The Vulnerability of Damaged River and Lake Dikes for Wave Overtopping

Abstract

Wave overtopping results in erosion of grass-covered flood defenses which can result in a dike breach. Damages to the dike cover decrease the cover strength and simultaneously increase the hydraulic load on the dike cover. Therefore, damages on the dike cover are vulnerable locations for wave overtopping failure. In this study, the failure probabilities of different types of damages are calculated and compared to the failure probability of a regular dike profile to determine the vulnerability of damages for wave overtopping. The method is applied to a river and lake dike where the model results show that the total failure probability is smaller on the crest and upper slope for the lake dike and higher on the lower slope and at the inner toe. The failure probability increases between a factor 4 and 14 for damaged location where the cover still contains grass vegetation. However, lake dikes are more vulnerable for damages compared to lake dikes in cases where only a bare clay cover is left. In that case, a dike with a damage is almost 3000 more likely to fail compared to a regular dike for a lake dike and around 120 times more likely to fail for a river dike.

The Cross-Dike Failure Probability by Wave Overtopping over Grass-Covered and Damaged Dikes

“…The framework is developed for river dikes where a constant water level during a storm is a good approximation. This approximation also holds for dikes at a lake, however, higher waves are expected at lake dikes due to a longer fetch length [51]. The framework is also applicable to sea dikes, but in this case the development of the hydraulic conditionsdriven by a combination of the storm and the tides-needs to be included.…”

Over the dike top: modelling the hydraulic load of overtopping waves including transitions for dike cover erosion

“…The framework is developed for river dikes where a constant water level during a storm is a good approximation. This approximation also holds for dikes at a lake, however, higher waves are expected at lake dikes due to a longer fetch length (Van Bergeijk et al, 2021b). The framework is also applicable to sea dikes, but in this case the development of the hydraulic conditions-driven by a combination of the storm and the tides-needs to be included.…”

“…Simulations for a lake dike in the Netherlands showed similar ratios for damages with a grass cover and therefore these ratios are also applicable to other case studies with similar cover types as mentioned above. However, the simulations for damages with solely a clay cover shows that these have a higher failure probability for lake dikes due to the difference in hydraulic conditions (Van Bergeijk et al, 2021b). Further research into damages with a clay cover needs to be done to determine in which cases these ratios can be applied.…”

“…The results in this thesis are applicable to the majority of the primary flood defences in the Netherlands that consist of grass-covered flood defences. The developed methods can be applied to river, lake and coastal dikes (Van Bergeijk et al, 2021b, 2020a. The methods can help to evaluate nature-based flood defences and innovative designs of flood defences such as a Double Dike system (Kwakernaak and Lenselink, 2015;Marijnissen et al, 2021) or a wide green dike (Peters, 2020) that increase the ecological value of the flood defences (Scheres and Schüttrumpf, 2019).…”

“…Anomalies of the grass cover are especially vulnerable for erosion due to a combination of a reduced cover strength and an increased load as the result of the height difference. Cover damages have a significant effect on the cross-dike failure probability (Chapter 6) where the decrease in failure probability depends on the type of damage, the cover quality and the type of dike (Van Bergeijk et al, 2021b). These results can be used in combination with information on where and when damages are expected to occur (Klerk, 2022) to determine the effect of damages on the failure probability of a dike segment and to study the effectiveness of inspection and maintenance schedules (Klerk et al, 2022).…”