Runup variability due to time dependence and stochasticity in the beach profiles: two extreme cases of the Spanish coast

Equations for extreme runup worked out from several experimental studies are compared. Infragraviatory oscillations dominate the swash in a dissipative state but not in intermediate - reflective states. Therefore two kinds of equation depending on either significant wave height, H-0, or the Iribarren number, xi(0), should be used. Through a sand bed physical model with a uniform sand bed slope, equations are proposed for both beach states, and results are compared with precedent field and physical model experiments. Once the equations are chosen, the time-longshore variability in a medium - long term time scale of the foreshore slope is evaluated in two extreme cases relating to the Spanish coast. The Salinas beach on the North coast (Bay of Biscay) displayed a permanent dissipative beach state with small variations in the beach foreshore slope both along the shore and in time, so foreshore slope deviations in a medium-long term period were irrelevant and extreme runup is predicted with the wave height worked out from the design return period. Peniscola beach on the East coast (Mediterranean sea) displayed an intermediate state. If only time variations are analysed, variations in determining extreme runup are irrelevant. In contrast, significant differences were found when the longshore variations were studied in this Mediterranean beach.

Wave runup on a 1 on 10 slope /

Bibliography: p. 25.

Extreme runup statistics on natural beaches /

"May 1987."

Revised wave runup curves for smooth slopes /

"July 1978."

Wave runup on rough slopes /

"July 1979."

Prediction of irregular wave runup /

Issued July 1977.

Irregular wave runup on smooth slopes /

"December 1981."

Reanalysis of wave runup on structures and beaches /

Example problems and methods of data analysis, together with general observations, are given. Smooth-slope runup results for both breaking and nonbreaking waves are presented in a set of curves similar to but revised from those in the Shore Protection Manual (SPM) (U.S. Army, Corps of Engineerings, Coastal Engineering Research Center, 1977). The curves are for structure slopes fronted by horizontal and 1 on 10 bottom slopes. The range of values of d sub s/H' sub o was extended to d sub s/H' sub o = 8; relative depth (d sub s/H' sub o) is important even for d sub s/H' sub o> 3 for waves which do not break on the structure slope. Rough-slope results are presented in similar curves if sufficient data were available. Otherwise, results are given as values of r, which is the ratio of rough-slope runup to smooth-slope runup. Scale-effect in runup is discussed.

Bed shear stress measurements in dam break and swash flows

A novel shear plate was used to make direct bed shear stress measurements in laboratory dam break and swash flows on smooth, fixed, impermeable beds. The pressure gradient due to the slope of the fluid free-surface across the plate was measured using pressure transducers. Surface elevation was measured at five locations using acoustic displacement sensors. Flow velocity was measured using an Acoustic-Doppler Velocimeter and calculated using the ANUGA inundation model. The measured bed shear stress at the dam break fluid tip for an initially dry, horizontal bed was close to twice that estimated using steady flow theory. The temporal variation of swash bed shear stress showed a large peak in landward directed stress at the uprush tip, followed by a rapid decay throughout the uprush flow interior. The peak seaward directed stress during the backwash phase was less than half that measured in the uprush. Close to the still water line, in the region of bore collapse and at the time of initial uprush, favourable pressure gradients were measured. In the lower swash region predominately weak adverse pressure gradients were measured.

Avaliação e gestão de riscos em áreas litorais. Contributo para o desenvolvimento de um sistema de previsão e alerta de inundação em zonas costeiras

Enquadrado no projeto Hidralerta, este trabalho tem como objetivo avaliar o risco de inundação na zona da Costa da Caparica, concelho de Almada, entre 2007 e 2012. As praias em estudo são: São João da Caparica, Praia do Norte, CDS, Traquínio, Dragão Vermelho, Praia Nova e Nova Praia. O projeto Hidralerta pretende desenvolver um sistema de previsão, alerta e análise de risco a longo prazo associado ao galgamento e inundação em zonas costeiras e portuárias, através da utilização de previsões da agitação marítima. Pela aplicação do modelo espetral SWAN foram transferidas as características de agitação marítima (altura de onda, período de pico e direção de onda) do largo, fornecidos pelo modelo de previsão WAVEWATCH III, para junto à costa, isto é, para pontos em frente a cada uma das praias. Para o cálculo do runup na praia de São João da Caparica, foram aplicadas as fórmulas empíricas desenvolvidas por Hunt (1959), Holman (1986), Stockdon et al. (2006), Nielsen e Hanslow (1991), Ruggiero et al. (2001), Guza e Thornton (1982), e Teixeira (2009). Esta praia é considerada uma praia natural, com sistema dunar, semelhante aos sistemas utilizados pelos autores para desenvolvimento e aplicação das suas fórmulas. Para as restantes praias, que possuem estrutura de proteção aderente, foi utilizada a metodologia de Mase et al. (2013), que permite calcular o runup/galgamento nas praias e estruturas. Os perfis transversais de todas as praias e das estruturas foram levantados no local, no decorrer deste estudo. Depois de calculado o nível máximo de inundação nas praias e o caudal médio galgado nas estruturas de proteção, procedeu-se à avaliação do risco de inundação. Para isso, cruzou-se a informação de tabelas do grau de probabilidade de ocorrência e do grau de consequência, o que possibilitou a determinação da aceitabilidade do risco. Como resultado destaca-se que existe um grau indesejável de galgamento e inundação nas praias da Costa da Caparica e que a prevenção de danos em pessoas e bens pode ser melhorada pela aplicação de sistemas de alerta. Os resultados obtidos devem ser analisados com cuidado uma vez que a metodologia tem limitações, quer ao nível dos dados (agitação marítima, perfis de praia utilizados), das formulações empíricas consideradas, as quais não foram desenvolvidas para as praias em estudo e a avaliação das consequências, em que se utiliza uma metodologia muito simples.

Mass Movement-Induced Tsunami Hazard on Perialpine Lake Lucerne (Switzerland): Scenarios and Numerical Experiments

Previous studies of the sediments of Lake Lucerne have shown that massive subaqueous mass movements affecting unconsolidated sediments on lateral slopes are a common process in this lake, and, in view of historical reports describing damaging waves on the lake, it was suggested that tsunamis generated by mass movements represent a considerable natural hazard on the lakeshores. Newly performed numerical simulations combining two-dimensional, depth-averaged models for mass-movement propagation and for tsunami generation, propagation and inunda- tion reproduce a number of reported tsunami effects. Four analysed mass-movement scenarios—three based on documented slope failures involving volumes of 5.5 to 20.8 9 106 m3—show peak wave heights of several metres and maximum runup of 6 to [10 m in the directly affected basins, while effects in neighbouring basins are less drastic. The tsunamis cause large-scale inundation over distances of several hundred metres on flat alluvial plains close to the mass-movement source areas. Basins at the ends of the lake experience regular water-level oscillations with characteristic periods of several minutes. The vulnerability of potentially affected areas has increased dramatically since the times of the damaging historical events, recommending a thorough evaluation of the hazard.

GPS raw data (control points and ground control points) from the Liguria Region, Borghetto Santo Spirito, Italy

Monitoring the impact of sea storms on coastal areas is fundamental to study beach evolution and the vulnerability of low-lying coasts to erosion and flooding. Modelling wave runup on a beach is possible, but it requires accurate topographic data and model tuning, that can be done comparing observed and modeled runup. In this study we collected aerial photos using an Unmanned Aerial Vehicle after two different swells on the same study area. We merged the point cloud obtained with photogrammetry with multibeam data, in order to obtain a complete beach topography. Then, on each set of rectified and georeferenced UAV orthophotos, we identified the maximum wave runup for both events recognizing the wet area left by the waves. We then used our topography and numerical models to simulate the wave runup and compare the model results to observed values during the two events. Our results highlight the potential of the methodology presented, which integrates UAV platforms, photogrammetry and Geographic Information Systems to provide faster and cheaper information on beach topography and geomorphology compared with traditional techniques without losing in accuracy. We use the results obtained from this technique as a topographic base for a model that calculates runup for the two swells. The observed and modeled runups are consistent, and open new directions for future research.

Direct estimation wave setup as a medium level in swash

The extreme runup is a key parameter for a shore risk analysis in which the accurate and quantitative estimation of the upper limit reached by waves is essential. Runup can be better approximated by splitting the setup and swash semi-amplitude contributions. In an experimental study recording setup becomes difficult due to infragravity motions within the surf zone, hence, it would be desirable to measure the setup with available methodologies and devices. In this research, an analysis is made of evaluated the convenience of direct estimation setup as the medium level in the swash zone for experimental runup analysis through a physical model. A physical mobile bed model was setup in a wave flume at the Laboratory for Maritime Experimentation of CEDEX. The wave flume is 36 metres long, 6.5 metres wide and 1.3 metres high. The physical model was designed to cover a reasonable range of parameters, three different slopes (1/50, 1/30 and 1/20), two sand grain sizes (D50 = 0.12 mm and 0.70 mm) and a range for the Iribarren number in deep water (ξ0) from 0.1 to 0.6. Best formulations were chosen for estimating a theoretical setup in the physical model application. Once theoretical setup had been obtained, a comparison was made with an estimation of the setup directly as a medium level of the oscillation in swash usually considered in extreme runup analyses. A good correlation was noted between both theoretical and time-averaging setup and a relation is proposed. Extreme runup is analysed through the sum of setup and semi-amplitude of swash. An equation is proposed that could be applied in strong foreshore slope-dependent reflective beaches.