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Hydrology Research Vol 42 No 4 pp 239–249 © IWA Publishing 2011 doi:10.2166/nh.2011.117

Relationships between rainfall intensity, duration and suspended particle washoff from an urban road surface

Ian M. Brodie and Prasanna Egodawatta

Faculty of Engineering and Surveying and Australian Centre for Sustainable Catchments, University of Southern Queensland, West Street, Toowoomba, Queensland 4350, Australia E-mail: brodiei@usq.edu.au
School of Urban Development, Queensland University of Technology, GPO Box 2434, Brisbane 4001, Australia


A basic understanding of the relationships between rainfall intensity, duration of rainfall and the amount of suspended particles in stormwater runoff generated from road surfaces has been gained mainly from past washoff experiments using rainfall simulators. Simulated rainfall was generally applied at constant intensities, whereas rainfall temporal patterns during actual storms are typically highly variable. This paper discusses a rationale for the application of the constant-intensity washoff concepts to actual storm event runoff. The rationale is tested using suspended particle load data collected at a road site located in Toowoomba, Australia. Agreement between the washoff concepts and measured data is most consistent for intermediate-duration storms (duration <5 h and >1 h). Particle loads resulting from these storm events increase linearly with average rainfall intensity. Above a threshold intensity, there is evidence to suggest a constant or plateau particle load is reached. The inclusion of a peak discharge factor (maximum 6 min rainfall intensity) enhances the ability to predict particle loads.

Keywords: buildup-washoff; particle washoff; road runoff; stormwater; suspended solids

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