The catastrophe of the Niedów dam – the dam break causes, development and consequences

Abstract. Due to extreme rainfalls in 2010 in the Lusatian Neisse river catchment, a flood event with a return period of over 100 years took place leading to the failure of the Niedów dam. The earth type dam was washed away with a result of a rapid release of nearly 8.5 million m³ of water volume and flooding of the downstream area with substantial material losses. The paper analyses the conditions and causes of the dam’s failure, while special attention is given to the mechanism and dynamics of the compound breaching process. Several empirical formulas for the dam breach prediction are tested with regards to their usefulness in assessing breach dimensions and outflow peak discharge. The paper also describes a numerical approach to simulate the flood propagation downstream the dam with the use of a two-dimensional hydrodynamic model. Considering the specific local conditions and available data set, an iterative, reversed solution of the unsteady state problem is made. This approach enabled to deliver realistic flood propagation estimates, verification of the dam breach outflow, and several important answers on the dam failure consequences.