A Practical Approach To Floodplain Mapping
For Large-scale Catastrophe Models
Author(s)
I. Carnacina & A. Jemberie
Abstract
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 use of a two-dimensional (2D) model avoids these problems, but at
a high computational cost, and requires high quality terrain and bathymetry data.
This paper presents a new methodology for mapping floodplains using water
elevation points along a river network obtained from a 1D hydraulic model and a
DTM. The methodology applies kinematic and diffusion wave equations in
a simplified manner, using water elevation points as internal boundary conditions.
Several parameters control the expansion and smoothing algorithms that generate
realistic flood extent maps for different return periods. This methodology is
particularly suitable for modeling large domains since it produces accurate results
but requires much less computational time than a 2D model. In addition, because
the computation uses several source points per cross section, the flood extent is
not limited by the cross-sectional length, making this methodology appropriate for
levee breaches and in cases where river banks are not well defined and the crosssectional
geometry is derived from a DTM.
Keywords
risk assessment, flood, flood mapping, large scale model.
Related Book
Other papers in this volume
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