Simulation of Levee Breach Using Delft Models: A Case Study of the Drava River Flood Event

Abstract

This paper focuses on the modelling of a real-world flood event and levee breach by using Delft3D model and a newly developed Delft-Flexible Mesh (Delft3D-FM) model coupled with feedback control module. The study area is located at the bordering section of the River Drava between Slovenia and Croatia around the Hydro Power Plant Formin. The major flood event on the River Drava in November 2012 caused significant damages in Slovenia and Croatia. During flood event, the levee breaches occurred at several locations around the Formin HPP. Two different numerical models were developed to simulate propagation of the November 2012 flood event in order to replicate the corresponding water levels and discharges on the complex river system with the HPP Formin. The Delft3D and Delft3D-FM models were developed to simulate the flood and levee breach as well as to evaluate the modelling approach by comparing curvilinear and unstructured numerical solvers. Delft3D-FM was also coupled with the feedback control module. The numerical model results were compared to the measured water levels and discharges. The results of Delft3D and Delft3D-FM models were intercompared as well. The levees in the Delft3D-FM model were parameterised as line elements with defined sill level of the levee and the resistance valid for large-scale model when grid size is relatively larger than width of the levee. Feedback control module was used to replicate the levee breach as lowering of the sill at the location of breaches. In Delft3D, levees were modelled as a part of bathymetry which was not changed at the time of breach. It was simply modelled by using discharge extraction–insertion functionality. Delft3D-FM successfully confirmed the time of levee breaches. The utilisation of a feedback control tool in Delft3D-FM allowed the simulation of levee breaches in a more realistic way than in the Delft3D model. Besides, our explorative study shows that the Delft3D-FM computations were up to 4 times slower than Delft3D for the same number of computational points. However, the unstructured grid (flexible mesh) model allows for a substantial reduction of computational points on complex geometries like current model domain. This resulted in 2.5 times faster computational time for Delft3D-FM model when compared to Delft3D simulation time for the river Drava study while preserving the same accuracy as well as with improved physics of the flood, time of the rise of the flood wave and levee breach simulation.