Please cite: Chen AS, Djordjevic S, Leandro J, Savic DA. (2010) An analysis of the combined consequences of pluvial and fluvial flooding, Water Science and Technology, 62(7), 1491-1498, DOI:10.2166/wst.2010.486. An analysis of the combined consequences of pluvial and fluvial flooding A. S. Chen*, S. Djordjević*, J. Leandro** and D. A. Savić* *Centre for Water Systems, School of Engineering, Computing and Mathematics, University of Exeter, North Park Road, EX4 4QF Exeter, U.K. (E-mail:a.s.chen@ex.ac.uk; s.djordjevic@ex.ac.uk;d.savic@ex.ac.uk) **Department of Civil Engineering, Faculty of Science and Technology, Rua Luís Reis Santos - Pólo II University of Coimbra, 3030-788 Coimbra, Portugal(E-mail:(E-mail:leandro@dec.uc.pt ) ABSTRACT Intense rainfall in urban areas often generates both pluvial flooding due to the limited capacity of drainage systems, as well as fluvial flooding caused by deluges from river channels. The concurrence of pluvial and fluvial flooding can aggravate their (individual) potential damages. To analyse the impact caused by individual and composite type of flooding, the SIPSON/UIM model, an integrated 1D sewer and 2D overland flow was applied to numerical modelling. An event matrix of possible pluvial scenarios was combined with hypothetic overtopping and breaching situations to estimate the surface flooding consequences in the Stockbridge area, Keighley (Bradford, UK). The modelling results identified different flooding drivers in different parts of the study area and showed that the worst scenarios resulted from synthesised events. KEYWORDS Urban inundation; integrated modelling; pluvial and fluvial flooding; sewer drainage. INTRODUCTION The continuous downpour within a basin often causes huge floods around river channels, as well as localised flooding in urban areas. When torrent flushes into rivers and raises the water level, which exceeds the crest elevation of banks, the flow spills out of channels toward floodplains and results in fluvial flooding. On the other hand, modern cities usually rely on drainage systems to convey surface runoff produced by rainfall. Nevertheless, the design capacity restricts the maximum discharge that a drainage system can cope with such that pluvial flooding takes place when heavy storm occurs. The time scale and the flood magnitude of a fluvial event significantly differ from those of a pluvial event. The former typically lasts for days, or even weeks, and have widespread influences on floodplains along rivers. On the contrary, pluvial flooding seldom lasts for more than one day, and only affects local regions. To estimate the consequences of flooding in urban areas, integrated numerical models that include various system components are emerging to describe the flooding process more accurately. However, due to the above-mentioned distinction most studies usually focus on one of these two types of flooding and not on their combined effect. For fluvial flood modelling, combined 1D channel and 2D overland flow models are widely applied to simulate flow dynamics between rivers and floodplains (Bradbrook et al., 2004; Horritt and Bates, 2002; Lin et al., 2006; Wongsa and Shimizu, 2001). Approaches of this type often route separately the flow in the river and the one on overland by solving 1D and 2D hydraulic equations, respectively, linking both components by weirs or pumps. The function of sewer drainage is often neglected. Regarding pluvial flooding studies, the 1D/1D dual drainage models were developed to simulate flow interactions among sub-catchments, and between the above ground and the below ground systems (Djordjević et al., 1999; Nasello and Tucciarelli, 2005). Natural flow paths and retention basins are regarded as the major drainage system for routing the surface flow, while sewer