The water level during a storm event is never constant but variable in nature. A variable water level leads to varying crest freeboards at the coastal defence structure. A change in crest freeboards is directly linked to a changing average overtopping discharge q over the coastal defence structure. The existing prediction formulae for q are developed for constant water level (CWL) and do not take into account its variability (VWL — variable water level) during a storm event. Hence, in this study the influence of the VWL on q was investigated experimentally. Model tests were conducted in the wave flume facility at Ghent University, where a range of VWL was modelled as representative for typical storm surges (total variation of the water level dh= 0.75–4.8 m) and a range of storm durations (time t= 2.7–22 h). During testing the q for these cases of VWL over a reference impermeable sloping (seaward slope of the structure cot(α) = 2) dike structure was measured. Initial validation of model results for the CWL situation showed that the model setup was capable of reproducing the predicted q values from Eurotop (2018). For the VWL situation it was noted that the existing prediction formulae (Eurotop, 2018) are overestimating the measured q value, especially for smaller relative crest freeboards (relative freeboards Rc/Hm0<1.5) when the smallest freeboard is considered. By using linear regression a new equivalent relative crest freeboard was derived to reduce the difference between q predicted by existing EurOtop (2018) and q measured during variable tests. The new equivalent freeboard is mainly dependent on the relative crest freeboard during the peak of the storm (Rcpeak/Hm0), as well as the total storm surge variation (dh). The existing formulation from EurOtop (2018) was kept by replacing Rc by this new equivalent crest freeboard. The adapted formula for q is able to accurately predict the overtopping discharge for both, CWL and VWL situation.
Pepi, Y., Streicher, M., Ricci, C., Franco, L., Bellotti, G., Hughes, S., et al. (2022). The effect of variations in water level on wave overtopping discharge over a dike: An experimental model study. COASTAL ENGINEERING, 178, 104199 [10.1016/j.coastaleng.2022.104199].
The effect of variations in water level on wave overtopping discharge over a dike: An experimental model study
Pepi Y.
;Franco L.;Bellotti G.;
2022-01-01
Abstract
The water level during a storm event is never constant but variable in nature. A variable water level leads to varying crest freeboards at the coastal defence structure. A change in crest freeboards is directly linked to a changing average overtopping discharge q over the coastal defence structure. The existing prediction formulae for q are developed for constant water level (CWL) and do not take into account its variability (VWL — variable water level) during a storm event. Hence, in this study the influence of the VWL on q was investigated experimentally. Model tests were conducted in the wave flume facility at Ghent University, where a range of VWL was modelled as representative for typical storm surges (total variation of the water level dh= 0.75–4.8 m) and a range of storm durations (time t= 2.7–22 h). During testing the q for these cases of VWL over a reference impermeable sloping (seaward slope of the structure cot(α) = 2) dike structure was measured. Initial validation of model results for the CWL situation showed that the model setup was capable of reproducing the predicted q values from Eurotop (2018). For the VWL situation it was noted that the existing prediction formulae (Eurotop, 2018) are overestimating the measured q value, especially for smaller relative crest freeboards (relative freeboards Rc/Hm0<1.5) when the smallest freeboard is considered. By using linear regression a new equivalent relative crest freeboard was derived to reduce the difference between q predicted by existing EurOtop (2018) and q measured during variable tests. The new equivalent freeboard is mainly dependent on the relative crest freeboard during the peak of the storm (Rcpeak/Hm0), as well as the total storm surge variation (dh). The existing formulation from EurOtop (2018) was kept by replacing Rc by this new equivalent crest freeboard. The adapted formula for q is able to accurately predict the overtopping discharge for both, CWL and VWL situation.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
