Submersible Pumps Tackle The River Murray Salinity Problems

Overview_TEXT

Overview

The Situation

The River Murray runs through the Murray-Darling Basin which is a naturally saline environment underlain by a vast saline groundwater system (with salinity levels often exceeding sea water).

As a result of the geological conditions, the River Murray is the only drainage path for the average 2 million tonnes of salt to be exported from the Murray-Darling Basin to the sea each year. A large proportion of the salt is also forced into the river within South Australia due to the direction of groundwater flow. Prior to European settlement it is estimated only 900 tonnes of salt per day naturally entered the River Murray within South Australia.

Since then, land clearing and irrigation practices has increasingly mobilised salt into the landscape and river. In addition more river flows have been diverted for irrigation, industrial and urban uses which means the river cannot effectively dilute inflows of saline groundwater.

South Australia is vitally dependent on the River Murray for much of its water supply and in a ‘dry year’, the River supplies up to 90% of the state's domestic and industrial water. As a result of this heavy dependence the increasing salinity levels was a major threat to the state’s water supply.

The Solution

In the late 1980’s the then Murray-Darling Basin Commission recognised the importance of the salinity problem and commenced construction of a series of groundwater pumping schemes. The purpose of the large scale groundwater pumping schemes was to intercept saline groundwater before it entered the Murray River.

The Woolpunda Salt Interception Scheme (175 km northeast of Adelaide) was commissioned in 1990 and consists of 49 bores and 85 km of pipelines, pumping at 200 litres per second, to intercept almost 200 tonnes of salt per day. Since then, similar Salt Interception Schemes have been built at Waikerie (in 1992 with additions in 2003 and 2009), Bookpurnong  (in 2005), Loxton (in 2007), Pike River (in 2010) and Murtho (in 2014). In total there are almost 200 bores in use with over 250 km of pipelines and a current capital value of approximately $200 million.

Based on early long term pumping trials it was identified that reliable, corrosion resistant pumps were required to withstand the harsh operating conditions of the very saline groundwater. As a result, Grundfos SP borehole pumps have been used exclusively throughout the Salt Interception Schemes since 1990.

In most cases N Series pumps (constructed from high grade AISI316 stainless steel) exceeded initial expectations and performed very well in the 20,000mg/L water encountered at Woolpunda and Waikerie. To this day, two of the pumps at Waikerie hold the record for operating continuously for 9 ½ years before requiring overhaul.  Other pumps were removed as required and overhauled, with generally only wearing parts requiring replacement.

Due to the severe hydrogen sulphide problems in the seven bores at Woolpunda,  higher grade Grundfos R Series submersible pumps (constructed from superior high grade AISI904 stainless steel) were installed. This solved the issue of corrosion, with no corrosion evident on the pumps after over 20 years of use. Subsequent schemes with groundwater salinities as high as 50,000mg/L have exclusively used Grundfos R series submersible pumps with great success.

Besides the salinity, a major maintenance problem across the groundwater pumping schemes was the presence of iron bacteria. Iron bacteria occurs when naturally occurring bacteria precipitate iron from the groundwater, severely clogging pumps and pipelines with a jelly like sludge. While operations personnel periodically clean the pipelines with foam rubber ‘pigs’ and chlorination systems (SA Water patented), occasional cleaning of the pumps is still required.

Over the years, various pipework configurations were trailed and results proved that the Wellmaster flexible rising main from Grundfos was the ideal solution. The corrosion resistant SP submersible pumps (R and N series) combined with the Wellmaster rising main allows the system to be cleaned in-situ without having to remove the pumps. This is achieved by flushing acids and surfactants down the riser hose and back through the pump (the check valve has a hole drilled in it to allow this). In most cases this process restores the pump’s flow without having to remove, disassemble and clean the components back in a workshop – saving time and money.

The Outcome

The Salt Interception Schemes are a great success in preventing approximately 500 tonnes of salt from entering the River Murray per day. The Schemes particularly proved their worth during the recent ‘Millennium Drought’ (from 2001 to 2010), when salinities were kept well below critical levels despite very low River flows.

Long term cooperation between the scheme operators and Grundfos personnel have led to a number of trials of different products, components and techniques that have been mutually beneficial. Based on the success of Grundfos SP submersible pumps in the South Australian schemes, around 100 pumps are now in use in similar schemes in New South Wales and Victoria.





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Topic:

Salinity Problems

Location:

The River Murray, South Australia

Company:

SA Water

Contacts_TEXT

Contact

If you need a similar solution, please contact us for further information.

Telephone

1300 337 733

Fax

1300 782 080

Address

HEAD OFFICE
515 South Road
Regency Park
SA 5010

Contact

If you need a similar solution, please contact us for further information.

Telephone

1300 337 733

Fax

1300 782 080

Address

HEAD OFFICE
515 South Road
Regency Park
SA 5010