Estimation of Major Floods: Applicability of a Simple Probabilistic Model

Abstract

Estimation of major flood flows is needed in the design and operation of large water infrastructure. This paper presents a simple probabilistic model (PM) that can be used to derive “easy to apply” prediction equations for estimation of major flood flows. The proposed method assumes that the maximum observed flood data over a large number of sites in a region can be pooled together by accounting for the across-site variations in the mean and standard deviation values. The method is developed and tested in this paper using data from 227 catchments across Victoria and NSW. The application to ungauged catchments involves the development of prediction equations using generalised least squares regression for the mean and coefficient of variation of the annual maximum flood series as a function of catchment characteristics. An independent test shows that the PM provides quite reasonable design flood estimation in the study area for average recurrence intervals in the range of 20 to 200 years, with median relative error values (compared to at-site flood frequency estimates) in the range of 10% to 35%. The method is under further development, eg. consideration of the inter-station correlation in pooling the standardised data from the nearby stations and comparison of results with the rainfall-based methods. The method has the potential to derive regional flood prediction equations for major floods by pooling the flood data from all the Australian states.

Key Words:

• Floods
• major floods
• large floods
• regional floods
• design floods
• regional flood frequency analysis

Additional information

Notes on contributors

K Haddad

Khaled Haddad is undertaking his PhD research at the University of Western Sydney. He obtained his BEng (Honours) and MEng (Honours) in Hydrology from University of Western Sydney. His research is focused on regional flood frequency analysis, with a particular emphasis on uncertainty in regional flood models and the regional modelling of large to rare floods. Prior to starting his PhD, Khaled was a floodplain management engineer with Liverpool City Council, working on many different flood mitigation and water resources projects, which included revisions to Council’s stormwater and wetlands asset management plans. Khaled is also involved in the current revision of Book 4 in the Australian Rainfall and Runoff series.

A Rahman

Dr Ataur Rahman is a Senior Lecturer in Water and Environmental Engineering in the School of Engineering, University of Western Sydney. He has over 18 years experience in water industries, research and universities in Australia and southeast Asia. He obtained his BScEng degree from Khulna University of Engineering and Technology in Bangladesh, MSc (Hydrology) degree from National University of Ireland Galway, and PhD degree in Hydrology from Monash University in Australia. His research interest includes flood hydrology, urban hydrology and environmental risk assessment. He received the GN Alexander Medal from Engineers Australia in 2002. He has published over 100 research papers in water and environmental engineering field. He is acting as Project 5 Leader (Regional flood methods in Australia) in the forthcoming revised version of Australian Rainfall and Runoff.

P E Weinmann

Erwin Weinmann is currently a Research Associate of the Department of Civil Engineering, Monash University. He holds a Diploma in Agricultural Engineering and Surveying from the Swiss Federal Institute of Technology in Zurich, and a MEngSc from Monash University. His professional career spans over 40 years, including a number of roles in the Victorian water industry, teaching and research at Monash University, and professional consulting. His main interests are in flood estimation, flood risk management, and water resource assessment and management. As a Project Leader with the CRC for Catchment Hydrology, Erwin contributed to the development of a number of improvements in flood estimation methodology and practice. He is a corresponding member of Engineers Australia’s National Committee on Water Engineering, and heavily involved in the current revision of Australian Rainfall and Runoff.