THE SALT PROBLEM IN THE RIVER MURRAYLarge amounts of salt have always entered the Murray from inflows of saline groundwater. At times of low flow before the  locks and weirs were built, salinity reached very high levels. With regulation of river flows early this century, those very high salinity levels were reduced because a greater volume  of water was retained during periods of low flow. Over the last 30-40 years, though, average salinity  levels have risen because of irrigation and associated drainage along  the Murray. This trend is continuing, although major salinity reduction  initiatives implemented since the late 1970s have interrupted the  rise. Maximum salinity levels have risen to the point where  they are of concern to domestic and industrial users of river water throughout South Australia, and of course to irrigators along the  Murray, particularly its lower reaches. Adequate measures to contain salinity are necessary  to ensure the continued use of Murray Water in the long term.

THE SALINITY AND DRAINAGE STRATEGY The Murray-Darling Basin Ministerial Council manages the natural resources of the Basin by identifying  problems, developing solutions and undertaking necessary works through  theMurray Darling Basin Commission. These activities are jointly funded by the Commonwealth Government and the State Governments of New South Wales, South Australia and Victoria. The Salinity and Drainage Strategy has been developed to provide a framework for the four Governments to  manage the pressing problems of salinity, waterlogging and land salinisation in the Murray and Murrumbidgee Valleys. The Strategy, adopted in 1988, aims  to achieve a long-term average decrease of 80 EC units measured at  Morgan. Elements of the Strategy include: New operating rules for major storages. Land management schemes. River salinity reduction schemes - of which the Waikerie Salt Interception Scheme is one.

THE WAIKERIE SCHEME In the Waikerie area 105 tonnes of salt a day enter  the river over a 20 kilometre length. This is exceptionally high. The scheme will prevent approximately 80 tonnes of this salt a day from entering the river, and will lower the average  salinity at Morgan by 22 EC units. The main source of the salt is naturally occurring highly saline groundwater which is being displaced into the river by irrigation drainage water. At Waikerie it is feasible to intercept most of this highly saline groundwater using a system of bores and pumps. Because the high inflows are concentrated in a relatively short distance, interception at Waikerie is more economic than in other parts of the river. Domestic, agricultural and industrial users of River Murray water downstream of the scheme will directly benefit. Irrigators  in the immediate area will benefit from the lowering of the level of saline groundwater.

DESIGN AND CONSTRUCTION OF THE SCHEME The layout of the scheme is shown on the map below. It consists of an initial 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 both  sides of the Murray, preventing it reaching the river. The total pumping capacity for the scheme is 21 ml/day. The scheme was commissioned in December 1992.

DISPOSAL BASIN The basin, in a well defined natural depression 15km southwest of Waikerie, is also being used to dispose of saline groundwater  from the recently commissioned Woolpunda Salt Interception Scheme.  It will eventually have a water spread of 680 hectares. At the basin the saline water is disposed of by evaporation  and by infiltration into the ground. The basin has a finite life, but the impact of the salt infiltration should not become significant  until after 400 years of pumping. If use of the basin is stopped after 100 years, the saline water will take approximately 50,000 years to  return to the River. Land around the basin was sheep grazing country. Since stock was removed, natural revegetation is being encouraged. The basin has already attracted a healthy bird population, and there may be  other recreational used to which the basin could be put.

ENVIRONMENTAL CONSIDERATIONS A Public Environmental Report was prepared by consultants  which assessed the following environmental issues: Disruption to Waikerie residents and rural land  holders during construction. Loss of native vegetation at the Stockyard Plain disposal basin. As a result of this report underground powerlines  were installed on the floodplain to avoid the aesthetic impact of overhead power distribution lines. Measures undertaken to enhance the environmental acceptability of the scheme include: Reducing the salinity of Ramco Lagoon to enhance its ecological value. Support for studies into revegetation of the floodplain  at Ramco. Developing a management plan for the disposal basin.

MONITORING The performance and effects of the scheme are monitored  to ensure that it performs as designed. The following aspects are monitored: River salinity is continuously measured up and down stream of the project to monitor the remaining salt load entering in the reach. Groundwater levels throughout the borefield are measured to ensure targets are met and that overpumping is not occurring. Groundwater levels surrounding the disposal basin  are measured to ensure infiltration proceeds as expected and the design  life of the basin can be confirmed. The salinity and chemical composition of the water being pumped is checked so that any changes can be investigated.

For further information contact :-Peter Forward
Telephone :- 08 82077725
FAX :- 08 85952218
Mail :- PO. Box 546 Vaughan Terrace, Berri 5343
Electronic mail :-peter.forward@sawater.sa.gov.au