Pub Date : 2023-10-10DOI: 10.5194/nhess-23-3219-2023
Simone Francesco Fornasari, Deniz Ertuncay, Giovanni Costa
Abstract. The Italian strong-motion network monitors the seismic activity in the region, with more than 585 stations with continuous data acquisition. In this study, we determine the background seismic noise characteristics of the network by using the data collected in 2022. We analyse the spatial and temporal characteristics of the background noise. It is found that most of the stations suffer from anthropogenic noises, since the strong-motion network is designed to capture the peak ground motions in populated areas. Hence, human activities enrich the low periods of noise. Therefore, land usage of the area where the stations are located affects the background noise levels. Stations can be noisier during the day, up to 12 dB, and during the weekday, up to 5 dB, in short periods. In long periods (≥ 5 s), accelerometric stations converge to similar noise levels and there are no significant daily or weekly changes. It is found that more than half of the stations exceed the background noise model designed for strong-motion stations in Switzerland by Cauzzi and Clinton (2013) in at least one of the calculated periods. We also develop an accelerometric seismic background noise model for periods between 0.0124 and 100 s for Italy by using the power spectral densities of the network. The model is in agreement with the background noise model developed by D’Alessandro et al. (2021) using broadband data for Italy in short periods, but in long periods there is no correlation among studies.
{"title":"Seismic background noise levels in the Italian strong-motion network","authors":"Simone Francesco Fornasari, Deniz Ertuncay, Giovanni Costa","doi":"10.5194/nhess-23-3219-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3219-2023","url":null,"abstract":"Abstract. The Italian strong-motion network monitors the seismic activity in the region, with more than 585 stations with continuous data acquisition. In this study, we determine the background seismic noise characteristics of the network by using the data collected in 2022. We analyse the spatial and temporal characteristics of the background noise. It is found that most of the stations suffer from anthropogenic noises, since the strong-motion network is designed to capture the peak ground motions in populated areas. Hence, human activities enrich the low periods of noise. Therefore, land usage of the area where the stations are located affects the background noise levels. Stations can be noisier during the day, up to 12 dB, and during the weekday, up to 5 dB, in short periods. In long periods (≥ 5 s), accelerometric stations converge to similar noise levels and there are no significant daily or weekly changes. It is found that more than half of the stations exceed the background noise model designed for strong-motion stations in Switzerland by Cauzzi and Clinton (2013) in at least one of the calculated periods. We also develop an accelerometric seismic background noise model for periods between 0.0124 and 100 s for Italy by using the power spectral densities of the network. The model is in agreement with the background noise model developed by D’Alessandro et al. (2021) using broadband data for Italy in short periods, but in long periods there is no correlation among studies.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"90 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136358894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Coastal areas can be tremendously biodiverse and host a substantial part of the world's population and critical infrastructure. However, there are often fragile environments that face various hazards such as flooding, coastal erosion, land salinization or pollution, earthquake-induced land motion, or anthropogenic processes. In this article, we investigate the stability of the Nice Côte d'Azur Airport, which has been built on reclaimed land in the Var River delta (French Riviera, France). This infrastructure, as well as the ongoing subsidence of the airport runways, has been a permanent concern since the partial collapse of the platform in 1979. Here, we used the full archive of ESA SAR (synthetic-aperture radar) images from 1992 to 2020 to comprehensively monitor the dynamics of the airport subsidence. We found that the maximum downward motion rate has been slowing down from 16 mm yr−1 in the 1990s to 8 mm yr−1 today. However, sediment compaction is still active, and an acceleration phase of the continuous creep leading to a potential failure of a part of the platform cannot be excluded. Our study demonstrates the importance of remotely monitoring of the platform to better understand the motion of coastal land, which will ultimately help evaluate and reduce associated hazards.
摘要沿海地区可以拥有巨大的生物多样性，并拥有世界上很大一部分人口和关键的基础设施。然而，往往有脆弱的环境面临各种危险，如洪水、海岸侵蚀、土地盐碱化或污染、地震引起的陆地运动或人为过程。在本文中，我们研究了尼斯Côte d'Azur机场的稳定性，该机场建在瓦尔河三角洲(法国里维埃拉，法国)的填海土地上。自1979年该平台部分坍塌以来，这一基础设施以及机场跑道的持续下沉一直是一个令人担忧的问题。本文利用1992 - 2020年的ESA SAR(合成孔径雷达)图像完整档案，对机场沉降动态进行了综合监测。我们发现，最大向下运动速率已经从20世纪90年代的16 mm yr - 1放缓到今天的8 mm yr - 1。然而，沉积物压实作用仍在进行，不能排除持续蠕变的加速阶段导致部分平台的潜在破坏。我们的研究证明了远程监测平台对更好地了解沿海土地运动的重要性，这将最终有助于评估和减少相关危害。
{"title":"Three decades of coastal subsidence in the slow-moving Nice Côte d'Azur Airport area (France) revealed by InSAR (interferometric synthetic-aperture radar): insights into the deformation mechanism","authors":"Olivier Cavalié, Frédéric Cappa, Béatrice Pinel-Puysségur","doi":"10.5194/nhess-23-3235-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3235-2023","url":null,"abstract":"Abstract. Coastal areas can be tremendously biodiverse and host a substantial part of the world's population and critical infrastructure. However, there are often fragile environments that face various hazards such as flooding, coastal erosion, land salinization or pollution, earthquake-induced land motion, or anthropogenic processes. In this article, we investigate the stability of the Nice Côte d'Azur Airport, which has been built on reclaimed land in the Var River delta (French Riviera, France). This infrastructure, as well as the ongoing subsidence of the airport runways, has been a permanent concern since the partial collapse of the platform in 1979. Here, we used the full archive of ESA SAR (synthetic-aperture radar) images from 1992 to 2020 to comprehensively monitor the dynamics of the airport subsidence. We found that the maximum downward motion rate has been slowing down from 16 mm yr−1 in the 1990s to 8 mm yr−1 today. However, sediment compaction is still active, and an acceleration phase of the continuous creep leading to a potential failure of a part of the platform cannot be excluded. Our study demonstrates the importance of remotely monitoring of the platform to better understand the motion of coastal land, which will ultimately help evaluate and reduce associated hazards.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136296357","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-05DOI: 10.5194/nhess-23-3199-2023
Subash Ghimire, Philippe Guéguen, Adrien Pothon, Danijel Schorlemmer
Abstract. Assessing or forecasting seismic damage to buildings is an essential issue for earthquake disaster management. In this study, we explore the efficacy of several machine learning models for damage characterization, trained and tested on the database of damage observed after Italian earthquakes (the Database of Observed Damage – DaDO). Six models were considered: regression- and classification-based machine learning models, each using random forest, gradient boosting, and extreme gradient boosting. The structural features considered were divided into two groups: all structural features provided by DaDO or only those considered to be the most reliable and easiest to collect (age, number of storeys, floor area, building height). Macroseismic intensity was also included as an input feature. The seismic damage per building was determined according to the EMS-98 scale observed after seven significant earthquakes occurring in several Italian regions. The results showed that extreme gradient boosting classification is statistically the most efficient method, particularly when considering the basic structural features and grouping the damage according to the traffic-light-based system used; for example, during the post-disaster period (green, yellow, and red), 68 % of buildings were correctly classified. The results obtained by the machine-learning-based heuristic model for damage assessment are of the same order of accuracy (error values were less than 17 %) as those obtained by the traditional RISK-UE method. Finally, the machine learning analysis found that the importance of structural features with respect to damage was conditioned by the level of damage considered.
{"title":"Testing machine learning models for heuristic building damage assessment applied to the Italian Database of Observed Damage (DaDO)","authors":"Subash Ghimire, Philippe Guéguen, Adrien Pothon, Danijel Schorlemmer","doi":"10.5194/nhess-23-3199-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3199-2023","url":null,"abstract":"Abstract. Assessing or forecasting seismic damage to buildings is an essential issue for earthquake disaster management. In this study, we explore the efficacy of several machine learning models for damage characterization, trained and tested on the database of damage observed after Italian earthquakes (the Database of Observed Damage – DaDO). Six models were considered: regression- and classification-based machine learning models, each using random forest, gradient boosting, and extreme gradient boosting. The structural features considered were divided into two groups: all structural features provided by DaDO or only those considered to be the most reliable and easiest to collect (age, number of storeys, floor area, building height). Macroseismic intensity was also included as an input feature. The seismic damage per building was determined according to the EMS-98 scale observed after seven significant earthquakes occurring in several Italian regions. The results showed that extreme gradient boosting classification is statistically the most efficient method, particularly when considering the basic structural features and grouping the damage according to the traffic-light-based system used; for example, during the post-disaster period (green, yellow, and red), 68 % of buildings were correctly classified. The results obtained by the machine-learning-based heuristic model for damage assessment are of the same order of accuracy (error values were less than 17 %) as those obtained by the traditional RISK-UE method. Finally, the machine learning analysis found that the importance of structural features with respect to damage was conditioned by the level of damage considered.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134975102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. A growing number of large cities are located near poorly understood faults that have not generated a significant earthquake in recent history. The Lembang Fault is one such fault located near the city of Bandung in West Java, Indonesia. The slip rate on this fault is debated, with estimates ranging from 6 to 1.95–3.45 mm yr−1, derived from a GNSS (global navigation satellite system) campaign and geological measurements respectively. In this paper we measure the surface deformation across the Bandung region and resolve the slip rate across the Lembang Fault using radar interferometry (InSAR – interferometric synthetic aperture radar) analysis of 6 years of Sentinel-1 satellite data and continuous GNSS measurements across the fault. Our slip rate estimate for the fault is 4.7 mm yr−1, with the shallow portions of the fault creeping at 2.2 mm yr−1. Previous studies estimated the return period of large earthquakes on the fault to be between 170–670 years. Assuming simplified fault geometries and a reasonable estimate of the seismogenic depth we derive an estimated moment deficit equivalent to magnitude 6.6–7.0 earthquakes, indicating that the fault poses a very real hazard to the local population. Using the Global Earthquake Model OpenQuake engine we calculate ground motions for these two earthquake scenarios and estimate that 1.9–2.7 million people within the Bandung metropolitan region would be exposed to ground shaking greater than 0.3 g. This study highlights the importance of identifying active faults, understanding their past activity, and measuring the current strain rates of smaller crustal active faults located near large cities in seismic zones.
摘要越来越多的大城市位于人们知之甚少的断层附近，这些断层在最近的历史上没有发生过大地震。伦邦断层是位于印度尼西亚西爪哇万隆市附近的一个这样的断层。该断层的滑动率存在争议，根据GNSS(全球导航卫星系统)活动和地质测量结果，估计滑动率为6至1.95-3.45 mm yr - 1。在本文中，我们测量了万隆地区的地表变形，并利用雷达干涉(InSAR -干涉合成孔径雷达)分析了6年的Sentinel-1卫星数据和连续的GNSS测量数据，解决了兰邦断层的滑动率。我们估计该断层的滑动速率为4.7 mm yr - 1，断层的浅部蠕动速率为2.2 mm yr - 1。以前的研究估计，断层上大地震的复发周期在170-670年之间。假设简化的断层几何形状和对孕震深度的合理估计，我们得出了相当于6.6-7.0级地震的估计力矩赤字，这表明该断层对当地居民构成了非常现实的危险。使用全球地震模型OpenQuake引擎，我们计算了这两种地震情景的地面运动，并估计万隆大都市区内190 - 270万人将暴露在大于0.3 g的地面震动中。这项研究强调了识别活动断层的重要性，了解它们过去的活动，并测量位于地震带大城市附近的较小地壳活动断层的当前应变率。
{"title":"The seismic hazard from the Lembang Fault, Indonesia, derived from InSAR and GNSS data","authors":"Ekbal Hussain, Endra Gunawan, Nuraini Rahma Hanifa, Qori'atu Zahro","doi":"10.5194/nhess-23-3185-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3185-2023","url":null,"abstract":"Abstract. A growing number of large cities are located near poorly understood faults that have not generated a significant earthquake in recent history. The Lembang Fault is one such fault located near the city of Bandung in West Java, Indonesia. The slip rate on this fault is debated, with estimates ranging from 6 to 1.95–3.45 mm yr−1, derived from a GNSS (global navigation satellite system) campaign and geological measurements respectively. In this paper we measure the surface deformation across the Bandung region and resolve the slip rate across the Lembang Fault using radar interferometry (InSAR – interferometric synthetic aperture radar) analysis of 6 years of Sentinel-1 satellite data and continuous GNSS measurements across the fault. Our slip rate estimate for the fault is 4.7 mm yr−1, with the shallow portions of the fault creeping at 2.2 mm yr−1. Previous studies estimated the return period of large earthquakes on the fault to be between 170–670 years. Assuming simplified fault geometries and a reasonable estimate of the seismogenic depth we derive an estimated moment deficit equivalent to magnitude 6.6–7.0 earthquakes, indicating that the fault poses a very real hazard to the local population. Using the Global Earthquake Model OpenQuake engine we calculate ground motions for these two earthquake scenarios and estimate that 1.9–2.7 million people within the Bandung metropolitan region would be exposed to ground shaking greater than 0.3 g. This study highlights the importance of identifying active faults, understanding their past activity, and measuring the current strain rates of smaller crustal active faults located near large cities in seismic zones.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"55 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134974962","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-28DOI: 10.5194/nhess-23-3147-2023
Gro B. M. Pedersen, Melissa A. Pfeffer, Sara Barsotti, Simone Tarquini, Mattia de'Michieli Vitturi, Bergrún A. Óladóttir, Ragnar Heiðar Þrastarson
Abstract. The 6-month-long effusive eruption at the Fagradalsfjall volcano in 2021 is the most visited eruption site in Iceland to date (June 2023), and it needed intense lava flow hazard assessment. In this study we document how strategies for lava flow modeling were implemented using the stochastic model MrLavaLoba to evaluate hazards during this effusive event. Overall, the purposes were threefold: (a) pre-eruption simulations to investigate potential lava inundation of critical infrastructure, (b) syn-eruption simulations for short-term (2-week time frame) lava flow hazard assessment and (c) syn-eruption simulations for long-term (months to years) hazard assessments. Additionally, strategies for lava barrier testing were developed, and syn-eruption topographic models were incorporated into simulations in near real time. The model provided promising results that were shared regularly at stakeholder meetings with the monitoring personnel, scientists and civil-protection representatives helping to identify potential short-term and long-term lava hazards. This included evaluation of the timing of barrier overflow and the filling and spilling of lava from one valley to another. During the crisis the MrLavaLoba model was updated to increase functionality such as by considering multiple active vents. Following the eruption, the model was optimized substantially, decreasing the computational time required for the simulations and speeding up the delivery of final products.
{"title":"Lava flow hazard modeling during the 2021 Fagradalsfjall eruption, Iceland: applications of MrLavaLoba","authors":"Gro B. M. Pedersen, Melissa A. Pfeffer, Sara Barsotti, Simone Tarquini, Mattia de'Michieli Vitturi, Bergrún A. Óladóttir, Ragnar Heiðar Þrastarson","doi":"10.5194/nhess-23-3147-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3147-2023","url":null,"abstract":"Abstract. The 6-month-long effusive eruption at the Fagradalsfjall volcano in 2021 is the most visited eruption site in Iceland to date (June 2023), and it needed intense lava flow hazard assessment. In this study we document how strategies for lava flow modeling were implemented using the stochastic model MrLavaLoba to evaluate hazards during this effusive event. Overall, the purposes were threefold: (a) pre-eruption simulations to investigate potential lava inundation of critical infrastructure, (b) syn-eruption simulations for short-term (2-week time frame) lava flow hazard assessment and (c) syn-eruption simulations for long-term (months to years) hazard assessments. Additionally, strategies for lava barrier testing were developed, and syn-eruption topographic models were incorporated into simulations in near real time. The model provided promising results that were shared regularly at stakeholder meetings with the monitoring personnel, scientists and civil-protection representatives helping to identify potential short-term and long-term lava hazards. This included evaluation of the timing of barrier overflow and the filling and spilling of lava from one valley to another. During the crisis the MrLavaLoba model was updated to increase functionality such as by considering multiple active vents. Following the eruption, the model was optimized substantially, decreasing the computational time required for the simulations and speeding up the delivery of final products.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135385814","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-28DOI: 10.5194/nhess-23-3169-2023
Ignace Pelckmans, Jean-Philippe Belliard, Luis E. Dominguez-Granda, Cornelis Slobbe, Stijn Temmerman, Olivier Gourgue
Abstract. Intertidal wetlands, such as mangroves in the tropics, are increasingly recognized for their role in nature-based mitigation of coastal flood risks. Yet it is still poorly understood how effective they are at attenuating the propagation of extreme sea levels through large (order of 100 km2) estuarine or deltaic systems, with complex geometry formed by networks of branching channels intertwined with mangrove and intertidal flat areas. Here, we present a delta-scale hydrodynamic modelling study, aiming to explicitly account for these complex landforms, for the case of the Guayas delta (Ecuador), the largest estuarine system on the Pacific coast of Latin America. Despite coping with data scarcity, our model accurately reproduces the observed propagation of high water levels during a spring tide. Further, based on a model sensitivity analysis, we show that high water levels are most sensitive to the mangrove platform elevation and degree of channelization but to a much lesser extent to vegetation-induced friction. Mangroves with a lower surface elevation, lower vegetation density, and higher degree of channelization all favour a more efficient flooding of the mangroves and therefore more effectively attenuate the high water levels in the deltaic channels. Our findings indicate that vast areas of channelized mangrove forests, rather than densely vegetated forests, are most effective for nature-based flood risk mitigation in a river delta.
{"title":"Mangrove ecosystem properties regulate high water levels in a river delta","authors":"Ignace Pelckmans, Jean-Philippe Belliard, Luis E. Dominguez-Granda, Cornelis Slobbe, Stijn Temmerman, Olivier Gourgue","doi":"10.5194/nhess-23-3169-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3169-2023","url":null,"abstract":"Abstract. Intertidal wetlands, such as mangroves in the tropics, are increasingly recognized for their role in nature-based mitigation of coastal flood risks. Yet it is still poorly understood how effective they are at attenuating the propagation of extreme sea levels through large (order of 100 km2) estuarine or deltaic systems, with complex geometry formed by networks of branching channels intertwined with mangrove and intertidal flat areas. Here, we present a delta-scale hydrodynamic modelling study, aiming to explicitly account for these complex landforms, for the case of the Guayas delta (Ecuador), the largest estuarine system on the Pacific coast of Latin America. Despite coping with data scarcity, our model accurately reproduces the observed propagation of high water levels during a spring tide. Further, based on a model sensitivity analysis, we show that high water levels are most sensitive to the mangrove platform elevation and degree of channelization but to a much lesser extent to vegetation-induced friction. Mangroves with a lower surface elevation, lower vegetation density, and higher degree of channelization all favour a more efficient flooding of the mangroves and therefore more effectively attenuate the high water levels in the deltaic channels. Our findings indicate that vast areas of channelized mangrove forests, rather than densely vegetated forests, are most effective for nature-based flood risk mitigation in a river delta.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"69 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135425281","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-27DOI: 10.5194/nhess-23-3111-2023
Clément Houdard, Adrien Poupardin, Philippe Sergent, Abdelkrim Bennabi, Jena Jeong
Abstract. The study aims to provide a complete analysis framework applied to an earthen dike located in Camargue, France. This dike is regularly submitted to erosion on the landward slope that needs to be repaired. Improving the resilience of the dike calls for a reliable model of damage frequency. The developed system is a combination of copula theory, empirical wave propagation, and overtopping equations as well as a global sensitivity analysis in order to provide the return period of erosion damage on a set dike while also providing recommendations in order for the dike to be reinforced as well as the model to be self-improved. The global sensitivity analysis requires one to calculate a high number of return periods over random observations of the tested parameters. This gives a distribution of the return periods, providing a more general approach to the behavior of the dike. The results show a return period peak around the 2-year mark, close to reported observation. With the distribution being skewed, the mean value is higher and is thus less reliable as a measure of dike safety. The results of the global sensitivity analysis show that no particular category of dike features contributes significantly more to the uncertainty of the system. The highest contributing factors are the dike height, the critical velocity, and the coefficient of seaward slope roughness. These results underline the importance of good dike characterization in order to improve the predictability of return period estimations. The obtained return periods have been confirmed by current in situ observations, but the uncertainty increases for the most severe events due to the lack of long-term data.
{"title":"Sensitivity analysis of erosion on the landward slope of an earthen flood defense located in southern France submitted to wave overtopping","authors":"Clément Houdard, Adrien Poupardin, Philippe Sergent, Abdelkrim Bennabi, Jena Jeong","doi":"10.5194/nhess-23-3111-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3111-2023","url":null,"abstract":"Abstract. The study aims to provide a complete analysis framework applied to an earthen dike located in Camargue, France. This dike is regularly submitted to erosion on the landward slope that needs to be repaired. Improving the resilience of the dike calls for a reliable model of damage frequency. The developed system is a combination of copula theory, empirical wave propagation, and overtopping equations as well as a global sensitivity analysis in order to provide the return period of erosion damage on a set dike while also providing recommendations in order for the dike to be reinforced as well as the model to be self-improved. The global sensitivity analysis requires one to calculate a high number of return periods over random observations of the tested parameters. This gives a distribution of the return periods, providing a more general approach to the behavior of the dike. The results show a return period peak around the 2-year mark, close to reported observation. With the distribution being skewed, the mean value is higher and is thus less reliable as a measure of dike safety. The results of the global sensitivity analysis show that no particular category of dike features contributes significantly more to the uncertainty of the system. The highest contributing factors are the dike height, the critical velocity, and the coefficient of seaward slope roughness. These results underline the importance of good dike characterization in order to improve the predictability of return period estimations. The obtained return periods have been confirmed by current in situ observations, but the uncertainty increases for the most severe events due to the lack of long-term data.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135585174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-27DOI: 10.5194/nhess-23-3125-2023
Wagner L. L. Costa, Karin R. Bryan, Giovanni Coco
Abstract. Topographic and bathymetric data are essential for accurate predictions of flooding in estuaries because water depth and elevation data are fundamental components of the shallow-water hydrodynamic equations used in models for storm surges and tides. Where lidar or in situ acoustic surveys are unavailable, recent efforts have centred on using satellite-derived bathymetry (SDB) and satellite-derived topography (SDT). This work is aimed at (1) determining the accuracy of SDT and (2) assessing the suitability of the SDT and SDB for extreme water level modelling of estuaries. The SDT was created by extracting the waterline as it tracks over the topography with changing tides. The method was applied to four different estuaries in Aotearoa / New Zealand: Whitianga, Maketū, Ōhiwa and Tauranga harbours. Results show that the waterline method provides similar topography to the lidar with a root-mean-square error equal to 0.2 m, and it is slightly improved when two correction methods are applied to the topography derivations: the removal of statistical bias (0.02 m improvement) and hydrodynamic modelling correction of waterline elevation (0.01 m improvement). The use of SDT in numerical simulations of surge levels was assessed for Tauranga Harbour in eight different simulation scenarios. Each scenario explored different ways of incorporating the SDT to replace the topographic data collected using non-satellite survey methods. In addition, one of these scenarios combined SDT (for intertidal zones) and SDB (for subtidal bathymetry), so only satellite information is used in surge modelling. The latter SDB is derived using the well-known ratio–log method. For Tauranga Harbour, using SDT and SDB in hydrodynamic models does not result in significant differences in predicting high water levels when compared with the scenario modelled using surveyed bathymetry.
{"title":"Modelling extreme water levels using intertidal topography and bathymetry derived from multispectral satellite images","authors":"Wagner L. L. Costa, Karin R. Bryan, Giovanni Coco","doi":"10.5194/nhess-23-3125-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3125-2023","url":null,"abstract":"Abstract. Topographic and bathymetric data are essential for accurate predictions of flooding in estuaries because water depth and elevation data are fundamental components of the shallow-water hydrodynamic equations used in models for storm surges and tides. Where lidar or in situ acoustic surveys are unavailable, recent efforts have centred on using satellite-derived bathymetry (SDB) and satellite-derived topography (SDT). This work is aimed at (1) determining the accuracy of SDT and (2) assessing the suitability of the SDT and SDB for extreme water level modelling of estuaries. The SDT was created by extracting the waterline as it tracks over the topography with changing tides. The method was applied to four different estuaries in Aotearoa / New Zealand: Whitianga, Maketū, Ōhiwa and Tauranga harbours. Results show that the waterline method provides similar topography to the lidar with a root-mean-square error equal to 0.2 m, and it is slightly improved when two correction methods are applied to the topography derivations: the removal of statistical bias (0.02 m improvement) and hydrodynamic modelling correction of waterline elevation (0.01 m improvement). The use of SDT in numerical simulations of surge levels was assessed for Tauranga Harbour in eight different simulation scenarios. Each scenario explored different ways of incorporating the SDT to replace the topographic data collected using non-satellite survey methods. In addition, one of these scenarios combined SDT (for intertidal zones) and SDB (for subtidal bathymetry), so only satellite information is used in surge modelling. The latter SDB is derived using the well-known ratio–log method. For Tauranga Harbour, using SDT and SDB in hydrodynamic models does not result in significant differences in predicting high water levels when compared with the scenario modelled using surveyed bathymetry.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"77 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135537861","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-25DOI: 10.5194/nhess-23-3095-2023
André Felipe Rocha Silva, Julian Cardoso Eleutério
Abstract. Economic damage and life-loss estimates provide important insights for the elaboration of more robust alerts and effective emergency planning. On the one hand, accurate damage analysis supports decision-making processes. On the other hand, the comparison of different flood alert scenarios through modeling techniques is crucial for improving the efficiency of alert and evacuation systems design. This work evaluates the use of flood damage and life-loss models in floods caused by tailings dams through the application of these models in the real case of the São Francisco dam failure, which occurred in January 2007 in the city of Miraí in Brazil. The model results showed great agreement with observed damage and loss of life. Furthermore, different simulations were done in order to measure the impact of increasing and decreasing alert system efficiency on life-loss reduction. The simulated scenarios exploring the inefficiency of flood alert and evacuation revealed that life loss could have reached the maximum rate of 8.7 % of the directly exposed population when considering the more pessimistic and uncertain scenario instead of the actual null life loss achieved. The results of this work indicate that the models could represent both the observed accident and different alert and evacuation efficiency impacts. It highlights the importance of developing and implementing robust alert and evacuation systems and regulations in order to reduce flood impacts.
{"title":"Analysis of flood warning and evacuation efficiency by comparing damage and life-loss estimates with real consequences related to the São Francisco tailings dam failure in Brazil","authors":"André Felipe Rocha Silva, Julian Cardoso Eleutério","doi":"10.5194/nhess-23-3095-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3095-2023","url":null,"abstract":"Abstract. Economic damage and life-loss estimates provide important insights for the elaboration of more robust alerts and effective emergency planning. On the one hand, accurate damage analysis supports decision-making processes. On the other hand, the comparison of different flood alert scenarios through modeling techniques is crucial for improving the efficiency of alert and evacuation systems design. This work evaluates the use of flood damage and life-loss models in floods caused by tailings dams through the application of these models in the real case of the São Francisco dam failure, which occurred in January 2007 in the city of Miraí in Brazil. The model results showed great agreement with observed damage and loss of life. Furthermore, different simulations were done in order to measure the impact of increasing and decreasing alert system efficiency on life-loss reduction. The simulated scenarios exploring the inefficiency of flood alert and evacuation revealed that life loss could have reached the maximum rate of 8.7 % of the directly exposed population when considering the more pessimistic and uncertain scenario instead of the actual null life loss achieved. The results of this work indicate that the models could represent both the observed accident and different alert and evacuation efficiency impacts. It highlights the importance of developing and implementing robust alert and evacuation systems and regulations in order to reduce flood impacts.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"90 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135769262","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-20DOI: 10.5194/nhess-23-3079-2023
Sandra Melzner, Marco Conedera, Johannes Hübl, Mauro Rossi
Abstract. Historical rockfall catalogues are important data sources for the investigation of the temporal occurrence of rockfalls, which is crucial information for rockfall hazard and risk assessments. However, such catalogues are rare and often incomplete. Here, we selected and analysed seven catalogues of historical rockfalls in Austria, Italy, and the USA to highlight existing relationships between data collection and mapping methods and representativeness of the resulting rockfall records. Heuristic and simple statistically based frequency analysis methods are applied to describe and compare the different historical rockfall catalogues. Our results show that the mapping strategy may affect the frequency of the assessed rockfall occurrence and the completeness and representativeness of the related time series of historical rockfalls. We conclude by presenting the advantages and limitations of the application of different frequency-based methods for analysing rockfall catalogues and providing recommendations for rockfall mapping. We furthermore present non-parametric statistical methods for dealing with typically small rockfall datasets, which are particularly suited for the characterization of basic rockfall catalogues. Such recommendations should help in the definition of standards for collecting and using temporal rockfall data in hazard and risk assessments.
{"title":"Lessons learnt from a rockfall time series analysis: data collection, statistical analysis, and applications","authors":"Sandra Melzner, Marco Conedera, Johannes Hübl, Mauro Rossi","doi":"10.5194/nhess-23-3079-2023","DOIUrl":"https://doi.org/10.5194/nhess-23-3079-2023","url":null,"abstract":"Abstract. Historical rockfall catalogues are important data sources for the investigation of the temporal occurrence of rockfalls, which is crucial information for rockfall hazard and risk assessments. However, such catalogues are rare and often incomplete. Here, we selected and analysed seven catalogues of historical rockfalls in Austria, Italy, and the USA to highlight existing relationships between data collection and mapping methods and representativeness of the resulting rockfall records. Heuristic and simple statistically based frequency analysis methods are applied to describe and compare the different historical rockfall catalogues. Our results show that the mapping strategy may affect the frequency of the assessed rockfall occurrence and the completeness and representativeness of the related time series of historical rockfalls. We conclude by presenting the advantages and limitations of the application of different frequency-based methods for analysing rockfall catalogues and providing recommendations for rockfall mapping. We furthermore present non-parametric statistical methods for dealing with typically small rockfall datasets, which are particularly suited for the characterization of basic rockfall catalogues. Such recommendations should help in the definition of standards for collecting and using temporal rockfall data in hazard and risk assessments.","PeriodicalId":18922,"journal":{"name":"Natural Hazards and Earth System Sciences","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136308190","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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