The major flooding of Lake Torrens in March 1989

Abstract

On 14th March 1989 an extreme rainfall event caused record historical floodings in Lake Torrens and in the Pirie-Torrens corridor. The results of a joint Flinders University/Army expedition to monitor these events in which the water level and major ion content of the floodwaters in Lake Torrens were measured over the duration of the flood (March–December 1989), and the volume flow and major ion content of the flood in the Pirie-Torrens corridor which discharged into Spencer Gulf at Port Augusta and peaked on 17th March 1989 were recorded. The bathymetry of Lake Torrens was also determined from hydrological and existing dry land surveys, and subsequently compared with transects obtained from the Ice, Cloud, and Land Elevation satellite (ICESat). We confirmed that the lake bottom slopes downwards towards the south at about 1.5 m per 100 km, and showed that the maximum water level in Lake Torrens was approximately 31.4 m AHD with a maximum depth of 1.4 m. The salinity of the floodwaters increased from south to north, and the decline in water level was mainly due to evaporation. Both Lake Torrens and the Pirie-Torrens corridor are characterised by the ingress of fresher water from the south. We suggest that this has given rise to a quasi-stable hydrological system in the Pirie-Torrens corridor and in Lake Torrens in which the gravitational head due to the gradient in bathymetry and the osmotic head due to the gradient in salts concentration are in balance.