SA Water Infrastructure

In reply to the Hon. J.A. DARLEY (9 March 2016).

The Hon. I.K. HUNTER (Minister for Sustainability, Environment and Conservation, Minister for Water and the River Murray, Minister for Climate Change): The Minister for Water and the River Murray has received this advice:

1. I am advised that SA Water's maintenance program follows both preventative and breakdown maintenance methodology.

2. I am advised that SA Water maintains an asset register of the location and asset attributes of every pipe, valve, fireplug and water meter in the network.

The condition and performance of individual pipes within the water network are also monitored and recorded every day by SA Water. A large detail desktop review of the total water network is conducted between February and March each year to set the following financial years capital works programme. Outside that period SA Water investigates individual pipes under individual projects and set priorities for either replacement or inspection.

3. As per the previous point, the entire water system including the suburbs of Campbelltown, Newton and Paradise are analysed between the months of February and March to set the capital programme. Outside that period SA Water investigates individual pipes and set priorities for either replacement or inspection.

4. Within the suburb of Campbelltown, there is 53.1 km of water mains laid between 1880 to 2014. The Campbelltown water network has an average age of 55 years.

Within the suburb of Newton, there is 35.5 km of water mains laid between 1889 and 2015. The Newton water network has an average age of 50.

Within the suburb of Paradise, there is 55.3 km of water mains laid between 1889 and 2014. The Paradise water network has an average age of 51 years.

5. A State of the Assets Report is tabled in parliament twice a year which reflects the performance of water main assets.

6. Within the metropolitan area, SA Water uses soil data that was collected and tested by the Department of Mines and Energy in 1996. Between 2006 and 2009, SA Water undertook an extensive investigation into soil movement and water main failures. This relationship between soil and pipe failures is still monitored by SA Water today with failure patterns observed in 2009 consistent in 2016.

Soil within metropolitan Adelaide is separated into two horizons. The A horizon is the higher level and the B horizon is the lower level.

There are 21 soil classification categories identified within the A soil horizon, which ranged from sandy alluvial material to the aggressive red brown and black earth clays and a variety of clays types within the lower (B) horizon. They include the Keswick clay and Hindmarsh clay to name a few.

Across Adelaide, Gilgai formations commonly occur when the increase in moisture content of a lower soil horizon (B) causes the soil to swell and heave itself upwards through the upper soil horizon (A) to provide micro relief. Within Adelaide the most significant occurrence of Gilgai formations would occur within a Keswick or Gley clay B horizon and a black earth A horizon.

Unfortunately the suburbs of Paradise, Newton and Campbelltown are predominately located within Black earth soils as an A horizon and Keswick clay as a B horizon. As a result, the majority of failures within this region are attributed to circumferential cracking and ground movement.

The influence of aggressive soil movement, due to changes in moisture content in both horizons, has the potential to apply multiple forces on the water main. First frictional forces from soil cracking can pull against the main, and second, swelling of soils can cause uplift and result in negative bending moments applied to the main. This supports the monthly failure trend within the network and sees peak number of water main failures in March to June and significantly lower number of failures in October and September.