A quantile regression technique to estimate design floods for ungauged catchments in south-east Australia

Design flood estimation in small to medium-sized ungauged catchments is frequently required in hydrological design and is of great economic significance. The currently recommended method in Australian Rainfall and Run-off for south-east Australia is the Probabilistic Rational Method, the central component of which is a run-off coefficient that is assumed to vary smoothly over the geographical space. This paper aims to develop an alternative method of design flood estimation in small to medium-sized ungauged catchments in south-east Australia based on a quantile regression technique. This uses stream flow and catchment characteristics data from 88 catchments in south-east Australia. The developed prediction equations satisfy the underlying model assumptions very well and include hydrologically meaningful predictor variables that are readily obtainable. An independent test indicates that these prediction equations can provide reasonably accurate design flood estimates in the study area for small to medium-sized ungauged catchments.