Flood hydrology in an arid area - findings from the gammon ranges project

Monitoring of the Arcoona Creek catchment in the Gammon Ranges commenced in 1988 with the installation of a single pluviometer, and the project now maintains five pluviometers and a stream gauge monitoring a 49.7km2 catchment with an average rainfall of approximately 250mm to 300mm. The catchment monitoring has extended to include Windy and Emu Creeks, which discharge into the Aroona Dam at Leigh Creek. Although runoff events are rare there are now four significant flood events in the nearly 20 years of record that can be used for calibration. Calibration was carried out using the RRR model, which allows for several runoff processes to occur. It was found that in most cases there is a significant slow response, as well as a very rapid response occurring in the hydrograph. It is postulated that the large gravel bed of the creek has a significant effect on flood flows, creating large losses and a slow response and for some events a very rapid time of rise as a flash flood occurs when the infiltration rate of the bed is exceeded. Water level data was sourced at the minimum obtainable 5 minute interval to gain some idea of the time of rise, and even then there was a measured rise of up to 1.7m within the five minutes. This flash flood possibility and the high probability of runoff from only part of the catchment for most events means that developing a model for accurate prediction of flood flows will prove very difficult. This paper describes the catchment and the calibration, compares the catchment hydrology with other arid catchments and discusses some of the issues associated with the collection of rainfall and stream flow data.