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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.