The need for large-scale and regional probabilistic simulations means that two-dimensional (2D) inundation models are still limited by computational requirements. In addition to parallelisation and physical process simplification, attempts to reduce runtimes typically involve coarsening the computational mesh, which can smooth important topographic features and hence limit accuracy. This paper presents a new 2D flow model that uses an enhanced diffusion-wave algorithm, and incorporates sub-element topography in a computational mesh that adapts to the terrain features. The model utilises a fine topographic resolution without having to use a fine computation mesh, and so achieves fast computational runtimes. The model has been tested against the UK Environment Agency's 2D benchmarking tests, and even though the model is designed to operate at larger spatial scales than those in the benchmarking tests, it is shown to provide comparable accuracy relative to a selection of conventional 2D models, at significantly faster computational speeds. The model therefore has the potential to offer a step change in performance of large-scale probabilistic flood mapping and systems flood risk analysis modelling.

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Risk analysis models of fluvial and coastal flood systems have been in use for over a decade. They have been applied to support a wide range of flood risk management decisions, including long term strategic planning and shorter term asset management. Models that are currently applied in practice make a number of simplifying assumptions. The development of a new model that offers a major improvement over these methods is described. The new model incorporates: a unique dynamic 2D inundation model that captures sub-mesh element topography (RFSM EDA); a new computationally efficient model of embankment breach growth (AREBA) and extends the range of consequences considered to include the loss of life. The model has been applied on a pilot site to demonstrate its capabilities. A flood system risk analysis model with dynamic sub-element 2D inundation model, dynamic breach growth and life-loss

Quantified models of flood risk that incorporate an explicit representation of the performance of flood defence infrastructure are becoming an increasingly important component of efforts to manage flood risk. The models have been applied to support a wide range of decisions, including long-term strategic planning, assessment of investment needs and shorter-term asset management. The model currently applied in practice by the Environment Agency in England and Wales makes a number of simplifying assumptions to achieve computationally practical run-times. One of these simplifications relates to the volume-based flood-spreading algorithm that is applied. This paper describes the implementation of a new time-based inundation model within the existing risk analysis modelling approach. The new inundation model offers a significant increase in the representation of the physical processes within the flood simulation component of the risk analysis model. It also offers new outputs in terms of estimates of maximum depths and flood velocities. Velocities are known to be an important factor in flood-related fatalities. A simplified method to estimate life-loss has been combined with new output from the improved inundation model to illustrate how estimates of risk to life could be provided.