On the correlation between earthen levees' vulnerability to seepage and flood events probability of occurrence

Earthen levees are one of the main structural measures against flooding in floodplain areas; however, these structures can fail due to different mechanisms. From the risk point of view, the construction of embarkments might paradoxically increase the overall risk because of a general decrease in flood hazard perception by the exposed population and urban planner (Castellarin et al., 2011). For this reason, ample research has been focused on studying the physical process affecting the levees during a flood event, such as overtopping and seepage/piping (Deverel et al., 2016; Palladino et al., 2019). Specifically, the piping process is very hazardous because it is not openly visible and, therefore, is hard to identify before the failure. Nevertheless, evaluating the vulnerability to seepage for different flood events affecting the earthen levee is fundamental to support territorial planning and risk management in quasi-real-time. In this context, the present work proposes a procedure to calculate the correlation between the probability of levee failure due to seepage process and the probability of occurrence of the flood event affecting the embankment. The vulnerability to seepage is quantified by identifying the saturation line location in the levee through the a two-dimensional numerical model SEEP/W. The analysis is carried out for flood events characterized by a different probability of occurrence estimated by applying a procedure based on stochastic generation of precipitation and temperature time series and continuous hydrological modelling. The proposed procedure is applied to an experimental levee located along the Tatarena stream, in central Italy. The results show that, as expected, the vulnerability increases while the magnitude of the flood increases, i.e. the probability of occurrence decreases, with increments in the range 5-10% for flood duration between 12-24 hours. In particular, 48 hours lasting flood waves are identified as the ones producing a huge increase of the levee vulnerability that is found to rise from 35% to 75%.

Castellarin, A., Di Baldassare, G., Brath. (2011). A floodplain management strategy for flood attenuation in the River Po. River Res. Appl. 27 (8), 1037–1047.

Deverel, S. J, Bachand, S., Brandenberg, S. J, Jones, C. E, Stewart, J. P, & Zimmaro, P. (2016). Factors and Processes Affecting Delta Levee System Vulnerability. San Francisco Estuary and Watershed Science, 14(4). doi: https://doi.org/10.15447/sfews.2016v14iss4art3.

Palladino M.R., Barbetta S., Camici S., Claps P., Moramarco T. (2020). ‘Impact of animal burrows on earthen levee body vulnerability to seepage’, J Flood Risk Management.2020;13 (Suppl. 1): e12559, https://doi.org/10.1111/jfr3.12559.