Significant water events
Summarised information of the significant water events occurring during the 2010–11 year in the Murray–Darling Basin (MDB) region is provided in this section.
Higher-than-average rainfall during the 2010–11 year has dramatically reversed the extreme dry conditions of recent years, with floods occurring multiple times along parts of the Murray, Barwon–Darling, Condamine, Murrumbidgee, Goulburn, Ovens, Campaspe, Loddon and many other rivers in the Murray–Darling Basin. While floodwaters replenished dams and rivers and revitalised wetlands and floodplains, they also caused significant damage to property and assets.
Until the floods arrived, Basin storage had been well below average for a number of years. Throughout the 2010–11 year, total volume held in storages increased from 32% to 83% of capacity. Total MDB active storage on 30 June 2011 was above the long-term average for this time of year.
High inflows combined with delivered environmental water have been critically important for many species recovering from the recent drought in the MDB. However, these unprecedented high inflows were large enough to cause a simultaneous blackwater event (Department of Primary Industries 2012) in the River Murray and in the Goulburn–Broken, Edward–Wakool, Murrumbidgee and Loddon rivers.
To counter the 2010–11 year blackwater event, Murray–Darling Basin Authority and New South Wales, Victorian and South Australian agencies implemented actions that targeted specific flow rates in the River Murray and its tributaries, which helped dilute blackwater as it returned to the river from the floodplains.
Flood waters also mobilised salt from the floodplains, with about 2,500,000 tonnes of salt estimated to have passed Morgan in South Australia in the 2010–11 year, compared with about 210,000 tonnes the previous year. River Murray salt interception schemes diverted approximately 324,000 tonnes of salt from the River Murray and helped limit the flood-induced salt mobilisation (Murray–Darling Basin Authority 2011b).
New South Wales
Menindee Lakes experienced high inflows due to major rainfall events in various Darling River catchments during the 2010–11 year. As a result of these multiple events, the lakes have remained close to the full capacity from September 2010 till the end of the 2010–11 year.
The NSW Office of Water has overseen the daily flood operations at the lakes since 6 December 2010, consistent with past practice. The normal minimum release was targeted from June to September. From October 2010, the daily release was increased to pass floodwater. Gradual reductions were made in releases along the lower Darling River in April and May to minimise the potential for riverbank damage.
It was a wetter than average year with minor to moderate flow events from August 2010 to January 2011, and again in March 2011. Flooding occurred in the lower reaches of the Border Rivers region, upstream of Mungindi due to significant flows in the Weir River, as well as in Condamine Balonne where Warwick recorded its highest flood since 1976. Gauging stations along the Condamine River from Talgai to Cotswold also recorded record flood heights over this period. Moonie peak flows were well below record flood levels, however, prolonged medium flows contributed to the significant total flow volume.
A new Department for Water commenced on 01 July 2010 to oversee the management of South Australia's water resources.
The total annual flow across the South Australian border, including additional dilution flow and unregulated flow, was about 15,100,000 ML, the highest since 1975–76. The Lower Lakes returned to their full supply level of 0.75 m (Australian height datum) during October 2010. The first releases of water through the barrages from the Lower Lakes since 2006 began in September 2010. More than 11,000,000 ML of water was estimated to have been released to the Southern Ocean during the 2010–11 year, resulting in the opening of the Murray Mouth and enabling salt export to the sea and improving fish passage. A further benefit was that dredging to keep the Murray Mouth open was no longer necessary.
Flow rates downstream of Yarrawonga Weir exceeded channel capacity of the River Murray through Barmah–Millewa Forest from late August 2010. Significant inflows from the Ovens and Kiewa rivers required releases from Lake Mulwala to be managed using flood procedures. Two peak releases occurred downstream of Yarrawonga Weir (in September and December 2010) as a result of a combination of high unregulated inflows from the Kiewa and Ovens rivers and, in December, a spill from Hume Reservoir.
During the 2010–11 year, the Barmah Choke was not a major constraint on operations. The rule preventing trade of allocations from above to below the choke has been relaxed since September 2007. The Murray–Darling Basin Authority has been undertaking fortnightly reviews of the relaxation, with the result that it has continued uninterrupted.
Flooding along the Campaspe, Loddon and Avoca rivers in northern and western Victoria during January 2011 added to existing high flows along the lower mid-Murray. These high flows required removal of the weirs at Torrumbarry (for periods during September, December and January), Euston, Mildura, and combined with flood releases from Menindee Lakes, at Wentworth (from December to April).
The rainfall associated with the La Niña and record warm sea surface temperatures in the Australian region contributed to widespread flooding across much of the Murray–Darling Basin (MDB) region during the 2010–11 year, particularly in spring and summer. Details of how high streamflows contributed to severe flooding in the jurisdictions have been provided under Significant water events.
Figures W1 to W3 show streamflow patterns, volumes and variations for the three gauging stations selected for the flow analysis for the 2011 Account (see Surface water streamflow summary for gauging station details).
Figure W1. Graph of total monthly flow during the 2010–11 year compared against long-term percentiles for the Murray River at Doctors Point (Albury)
Source: Bureau of Meteorology
Figure W2. Graph of total monthly flow during the 2010–11 year compared against long-term percentiles for the Darling River at Bourke
Source: Bureau of Meteorology
Figure W3. Graph of total monthly flow during the 2010–11 year compared against long-term percentiles for the Ovens River at Peechelba
Source: Bureau of Meteorology
Streamflows analysed for the 2011 Account for the stations within the MDB region were well above mean annual flows (Figures W1 to W3) for the 2010–11 year. For example, the Darling River at Bourke in the Northern Basin and the Ovens River at Peechelba in the Southern Basin recorded 7,758,100 ML (261% of mean annual flow) and 3,438,600 ML (275% of mean annual flow) respectively for the 2010–11 year.
Major water initiatives
On 8 October 2010, Murray–Darling Basin Authority published the Guide to the Proposed Basin Plan. Volume 1 of this suite of publications outlined the basis of the draft Basin Plan; the technical detail was set out in parts 1, 2 and 3 of Volume 2 of the guide. Preparation of a draft Basin Plan continued for release later in 2011.
One of the key elements pf the Guide to the proposed Basin Plan is the setting of new limits – sustainable diversion limits, or SDLs – on the amount of water used in the Basin. Sustainable diversion limits will be enforced through state water resource plans.
Following release of the Guide to the proposed Basin Plan (the Plan) a Parliamentary inquiry (House of Representatives Standing Committee on Regional Australia – Inquiry into the impact of the Murray–Darling Basin Plan in Regional Australia) was initiated to examine the impact of the Plan on regional communities.
Australian Capital Territory
Work commenced in late 2009 on the construction of an enlarged Cotter Reservoir increasing capacity to around 78,000 ML. Significant rain events and flooding in 2012 have delayed construction.
Construction works for the Murrumbidgee to Googong water transfer pipeline, which will allow the transfer of water from the Murrumbidgee River to Burra Creek, where it will flow into Googong Reservoir commenced in early 2011.
New South Wales
The water sharing plan for Peel Valley Regulated, Unregulated, Alluvium and Fractured Rock commenced in July 2010.
Above-ground works commenced for the Adelaide desalination project. Intake flooding and the subsequent introduction of seawater allowed raw saltwater into the plant for the first time to start the live commissioning process.
Victoria passed a legislation in August 2010 to make necessary provisions to establish the Victorian Environmental Water Holder, to decide on the best use of environmental water entitlements for Victoria's rivers and wetlands.