Evaluation of 1D and 2D numerical models for predicting river flood inundation

This paper reviews state-of-the-art empirical, hydrodynamic and simple conceptual models for determining flood inundation. It explores their advantages and limitations, highlights the most recent advances and discusses future directions. It addresses how uncertainty is analysed in this field with the various approaches and identifies opportunities for handling it better. The aim is to inform scientists new to the field, and help emergency response agencies, water resources managers, insurance companies and other decision makers keep up-to-date with the latest developments. Guidance is provided for selecting the most suitable method/model for solving practical flood related problems, taking into account the specific outputs required for the modelling purpose, the data available and computational demands. Multi-model, multi-discipline approaches are recommended in order to further advance this research field. This paper reviews state-of-the-art flood inundation models.It explores their advantages and limitations.It highlights the most recent advances and discusses future directions.It addresses how uncertainty is analysed and identifies opportunities for handling it better.

Flood inundation modelling

Southern Louisiana is characterized by low-lying topography and an extensive network of sounds, bays, marshes, lakes, rivers, and inlets that permit widespread inundation during hurricanes. A basin- to channel-scale implementation of the Advanced Circulation (ADCIRC) unstructured grid hydrodynamic model has been developed that accurately simulates hurricane storm surge, tides, and river flow in this complex region. This is accomplished by defining a domain and computational resolution appropriate for the relevant processes, specifying realistic boundary conditions, and implementing accurate, robust, and highly parallel unstructured grid numerical algorithms. The model domain incorporates the western North Atlantic, the Gulf of Mexico, and the Caribbean Sea so that interactions between basins and the shelf are explicitly modeled and the boundary condition specification of tidal and hurricane processes can be readily defined at the deep water open boundary. The unstructured grid enables highly refi...

A Basin to Channel-Scale Unstructured Grid Hurricane Storm Surge Model Applied to Southern Louisiana

Simple spatially-distributed models for predicting flood inundation: A review

High-resolution data obtained from airborne remote sensing is increasing opportunities for representation of small-scale structural elements (e.g. walls, buildings) in complex floodplain systems using two-dimensional (2D) models of flood inundation. At the same time, 2D inundation models have been devel-oped and shown to provide good predictions of flood inundation extent, with respect to both full solution of the depth-averaged Navier-Stokes equations and simplified diffusion wave models. However, these models have yet to be applied extensively to urban areas. This paper applies a 2D raster-based diffusion wave model to determine patterns of fluvial flood inundation in urban areas using high-resolution topog-raphic data. The aim of this paper is to explore the effects of spatial resolution upon estimated inundation extent and flow routing process. This is important as the complexity of urban surfaces is such that chang-ing data resolution may have a major effect upon surface representation and hence flow routing. Similarly, few applications to date have explicitly considered the timing of the inundation process. The model assumes that the prime source of the flood is fluvial: pluvial floods and floods associated with urban drainage systems are not addressed. The topographic data are based upon airborne laser altimetry (Li-DAR) obtained for the City of York, U.K. A series of image processing steps are used to pre-prepare the topographic data. A one-dimensional hydraulic model of the Ouse from Skelton (upstream of the city) through to Naburn Weir (downstream of the city) is used to provide estimates of flux from the river to the floodplain for a major flood inundation event (estimated to have a return period of greater than 100 years) in November 2000. Validation data were available in the form of inundation patterns obtained using aerial photography at a point on the falling limb of the flood event. Model response shows that even relatively small changes in model resolution have considerable effects on the predicted inundation extent and the timing of flood inundation. Timing sensitivity would be expected given the relatively poor representation of inertial processes in a diffusion wave model. Compared with previous work, sensitivity to inundation extent is more surprising and is associated with three connected effects: (1) the smoothing effect of mesh coarsening upon input topographical data; (2) poorer representation of both cell blockage and surface routing processes as the mesh is coarsened, where the flow routing is especially complex; and (3) the ef-fects of (1) and (2) upon water levels and velocities which in turn determine which parts of the floodplain the flow can actually travel to. The combined effects of wetting and roughness parameters can compen-sate in part for a coarser mesh resolution. However, the coarser the resolution, the poorer the ability to control the inundation process as these parameters not only affect the speed but also the direction of wet-ting. Thus, high resolution data will need to be coupled to more sophisticated representation of the inun-dation process in order to obtain effective predictions of flood inundation extent. This is explored in a companion paper.

Urban fluvial flood modelling using a two‐dimensional diffusion‐wave treatment, part 1: mesh resolution effects

TELEMAC: A new numerical model for solving shallow water equations

TELEMAC modelling system: an overview

Morphodynamic modeling using the Telemac finite-element system

La rupture du barrage de Malpasset a eu lieu dans le sud de la France en 1959 et a cause 421 victimes. Cet exemple de rupture totale d'un barrage-voute en fait un cas exceptionnellement interessant pour tester et valider les logiciels. Dans le passe, un modele reduit et un calcul unidimensionnel ont ete realises pour reproduire l'accident. Cet article presente des calculs bidimensionnels de la ruptute du barrage de Malpasset realises avec TELEMAC-2D. Les resultats sont meilleurs que ceux du modele unidimensionnel dans les coudes serres de la riviere ainsi que lorsque l'onde debouche dans la plaine littorale. L'etude conclut que les simulations bidimensionnelles d'ondes de crues sont possibles sur des domaines de plusieurs dizaines de kilometres de longueur.

Malpasset dam-break revisited with two-dimensional computations

The evolution of laws on dam safety in France is briefly described. Most simulation studies for such problems are currently attempted using one-dimensional models, and we investigate here the possibility of moving to two-dimensional simulations. To date, these have been constrained by lack of available computational power. Parallel processing is an obvious solution, however, to date, an efficient parallel processing method that does not require major software recoding has proved elusive. Domain-decomposition is identified as being capable of overcoming these problems, as it allows pre-existing software to be adapted to run on clusters of supercomputer processors, workstations or PCs. The development of this new parallel method is outlined and its accuracy and efficiency tested in terms of the TELEMAC-2D model applied to the Malpasset dam break accident, which occurred in 1959 in the south of France. After a discussion of the data available, a sensitivity study is performed to evaluate some physical parameters in the equations, mainly the diffusion coefficient and the bottom friction. The friction appears to be the most important. A discrepancy of 3·4% on the wave celerity is obtained between the model and field observations for a number of locations where the arrival time of the flood wave is perfectly known. The efficiency of different scalar and parallel machines is assessed. The study concludes that 2-D simulations of flood waves are already possible on domains with a length of some 10 s of kilometres. Larger domains (100 to 400 km) are also within reach with supercomputers, or with parallel architectures. Copyright © 2000 John Wiley & Sons, Ltd.

Jean-Michel Hervouet

Papers

TELEMAC: A new numerical model for solving shallow water equations

TELEMAC modelling system: an overview

Morphodynamic modeling using the Telemac finite-element system

Malpasset dam-break revisited with two-dimensional computations

A high resolution 2-D dam-break model using parallelization