Estimation of large to extreme floods using a regionalization model

Estimation of large to extreme floods in the range of 100 years return periods to probable maximum floods (PMF) is needed in planning and designing of large water resources management projects. Due to the limited availability of observed flood data, the estimation of large to extreme floods requires significant extrapolation beyond the observed flood and rainfall data. This chapter provides a review of various techniques to estimate large to extreme floods. It also presents a case study in Australia where based on observed flood data, a large to extreme flood regionalization (LEFR) model has been developed which can be applied relatively easily as compared with rainfall runoff modeling. The LEFR model assumes that the maximum observed flood data over a large number of sites in a region can be pooled together by accounting for the at-site variation in the mean and coefficient of variation of the observed annual maximum flood data. The LEFR model has been developed and tested using data from 227 catchments in New South Wales and Victoria States in Australia. The method can easily be adapted to other Australian states and countries.