The inundation of the Ziltendorfer Lowland, a farmland polder with some villages, during the major flooding event in July 1997 in the Odra watershed, is simulated with the two-dimensional hydrodynamic model TRIM2D. Inflow and outflow through three consecutive embankment breaches make up a complex flow regime which governs the inundation and the water level in the Odra river. With reasonable assumptions for the dam breach genesis the inundation and depletion are simulated in good agreement with the observed flooding front positions. Simulations with a one-dimensional hydrodynamic model for “dam breach” and “no dam breach” scenarios confirm analytical considerations of an increase of the water level downstream in the main river for the “dam breach” scenario because of an outflow from the Ziltendorfer Lowland into the Odra river during the peak flooding period.