Rising salinity in the River Murray has long been recognised as a major problem, particularly for South Australia where we rely heavily on the River to supplement our water supply.
SA Water has been addressing the issue of salinity in the River Murray since the early 1960s and now operates several large salt interception schemes on behalf of the Murray Darling Basin Commission, which is leading the national campaign to combat the salinity problem.
SA Water's first salt interception schemes are located at Waikerie and Woolpunda in the State's Riverland region. These work by capturing saline groundwater using deep bores near the river and pumping it away to a specially created disposal basin at Stockyard Plain.
Prior to the implementation of the Woolpunda and Waikerie schemes, the River Murray was carrying up to 250 tonnes per day of salt past Woolpunda and 100 tonnes a day past Waikerie.
Recent surveys show these salinity levels have decreased to less than 10 tonnes a day in each area.
SA Water's newest Salt Interception Schemes are located at Bookpurnong (commissioned in 2005) and Loxton (under construction). These two schemes utilise a similar system of interception bores along the southern bank of the river in floodplain and highland areas to intercept a total of 134 tonnes per day when fully commissioned. These two Salt Interception Schemes will pump the intercepted saline groundwater to the Noora Basin located some 20km south east of Renmark via the existing and underutilised Noora Drainage Disposal Pipeline.
The floodplain area of the Loxton Salt Interception Scheme will be commissioned in 2007 with the highland area to be completed by 2009 following the trials of alternative interception techniques targeting saline groundwater in the highland areas. The highland areas of Loxton have unique geological features which preclude the use of conventional interception techniques using vertical bores. A trial has commenced using a directionally drilled horizontal bore using slotted HDPE pipe and a subsequent trial using a conventional drainage trench at the toe of the highland cliff areas is about to begin. The system to be utilised to complete the Loxton SIS will depend on the result of these trials.
SA Water also operates the Rufus River groundwater interception scheme in the south-west corner of New South Wales.
At Morgan, the level of salinity is now about 25% less than it would have been without the schemes along the River to the east.
Despite the excellent work now being undertaken, the salinity problem continues to increase and over coming years $50 million will be invested within South Australia building additional schemes at Waikerie (near Lock 2), Pike River, Murtho and Chowilla. The construction of the Murtho SIS is expected to commence in 2008.
These schemes will intercept a further 370 tonnes of salt per day.
The salt interception schemes are funded by the Murray-Darling Basin Commission and are designed, constructed and operated by SA Water.
In 2002, in conjunction with hydrogeological consultants Australian Water Environments and the Murray Darling Basin Commission, SA Water received the Sir William Hudson Award for most outstanding engineering project and the Environmental Engineering Excellence Award for the River Murray Salt Interception Schemes.
The $25 million Woolpunda SIS situated between Waikerie and Overland Corner was commissioned in December 1990.
The largest of the schemes, Woolpunda, features 49 interception bores, approximately 1000 metres apart and 500 metres back from the River valley, set out in two lines, one on each side of the River Murray.
Each 250 mm diameter bore is about 110 metres deep with a fibreglass slotted casing. The standing water level in the bores is generally 40 metres below the surface.
A stainless steel electric submersible pump is installed in each bore at a depth of 70 metres and pumps water at the rate of between 2 and 10 litres per second.
The saline groundwater is pumped at a rate of 15 mega litres per day through a series of underground pipes 85 kilometres to the Stockyard Plain Disposal Basin 15 kilometres south-west of Waikerie.
During its first year of operation the Woolpunda SIS intercepted 4300 megalitres of saline groundwater carrying 83,000 tonnes of salt.
Waikerie
The Waikerie SIS consists of a line of 17 interception bores, 90 -125 metres deep and 27 kilometres of pipeline to convey the intercepted saline groundwater to the Stockyard Plain Disposal Basin.
Electrically driven stainless steel pumps are installed 50 metres below river level, and draw saline groundwater from beneath both sides of the Murray, preventing it from reaching the river. The total pumping capacity for the scheme is 11 megalitres a day.
The scheme was commissioned in December 1992.
The recently constructed $3.4 million Waikerie Salt Interception Scheme Stage 2A interception scheme is an enhancement of the original scheme and an extension of it downstream with a total of 12 bores to intercept an additional 35 tonnes of salt per day.
Bookpurnong
The $11.2 million Salt Interception Scheme at Bookpurnong in the Riverland was commissioned in 2005 and will prevent about 20,000 tonnes of salt entering the River Murray annually.
40 bores have been drilled on the floodplain at Bookpurnong to intercept the saline groundwater.
Bookpurnong SIS pumps the saline water from these bores to the Noora evaporation basin, about 20km east of Loxton.
By 2040 it is expected this scheme will prevent about 200 tonnes of salt per day from entering the River Murray.
Loxton
In March 2004, final approval was given for the construction of a $21.4 million salt interception scheme at Loxton that could remove 66 tonnes of salt from the River Murray each day.
Construction of the Loxton SIS commenced in 2006 with the installation of the SIS pipeline and associated spurlines, drilling and equipping of the interception and observation bores in the floodplain areas and the supply of power.
The floodplain section of the Loxton Salt Interception Scheme will be commissioned in August 2007 with the remainder of the works in the highland area to be completed by 2009 following the trials of alternative interception techniques targeting saline groundwater in the highland areas. The highland areas of Loxton have unique geological features which preclude the use of conventional interception techniques using vertical bores. A trial has commenced using a directionally drilled horizontal bore using slotted HDPE pipe and a subsequent trial using a conventional drainage trench at the toe of the highland cliff areas is about to begin. The system to be utilised to complete the Loxton SIS will depend on the result of these trials.
The disposal main for the Loxton Scheme joins the Bookpurnong SIS main and disposes saline groundwater to the Noora Basin, a series of natural depressions on farming property, about 20 kilometres from the river. The basin was first used in the early 1980s for disposal of drainage water from the Riverland irrigation areas.
Rufus River
The Rufus River Groundwater Interception Scheme was commissioned in 1984 and funded by the River Murray Commission at a cost of $3.3 million.
Lake Victoria is the source of the salinity problem in the area. The lake was a natural lake which in 1928 was converted into a vast off-stream storage for the River Murray.
The pressure generated by the water stored in the lake forces salty groundwater in the aquifers beneath the lake to migrate towards the Rufus River - the channel used to return the lake water to the River Murray.
Before the construction of Rufus River Groundwater Interception Scheme it was estimated about 200 tonnes of salt were being flushed into the river every day.
The scheme consists of 178 wellpoints connected to four pumping stations which intercept the saline groundwater and pump it into two dams and then into an evaporation basin located around four kilometres to the north-east of the interception works.
Stockyard Plain Disposal Basin
Stockyard Plain, 15 kilometres southwest of Waikerie, was a degraded area, virtually devoid of vegetation but providing a well defined natural depression suitable for holding water.
Saline water is disposed into the basin and, in the long term, the water either evaporates or filters into the ground, where the aquifer is already naturally saline. The movement of this saline water through the aquifers is so slow that it will take many hundreds of years for it to have any significant impact back on the River.
Since the commissioning of the Woolpunda and Waikerie schemes in 1990 and 1992, the saline groundwater taken from the two schemes has now formed four large ponds totalling more than 350 hectares, around which SA Water has planted more than 10,000 trees and carried out 60 kilometres of direct seeding.
Today Stockyard Plain is an 1870 hectare oasis for kangaroos, emus and reptiles and over 130 other species of birds. It has become a popular destination for bird watchers and environmentalists.
Camping is allowed at two sites within the grounds by obtaining a permit from SA Water's Berri office.
Noora Disposal Basin
The Noora Drainage Disposal Scheme was commissioned in 1982 as a site for the disposal of excess drainage water pumped from the Berri and Disher Creek Basins to minimise salinity impacts on the River Murray.
Until 1982, all drainage water from the Berri and Renmark Irrigation areas was directed to the Berri Evaporation Basin, and the Disher Creek and Bulyong Island Evaporation Basins respectively, which were located on the River Murray floodplain. However, the consequent high water levels in these Basins altered the hydrogeological regime, causing highly saline groundwater beneath the floodplain to flow into the River Murray. In an attempt to combat this problem, the Noora Drainage Disposal Scheme was commissioned in 1982. Noora was chosen as a site for the disposal of excess drainage water due to its low elevation, and the fact it was already acting as a groundwater discharge area.
Both the Noora Basin and the Noora Gravity Main have the capacity to transfer and dispose all groundwater intercepted by the Bookpurnong and Loxton schemes and the future Murtho and Pike SIS schemes as well. As the Noora Disposal Scheme is becoming underutilised as a drainage basin due to increased irrigation inefficiencies and reduced drainage flows, it is expected that salt interception schemes will be the predominant users of this infrastructure.