Significant progress is now being made to complete some outstanding reviews.
Rolling five-year reviews are also undertaken for joint works (salt interception schemes and groundwater control schemes). In the 2005–06 year, reviews of several schemes were completed and this is discussed in Section 3.5.
Queensland completed reviews of three valleys. The Border Rivers and Moonie Catchment Salinity Audit has been completed. Results indicate that base flow is only a very small part of flows and that there is little regolith saturation. Elevated groundwater tables under some floodplain irrigation areas and potential expansion of irrigated cropping pose the largest threat to water quality and land salinisation.
The Warrego–Paroo salinity audit has found a minimal threat from dryland salinity and the salt accessions from the Great Artesian Basin flowing bores are being addressed through a capping and piping program. Scalding within the landscape from the exposure of naturally saline sub-soils through erosion is considered a more serious risk to farming and grazing land but has minimal impact on major rivers (less than 0.1 EC over 100 years).
The Condamine–Balonne salinity audit is under way and highlights the complexity of the landscape and the pattern of development.
New South Wales undertook a review of the upland dryland portion of the NSW catchments, as was done in the Commission’s 1999 Murray-Darling Basin Salinity Audit. Preliminary results suggest that, while salinity remains a significant issue, trends in salinity are not as high as previously predicted and most catchments have now been judged to be in a state of dynamic equilibrium. When the final report is available, any implications for the Salinity Registers will need consideration.
New South Wales has also prepared a draft review report on the Murray Irrigation Land and Water Management Plan. Register A has been adjusted based on the results of this study, however, the methodology and basis for the Register update requires peer review.
Victoria has deferred dryland valley reviews until the Victorian catchment management authorities are developing their next-generation salinity management plans.
The Shepparton Irrigation Region Catchment Strategy Review was completed at the end of the 2005–06 year and is undergoing peer review. Drainage outfalls have been reduced, which has reduced salt loads; however, the reduced tailwater flows have been found to have also reduced dilution downstream. Further investigations have been recommended to identify the relative contributions to reduced drainage flows arising from low (drought-induced) irrigation allocations and improved water–use efficiencies.
The notion of rolling five-year valley reviews applies to the whole Basin. The tri-State region of the Mallee Zone from Swan Hill to Goolwa can be considered as a valley for this purpose. The end-of-valley target for this region is the Basin Salinity Target at Morgan. An agreement was made between Victoria, New South Wales and South Australia to consider the Mallee region as a whole. A suite of groundwater models to address the ‘legacy of history’ resulting from past dryland clearing and irrigation developments has been developed.
In New South Wales and Victoria, a groundwater model (the Eastern Mallee Model Version 1 (EM1)) has been jointly developed to assess these impacts. It is currently being peer-reviewed.
Within South Australia, three sub-regional groundwater models have been developed (Border to Lock 3, Lock 3 to Morgan, and Morgan to Tailem Bend). These models were used in 2004 to review the dryland clearing and farming impacts and resulted in a Register B entry (2004–05). Assessment of the irrigation impacts has been undertaken in association with salt interception investigations. However, further refinements to the models are in hand.
3.5 Joint investment in salt interception works
Operate, maintain and renew existing SIS
In accordance with Schedule C to the Agreement and as set out on the Basin Salinity Management Strategy Operational Protocols, a program of joint salt interception schemes (SIS) has been established. The schemes are intended to offset a predicted future increase of 61 EC in average salinity at Morgan by December 2007. The expected increase is from the impact of past actions, ‘legacy of history’, and also from identified Accountable Actions.
The MDBC operates nine jointly funded SIS along the Murray River from Pyramid Creek in Victoria to Waikerie in South Australia. These schemes intercept saline groundwater flows and saline surface drainage that would have otherwise entered the Murray River. The efficiency and capacity of these schemes are constantly monitored to ensure that their performance can be optimised to deliver agreed salinity benefits.
In the 2005–06 year, the schemes prevented approximately 500 000 tonnes of salt from entering the River Murray (1370 tonnes per day). Salt interception schemes (operating, under construction and approved for construction) will achieve an estimated reduction in salinity at Morgan, South Australia, of approximately 40 EC.
Table 7 provides a summary of the schemes’ performance including a measurement of target achievement. Key activities undertaken in 2005–06 are outlined below for each operational scheme.
Barr Creek Drainage Disposal Scheme (Victoria)
The Barr Creek Drainage Diversion Scheme has, once again, been effective in reducing base salt loads in the Murray River by diverting drainage flows and intercepting saline groundwater from Barr Creek to the Tutchewop Disposal Basins. During the year, the scheme operated according to the agreed rules and diverted approximately 11 078 ML of drainage water containing approximately 54 112 tonnes of salt to the disposal basins. This represents approximately 96 per cent of the flow and salt load in the Barr Creek catchment that would otherwise have reached the Murray River.
An ongoing program of investigations and works looking at how best to sustain the functional use of the disposal basins in the long term was substantially progressed over the period with the completion of an Independent Technical Review of Future Management Options.
Mildura–Merbein Salt Interception Scheme (Victoria)
The scheme, built in the 1970s, continues to operate at approximately 60–70 per cent of its design effectiveness due to a number of ongoing systemic problems with the original design and the operating environment. Five of the bores have been inoperable over the past year, and diversions from the floodplain-based Lake Ranfurly Basin to the Wargan Basin have been kept to 136 ML due to the ongoing dry conditions.
Mallee Cliffs Salt Interception Scheme (New South Wales)
The Mallee Cliffs SIS performance has been highly effective during the course of the year, with salinity impacts from saline groundwater significantly reduced. The focus during the year has been on optimisation of the pumping network, which will enable more efficient operation of the scheme whilst maintaining downstream salinity benefits to the Murray River. The 2005–06 period has seen the scheme operating according to the agreed rules and intercepting approximately 2500 ML of saline groundwater (containing approximately 84 000 tonnes of salt) to the disposal basins.
Buronga Salt Interception Scheme (New South Wales)
After undergoing a rehabilitation program in 2003–04 and 2004–05, the Buronga SIS has now been successfully pumping intercepted groundwater for twelve months. The scheme has operated in accordance with the agreed operating rules and its performance has been excellent. During the year, approximately 3000 ML of saline water, containing approximately 86 000 tonnes of salt, was intercepted and delivered to the Mourquong Disposal Basin.
Woolpunda Salt Interception Scheme (South Australia)
In general, the Woolpunda SIS has continued to meet its design targets with ongoing fine tuning of pumping rates to meet groundwater level targets and maximisation of off-peak power use.
With the scheme now over 16 years old, there are increasing challenges to keep maintenance costs down. Deterioration due to age and corrosion of some assets is increasing, with bore performance starting to reduce. As a result, the pipe work and ‘spur-main’ valves associated with the bores on the southern side of the River Murray were replaced during the year. It is expected that a bore rehabilitation program will be implemented in 2006–07 to counter the clogging effects of iron bacteria.
Waikerie Salt Interception Scheme (South Australia)
The Waikerie SIS continues to operate effectively with further optimisation, to be implemented in 2006–07 which will reduce pumping rates without compromising the effectiveness of the scheme. Similar to the Woolpunda SIS, it is expected that a bore rehabilitation program will be implemented in 2006–07 to counter the effects of iron bacteria clogging. Further interception opportunities to the west of the existing scheme have been identified and will be presented to the Commission for consideration during 2006–07.
Rufus River Salt Interception Scheme (South Australia)
The Rufus River SIS is a pre-S&DS (pre-1988) salt interception scheme. Operation of the scheme is covered under Baseline Conditions, and is therefore not an Accountable Action requiring entry to the BSMS Registers.
All four wellpoint lines have been successfully operating in accordance with the operating criteria and have generally drawn the groundwater levels down to near or below target.
South Australia’s review of the Rufus River Salt Interception Scheme showed operation in accordance with the design rules. It pumps an average of 32 tonnes per day of salt, significantly below the original design estimate but it remains effective in controlling groundwater discharge into the Rufus River.
New salt interception schemes
The 2005–06 period has seen a number of significant milestones achieved for the salt interception program. Two new schemes were completed, one of which was commissioned. These schemes have increased the overall SIS capacity by more than 70 000 tonnes per annum.
Pyramid Creek Salt Interception Scheme (Victoria)
The most significant milestone was the commissioning, benefit accreditation and official opening of the Pyramid Creek SIS in April 2006. The scheme, located downstream of Kow Swamp on the Pyramid Creek, was the first of the BSMS Joint Works program to be deemed effective, with the salinity benefits for Stage I being placed on the MDBC Salinity Register.
The scheme, when fully operational, will intercept approximately 22 000 tonnes of salt per annum that would have otherwise discharged to the Pyramid Creek, causing significant negative impacts upon the region’s agricultural production, the environmental attributes of the Ramsar-listed Kerang Lakes, and downstream Murray River water users.
A unique feature of this scheme when compared to other Joint Works SIS is the incorporation of commercial salt-harvesting ponds into the scheme’s design and operation. The ponds provide a sustainable disposal option for the scheme through a partnership with a commercial salt harvester.
These features were a factor in the scheme’s winning the 2006 Engineers Australia National Salinity Prize for new technology and other practical outcomes tackling salinity. Design innovation, sustainable methods of salt disposal, and community acceptance of salt basins were referred to as significant factors in the decision.
Bookpurnong Salt Interception Scheme (South Australia)
In March 2003, the Ministerial Council approved the construction of the Bookpurnong scheme as a shared scheme – that is, a combined Joint Works and State Action, as defined in Schedule C of the Agreement. The total estimated cost is $11.1 million.
It is estimated that the interception of saline groundwater will achieve a total benefit at Morgan of 17.9 EC units (10.9 EC for the Joint Works component and 7.0 EC for the State Action component).
Construction of the scheme commenced in late 2003, with the first water being pumped to the Noora Disposal Basin in July 2005. By June 2006, commissioning was substantially complete. Preliminary indications from river salinity surveys were that the scheme had already begun to significantly reduce saline groundwater inflow in some areas.
Loxton Salt Interception Scheme (South Australia)
In March 2004, Ministerial Council approved the construction of the Loxton scheme as a shared Joint Works and State Action scheme as defined in Schedule C of the Agreement, at a total estimated cost of $24 million.
It is estimated that the interception of saline groundwater will achieve a total benefit at Morgan of 18.7 EC units (18.3 EC for the Joint Works component and 0.4 EC for the State Action component).
By June 2006, the majority of the floodplain observation and production bores had been drilled, about 80 per cent of the major pipe laying for the disposal pipeline had been completed, and about 35 per cent of the floodplain interception pipes had been installed. The remaining pipe laying will be completed by late 2006. The first intercepted water from the floodplain is expected to be pumped to the Noora Disposal Basin by November 2006, and all floodplain bores are expected to be operational by mid-2007.
Subject to funding, the scheme is expected to be fully commissioned by 2008–09.
Construction program and feasibility investigations
As noted above, the SIS are intended to offset salinity levels at Morgan by 61 EC. While the original target date was 2007, funding and construction constraints had predicated an expected delay in achieving the target until 2013, as noted by the IAG-Salinity in its 2004–05 report. The increased funding from the Australian Government in 2005–06 has meant that the expected date to achieve the target is now 2010.
The remaining 21 EC to be delivered under the BSMS are the subject of current investigations. Preliminary indications are that these potential schemes will yield in excess of the required 21 EC. Completion of these schemes by 2010 would enable the SIS target to be fully met. Table 8 shows the planned construction program to achieve the 61 EC by 2010, and Figure 4 shows the impact of the revised budget decisions on the delivery timetable. Schemes listed have either been completed during the 2005–06 year or granted approval for investigation.
Figure 4. Salt interception – Joint Works Program delivery of EC benefits (revised November 2006)
In addition, the following feasibility investigations have been undertaken during the 2005–06 year to enhance Basin-wide salinity management.
Integration and optimisation of salt interception in the Sunraysia Region
A comprehensive study to investigate optimising salt interception in the Sunraysia Region, on a regional ‘no borders’ approach, was initiated in 2000–01.
In 2004, the Commission established a Sunraysia Regional Steering Committee to oversee a cross-borders approach to salt interception and to immediately progress a program of investigations. The investigations were to include the establishment of an integrated monitoring program, a review of disposal requirements for the region, rehabilitation and augmentation of the Mildura–Merbein Salt Interception Scheme and the future operation of Lakes Hawthorne and Ranfurly.
Sunraysia Regional disposal strategy
During the year, considerable effort has been focused on understanding the present and future disposal requirements for the Sunraysia Region. The Steering Committee has now finalised an options paper and will be presenting this together with a preferred way forward to the Commission early next year.
Mildura–Merbein Salt Interception Scheme (Victoria)
A detailed program of investigations into the potential full refurbishment of the existing scheme and a possible extension to intercept additional salt loads downstream of the existing works is progressing well. Concept designs for the refurbishment are scheduled for completion in the next twelve months.
Surface water monitoring program
Following a detailed review of surface water salinity monitoring within the Sunraysia Region, the Steering Committee supported the installation of six new salinity measurement pontoons. The pontoons have been strategically located to provide information on the performance of current interception schemes within the region and to assist in monitoring further interception opportunities.
3.6 Models and tools for assessment of Registers and end-of-valley targets reporting
Over the past five years, the partner governments and the Commission have developed and accredited tools and models for the assessment of actions in accordance with Schedule C and the Operational Protocols. It is recognised that there are varying levels of historic data across the Basin, so the models are assessed against the local and Basin-wide perceived risk of salinity – a ‘fit for purpose’ test is applied.
The implementation of the BSMS relies heavily upon these practical hydrologic models. The models are computer simulations of the flow, salinity, salt load accessions and reductions, and the associated salinity costs to human users (irrigation and urban). This is particularly important because the performance measures for the Strategy (the end-of-valley targets) are based upon an historic climatic sequence – the Benchmark Period (1975–2000).
This provides the Strategy with a stable basis for comparison of the salinity predictions, which are given as ‘with intervention’ or ‘no intervention’. Owing to the variability of the climate, measurements in any one year need careful consideration and explanation. Therefore, the implementation of the BSMS has relied heavily on the development and use of models that can consider impacts over a longer timeframe.
More specifically, Schedule C requires the models used to be thoroughly peer-reviewed and then submitted to the Commission for accreditation. This is essential so that there is confidence in the process to reach agreement on the Baseline Conditions, end-of-valley targets and the resulting entries onto the Registers. The work must be underpinned by a robust, well-documented process.
It is particularly important for the Register A entries, which rely on the rolling 30-year average impact. The assessments that develop the 10, 20 and 30 year predictions are sensitive to variations in the modelling assumptions. The Registers also record the predictions for 50 and 100 years but these are for information only, and such assessments become accountable on the Registers as the rolling 30-year average catches up with them. Nevertheless, the future risk is at least flagged.
In reality, salt mobilisation and its movement through the landscape and rivers involves significant lag times, which are difficult to assess. It is often easier to make predictions about the ultimate steady state equilibrium, which can vary from a few decades to more than a century into the future. Land and water use that is expected to become an Accountable Action is translated as inputs into groundwater models. These models then generate predictions for salt discharge to the river, which are reflected in the Register A entries using hydrological models (MSM-BIGMOD, IQQM, REALM).
In contrast, the Register B debit entries use the models to assess the continuing incremental deterioration which can occur if there were to be no further intervention. The Register entries then use a linear approach based on the current 50-year prediction.
The Basin can be divided into three broad hydrogeological regions:
- the upland dryland areas that deliver most of the water and some of the salt;
- the Riverine Plains region comprising most of the irrigated area within the Basin;
- the Mallee Zone in the lower Murray and lower Darling, which receives relatively little rainfall but where there is highly saline groundwater.
Salt storage and mobilisation drivers are different within each of these landscapes yet they are hydrologically linked by the rivers which pass though them.
There is now modelling for all the Basin’s river systems. In 2003–04, the Commission accredited and implemented the hydrologic models of the Murray River and its tributaries, apart from the Barwon-Darling. These models simulate the in-stream historical record over the Benchmark Period.
For the Murray and lower Darling, the Commission office MSM-BIGMOD model is used. It includes the cost functions associated with the use of differing salinity water. In New South Wales and Queensland, the States use IQQM (Integrated Quantity/Quality Model) and, in Victoria, the REALM modelling package is used.
In the larger irrigation areas of the Riverine Plains, there are a range of surface water/groundwater models and statistical tools used to simulate and understand water and salt export from the irrigation areas.
A suite of groundwater models has been developed and accredited for the assessment of the salt interception schemes and the future impact of existing irrigation developments (pre-1988). These use the commercial MODFLOW modelling package as their platform.
SIMRAT is the accredited model used to assess the salinity impacts of irrigation development stemming from water trade in the Mallee region.
In upland dryland areas a framework, known as 2Csalt, has been developed under the auspices of the CRC for Catchment Hydrology, through an intensive multi-jurisdictional collaborative effort strongly supported by the Commission. 2Csalt is suitable for assessing the impacts of changes in land use practices on stream flow and salinity in the dryland upper reaches of catchments. It is capable of evaluating scenarios for Programs of Actions as well as Baseline Conditions for dryland agriculture, land use management and the ‘without intervention’ scenario, as required by Schedule C.
2Csalt has been validated over nine sub-catchments and is expected to be rolled out across all upland dryland catchments in the Basin over the next few years. It has been submitted for accreditation, however, this process will require results from extended use of the model in New South Wales and Queensland.
3.7 Assessment of the salinity impacts of water trade
The movement of water allocation has the potential for mobilising additional salt and is therefore regarded as an Accountable Action. There is a tendency for water to be moved from low to high risk zones as the soils in the higher risk zones are more suitable for horticulture, leading to higher value use of the water.
Mallee Zone
Salinity impacts associated with irrigation development are a recognised factor within the Mallee region (Swan Hill, Victoria, to Murray Bridge, South Australia) because of the presence of saline groundwater and its influence on the river.
Recent developments are located close to the river, which presents an increased salinity risk in the short to medium term.
The central tool for ensuring a no–net increase in river salinity from new developments in the Victorian Mallee is through a salinity impact zoning approach that is commonly referred to as the ‘Nyah to South Australian Border’ model. This model essentially divides the Victorian Mallee into a High Impact Zone and a series of low impact zones based on local hydrogeology.
South Australia uses a GIS-based individual site assessment model, referred to as SIMRAT.
The South Australian and Victorian approaches have been formally accredited, subject to conditions and reviews. New South Wales is yet to document its preferred approach but is considering SIMRAT and the EM1 (MODFLOW) model (discussed in Section 3.4).
Further work is under way to improve the models, including the assumptions concerning root zone drainage.
Riverine Plains
On 19 May 2006, the Ministerial Council endorsed a revised Schedule E to the Murray-Darling Basin Agreement which enabled the geographic expansion (into the Riverine Plains area) of interstate water trade within the jurisdictions of New South Wales, Victoria and South Australia. Ministerial Council determined that exchange rate trade of entitlements between Victoria and South Australia would commence implementation on 1 July 2007. However, entitlement trading with New South Wales would not be available from 1 July 2007 until tagged trading had been fully developed and the jurisdictions have the necessary legislation in place to implement the new mechanism.
Ministerial Council has requested that a framework be developed to establish consistent measures for assessing the salinity impacts of water trade across jurisdictions. An irrigation salinity accountability framework is currently being developed by staff of the Commission and the partner agencies.
In developing this framework, a study of the Riverine Plains, necessary to establish a common understanding of the areas and the relevant issues, is under way.
Although the Riverine Plains have an area/volume of irrigation about ten times that of the Mallee Zone, the overall salt mobilisation is of a similar order.
In the Riverine Plains, irrigation is used mostly for rice, annual and perennial crops and horticulture, unlike the more intensive agriculture in the Mallee Zone. Consistent with current trends, it is expected that, in general, trade would be from the Riverine Plains into the Mallee Zone, thus establishing an accountability issue for the Mallee Zone.
The framework will include evaluation of the long-term salinity implications of changing allocations, implementation of land and water management plans, and the ongoing development of groundwater resources.
In developing the assessment framework, consultation will be undertaken with relevant water trade groups both in jurisdictions and the Commission.
3.8 Flow and salinity relationships – The Living Murray
The Living Murray (TLM) commitment by the Initiative partners has recently been considerably strengthened by an additional investment from the Australian Government.
Environmental flows and watering of TLM icon sites will have implications for salinity management in the southern Basin. A joint TLM/BSMS Task Force is investigating issues common to both groups, including:
- development of a common, transparent accounting process for use across TLM and BSMS;
- design of protocols for evaluating investment decisions across programs.
Weir on Barr Creek
Photo: P. Pfeiffer