One of the failure mechanisms of a breakwater is overtopping. Overtopping is defined as the amount of water passing over the crest of the structure per unit of time, in practice the discharge is often expressed per meter width of the breakwater as q [l/s/m].
Warning
The specific discharge per meter width, q, must be given in l/s/m, this is automatically converted to m3/s/m
The EurOtop manual is the result of extensive research and experimental studies on overtopping. All formulas in this module can be found in the second edition of this manual. The following structures are defined: coastal dikes, rubble mound breakwaters, vertical walls and vertical composite walls
Rubble mound breakwaters are characterized by a core with some porosity or permeability, covered by a sloping porous armour layer consisting of large rock or concrete armour units (for example Xbloc). However, the formula for coastal and river dikes can be used for a wider range of slopes, and therefore allows for more flexible input parameters. Since the formula for a rubble mound breakwater is a simplified case of the coastal or river dike, the formula for the dike is implemented. The definitions of the variables are presented in Figure 10.1.
The general formula for the average overtopping discharge on a slope (dike, levee, embankment) implemented is the mean value approach (EurOtop, 2018). EurOtop (2018) advises against the use of a mean value approach for design or assessment purposes. Instead, EurOtop (2018) advises to increase the average discharge by one standard deviation for a design or assessment. Therefore, 1 is the default setting for the :pysafety parameter.
breakwater.core.overtopping.rubble_mound
The influence of roughness elements, oblique wave attack, berms, etc. are taken into account by introducing influence factors
breakwater.core.overtopping.gamma_f
breakwater.core.overtopping.gamma_beta
Note
The formulas for γb, γv, γ* have not yet been implemented. These must thus be computed by hand.
The vertical and composite vertical walls are comparable structure, the difference between is the depth in front of the vertical wall. A composite vertical wall is fronted by a berm or toe mound below the water level, whereas a vertical wall is not fronted by such a berm, in that case d = h. In figure 10.2 a definition sketch of both structures is presented.
More than one equation have been derived to compute the overtopping discharge, or crest freeboard. Therefore, a general formula is implemented which automatically classifies the structure in order so that the correct formula is used.
The general formula is an implementation of the decision chart from EurOtop (2018). In figure 10.3 the implemented decision chart is depicted with the references to the individual formulas.
Figure 10.3: decision chart for prediction of overtopping discharge for a vertical or composite vertical wall
breakwater.core.overtopping.vertical
breakwater.core.overtopping.vertical_deep
breakwater.core.overtopping.vertical_no_breaking
breakwater.core.overtopping.vertical_normal
breakwater.core.overtopping.vertical_low
breakwater.core.overtopping.composite_normal
breakwater.core.overtopping.composite_low