Improvements to the detection and analysis of external surges in the North Sea

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 1m 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 72h 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

Spatiotemporal Scouring Processes around a Square Column on a Sloped Beach Induced by Tsunami Bores

Tsunamis continue to pose an existential threat to life and infrastructure in many coastal areas around the world. One of the risks associated with tsunamis is the formation of deep scour holes around critical infrastructure and other coastal buildings, compromising their structural integrity and stability. Despite its importance, tsunami-induced scour is still given limited and simplified consideration in design guidelines for coastal structures. To further improve the understanding of tsunami-induced scour processes, and thus provide the basis for safer design of coastal structures, novel large-scale laboratory experiments have been conducted. The experiments featured a unique combination of boundary conditions, including a square coastal structure on a sloping and dry sandy beach. Single broken solitary waves were used to simulate tsunami bores. The spatiotemporal scour development directly at the square column was monitored by a high-resolution camera system, allowing a detailed description of the highly dynamic flow and scour process. Differences in the scour process between the wave runup and drawdown phases are described, and maximum and final scour depths are given as a function of inundation depth, wave height, and distance of the column from the shoreline. The scour process is characterized by several distinct phases of varying intensity and scour rate, the sequence of which varies depending on the location on the sides of the column. It is shown that the drawdown phase has a large influence on the overall scour development, adding up to 58% to the scour depth obtained during the wave runup phase. As a result of significant sediment infilling during the drawdown phase, the maximum scour depths achieved during the drawdown phase are up to twice the final scour depths at the end of a test. This discrepancy between final and maximum scour depths is greater than in previous studies using a flat sediment bed. The results of this study therefore help to interpret scour depths measured during field investigations after a tsunami event and provide a basis for extending design guidelines for coastal structures

Dam-Break Waves’ Hydrodynamics on Composite Bathymetry

Among others, dam-break waves are a common representation for tsunami waves near- or on-shore as well as for large storm waves riding on top of storm surge water levels at coasts. These extreme hydrodynamic events are a frequent cause of destruction and losses along coastlines worldwide. Within this study, dam-break waves are propagated over a composite bathymetry, consisting of a linear slope and an adjacent horizontal plane. The wave propagation on the slope as well as its subsequent inundation of the horizontal hinterland is investigated, by varying an extensive set of parameters, for the first time. To that end, a numerical multi-phase computational fluid dynamics model is calibrated against large-scale physical flume tests. The model is used to systematically alter the parameters governing the hydrodynamics and to link them with the physical processes observed. The parameters governing the flow are the slope length, the height of the horizontal plane with respect to the ocean bottom elevation, and the initial impoundment depth of the dam-break. It is found that the overland flow features are governed by the non-dimensional height of the horizontal plane. Empirical equations are presented to predict the features of the overland flow, such as flow depth and velocities along the horizontal plane, as a function of the aforementioned parameters. In addition, analytical considerations concerning these dam-break flow features are presented, highlighting the changing hydrodynamics over space and time and rising attention to this phenomenon to be considered in future experimental tests

Experimental dataset describing the debris motion due to the obstruction from fixed obstacles in tsunami-like flow conditions

This dataset details the experimental data that were addressed and analysed in Goseberg et al. (2016, http://dx.doi.org/10.1016/j.coastaleng.2016.08.012), titled "Experimental analysis of debris motion due the obstruction from fixed obstacles in tsunami-like flow conditions". The data were collected in 2015 at Waseda University, Tokyo, Japan. The data was recorded in the tsunami wave basin of the Shibayama group at Waseda University. The data publication contains all relevant data that are needed to reproduce the figures printed in the original publication; this data publication was produced and stored on the occasion of and in preparation to the "Mapping & Modelling Benchmarking Workshop: Tsunami Debris", to be held May 22-23, in Newport, Oregon, US. The workshop has been organized under the leadership co-chairs Dan Cox and Patrick Lynett

Collapse processes and associated loading of square light-frame timber structures due to bore-type waves

Extreme hydrodynamic events such as hurricanes or tsunamis threaten coastal regions in particular. Such hazards must be assessed and appropriately incorporated into building codes to mitigate casualties and damages to coastal structures. Guidelines are often developed through experimental investigations that assume buildings remain rigid during hydrodynamic loading. To challenge this ‘rigid building paradigm’, test specimens were designed to replicate the deformation characteristics of an idealized light-frame timber structure using Froude-Cauchy similarity. Subsequently, a large-scale experimental study was conducted at the Large Wave Flume of the Coastal Research Center in Hannover. Hydrodynamic loads and load gradients were investigated to describe both the influence of an elasto-plastically modeled test specimen compared to a rigid reference model and the effect of load history on the structural loads. Finally, the collapse sequences of elasto-plastic specimens were extracted from high-speed photographs and classified into three failure mechanisms. In this study, data analyses are presented with the intention to not only inform local authorities for future development of guidelines but also serve as calibration and validation data for improving numerical methods

CollStruct - Videos of Collapsing Structures in Experimental Hydraulics in the Large Wave Flume (GWK) of the Coastal Research Center (FZK), Hannover, Germany

Extreme hydrodynamic events like hurricanes or tsunamis threaten coastal regions in particular. Such hazards must be assessed and appropriately incorporated into building codes to mitigate casualties and damages to coastal structures. Guidelines are often developed through experimental investigations that assume buildings remain rigid during hydrodynamic loading. To challenge this ‘rigid building paradigm’, test specimens were designed to replicate the deformation characteristics of an idealized light-frame timber structure using Froude-Cauchy similarity. Subsequently, a large-scale experimental study was conducted at the Large Wave Flume of the Coastal Research Center in Hannover. The collapse sequences of elasto-plastic specimens were extracted from high-speed photographs and classified into failure mechanisms. Data analyses are to be performed with the intention to not only inform local authorities for future development of guidelines but also serve as calibration and validation data for improving numerical methods

Engineering Lessons from the 28 September 2018 Indonesian Tsunami: Debris Loading

A field survey team went to Palu City, Indonesia in the aftermath of the September 28th, 2018 earthquake and tsunami to investigate its effects on local infrastructure and buildings. The study focused on the coast of Palu Bay, where a tsunami wave between approximately 2 and 7 m high impacted the local community as a result of several complex tsunami source mechanisms. The following study outlines the results, focused on loading caused by debris entrained within the inundating flow. Damage to timber buildings along the coast was widespread, though reinforced concrete structures for the most part survived, providing valuable insights into the type of debris loads and their effects on structures. The results of this survey are placed within the context of Canadian tsunami engineering challenges and are compared to the recently-released ASCE 7 Chapter 6 – Tsunami Loads and Effects, detailing potential research gaps and needs.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Iridium-Catalyzed Regio- and Enantioselective Allylic Substitution of Silyl Dienolates Derived from Dioxinones

We report Ir-catalyzed, regio- and enantioselective allylic substitution reactions of unstabilized silyl dienolates derived from dioxinones. Asymmetric allylic substitution of a variety of allylic trichloroethyl carbonates with these silyl dienolates gave γ-allylated products selectively in 60–84% yield and 90–98% ee