Will the river really run dry?

While the Prime Minister yesterday did not release the report on contingency plans for water availability in the Murray-Darling Basin, the Murray Darling Commission’s update on drought conditions did become available and it reveals irrigation in 2007/08 is much more dependent on rain and run-off than in any previous year since Dartmouth Dam was completed in 1979.

Yet even if very dry conditions are experienced as over the last year, it is expected that Murray catchment inflows, together with any future contributions from the Snowy Mountains Scheme, would be sufficient to meet basic human, stock and domestic requirements (subject to appropriate levels of restriction).

The Commission reports the 12 month period ending March 2007 was the driest 12 month period for the River Murray in 115 years of historical inflow record. A repeat of the same rainfall pattern for another 12 months would result in even lower inflows due largely to reduced inflows from groundwater systems. This trend is evident for the last three months with inflows to the River for February and March 2007 (excluding Snowy Scheme releases and inflows to Menindee Lakes) compared with 2006 are as follows:

If the Snowy Mountains Scheme continues to experience record low inflows, then releases from the Scheme to the Murray would also be less than the record low releases in 2006/07.

The Commission report continues:

Under this scenario, contingency measures would need to continue to ensure that there would be enough water in the Murray to meet evaporative losses and critical water needs of all the towns and cities that rely on the Murray from Albury to Adelaide and beyond, as well as other domestic and stock requirements. Under that extreme scenario, there would be no water available for irrigation or the environment.

Although the probability of this extreme scenario eventuating is very low, and has never been experienced in our records, it is nevertheless prudent that contingency planning and implementation continue until such time that there is sufficient rain and inflow to give confidence that the water crisis has passed. Inflows in the first three months of 2007 are only slightly in excess of inflows incorporated in the worst case planning scenario, reflecting the continuation of the record low inflow sequence experienced since mid 2006.

While Mr Howard is waiting for State Premiers for permission to release his contingency report, the Murray Basin Commission has given some indications of what the group of senior officials have recommended. The Contingency Plan covers a range of measures a number of which have already been initiated, including:

• conserving as much water in upstream storages as possible;
• adopting a very low target reserve for storage in Lake Victoria for end May 2007;
• reduced targets for minimum flow along the River Murray;
• early pumping of water to Mt. Lofty storages in South Australia; and
• temporarily disconnecting selected permanent wetlands from the River Murray.

Planning is continuing for other measures which would be implemented if extremely dry conditions persist.

As to whether they will persist, the Australian Bureau of Meteorology has indicated that for the southern part of the Murray-Darling Basin, there is about a 50% chance that rainfall would be above the median. This is a slightly lower chance than was announced for the three month outlook for February to April 2007 inclusive. The Bureau has announced in recent weeks that the 2006/07 El Niño event has ended, and there is an increased chance of a La Niña event developing in 2007. The Bureau has noted that the confidence level in the Rainfall Outlook from the computer models is low in autumn months but improves between July and January.

Chance of exceeding the median rainfall April to June 2007

As to the River Murray actually stopping flowing, the Commission concedes it is possible that flows may need to be reduced to zero but only in the extreme, and very low probability, circumstances “of inflow conditions being significantly lower than the record dry of 2006/07. Under those circumstances, it is possible that flows may need to be temporarily suspended in the River Murray over summer of 2007/08. Temporary measures would be needed to access deeper pools for those towns not already connected to weir pools or natural deep pools.”