Individual Overtopping Events at Dikes

Abstract

Recently, formulae have been derived for maximum flow depths and velocities on the crest and inner slope of dikes or levees at wave overtopping. Two independent physical model test programs in different wave flumes showed, however, a large difference in the results. The present paper clarifies this discrepancy and shows that the empirical coefficients are dependent on the gradient of the outer slope. Subsequently, a formula for the overtopping time was created, based on the difference between fictive wave run-up and crest freeboard. The overtopping time appeared not to be a function of the outer slope. The variation of flow depth and velocity in time can be approached with a linear function.

Flow Depths and Velocities at Crest and Landward Slope of a Dike, in Theory and With the Wave Overtopping Simulator

“…The EurOtop Manual (2007) also gives the equations. Bosman et al (2008) investigated this discrepancy and discovered that the difference in predicted flow depth could possibly be explained by the different seaward slopes (1:4 and 1:6) used by the different authors. He used a sinα to combine the equations.…”

“…Bosman et al (2008) used a sinα in his equations (Equations 3 and 4), which for fairly gentle slopes is almost equal to the more often used cotα. The extra data by the Flowdike project showed that the flow depth h 2% could not be described by Equation (3) as the data for the 1:3 slope fell in between the data for the 1:4 and 1:6 slope.…”

Spatial distribution of wave overtopping water behind coastal structures

“…Therefore, the velocity changes along the dike crest can be ignored. The horizontal velocity at the landward end of the crest (x =0 m) u A,50% , which is exceeded by 50% of the incoming waves, is usually used to describe the fluid velocity on the structure crest by previous researchers, such as Schüttrumpf and Oumeraci (2005); Bosman et al (2008) and this velocity is convenient to be used due to its relationship with the wave run-up. Therefore, u A,50% can be calculated as (Schüttrumpf and Oumeraci, 2005):…”

“…Given incident wave conditions (H s =0.12 m, T m =1.6 s) and structural geometry, the proportion of wave overtopping volume passing x increases significantly as the relative crest width decreases from 0.3 to 0. This is because large relative crest width leads to large deductions of velocity and layer thickness on the structure crest due to the friction and the deformation of the overtopping tongue on the structure crest respectively (Schüttrumpf and Oumeraci, 2005;Bosman et al, 2008). Therefore, for the same velocity and layer thickness on the seaward end of structure crest (x=−B), larger relative crest width corresponds to a smaller velocity and layer thickness on the landward end of structure crest (x=0 m).…”

Upgrade and Design of Coastal Structures Exposed to Climate Changes

“…The formulae were calibrated against small and large-scale model tests in wave flumes. Bosman (2008) carried out further analysis on the test data by Schüttrumpf (2001) and Van Gent (2002), where the formulae were extended to include a better description of the influence from the seaward slope.…”