Investigation of Continuing Losses for Design Flood Estimation: A Case Study in Queensland

The rainfall based design flood estimation techniques are commonly adopted 'in hydrological design, and require a number of inputs including information on loss characteristics. A conceptual loss model known as the 'initial loss-continuing loss model' is a widely used model in Australia. The initial loss occurs at the beginning of the rainfall event, prior to the commencement of surface runoff and the continuing loss is the average rate of loss throughout the remainder of the storm. The currently recommended design loss values in Queensland have some basic limitations. This paper presents a case study of continuing loss estimation for three catchments in south-east Queensland. The study employs a baseflow separation method that is based on streamflow data and is characterised by a single parameter a. It has been found that the continuing loss estimates are not sensitive to the a value. The observed median continuing loss value, obtained from the three study catchments, is found to be much smaller than that recommended by the Australian Rainfall and Runoff for the study area.