A SWOT analysis of hydrodynamic models with respect to simulating breaching

Deriving the bed shear stresses from hydrodynamic models in breach models is challenging due to the continuous changing hydraulic head over the breach in combination with horizontal and vertical flow contractions, and the continuous rapidly changing breach geometry. Three stages can be distinguished in breach flows. Stage 1 initiates when the embankment starts to overflow and is characterized by flows over the embankment crest and down the landside slope. Stage 2 initiates when the landside slope has retreated towards the waterside slope. The hydraulic head increases rapidly and the flow contracts both horizontally and vertically resulting in a fully 3-dimensional flow. During Stage 3 a full breach has developed and the flow contracts mainly horizontally. This paper presents a SWOT analysis of flow modelling methods applied in breach models to derive the bed shear stresses. The paper shows that for a number of cases analytical methods are more accurate than numerical methods due to the fact that they give a more accurate description of the shear stresses on the embankment surface, whereas for some numerical methods errors are found of the order of 50%.