Pipe Dreams: The Mannum-Adelaide Pipeline and its effects on the aquatic environment of the Upper River Torrens catchment, South Australia

Abstract

In order to assess nutrient and sediment pollution in the upper River Torrens catchment a palaeoenvironmental investigation from sediments in Gumeracha Weir was undertaken. The geochemistry of core samples from Gumeracha Weir, was compared to suspended sediment samples taken from tributaries upstream of the weir, samples of Murray River water and also from sites with various land use types scattered throughout the upper River Torrens catchment.

Sediment accumulation rates in the Gumeracha Weir appear to have increased in the last 50 years. A major source of sediments in Gumeracha Weir is the River Murray, via water being diverted into the river through the Mannum-Adelaide pipeline. A second important source, associated with high silica sediments deposited in high energy flows, originated from in the Torrens catchment. No single type of land use, (eg roads or pasture) could be identified as the source of these sediments.

Through diatom analysis a history of changes in water chemistry was also established. The results indicate that there has been a significant increase in pH from approximately pH 7.6 units in samples pre-pipeline to an average of pH 8.4 units at present. The decline in Rhicosphenia abbrevata indicates that turbidity has also increased markedly since the commencement of River Murray water input.

It was therefore determined that the divergence of River Murray water into the upper River Torrens catchment has consequently added to an increase in both sediment and nutrient concentrations of the River Torrens.