Abstract
Abstract. The Flood Frequency Analysis (FFA) concentrates on probability distribution of peak flows of flood hydrographs. However, examination of floods that haunted and devastated the large parts of Poland lead us to revision of the views on the assessment of flood risk of Polish rivers. It turned out that flooding is caused not only by the overflow of the levee crest but also due to the prolonged exposure to high water on levees structure causing dangerous leaks and breaches that threaten their total destruction. This is because the levees are weakened by long-lasting water pressure and as a matter of fact their damage usually occurs after the culmination has passed the affected location. The probability of inundation is the total of probabilities of exceeding embankment crest by flood peak and the probability of washout of levees. Therefore, in addition to the maximum flow one should also consider the duration of high waters in a river channel. In the paper the new two-component model of flood dynamics: "Duration of high waters–Discharge Threshold–Probability of non-exceedance" (DqF), with the methodology of its parameter estimation was proposed as a completion to the classical FFA methods. Such a model can estimate the duration of stages (flows) of an assumed magnitude with a given probability of exceedance. The model combined with the technical evaluation of the probability of levee breaches due to the duration (d) of flow above alarm stage gives the annual probability of inundation caused by the embankment breaking. The results of theoretical investigation were illustrated by a practical example of the model implementation to the series of daily flow of the Vistula River at Szczucin. Regardless of promising results, the method of risk assessment due to prolonged exposure of levees to high water is still in its infancy despite its great cognitive potential and practical importance. Therefore, we would like to point out the need for and usefulness of the DqF model as complementary to the analysis of the flood peak flows, as in classical FFA. The presented two-component model combined with the routine flood frequency model constitutes a new direction in FFA for embanked rivers
Highlights
The most popular way of flood protection in Poland is the embankment of the rivers
The aim of this study is to introduce formal aspects of the duration–flow–frequency (DqF) modelling in stationary and non-stationary conditions, to use it to assess the inundation risk due to the levees breach and to combine it with the annual maximum (AM) flow model to get the cumulative probability of inundation
Finding that flood persistence is a factor of flood hazard for embanked rivers, Bogdanowicz et al (2008) modified the above model redefining Q as the annual maximum flow discharge (Qd) which is continuously exceeded during the period d, wherein the d variable is still treated as a deterministic value (Fig. 3b)
Summary
A consequence of this passive way of protection is that floods in Poland occur mostly due to levee breach or to flow over the crest of dikes. Warning and alarm stages are assigned to the places where water levels are observed, to the hydrological stations, their determination procedures as well as other inundation risk characteristics take into account, inter alia, the elevation of the embankment system for the whole river reach. The aim of this study is to introduce formal aspects of the duration–flow–frequency (DqF) modelling in stationary and non-stationary conditions, to use it to assess the inundation risk due to the levees breach and to combine it with the AM flow model to get the cumulative probability of inundation. To illustrate the proposed way of inundation risk assessment the case study for the Szczucin gauging station at the Vistula River (Southern Poland) is presented
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
