Modelling effects of an asphalt road at a dike crest on dike cover erosion onset during wave overtopping

Abstract

Structures integrated in a grass-covered dike may increase erosion development. Currently, safety assessment methods for flood defences are only applicable for a conventional grass-covered dike and the effects of structures on dike cover erosion are poorly understood. Since many dikes have a road on top, it is important to study the effect of such a road structure on erosion onset during wave overtopping. To investigate this effect, a coupled hydrodynamic-erosion model was developed. The erosion onset caused by overtopping waves was predicted by combining the time-varying bed shear stresses from the hydrodynamic model with a depth-dependent erosion model. The results show that roads on top of a dike increase the erosion of the neighbouring grass cover. This increase in erosion may have a negative impact on dike stability. Therefore, we recommend considering effects of constructions on top of dike profiles during safety assessments. Explicitly, consideration of the roughness transitions in the safety assessments of dikes is recommended.Electronic supplementary material The online version of this article (https://doi

Failure of Grass Covered Flood Defences with Roads on Top Due to Wave Overtopping: A Probabilistic Assessment Method

“…While the erosion is generated by one single wave, it has been observed that failure of the dike cover is mostly achieved by the overtopping of numerous waves during a storm event [12]. The time span in which erosion caused by a single wave takes place at a specific location is in the order of seconds [26] and it is termed total wave overtopping time (…”

“…The first CFD model (RCD), originally built in Ref. [26,35], was based on the scanned profile obtained as a final condition after the 0.01 m 3 /s/m experiment (q10_sc2: where q implies the mean overtopping discharge in l/s/m and sc2 refers to scan 2, the first profile scan after the q10 event, see Table 1). This profile includes an asphalt road of 3.1 m width with adjacent eroded transition gaps on each side of approximately 0.5 m each ( Figure 4).…”

“…For a detailed description of the RCD model setup, the accuracy of the mesh refinement and selected turbulence model we refer to Ref. [26].…”

“…The work presented in Ref. [26] used a more detailed computational fluid dynamics (CFD) model and showed that the presence of a road leads to higher scour depths in places with little to non-existent grass cover. In this paper, we extend the deterministic CFD approach of Ref.…”

“…In this paper, we extend the deterministic CFD approach of Ref. [26] towards a fully probabilistic assessment method for failure of the grass cover due to wave overtopping erosion.…”