A copula-based model to describe the uncertainty of overtopping variables on mound breakwaters

A copula-based model to describe the uncertainty of overtopping variables on mound breakwaters

Mares Nasarre, P. (TU Delft Hydraulic Structures and Flood Risk)
van Gent, M.R.A. (TU Delft Coastal Engineering; Deltares)
Morales Napoles, O. (TU Delft Applied Probability)

2024

Rising sea levels caused by climate change are increasing the risk of overtopping on coastal structures. Moreover, there is a growing societal concern about the visual impact of these structures, which leads to the lowering of their crest freeboards. In previous studies, safety during overtopping events was assessed considering the overtopping layer thickness (h_c), the overtopping flow velocity (u_c) and the individual wave overtopping volume (V). Existing models in the literature to estimate h_c, u_c and V on mound breakwater crests are mainly deterministic, involve a chain of successive estimations leading to accumulated errors and/or do not account for the dependencies between h_c, u_c and V. This study proposes a model to describe the joint probability distribution of h_c, u_c and V based on bivariate copulas. Experimental data from small-scale 2D physical tests conducted on mound breakwaters with three armor layers (single-layer Cubipod®, and double-layer cubes and rocks) in depth-limited breaking wave conditions on two mild bottom slopes and dimensionless crest freeboards between 0.33 and 3.20 is used. Lognormal distribution functions are proposed for each variable and a multivariate dependence model is developed through a one-tree vine-copula. The parameters of this model are quantified directly using wave characteristics and the structure geometry minimizing the accumulated errors in the final predictions. The application of the model is illustrated by computing the probability of not fulfilling at least a tolerability limit for one of the studied variables (OR probability). The OR probability is computed both considering the dependence and assuming independence between the variables and a significant difference is obtained. It is concluded that by accounting for the multivariate dependence between the variables, it is possible to reduce the crest freeboard and, thus, achieve a more economic design within the required safety level.

Copula
Dependence
Mound breakwater
Overtopping
Overtopping flow velocity
Overtopping layer thickness
Overtopping volume
Probability
Uncertainty

http://resolver.tudelft.nl/uuid:0db46967-fec3-4fe3-91d8-a442fa9797ba

https://doi.org/10.1016/j.coastaleng.2024.104483

0378-3839

Coastal Engineering, 189

Institutional Repository

journal article

© 2024 P. Mares Nasarre, M.R.A. van Gent, O. Morales Napoles