Investigation of continuing loss estimation for medium sized tropical catchments

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 losscontinuing loss model’ is widely used in Australia. The initial loss (IL) occurs at the beginning of the rainfall event, prior to the commencement of surface runoff and the continuing loss (CL) is the average rate of loss throughout the remainder of the storm. The currently recommended design loss values in Australian Rainfall and Runoff (ARR) for Queensland have some basic limitations. This paper investigated how more accurate CL values can be estimated and derived for medium sized tropical Queensland catchments using long term rainfall and stream-flow data. A base-flow separation method was used, which was characterised by a single parameter (α). This paper shows that the continuing loss estimates are not sensitive to α. Importantly, the median continuing loss values derived for three Queensland catchments are found to be much smaller than the present recommended design continuing loss values documented in the ARR (I. E. Aust., 1998), which are used by design engineers The derived value has important implications to improve the design flood estimate. The sensitivity analysis between derived and existing recommended CL values shows that the derived CL value produces higher flood peak than the existing recommended CL value in ARR (I. E. Aust., 1998).