Régionalisation of Skew for Flood Frequency Analysis: A Case Study for Eastern NSW

Abstract

In flood frequency analyses, skew plays an important role in characterising the tails of the flood frequency distributions for which a three-parameter distribution like Log-Pearson Type 3 (LP3) is often preferred over two-parameter distributions. For fitting the LP3 distribution to a station’s data, an estimation of skew is needed. Since the length of streamflow data is limited for the majority of stations in Australia, the at-site estimation of skew is highly uncertain. To overcome this problem, the use of regional skew has been advocated, however, this has not been well investigated with Australian data. This paper presents a Bayesian generalised least squares (B-GLS) regression approach to regionalise the skew coefficient for eastern NSW. It has been found that the B-GLS regression approach is quite capable of providing stable estimation of skew, which is equivalent to an at-site skew estimator based on over 90 years of data. The results of this study suggest that the B-GLS model can provide an avenue to develop a regional skew map for Australia using the national database being prepared as a part of the on-going revision of Australian Rainfall and Runoff.

Key Words:

• Skew
• GLS regression
• food frequency analysis
• regional flood frequency analysis
• regionalisation;
• moments
• floods

Additional information

Notes on contributors

K Haddad

Khaled Haddad is currently a PhD scholar at the University of Western Sydney, where he also obtained degrees in Civil Engineering and Masters of Engineering in hydrology. 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 a number of different flood mitigation and water resources projects, which included revisions to Council’s stormwater and wetland asset management plan. Khaled is heavily involved with the research work related to Project 5 Regional flood methods in Australia (Australian Rainfall and Runoff revision project).

M Zaman

M Zaman has been working as a Research Assistant in the School of Engineering, University of Western Sydney, since 2009. He is currently involved with the research work related to Project 5 Regional flood methods in Australia (Australian Rainfall and Runoff revision project). He has over 10 years’ experience in consulting engineering. He completed his BSc Eng degree from Bangladesh University of Engineering and Technology. His research interests include flood hydrology and environmental engineering.

A Rahman

Dr Ataur Rahman is a Senior Lecturer in Water and Environmental Engineering in the School of Engineering, University of Western Sydney, Australia. He has over 18 years’ experience in water industries, research and universities in Australia and southeast Asia. He obtained his BSc Eng 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 interests include flood hydrology, urban hydrology and environmental risk assessment. He received The GN Alexander Medal from the Institution of 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.