A 2D saturated–unsaturated unsteady-flow numerical study has been carried out to analyze the behavior of levees stressed by flood events. The investigation has involved: i) simulation of the seepage process in a simplified levee over a long period of river flows; ii) the use of a synthetic design hydrograph to be utilized as an alternative to a long-term history of river stages and iii) the influence of the unsaturated parameters on the maximum saturation depth in the levee soil. The results of the analysis show that the statistical properties of the maximum annual phreatic levels are different from those of the corresponding river levels, and that the tested synthetic design-hydrograph is able to guarantee a well-balanced, conservative margin. The analysis shows that the role of the unsaturated zone is also very important. Furthermore, a comparison of the piezometric levels, computed by means of the numerical model, with those computed through simplified solutions, shows that the latter ones may not be conservative.
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