Assessing the contribution of precipitation to urban flood inundation using a hydraulic modelling approach

Abstract

Improving the capacity to model urban flood inundation was identified by Wheater (2002) as a key priority within contemporary flood risk science. Although an increasing emphasis has been placed upon urban environments within flood modelling studies, current approaches remain somewhat rooted within the context of rural areas. This has begun to be addressed through the development of model codes specifically designed for application to urban flooding problems (Yu and Lane, 2006a, Bates et al., 2010). However studies of urban flooding have thus far failed to address the potential importance of rainfall, which is hypothesised to attain a greater significance within urban environments due to the pre eminence of impermeable land cover (Hall, 1984). This is particularly relevant in the light of recent increases in pluvial flooding (Pitt, 2007). Accordingly, this study provides the first attempt to include rainfall within a hydraulic flood inundation model. An improvised representation of rainfall has subsequently been developed using a negative manipulation of the infiltration and evaporation terms within a simple storage cell model, LISFLOOD-FP. This has facilitated testing of the potential significance of rainfall to flooding within urban areas, with specific reference to the flood event which occurred on 25th-26th June 2007 in Sheffield. The proliferation of uncertainty from various sources has necessitated analysis with respect to bulk contribution of precipitation here. Addition of rainfall to the parameterisation of the model has lead to an increase in model performance from F=0.56 to F=0.60, suggesting that precipitation provided a modest but significant contribution to the aforementioned flood event. The findings of this modelling study are in agreement with several independent assessments of the June 2007 flooding within Sheffield (Dickson and Berry, 2008, Environment Agency, 2007). Moreover, this study illustrates that the utilisation of new, more efficient modelling tools (Bates et al., 2010), may facilitate further comprehensive assessment of the potential contribution of rainfall to urban flood inundation