Design Flood Estimation in Ungauged Catchments: A Comparison Between the Probabilistic Rational Method and Quantile Regression Technique for NSW

Abstract

Design flood estimation for ungauged catchments is often required in hydrologie design. The most commonly adopted regional flood frequency analysis methods used for this purpose include the index flood method, regression based techniques and various forms of the rational method. This paper first examines the similarities and differences between the probabilistic rational method (PRM) (the currently recommended method for Victoria and eastern NSW in Australian Rainfall and Runoff) and the generalised least squares (GLS) based quantile regression technique (QRT). It then uses data from 107 catchments in NSW to compare the performance of these two methods. To make a valid comparison, the same predictor variables and data set have been used for both methods. Based on one-at-a-time and split sample validation tests and a range of evaluation statistics, it has been found that the GLS-based QRT performs better than the PRM. The particular advantage of the QRT is that it does not require a contour map of the runoff coefficient as with the PRM. The QRT also offers potential for improvement through inclusion of additional predictor variables. The QRT can also be integrated with the region of influence approach, where a region can be formed around an ungauged catchment by selecting an “appropriate number” of neighbouring gauged catchments. Overall, the QRT offers much greater flexibility and potential in terms of error analysis and further development as compared to the PRM.

Key Words:

• Ungauged catchments
• rational method
• regression
• floods
• regional flood frequency analysis

Additional information

Notes on contributors

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.

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.

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 BScEng degree from Bangladesh University of Engineering and Technology. His research interest includes flood hydrology and environmental engineering.

G Kuczera

George Kuczera is Professor of Water Engineering in the School of Engineering at the University of Newcastle. He obtained his PhD from Harvard University in 1980 and spent 5 years in the water industry before joining the University of Newcastle in 1986. His research interests cover a range of areas including Bayesian calibration and testing of hydrologic models, stochastic hydrology and risk assessment, water resource systems analysis, and multi-criteria optimisation. He has published extensively on these topics, and has developed a range of software for use in research, education and industry. George has been recipient of the GN Alexander and Warren Medals from the Engineers Australia, and has served as Chairman of the National Committee on Water Engineering.

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.