Enhanced Field Observation Based Physical and Numerical Modelling of Tsunami Induced Boulder Transport Phase 1: Physical Experiments

Oetjen, Jan; Engel, Max; Brückner, Helmut; Pudasaini, Shiva P.; Schüttrumpf, Holger

doi:10.9753/icce.v35.management.4

Cited by 5 publications

(5 citation statements)

References 26 publications

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“…(Engel & May, 2012). Given the uncertainties associated with 'initiation of motion' approaches (Nandasena et al, 2011;Terry et al, 2013;Oetjen et al, 2017), even lower-density point clouds and reduced overlap still provide acceptable results and only small errors (see table II in Gienko & Terry, 2014). Large overestimation of boulder volume derived from the multiplication of main axes is shown in the mean value of V SfM /V abc = 0Á54 (Table 2), which compares well with similar observations in previous studies (Engel & May, 2012;Gienko & Terry, 2014;Hoffmeister et al, 2014;May et al, 2015).…”

Section: Boulder Mapping From Orthophotographs and The Digital Surfacsupporting

confidence: 86%

“…This data is useful to derive the weight of boulders in combination with rock density data; and are also relevant where ‘initiation of motion’ approaches are applied in order to reconstruct flooding characteristics such as minimum flow velocities (Nandasena et al ., ), in particular if volume is kept as a discrete variable in the equations (Engel & May, ). Given the uncertainties associated with ‘initiation of motion’ approaches (Nandasena et al ., ; Terry et al ., ; Oetjen et al ., ), even lower‐density point clouds and reduced overlap still provide acceptable results and only small errors (see table II in Gienko & Terry, ). Large overestimation of boulder volume derived from the multiplication of main axes is shown in the mean value of V SfM / V abc = 0·54 (Table ), which compares well with similar observations in previous studies (Engel & May, ; Gienko & Terry, ; Hoffmeister et al ., ; May et al ., ).…”

Section: Discussionmentioning

confidence: 93%

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Digital mapping of coastal boulders – high‐resolution data acquisition to infer past and recent transport dynamics

et al. 2019

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Coastal boulder fields provide clues to long‐term frequency‐magnitude patterns of coastal flooding events and have the potential to play an important role in coastal hazard assessment. Mapping boulders in the field is time and labour‐intensive, and work on intertidal reef platforms, as in the present study, is physically challenging. By addressing coastal scientists who are not specialists in remote sensing, this contribution reports on the possibilities and limitations of digital applications in boulder mapping in Eastern Samar, Philippines, where recent supertyphoons Haiyan and Hagupit induced high waves, coastal flooding and boulder transport. It is demonstrated how satellite imagery of sub‐metre resolution (from Pléiades and WorldView‐3 imagery) enables efficient analysis of transport vectors and distances of larger boulders, reflecting variation in latitudes of both typhoon tracks and approaching angles of typhoon‐generated waves. During the investigated events, boulders with a‐axes of up to 8 m were clearly identified to have been shifted for up to 32 m, mostly along the seaward margin of the boulder field. It is, however, hard to keep track of smaller boulders, and the length of a‐axes and b‐axes including their orientation is often impossible to map with sufficient accuracy. Orthophotographs and digital surface models created through the application of an unmanned aerial vehicle and the ‘Structure from Motion’ technique provide ultra‐high‐resolution data, and have the potential to not only improve the results of satellite image analysis, but also those from field mapping and may significantly reduce overall time in the field. Orthophotographs permit unequivocal mapping of a‐axes and b‐axes including their orientation, while precise values for c‐axes can be derived from the respective digital surface models. Volume of boulders is best inferred from boulder‐specific Structure from Motion‐based three‐dimensional models. Battery power, flight speed and altitude determine the limits of the area covered, while patches shielded by the boulders are difficult to resolve. For some tasks, field mapping remains mandatory and cannot be replaced by currently available remote sensing tools: for example, sampling for rock type, density and age dating, recording of lithological separation of boulders from the underlying geological unit and of geomorphic features on a millimetre to decimetre‐scale, or documentation of fine‐grained sediment transport in between the boulders in supratidal settings. In terms of future events, the digital products presented here will provide a valuable reference to track boulder transport on a centimetre to decimetre‐scale and to better understand the hydrodynamics of extreme‐wave events on a fringing reef coastline.

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Section: Boulder Mapping From Orthophotographs and The Digital Surfacsupporting

confidence: 86%

Section: Discussionmentioning

confidence: 93%

Digital mapping of coastal boulders – high‐resolution data acquisition to infer past and recent transport dynamics

et al. 2019

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“…In general, TLS-based and UAV-based SFM derived areal monitoring and 3D models of dislocated boulders are considered to offer a reliable method for detecting the effects of changes in the sedimentary budgets, to determine the results of high-energy impacts and to serve as a basis for further hydraulic modelling approaches (Oetjen et al, 2017). Evidence of high-energy impact can only partly be proven, which might also be a consequence of the incorporated wave transport equations.…”

Section: Boulders and Detected Changesmentioning

confidence: 99%

“…Imamura et al (2008), introduced a more sophisticated modelling approach, achieved through experimentation with cubic and rectangular shaped boulder models in a water channel. Rolling and saltation were determined to be the major transport mechanisms; however, flume-based experiments indicate that the complexity of boulder movement is much greater (Oetjen et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Monitoring the sedimentary budget and dislocated boulders in western Greece – results since 2008

2020

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Dislocated boulders are one sign of high‐energy wave impacts on coasts. These high‐energy impacts, caused by severe storms or tsunamis, can trigger initial cracking and transport of boulders. Monitoring of these boulders, as well as the associated coastal sites is important in distinguishing between gradual coastal processes and high‐energy events. Western Greece is a seismically active area, where tsunamis and high‐energetic storms might occur and such past events are documented by historic and geoscientific research, making it an ideal location for monitoring dislocated boulders. Since 2008, monitoring of eight different coastal sites in this region was conducted by terrestrial laser scanning and photogrammetric approaches, with low‐cost unmanned aerial vehicles. The re‐use of similar surveying points in following years, allowed highly accurate monitoring. Point clouds derived from these methods were evaluated for change detection by point cloud comparisons. The data were also used to establish accurate three‐dimensional models of dislocated boulders (n = 70). The determined boulder volumes of these accurate three‐dimensional models were incorporated in wave transport equations and wave decay curves, and compared with monitoring results. A comprehensive overview of dislocated boulders in western Greece is presented. Three‐dimensional boulder reconstruction is compared to an approach which uses a tape‐based measuring of boulder axes, with the tape‐based measurement showing a mean overestimation of mass by 32%. Accurate monitoring over time by both methods, is achieved by using fixed networks of reference points. Changes for each site over time, detected by direct point cloud comparisons, are fit to the possible inundation calculated by wave decay curves based on computed minimum wave heights for boulder transport. Both storm and tsunami waves may have initiated movement from the cliff edge and further transport is also possible. However, boulders showed no further movement from their current position in the area for the time period of this study.

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“…At present, there are few studies on boulder movement in debris flow, but there is substantial research on boulders or various tsunami-driven objects such as shipping containers, vehicles, boats, and trees near coastlines caused by storms or tsunami [24][25][26][27][28][29][30][31][32]. The research contents include the initiation, the transportation modes, hydrodynamic forces of boulders, or tsunami-driven objects and the influence of wave characteristics on their movement under the action of tsunamis [30,31,[33][34][35][36][37]. For example, Oetjen et al studied the influence of boulder shape and coastline type on the movement process of boulders under the action of tsunami through a flume model [38].…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Boulder Fluid–Solid Coupling in Debris Flow: A Case Study in Zhouqu County, Gansu Province, China

Wang

Chen

et al. 2022

Water

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Boulders mixed with debris flows roll downstream under interactions with debris flow slurry, which poses a great threat to the people, houses, bridges, and other infrastructure encountered during their movement. The catastrophic debris flow in Zhouqu County, which occurred on 7 August 2010, was used as an example to study the motion and accumulation characteristics of boulders in debris flows. In this study, a fluid–solid coupling model utilizing the general moving objects collision model and the renormalization group turbulent model was used in the FLOW-3D software, treating boulders with different shapes in the Zhouqu debris flow as rigid bodies and the debris flow as a viscous flow. Numerical simulation results show that this method can be used to determine the motion parameters of boulders submerged in debris flows at different times, such as the centroid velocity, angular velocity, kinetic energy, and motion coordinates. The research method employed herein can provide a reference for studying debris flow movement mechanisms, impact force calculations, and aid in designing engineering control structures.

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Enhanced Field Observation Based Physical and Numerical Modelling of Tsunami Induced Boulder Transport Phase 1: Physical Experiments

Cited by 5 publications

References 26 publications

Digital mapping of coastal boulders – high‐resolution data acquisition to infer past and recent transport dynamics

Digital mapping of coastal boulders – high‐resolution data acquisition to infer past and recent transport dynamics

Monitoring the sedimentary budget and dislocated boulders in western Greece – results since 2008

Numerical Simulation of Boulder Fluid–Solid Coupling in Debris Flow: A Case Study in Zhouqu County, Gansu Province, China

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