Examination of the exponential wash-off function using experimental data

Abstract

The standard exponential wash-off function has been widely adopted in urban stormwater quality models and tested in many studies of sediment wash-off experiments. There is neither sufficient information on the wash-off coefficients for other types of pollutant nor a good mathematical interpretation that accounts for the effects of surface features on wash-off processes. This study assesses the standard exponential wash-off function using experimental data on the wash-off of various types of pollutant. In-situ wash-off experiments using simulated rainfalls were conducted in typical urban areas with various landuse. Experimental data from the literature were also analysed to support the examination. Mass balance requirement was always applied as a criterion in the experimental data analysis and wash-off model examination. The experimental results indicate that wash-off processes of organic pollutants (BOD₅), nitrate (NO₃), total oil and grease (TOG), total petroleum hydrocarbon (TPH) and coliform stochastically comply with the standard exponential function.

Highlights

• In-situ wash-off experiments were conducted for BOD₅, NO₃, TOG, TPH, coliforms and TSS.

• Wash-off coefficients of BOD₅, NO₃, TOG, TPH, coliforms and TSS are identified stochastically.

• Mass balance requirement is introduced to examine the mathematical interpretations of wash-off models.

• An improved exponential wash-off function with more input parameters is suggested.

KEYWORDS:

• Non-point source pollution
• stormwater quality
• wash-off function
• wash-off coefficient

Acknowledgements

This project is to develop the most cost-effective strategy for the pollution control of both point and non-point sources to the Brunei River. The authors sincerely thank our colleague, Rozeana binti Hj Md. Juani, for her assistance in conducting laboratory tests on the water samples in this study. Many thanks also to Prof Y. Xiao, Prof Y. Li, Dr O. Wani and Prof A. Goonetillete for sharing their publications.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was conducted under the research project granted by the Brunei Research Council RNK10 (2012-2017)-1022-1.

Notes on contributors

Zhenren Guo

Dr. Zhenren Guo is a professor at China's South China University of Technology (SCUT) and a former professor at Brunei Darussalam's Universiti Teknologi Brunei (UTB). His research interests cover aquatic environments, wastewater treatment, and hydraulics. He has published more than 100 papers and five books.

Nabiihah Abd Salam

Nabiihah Abd Salam is a civil servant from the Energy Department in the Prime Minister's Office, who is currently overseeing oil and gas downstream projects in Brunei. She graduated from Universiti Teknologi Brunei (UTB) with a master's degree, majoring in Civil Engineering. Prior to receiving her Master's award in September 2019, she served as a research assistant to continue working on the Brunei Grant research project under the National Development Plan funded by the Brunei Research Council. In her spare time, she enjoys outdoor activities and travelling.

Hj Mohd Khairuldini Hj Metali

Hj Mohd Khairuldini bin Hj Metali is a graduate member of The Institution of Civil Engineers (GMICE). He is an engineer, having graduated from Queen’s University of Belfast, Northern Ireland, United Kingdom, with a Master of Engineering in Civil Engineering. He worked as a Technical and Structural Engineer at Goldmyne Hardware Sdn Bhd for nearly four years. Then, he worked as a Civil and Structural Engineer at Baharuddin Associates and Consultancy Engineering Sdn Bhd for nearly one year before being permanently employed by the Brunei Government as a water and Structural Engineer at the Department of Water Services, Public Works Department. As a Water and Structural Engineer, he is responsible for the maintenance and operation of the water tank reservoir to ensure that the treated water is continuously supplied to the public.

Asmaal Muizz Sallehhin Hj Mohammad Sultan

Asmaal Muizz Sallehhin bin Hj Mohammad Sultan is a Senior Lecturer in the Civil Engineering Programme Area, Faculty of Engineering, Universiti Teknologi Brunei (UTB). He completed his B.Sc. degree from the University of Salford and M.Sc. from Cardiff University, UK. His research interest includes water and the environment.

Shahriar Shams

Dr Shahriar Shams is currently working as an Assistant Professor in Civil Engineering Programme Area, Faculty of Engineering, Universiti Teknologi Brunei (UTB) since December 2012. Before joining UTB, he worked as an Assistant Professor in the Department of Civil and Environmental Engineering at the Islamic University of Technology (IUT), a subsidiary organ of the OIC. He has published over 80 refereed journals and conference papers, including book chapters and technical reports. His research interest includes Integrated Water Resources Management, Climate Change and Solid Waste Management.