Potentials and limitations of 1D, 2D and coupled 1D-2D flood modelling in HEC-RAS

Sammanfattning: Hydraulic models can be used to predict the consequences of flooding events. In this project, three hydraulic models were constructed using the software HEC-RAS, and compared through a case study on Höje river catchment. The models include (i) a 1-dimensional (1D) model, where river and floodplain flow is modeled in 1D, (ii) a coupled 1D-2D model, where river flow is modeled in 1D and floodplain flow is modeled in 2D, and (iii) a pure 2D model, where river and floodplain flow is modeled in 2D. Important differences between data requirements, pre-processing, model set-up and results were highlighted and summarized, and a rough guide that may be used when deciding the appropriate type of model for a project, was presented. In addition, the sub-grid technique used in 2D HEC-RAS modelling was studied by investigating the influence of computational mesh structure and coupling between 1D and 2D areas. The results showed that all three models could successfully reproduce a historic flooding event. The 2D and 1D-2Ds model could also provide more detailed information regarding flood propagation and velocities on the floodplain. The results from the 2D mesh analysis show that model result is very sensitive to mesh alignment along barriers. In rural floodplains with clear barriers, computational cell alignment is more important than computational cell size. With regards to the 1D-2D model, the results showed that the parameters describing the coupling between the 1D and 2D domain have large impact on model results.