Browsing by Issue Date, starting with "2024-05-09"
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- Estimating wave runup using satellite multi-spectral imageryPublication . Ilekura, Idowu Oselumhe; Almeida, Luis Pedro; Ferreira, Óscar ManuelThe wave runup is one of the most important processes responsible for coastal hazards, including overtopping or erosion. Understanding and predicting wave runup in any coastal environment is crucial for risk and vulnerability assessment studies. Nevertheless, the lack of field observations of wave runup is one of the main limitations of the predictability of this process. Past studies have used shore-based video monitoring techniques to observe wave runup in coastal areas. However, these studies were limited in time (data acquisition periods of several months or years) and space (spatial coverage of a single beach or extension of hundreds of meters or a few kilometres). In recent years, remote sensing, in particular Satellite Imagery, have improved the capability of the onboard sensor (e.g., improved spatial resolution of optical sensors) and revisit times (time between consecutive data collection in the same point on the earth’s surface), making of this technology one with the most significant potential to overcome earth sciences challenges. The present project’s general objective is to utilize multi-spectral imagery to monitor wave runup in coastal areas, representing a novel approach compared to past runup monitoring methodologies. Wetsand (boundary between the dry and wet beach) and Waterline (boundary between the water and the beach) were extracted from the satellite images as potential runup proxies. The satellite-derived runup proxies were compared to existing wave runup formulations. The error quantification was performed using statistical descriptive parameters (e.g., RMSE, correlation coefficient, and Bias). The waterline-derived runup proxies demonstrated high correlation (Bias = 0.35, R² = 0.63, RMSE = 0.65) with the existing runup formulation, whereas the Wetsand proxies exhibited lower correlation (Bias = -0.41, R² = 0.17, RMSE = 0.95). Averaging the Wetsand and Waterline proxies improved the Bias and RMSE to 0.12 and 0.611, respectively. The optimal formulation for each proxy was employed to correct the runup formulation, which was then used to compute the 𝑅2, resulting in a refined runup formulation. The corrected formulations for each proxy were utilized to predict extreme runup events. The waterline and the average Wetsand/Waterline proxies outperformed the Wetsand proxies during low wave and tide conditions. In contrast, the Wetsand proxy outperformed both alternatives in predicting extreme runup under high wave and tide conditions. Overall, the study noted the prospect of using satellites to measure and estimate runup globally.
- Assessing the impact of beach nourishment on reducing wave overtoppingPublication . Sproul, Vega Alexander; Garzón Hervás, Juan Luis; Mendes, DiogoAs zonas costeiras densamente povoadas podem estar sujeitas aos efeitos das tempestades costeiras, que promovem galgamento oceânico e consequentes inundações costeiras. As obras de defesa costeira, como esporões e defesas longitudinais aderentes, têm sido usadas para proteger contra estes perigos e salvaguardar as áreas urbanas costeiras. Nas últimas décadas, no entanto, houve uma mudança de paradigma promovendo o uso de outras soluções de engenharia, como a alimentação artificial de praias. A praia de Quarteira é um exemplo desta mudança de paradigma. Delimitada por um campo de esporões e apoiada por uma defesa longitudinal aderente, ambos construídos no início da década de 1970, a praia foi alvo de uma alimentação artificial em 1998, com outra planeada para 2024. Apesar da sua implementação, não se quantificou a eficácia da alimentação artificial na mitigação do galgamento oceânico em Quarteira. Esta dissertação pretende determinar a eficácia do projeto de alimentação artificial planeado para Quarteira na redução do galgamento oceânico com recurso a modelação numérica. Utilizando o modo não hidrostático do modelo XBeach, este estudo simula o galgamento oceânico para três cenários: antes da alimentação artificial, após a alimentação artificial e cinco anos após a alimentação artificial. Simulou-se o impacto de cinco tempestades sintéticas, com diferentes alturas significativas da agitação marítima e períodos de onda, para períodos de retorno variando entre 5 e 65 anos. Foram analisadas as relações entre a crista do revestimento, a largura da berma e os caudais médios de galgamento das ondas obtidos nas simulações do XBeach. Esta análise levou ao desenvolvimento de duas equações empíricas para estimar os caudais médios de galgamento em função das condições hidrodinâmicas (altura significativa e comprimento de onda ao largo) e da geometria da alimentação de praia (largura da berma). Este trabalho contribuiu para o desenvolvimento de uma metodologia para dimensionar e avaliar a eficácia dos projetos de alimentação artificial de praias.
- Changes in storm impacts along the Portuguese sandy coast for different climate scenariosPublication . Kazi, Maysha; Loureiro, Carlos; Ferreira, ÓscarStorms can result in extensive damage to the socioeconomic and environmental balance along the sandy coasts. Therefore, it is crucial to understand how the hydro-geomorphological response of sandy barriers will change due to future changes in storminess. This study aims to investigate future storm impacts on two contrasting sandy barriers along the Portuguese coast, Maceda and Tavira located respectively in the northwestern and southeastern coast, and evaluate how these will change in relation to the present situation. The approach is based on the application of the storm impact scale for the present and future climate change scenarios (mid- and end-century). Modelled wave, storm surge, and sea level data were combined with high-resolution topographic data and a conceptual model of barrier evolution to determine dune morphological parameters and impact regimes for future scenarios. The main findings of this work are that, extreme water levels will consistently increase throughout the twenty first century, mostly due to the contribution of sea level rise when compared to changes in storminess. From mid to the end-century, a reduction in dune crest elevations can be observed on the southernmost section of the Maceda coast and on the western to central section of the Tavira island. Compared to the current situation, by the mid- and end-century the intensity of collision and overwash regimes is expected to become severe in Maceda. For Tavira island, the most severe storm impact regimes are expected to be overwash and inundation, which will occur over almost half of the barrier island by 2100. From the mid-to-end century for all storm return periods, the mean overwash potential will increase substantially on the southernmost section of Maceda and on the west to the central section of Tavira island, while the mean inundation potential will gradually rise along with the mean overwash potential in Tavira. The influence of sea level rise and potential changes on the barrier morphological characteristics, particularly on the dune crest, are crucial factors influencing future changes to storm impacts.