A Practical Approach To Floodplain Mapping For Large-scale Catastrophe Models

Catastrophe models often cover large geographic areas spanning multiple countries or, in the case of flood models, entire watersheds. Models must be sufficiently detailed to accurately account for hydrologic variation, which is notably challenging when the modeled region is large. This is particularly true for flood models, which require a highly detailed dataset, usually derived from a digital terrain model (DTM), for reliable floodplain mapping. For one-dimensional (1D) hydraulic models, the floodplain mapping approach tends to yield flat surfaces often resulting in artefacts and inconsistencies near river confluences. Because flood extent is limited by the length of cross-sectional lines along the floodplain, these flat surfaces tend to drop sharply when the simulation reaches a flat delta. The methodology applies kinematic and diffusion wave equations in a simplified manner, using water elevation points as internal boundary conditions. This methodology is particularly suitable for modeling large domains since it produces accurate results but requires much less computational time than a 2D model.