Effects of Water Level Variations on the Stability of Rock Armoured Slopes

Abstract

Physical model tests on the stability of rock armoured slopes have been performed to demonstrate the importance of water level variations during a storm, due to a tide or a storm surge. For the stability of rock armoured slopes also the importance of the sequence of storms at various water levels has been studied. The test results indicate that a smooth sinusoidal water level variation leads to an increase in damage compared to the same wave conditions at a constant water level. Furthermore, a stepwise approach of the sinusoidal water level elevation leads to other results than the approach with a continuous water level variation, whereas the continuous water level variation resembles the peak of a storm or the tidal water level variation better than a stepwise approach. If storms with different water levels attack the armour layer, the damage is generally smaller than if all storms attack the armour layer at the same water level. Furthermore, the results have been discussed based on earlier analyses where the statistics of rock armoured slopes have been addressed and the importance of the length effect has been illustrated using a method to apply results from physical model tests to real structures.

Effect of Variations in Water Level and Wave Steepness on the Robustness of Wave Overtopping Estimation

“…As the present set-up focused on influences on mean wave overtopping volumes, a rigid model set-up was chosen. Influences of dynamic water levels on the slope stability of a breakwater are published elsewhere [11].…”

“…However, from a constructional perspective, a dynamic SWL might strongly influence the maximum overtopping of a single wave emerging from the spectrum (important for a rear-slope stability assessment). Consequently, the exerted stress on the structure, the design of filter layers, and the overall stability assessment in classical breakwater studies must be considered [11]. Breaking or broken wave conditions in shallow water were not tested in this study.…”

The effect of variations in water level on wave overtopping discharge over a dike: An experimental model study

“…Furthermore, the active wave absorption was used and the water depth was varied continuously during the tests. The rationale for this, as stated by Van Gent et al (2018), was that a stepwise approach of the water level elevation leads to different results than the approach with a continuous water level variation, which better resembles the peak of a storm than a stepwise approach.…”

“…TheKerpen et al (2020) study mentioned above gave snapshots of realistic storm conditions, but in the present study a more parametric approach has been used. In the work byKerpen et al (2020) a very gentle dike slope (1:6) was tested while here the performance of a steeper slope was evaluated as inVan Gent et al (2018), in line with the most common dike slopes used in experiments to derive the overtopping discharge equations. Different durations were tested between ∼1 h and ∼11 h in prototype (Froude length scale λ = 30); and for the shortest wave time series and the highest wave period,…”