«Back Torrens River @ Seaview Road Bridge - A5041014
Land Use

This site is the End of Catchment site for water quality and flow measurement in the Torrens Catchment, which has an area of just over 500km2.  The upstream landuse therefore includes both the rural and urban Torrens Catchment.  While the extent of the catchment encompasses this broad area, water quality and flow at this site is driven by more local pollutant sources as water from the headwaters of the catchment is substantially utilised within the catchment (for agriculture or domestic purposes) or stored in either Kangaroo Creek or Millbrook Reservoir and then used for the metropolitan drinking water supply. This impact occurs particularly during the summer months when, with the exception of extreme storm events, no flow passes over the Gorge Weir.

The urbanised Adelaide foothills and plains are traversed by the highly modified First to Fifth Creeks which flow into the River Torrens through the Linear Park, the Torrens Lake and then out into Gulf St Vincent through the artificial channel, Breakout Creek. This system doubles as part of the City’s stormwater drainage system and along the River, much of the Adelaide Parklands and recreational open space assets are located.

The Torrens Lake, in the centre of Adelaide, is the focus of national and international attention during the many and varied community events that take place on its waters, banks and in surrounding parks. The Lake supports the culture of Adelaide and is a feature of the city in which we should all take pride. The Torrens Lake is high profile water body and a major Parkland asset which accumulates litter and debris, sediment and nutrients. During summer it is prone to cyanobacterial (bluegreen algae) blooms. Closures of the Lake to boating and rowing activities are required, to mitigate public health risks associated with blooms of cyanobacterial and also high microbiological counts after summer storms.

The urban catchment has a very high proportion of impermeable surfaces (roads, roof and pavement) and runoff is very flashy and intense (short duration - high peak flows). The efficient drainage system (to minimise flooding) helps create short term high flows which on the Adelaide plains are very difficult (virtually impossible) to store in any significant volume. In contrast the rural catchment, even in its cleared state, only produces significant runoff after the catchment has been saturated, usually well into winter. Flows are generally slower to peak due to the surface storages, however when rain events are long and local farm dams become full, flows persist for many days.

Managing water quality outcomes requires a good understanding of the catchments’ hydrology.

An independent study (undertaken within the Torrens Taskforce) has been undertaken to sample and tested sediments from the River Torrens and First Creek.  The results of the survey, showed concentrations of cadmium, lead, zinc, copper and phosphorus above the national trigger value for sediment quality at some point along the course of the Torrens.  High levels have been associated with historic landuses and pollutant discharge. For example, the worst contaminated sites are along the industrial stretch of the Torrens from the West End Brewery through to Underdale and are highly likely to be related to the historical location of noxious industries, including metal foundries and chemical works. The trigger value for lead in sediments is 50 μg g-1 and the high value (beyond which ecological damage is deemed to have already occurred) is 220 μg g-1; measurements at the worst industrial site were 832 μg g-1 in the <2.00 mm fraction and 4769 μg g-1 in the mud and plant organic fractions. Despite the high metal levels in the sediments there is no evidence of them becoming bioavailable in the River. Macro invertebrate sampling in the River has not produced any concerning results.