Flood risk estimation in Australia’s coastal zone: modelling the dependence between extreme rainfall and storm surge

This paper provides a proposed methodology for estimating flood risk in situations where the potential exists for floods to be caused by the combination of catchment-derived flows from an extreme rainfall event together with elevated ocean water levels. The statistical basis of the methodology has been developed over a period of three years of research as part of Project 18 of the Australian Rainfall and Runoff revision. The methodology has the following elements: (1) assessment of whether a joint probability analysis is required, based on a pre-screening analysis; (2) estimation of the strength of dependence between extreme rainfall and storm surge, which will be based on the location of the catchment and the storm burst duration; (3) estimation of a set of flood levels corresponding to different combinations of rainfall and storm surge; and (4) estimation of the design flood levels based on the dependence parameter and the set of flood levels. This paper describes the overall methodology, provides an Australia-wide map of dependence parameters corresponding to different storm burst durations, and illustrates the methodology using a case study.