Derivation of New Design Initial Losses for Flood Estimation in Queensland

The rainfall based design flood estimation techniques are widely used in hydrological design. Initial loss is an important input to rainfall runoff models. There is limited design data on initial losses in many parts of Australia, which is regarded as a major weakness in Australian hydrology. This paper examines the initial losses on 15 Queensland catchments. The observed initial losses are found to be much greater than the currently recommended values for eastern Queensland. The initial loss values are found to increase with rainfall duration. There is a lack of strong seasonality in observed initial loss values. The antecedent precipitation indexes associated with smaller initial loss values are found to be generally higher. The initial losses in eastern Queensland are relatively higher and show a greater variability than that of Victoria. It has been found that the distributions of initial losses in eastern Queensland can be approximated by a fourparameter Beta distribution.