The wave run-up height is a crucial design parameter that determines the crest height of a sea dike and is used for estimating the number of overtopping waves. Therefore, a reduction of the wave run-up height is generally aspired in the design of dikes, which can be achieved by mortar-grouted riprap revetments (MGRR). Although MGRRs are widely utilized revetments along the German North Sea coast, no investigations into the wave run-up height on this revetment type are available to date. Full-scale hydraulic model tests were hence conducted to investigate wave run-up heights on partially grouted and fully grouted MGRRs. The wave run-up was determined using 2D-LIDAR measurements, which were validated by video data. Partially grouted MGRRs, due to their roughness, porosity, and permeability, reduce wave run-up heights from 21% to 28%, and fully grouted MGRRs due to their roughness reduce wave run-up heights from 12% to 14% compared to smooth impermeable revetments. Influence factors have been determined for four widely used revetment configurations, which can now be used for design purposes. A comparison and subsequent discussion about the representation of the physics of wave run-up by different parameters is carried out with the results presented.

Abstract. External surges are a key component of extreme water levels in the North Sea. Caused by low-pressure cells over the North Atlantic and amplified at the continental shelf, they can drive water-level changes of more than 1 m at the British, Dutch and German coasts. This work describes an improved and semi-automated method to detect external surges in sea surface time histories. The method is used to analyse tide gauge and meteorological records from 1995 to 2020 and to supplement an existing dataset of external surges, which is used in the determination of design heights of coastal protection facilities. Furthermore, external surges are analysed with regard to their annual and decadal variability, corresponding weather conditions, and their interaction with storm surges in the North Sea. A total of 33 % of the 101 external surges occur within close succession of each other, leading to the definition of serial external surges, in which one or more external surges follow less than 72 h after the previous external surge. These serial events tend to occur more often during wind-induced storm surges. Moreover, the co-occurrence with a storm surge increases the height of an external surge by 15 % on average, highlighting the importance of the consideration of combined events in coastal protection strategies. The improved dataset and knowledge about serial external surges extend the available basis for coastal protection in the North Sea region.

<p><strong>Computational fluid dynamics (CFD)  for “typical Dutch” houses failure: experiments and numerical modelling comparison.</strong></p><p>Authors: Andres Diaz Loaiza<sup>1</sup>, Benedikt Bratz<sup>1,2</sup>, Jeremy Bricker<sup>1</sup> and Paul Korswagen<sup>1</sup></p><p>1- Hydraulic Structures and Flood Risk, Technical University of Delft, 1- Technische Universität Braunschweig</p><p> </p><p>Coastal and riverine floods can be a catastrophic natural hazard with importance consequences. Many of the casualties occurring during these events can be attributed to the collapse of residential houses, and it is thus required to gain knowledge about the failure mechanism of these structures. Multiple variables can lead to various flow conditions that will in turn represent different load pressures over the house; among these, the type of the material (used in the construction), the orientation angle in respect to the main flow direction, the shape of the structure, and the urban density (blockage ratio), are relevant. In the present paper, small scale experiments are compared with CFD simulations performed with openFOAM in order to obtain a numerical model than can predict different combinations of load pressures for various flood events.</p><p> </p><p>The present study aims to represent different “typical Dutch” houses near or close to a dam break in which rapid high flow velocities and depths can be presented. The flow conditions and load pressures outputs are compared to physical results in order to validate the numerical model.</p>

Abstract. External surges are a key component of extreme water levels in the North Sea. Caused by low pressure cells over the North Atlantic and amplified at the continental shelf, they can drive water level changes of more than one meter at the British, Dutch and German coast. This work describes an improved and automated method to detect external surges in sea surface time histories. The method is used to analyse tide gauge and meteorological records from 1995 to 2020 and to supplement an existing dataset of external surges, which is used in the determination of design heights of coastal protection facilities. Furthermore, external surges are analysed with regard to their annual and decadal variability, corresponding weather conditions and their interaction with storm surges in the North Sea. 33 % of the 101 external surge occur within close succession of each other, leading to the definition of serial external surges, in which one or more external surges follow less than 72 h after the previous external surge. These serial events tend occur more often during wind–induced storm surges. Moreover, the co–occurrence with a storm surge increases the height of an external surge by 15 % on average, highlighting the importance of the consideration of combined events in coastal protection strategies. The improved dataset and knowledge about serial external surges extend the available basis for coastal protection in the North Sea region.

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