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Raul Villanueva; Moritz Thom; Jan Visscher; Maike Paul; Torsten Schlurmann. Wake length of an artificial seagrass meadow: a study of shelter and its feasibility for restoration. Journal of Ecohydraulics 2021, 1 -15.
AMA StyleRaul Villanueva, Moritz Thom, Jan Visscher, Maike Paul, Torsten Schlurmann. Wake length of an artificial seagrass meadow: a study of shelter and its feasibility for restoration. Journal of Ecohydraulics. 2021; ():1-15.
Chicago/Turabian StyleRaul Villanueva; Moritz Thom; Jan Visscher; Maike Paul; Torsten Schlurmann. 2021. "Wake length of an artificial seagrass meadow: a study of shelter and its feasibility for restoration." Journal of Ecohydraulics , no. : 1-15.
This study explores the projected responses of tidal dynamics in the North Sea induced by the interplay between plausible projections of sea-level rise (SLR) and morphological changes in the Wadden Sea. This is done in order to gain insight into the casual relationships between physical drivers and hydro-morphodynamic processes. To achieve this goal, a hydronumerical model of the northwest European shelf seas (NWES) was set-up and validated. By implementing a plausible set of projections for global SLR (SLRRCP8.5 of 0.8 m and SLRhigh−end of 2.0 m) by the end of this century and beyond, the model was run to assess the responses of the regional tidal dynamics. In addition, for each considered SLR, various projections for cumulative rates of vertical accretion were applied to the intertidal flats in the Wadden Sea (ranging from 0 to 100% of projected SLR). Independent of the rate of vertical accretion, the spatial pattern of M2 amplitude changes remains relatively stable throughout most of the model domain for a SLR of 0.8 m. However, the model shows a substantial sensitivity toward the different rates of vertical accretion along the coasts of the Wadden Sea, but also in remote regions like the Skagerrak. If no vertical accretion is assumed in the intertidal flats of the Wadden Sea, the German Bight and the Danish west coast are subject to decreases in M2 amplitudes. In contrast, those regions experience increases in M2 amplitudes if the local intertidal flats are able to keep up with the projected SLR of 0.8 m. Between the different scenarios, the North Frisian Wadden Sea shows the largest differences in M2 amplitudes, locally varying by up to 14 cm. For a SLR of 2.0 m, the M2 amplitude changes are even more amplified. Again, the differences between the various rates of vertical accretion are largest in the North Frisian Wadden Sea (> 20 cm). The local distortion of the tidal wave is also significantly different between the scenarios. In the case of no vertical accretion, tidal asymmetry in the German estuaries increases, leading to a potentially enhanced sediment import. The presented results have strong implications for local coastal protection strategies and navigation in adjacent estuaries.
Christian Jordan; Jan Visscher; Torsten Schlurmann. Projected Responses of Tidal Dynamics in the North Sea to Sea-Level Rise and Morphological Changes in the Wadden Sea. Frontiers in Marine Science 2021, 8, 1 .
AMA StyleChristian Jordan, Jan Visscher, Torsten Schlurmann. Projected Responses of Tidal Dynamics in the North Sea to Sea-Level Rise and Morphological Changes in the Wadden Sea. Frontiers in Marine Science. 2021; 8 ():1.
Chicago/Turabian StyleChristian Jordan; Jan Visscher; Torsten Schlurmann. 2021. "Projected Responses of Tidal Dynamics in the North Sea to Sea-Level Rise and Morphological Changes in the Wadden Sea." Frontiers in Marine Science 8, no. : 1.
Reconstructing the topography of shallow underwater environments using Structure-from-Motion—Multi View Stereo (SfM-MVS) techniques applied to aerial imagery from Unmanned Aerial Vehicles (UAVs) is challenging, as it involves nonlinear distortions caused by water refraction. This study presents an experiment with aerial photographs collected with a consumer-grade UAV on the shallow-water reef of Fuvahmulah, the Maldives. Under conditions of rising tide, we surveyed the same portion of the reef in ten successive flights. For each flight, we used SfM-MVS to reconstruct the Digital Elevation Model (DEM) of the reef and used the flight at low tide (where the reef is almost entirely dry) to compare the performance of DEM reconstruction under increasing water levels. Our results show that differences with the reference DEM increase with increasing depth, but are substantially larger if no underwater ground control points are taken into account in the processing. Correcting our imagery with algorithms that account for refraction did not improve the overall accuracy of reconstruction. We conclude that reconstructing shallow-water reefs (less than 1 m depth) with consumer-grade UAVs and SfM-MVS is possible, but its precision is limited and strongly correlated with water depth. In our case, the best results are achieved when ground control points were placed underwater and no refraction correction is used.
C. Gabriel David; Nina Kohl; Elisa Casella; Alessio Rovere; Pablo Ballesteros; Torsten Schlurmann. Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry. Coral Reefs 2021, 40, 835 -851.
AMA StyleC. Gabriel David, Nina Kohl, Elisa Casella, Alessio Rovere, Pablo Ballesteros, Torsten Schlurmann. Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry. Coral Reefs. 2021; 40 (3):835-851.
Chicago/Turabian StyleC. Gabriel David; Nina Kohl; Elisa Casella; Alessio Rovere; Pablo Ballesteros; Torsten Schlurmann. 2021. "Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry." Coral Reefs 40, no. 3: 835-851.
Stepped revetments are effective in limiting wave overtopping. Small-scale studies provided insights in the design of crest-levels and step geometries of these structures. The validation of these insights at large scale, along with the analysis of individual overtopping volumes, is required to formulate recommendations for detail design. This paper investigates wave overtopping rates and individual overtopping volumes at stepped revetments by means of full-scale flume experiments. Two cross-sections, each with a slope of 1:3, were studied with uniform step heights of 0.17 m and 0.50 m. The revetments reduced wave overtopping rates in comparison to smooth dikes with influence factor for roughness (γf) between 0.43 and 0.73. An empirical formula for γf is proposed with which the wave overtopping rate at stepped revetments can be determined. Previous small-scale studies underestimate γf of this study by 2-31 %. Individual overtopping volumes were described by a Weibull distribution, revealing a higher median shape factor (b=1.63) for stepped revetments compared to breakwaters, smooth dikes or vertical walls.
Talia Schoonees; Nils B. Kerpen; Torsten Schlurmann. Full-scale experimental study on wave overtopping at stepped revetments. Coastal Engineering 2021, 167, 103887 .
AMA StyleTalia Schoonees, Nils B. Kerpen, Torsten Schlurmann. Full-scale experimental study on wave overtopping at stepped revetments. Coastal Engineering. 2021; 167 ():103887.
Chicago/Turabian StyleTalia Schoonees; Nils B. Kerpen; Torsten Schlurmann. 2021. "Full-scale experimental study on wave overtopping at stepped revetments." Coastal Engineering 167, no. : 103887.
Beach nourishments are a widely used method to mitigate erosion along sandy shorelines. In contrast to hard coastal protection structures, nourishments are considered as soft engineering, although little is known about the cumulative, long-term environmental effects of both marine sediment extraction and nourishment activities. Recent endeavours to sustain the marine ecosystem and research results on the environmental impact of sediment extraction and nourishment activities are driving the need for a comprehensive up-to-date review of beach nourishment practice, and to evaluate the physical and ecological sustainability of these activities. While existing reviews of nourishment practice have focused on the general design (motivation, techniques and methods, international overview of sites and volumes) as well as legal and financial aspects, this study reviews and compares not only nourishment practice but also the accompanying assessment and monitoring of environmental impacts in a number of developed countries around the world. For the study, we reviewed 205 openly-accessible coastal management strategies, legal texts, guidelines, EIA documents, websites, project reports, press releases and research publications about beach nourishments in several developed countries around the world (Germany, Denmark, the Netherlands, Belgium, Spain, UK, USA and Australia). Where information was not openly available, the responsible authorities were contacted directly. The study elaborates on the differences in coastal management strategies and legislation as well as the large dissimilarities in the EIA procedure (where applicable) for both marine sediment extraction and nourishment activities. The spatial disturbance of the marine environment that is considered a significant impact, a factor which determines the need for an Environmental Impact Assessment, varies substantially between the countries covered in this study. Combined with the large uncertainties of the long-term ecological and geomorphological impacts, these results underline the need to reconsider the sustainability of nourishments as “soft” coastal protection measures.
Franziska Staudt; Rik Gijsman; Caroline Ganal; Finn Mielck; Johanna Wolbring; H. Christian Hass; Nils Goseberg; Holger Schüttrumpf; Torsten Schlurmann; Stefan Schimmels. The sustainability of beach nourishments: a review of nourishment and environmental monitoring practice. Journal of Coastal Conservation 2021, 25, 1 -24.
AMA StyleFranziska Staudt, Rik Gijsman, Caroline Ganal, Finn Mielck, Johanna Wolbring, H. Christian Hass, Nils Goseberg, Holger Schüttrumpf, Torsten Schlurmann, Stefan Schimmels. The sustainability of beach nourishments: a review of nourishment and environmental monitoring practice. Journal of Coastal Conservation. 2021; 25 (2):1-24.
Chicago/Turabian StyleFranziska Staudt; Rik Gijsman; Caroline Ganal; Finn Mielck; Johanna Wolbring; H. Christian Hass; Nils Goseberg; Holger Schüttrumpf; Torsten Schlurmann; Stefan Schimmels. 2021. "The sustainability of beach nourishments: a review of nourishment and environmental monitoring practice." Journal of Coastal Conservation 25, no. 2: 1-24.
The integrity of a sea dike, especially its surface soil and biological revetment, is indispensable for coastal protection, as a dike breach would result in damages and economic losses. Estimates of the condition of a sea dike are typically established by on-site inspections and expert judgement at regular intervals. These status assessments of the protection level of the sea dike evaluate grass coverage and animal burrows, since structural inconsistencies deter the overall safety levels on coastal protection. In laboratory settings, erosion resistance of a sea dike is often determined by means of assessing critical shear stress induced by wave-run up and overtopping. Whereby the grain size distribution and soil aggregate formation on the one hand and the root penetration of the sample on the other are significant factors influencing critical shear stress and therefore erosion resistance.
Drone-/UAV-based remote sensing can be used to easily determine the degree of coverage of the dike revetment via green value detection. Thermal spectroscopy is also already used in agriculture to detect the state of health of plants at an early stage, for example due to a shortage of water. In addition, plants can be classified using hyperspectral imaging data.
We aim to derive transfer functions correlating ground truthing data, drawn from coastal real world- and a full scale laboratory dike, with plant species, its characteristic taxonomic traits and assessed top soil parameters. This approach bears the advantage of yielding an erosion-resistance estimate of the dike cover based on the plant classification using UAV-derived hyperspectral information. Furthermore, taxonomic species are sought to be paired with their respective, site specific, root architecture. Soil parameters such as nutrient availability and humidity will be observed and integrated into the approach, as they bear an impact on subterranean vegetation growth in that plants with lower nutrient availability develop a higher root network (high root length density [cm/cm³]). Finally, grazing livestock on the dike impacts the root system and soil structure as well and both aspects will be investigated comparing mowed against grazed areas as preliminary results show a dike cover void of grazing livestock exhibits a higher root shoot ratio than one with grazing. We hypothesize that classifying plants based on optical, hyperspectral UAV-derived data and the knowledge about the composition of the subsoil, the correlation of plant-specific root architecture and root growth with nutrient availability and agricultural maintenance could provide valuable information about erosion resistance of the dike cover to support dike inspection on an objective basis.
Jan-Michael Schönebeck; Maike Paul; Oliver Lojek; Boris Schröder; Jan Visscher; Torsten Schlurmann. Measuring soil erosion resistance on coastal dikes linking hyperspectral UAV-data, plant traits and soil information. 2021, 1 .
AMA StyleJan-Michael Schönebeck, Maike Paul, Oliver Lojek, Boris Schröder, Jan Visscher, Torsten Schlurmann. Measuring soil erosion resistance on coastal dikes linking hyperspectral UAV-data, plant traits and soil information. . 2021; ():1.
Chicago/Turabian StyleJan-Michael Schönebeck; Maike Paul; Oliver Lojek; Boris Schröder; Jan Visscher; Torsten Schlurmann. 2021. "Measuring soil erosion resistance on coastal dikes linking hyperspectral UAV-data, plant traits and soil information." , no. : 1.
Subaqueous bedforms are a fascinating morphological feature that concerns natural scientists and engineers alike. Under certain conditions, the different scales of these natural seafloor patterns merge into compound dunes consisting of large-scale primary and superimposing secondary bedforms. When it comes to the measuring of these composites, however, scholarly opinion varies depending on the investigator’s perspective. Specifically, compound dunes can either be interpreted as a superposition of their respective constituents, whose individual heights are measured independently after mathematical disintegration, or as one coherent bedform with readily measurable extents. Both methodologies, undoubtedly, have fully legitimate scopes of application, but little is written about the actual discrepancy that can result from signal pre-processing or differing geometric height definitions.
We experienced this problem when recently validating a method for the decomposition of compound dunes by comparison with three alternative approaches, of which two relied on detrending the bed elevation profiles before examination, whereas the third approach (similar to the newly proposed one) assessed unfiltered profiles. Although all tools were applied to the same bathymetric raw data, the statistical values of obtained dune dimensions diverged significantly. Even between approaches that generally showed comparable mean dune lengths, the corresponding height values differed by a factor of 2 or so. These results suggest that detrending or band-pass filtering of bed elevation profiles, as it is commonly applied before dune identification, leads to a systematic underestimation of profile amplitudes and thus dune heights. We therefore recommend refraining from these pre-processing steps in all cases where unambiguous absolute heights are needed. Dune identification from unfiltered bed elevation profiles, in return, necessitates that dune dimensions are calculated in consideration of the inherent inclinations. When analyzing the respective behavior of primary and secondary bedforms and their complex interplay, however, mathematical disintegration is the method of choice and, accordingly, dune height remains a matter of perspective.
Leon Scheiber; Jan Visscher; Oliver Lojek; Torsten Schlurmann. The measuring of compound dunes – when height becomes a matter of perspective. 2021, 1 .
AMA StyleLeon Scheiber, Jan Visscher, Oliver Lojek, Torsten Schlurmann. The measuring of compound dunes – when height becomes a matter of perspective. . 2021; ():1.
Chicago/Turabian StyleLeon Scheiber; Jan Visscher; Oliver Lojek; Torsten Schlurmann. 2021. "The measuring of compound dunes – when height becomes a matter of perspective." , no. : 1.
Sriram Venkatachalam; Shagun Agarwal; Shiqiang Yan; Zhihua Xie; Shaswat Saincher; Torsten Schlurmann; Qingwei Ma; Thorsten Stoesser; Yuan Zhuang; Bo Han; Weiwen Zhao; Xiaotong Yang; Z Li; Decheng Wan; Yi Zhang; Bin Teng; Dezhi Ning; Ningbo Zhang; Xing Zheng; Guochun Xu; Jiaye Gong; Yunbo Li; Kangping Liao; Wenyang Duan; Ronggui Han; Windiman Asnim; Zana Sulaiman; Zhongbing Zhou; Jianmin Qin; Yucheng Li; Zhiwei Song; Xiaofan Lou; Lin Lu; Changfu Yuan; Yuxiang Ma; Congfang Ai; Guohai Dong; Hanbing Sun; Qiang Wang; Zhi-Tao Zhai; Yan-Lin Shao; Zaibin Lin; Ling Qian; Wei Bai; Zhihua Ma; Pablo Higuera; Eugeny Buldakov; Dimitris Stagonas; Santiago Martelo Lopez; Aristos Christou; Pengzhi Lin; Yanyan Li; Jinshu Lu; Sa Young Hong; Yoon-Jin Ha; Kyong-Hwan Kim; Seok-Kyu Cho; Dong-Min Park; Wojciech Laskowski; Claes Eskilsson; Mario Ricchiuto; Allan P Engsig-Karup; Lin Cheng; Jinhai Zheng; Hanbin Gu; Guangnian Li. A Comparative Study on the Nonlinear Interaction Between a Focusing Wave and Cylinder Using State-of-the-art Solvers: Part A. International Journal of Offshore and Polar Engineering 2021, 31, 1 -10.
AMA StyleSriram Venkatachalam, Shagun Agarwal, Shiqiang Yan, Zhihua Xie, Shaswat Saincher, Torsten Schlurmann, Qingwei Ma, Thorsten Stoesser, Yuan Zhuang, Bo Han, Weiwen Zhao, Xiaotong Yang, Z Li, Decheng Wan, Yi Zhang, Bin Teng, Dezhi Ning, Ningbo Zhang, Xing Zheng, Guochun Xu, Jiaye Gong, Yunbo Li, Kangping Liao, Wenyang Duan, Ronggui Han, Windiman Asnim, Zana Sulaiman, Zhongbing Zhou, Jianmin Qin, Yucheng Li, Zhiwei Song, Xiaofan Lou, Lin Lu, Changfu Yuan, Yuxiang Ma, Congfang Ai, Guohai Dong, Hanbing Sun, Qiang Wang, Zhi-Tao Zhai, Yan-Lin Shao, Zaibin Lin, Ling Qian, Wei Bai, Zhihua Ma, Pablo Higuera, Eugeny Buldakov, Dimitris Stagonas, Santiago Martelo Lopez, Aristos Christou, Pengzhi Lin, Yanyan Li, Jinshu Lu, Sa Young Hong, Yoon-Jin Ha, Kyong-Hwan Kim, Seok-Kyu Cho, Dong-Min Park, Wojciech Laskowski, Claes Eskilsson, Mario Ricchiuto, Allan P Engsig-Karup, Lin Cheng, Jinhai Zheng, Hanbin Gu, Guangnian Li. A Comparative Study on the Nonlinear Interaction Between a Focusing Wave and Cylinder Using State-of-the-art Solvers: Part A. International Journal of Offshore and Polar Engineering. 2021; 31 (1):1-10.
Chicago/Turabian StyleSriram Venkatachalam; Shagun Agarwal; Shiqiang Yan; Zhihua Xie; Shaswat Saincher; Torsten Schlurmann; Qingwei Ma; Thorsten Stoesser; Yuan Zhuang; Bo Han; Weiwen Zhao; Xiaotong Yang; Z Li; Decheng Wan; Yi Zhang; Bin Teng; Dezhi Ning; Ningbo Zhang; Xing Zheng; Guochun Xu; Jiaye Gong; Yunbo Li; Kangping Liao; Wenyang Duan; Ronggui Han; Windiman Asnim; Zana Sulaiman; Zhongbing Zhou; Jianmin Qin; Yucheng Li; Zhiwei Song; Xiaofan Lou; Lin Lu; Changfu Yuan; Yuxiang Ma; Congfang Ai; Guohai Dong; Hanbing Sun; Qiang Wang; Zhi-Tao Zhai; Yan-Lin Shao; Zaibin Lin; Ling Qian; Wei Bai; Zhihua Ma; Pablo Higuera; Eugeny Buldakov; Dimitris Stagonas; Santiago Martelo Lopez; Aristos Christou; Pengzhi Lin; Yanyan Li; Jinshu Lu; Sa Young Hong; Yoon-Jin Ha; Kyong-Hwan Kim; Seok-Kyu Cho; Dong-Min Park; Wojciech Laskowski; Claes Eskilsson; Mario Ricchiuto; Allan P Engsig-Karup; Lin Cheng; Jinhai Zheng; Hanbin Gu; Guangnian Li. 2021. "A Comparative Study on the Nonlinear Interaction Between a Focusing Wave and Cylinder Using State-of-the-art Solvers: Part A." International Journal of Offshore and Polar Engineering 31, no. 1: 1-10.
Sriram Venkatachalam; Shagun Agarwal; Torsten Schlurmann. Laboratory Study on Steep Wave Interactions with Fixed and Moving Cylinder. International Journal of Offshore and Polar Engineering 2021, 31, 19 -26.
AMA StyleSriram Venkatachalam, Shagun Agarwal, Torsten Schlurmann. Laboratory Study on Steep Wave Interactions with Fixed and Moving Cylinder. International Journal of Offshore and Polar Engineering. 2021; 31 (1):19-26.
Chicago/Turabian StyleSriram Venkatachalam; Shagun Agarwal; Torsten Schlurmann. 2021. "Laboratory Study on Steep Wave Interactions with Fixed and Moving Cylinder." International Journal of Offshore and Polar Engineering 31, no. 1: 19-26.
Shagun Agarwal; Shaswat Saincher; Sriram Venkatachalam; Shiqiang Yan; Zhihua Xie; Torsten Schlurmann; Qingwei Ma; Xiaotong Yang; Decheng Wan; Jiaye Gong; Yunbo Li; Yanyan Li; Jinshu Lu; Hanbing Sun; Yan Liu; Beilei Zou; Shuling Chen; Jing Lu; Jianguo Lin; Sa Young Hong; Yoon-Jin Ha; Kyong-Hwan Kim; Seok-Kyu Cho; Dong-Min Park; Aliyar Sithik; Benjamin Bouscasse; Guillaume Ducrozet; Pierre Ferrant. A Comparative Study on the Nonlinear Interaction Between a Focusing Wave and Cylinder Using State-of-the-art Solvers: Part B. International Journal of Offshore and Polar Engineering 2021, 31, 11 -18.
AMA StyleShagun Agarwal, Shaswat Saincher, Sriram Venkatachalam, Shiqiang Yan, Zhihua Xie, Torsten Schlurmann, Qingwei Ma, Xiaotong Yang, Decheng Wan, Jiaye Gong, Yunbo Li, Yanyan Li, Jinshu Lu, Hanbing Sun, Yan Liu, Beilei Zou, Shuling Chen, Jing Lu, Jianguo Lin, Sa Young Hong, Yoon-Jin Ha, Kyong-Hwan Kim, Seok-Kyu Cho, Dong-Min Park, Aliyar Sithik, Benjamin Bouscasse, Guillaume Ducrozet, Pierre Ferrant. A Comparative Study on the Nonlinear Interaction Between a Focusing Wave and Cylinder Using State-of-the-art Solvers: Part B. International Journal of Offshore and Polar Engineering. 2021; 31 (1):11-18.
Chicago/Turabian StyleShagun Agarwal; Shaswat Saincher; Sriram Venkatachalam; Shiqiang Yan; Zhihua Xie; Torsten Schlurmann; Qingwei Ma; Xiaotong Yang; Decheng Wan; Jiaye Gong; Yunbo Li; Yanyan Li; Jinshu Lu; Hanbing Sun; Yan Liu; Beilei Zou; Shuling Chen; Jing Lu; Jianguo Lin; Sa Young Hong; Yoon-Jin Ha; Kyong-Hwan Kim; Seok-Kyu Cho; Dong-Min Park; Aliyar Sithik; Benjamin Bouscasse; Guillaume Ducrozet; Pierre Ferrant. 2021. "A Comparative Study on the Nonlinear Interaction Between a Focusing Wave and Cylinder Using State-of-the-art Solvers: Part B." International Journal of Offshore and Polar Engineering 31, no. 1: 11-18.
Tsunami remain a focal point of coastal engineering research, particularly when interacting with near-shore bathymetry and coastal developments. A recent push in experimentation involving long waves has led to novel methods, to generate and accurately control long waves in laboratories. This work showcases a recent implementation of a pump-driven long wave generation, with novel control strategies, an optimized inlet geometry, and an extra-wide and uniquely long propagation flume with the overall aim to provide the latest insight into experimental long wave generation.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/ZR0r88i2ev0
Nils Goseberg; Hajo von Hafen; Pablo Ballesteros; Nils B. Kerpen; Torsten Schlurmann. ARBITRARY GENERATION OF VERY LONG, AND TSUNAMI-LIKE WAVES USING AN OPTIMZED PUMP-DRIVEN METHOD. Coastal Engineering Proceedings 2020, 17 -17.
AMA StyleNils Goseberg, Hajo von Hafen, Pablo Ballesteros, Nils B. Kerpen, Torsten Schlurmann. ARBITRARY GENERATION OF VERY LONG, AND TSUNAMI-LIKE WAVES USING AN OPTIMZED PUMP-DRIVEN METHOD. Coastal Engineering Proceedings. 2020; (36v):17-17.
Chicago/Turabian StyleNils Goseberg; Hajo von Hafen; Pablo Ballesteros; Nils B. Kerpen; Torsten Schlurmann. 2020. "ARBITRARY GENERATION OF VERY LONG, AND TSUNAMI-LIKE WAVES USING AN OPTIMZED PUMP-DRIVEN METHOD." Coastal Engineering Proceedings , no. 36v: 17-17.
Adapting to sea level rise, climate change, and associated effects is especially challenging in sensitive small-island environments where false adaptation can lead to adverse impacts on natural and societal dynamics. Framing and interest play a decisive role for the successful implementation of any adaptation measures. An interdisciplinary perspective on the interaction of natural dynamics, societal demands, and political decisions is crucial. This study scrutinizes the coastal processes and socio-political dimensions of erosion on the reef island Fuvahmulah, the Maldives. The national government and Fuvahmulah's population have opposed perception and attribution about the cause and effect of the retreating shoreline. To review these perceptions and determine the drivers and processes behind Fuvahmulah's most pressing coastal issue, natural dynamics are recreated with process-based numerical methods and discussed regarding the present and projected sea levels and wave climate. The numerical results are based on high resolution digital elevation models from airborne imagery and in-situ bathymetric measurements. Interviews with national and local actors in coastal development and population surveys complement the physical insights into erosion on the island and scrutinize the socio-political dimension of climate change adaptation on small islands. The results of the interdisciplinary approach demonstrate how small-islands' adaptive capacities are typically impaired in dealing with climate-related changes, they reveal the structural challenges of top-down processes, and disclose the potential of local knowledge to overcome maldevelopment.
C. Gabriel David; Arne Hennig; Beate M. W. Ratter; Volker Roeber; Zahid; Torsten Schlurmann. Climate change induced effects or maldevelopment: small islands and conflicting attribution of root causes. 2020, 1 .
AMA StyleC. Gabriel David, Arne Hennig, Beate M. W. Ratter, Volker Roeber, Zahid, Torsten Schlurmann. Climate change induced effects or maldevelopment: small islands and conflicting attribution of root causes. . 2020; ():1.
Chicago/Turabian StyleC. Gabriel David; Arne Hennig; Beate M. W. Ratter; Volker Roeber; Zahid; Torsten Schlurmann. 2020. "Climate change induced effects or maldevelopment: small islands and conflicting attribution of root causes." , no. : 1.
In this study, the wave-induced distribution of 13 microplastic (MP) samples of different size, shape, and density was investigated in a wave flume with a sandy mobile beach bed profile. The particle parameter were chosen based on an occurrence probability investigated from the field. MP abundances were analyzed in cross-shore and vertical direction of the test area after over 40,000 regular waves. It was found, that MP particles accumulated in more shallow waters with increasing size and density. Particles with high density (ρs>1.25 g/cm3) have been partly confined into deeper layers of the sloping beach during the formation of the bed profile. Particles with a density lower than that of water used in the experiments floated constantly in the surf zone or deposited on the beach caused by wave run-up. A correlation was found between the settling velocity of the MP particles and the flow velocity at the accumulation point and a power function equation developed. The obtained results were critically discussed with findings from the field and further laboratory studies.
Nils B. Kerpen; Torsten Schlurmann; Alexander Schendel; Jannek Gundlach; Daniel Marquard; Markus Hüpgen. Wave-Induced Distribution of Microplastic in the Surf Zone. Frontiers in Marine Science 2020, 7, 1 .
AMA StyleNils B. Kerpen, Torsten Schlurmann, Alexander Schendel, Jannek Gundlach, Daniel Marquard, Markus Hüpgen. Wave-Induced Distribution of Microplastic in the Surf Zone. Frontiers in Marine Science. 2020; 7 ():1.
Chicago/Turabian StyleNils B. Kerpen; Torsten Schlurmann; Alexander Schendel; Jannek Gundlach; Daniel Marquard; Markus Hüpgen. 2020. "Wave-Induced Distribution of Microplastic in the Surf Zone." Frontiers in Marine Science 7, no. : 1.
Underwater dunes are a morphological feature that are explored by marine scientists and coastal engineers alike. This study presents new methodologies in order to simplify bedform identification and morphodynamic analyses. Specifically, subaqueous compound dunes are decomposed with a simple yet extensive tracking algorithm which relies on a repeated evaluation of unfiltered bed elevation profiles according to five pre‐defined length classes. In a second step, morphological trends are assessed in the form of bed migration rates, bed slope asymmetries and net sediment changes, whereat all parameters are referred to equidistant sections of the examined fairway stretch. This integrated approach not only avoids the challenges in weighting the varying size and abundance of dunes of different scales but also ensures comparability between dune‐specific and areal parameters which significantly improves the interpretation of the morphological setting as a whole. The developed methods are applied to the Outer Jade fairway, an anthropogenically influenced and regularly maintained waterway in the German Bight, and allow scrutiny of spatio‐temporal trends in this region. Based on a unique data set of 100 sequential high‐quality echo‐sounding surveys, various types of bedforms are identified comprising large‐scale primary as well as superimposing secondary dunes that are assumed to interfere with each other. Temporal trends show a long‐term rise of the troughs of major bedforms and constant maximum crest elevations near the official maintenance depth, which matches the observed long‐term aggradation of sediments. The spatial distribution of integrated morphodynamic parameters reflects a previously described zone of primary dune convergence and facilitates the precise localisation of this geophysical singularity. The presented findings both confirm the robustness of the proposed methodologies and, in return, enhance the understanding of morphological processes in the Outer Jade.
Leon Scheiber; Oliver Lojek; Axel Götschenberg; Jan Visscher; Torsten Schlurmann. Robust methods for the decomposition and interpretation of compound dunes applied to a complex hydromorphological setting. Earth Surface Processes and Landforms 2020, 46, 478 -489.
AMA StyleLeon Scheiber, Oliver Lojek, Axel Götschenberg, Jan Visscher, Torsten Schlurmann. Robust methods for the decomposition and interpretation of compound dunes applied to a complex hydromorphological setting. Earth Surface Processes and Landforms. 2020; 46 (2):478-489.
Chicago/Turabian StyleLeon Scheiber; Oliver Lojek; Axel Götschenberg; Jan Visscher; Torsten Schlurmann. 2020. "Robust methods for the decomposition and interpretation of compound dunes applied to a complex hydromorphological setting." Earth Surface Processes and Landforms 46, no. 2: 478-489.
Assessing the resilience of islands toward altered ocean climate pressures and providing robust adaptation measures requires an understanding of the interaction between morphological processes and the underlying hydrodynamic drivers. In this sense, this study presents changing sediment volumes on various temporal scales for the fringing reef island Fuvahmulah. Based on three field campaigns, conducted over 2 years, aerial imagery provides information on marine aggregates of the island's beaches. In addition, high resolution climate reanalysis data serves as input into an empirical and a numerical approach. Together, both approaches describe the driving processes behind volumetric seasonal and interannual changes: On the one hand, the empirical method quantifies sediment transport rates for calcareous sediments over the whole time span of the data set by considering wind and swell waves from multiple directions. On the other hand, the numerical method gives insights into the complexity of currents induced by dominant wave components. Combining these methods facilitates hindcasting and predicting morphological changes under varying wave climate, assessing sediment pathways over the whole reef, and describing the seasonal and interannual evolution of the sand spit Thoondu. As a result, this study reveals sediment distribution on different spatio-temporal scales and elucidates their significance in the design of conventional and alternative low-regret coastal adaptation.
C. Gabriel David; Torsten Schlurmann. Hydrodynamic Drivers and Morphological Responses on Small Coral Islands—The Thoondu Spit on Fuvahmulah, the Maldives. Frontiers in Marine Science 2020, 7, 1 .
AMA StyleC. Gabriel David, Torsten Schlurmann. Hydrodynamic Drivers and Morphological Responses on Small Coral Islands—The Thoondu Spit on Fuvahmulah, the Maldives. Frontiers in Marine Science. 2020; 7 ():1.
Chicago/Turabian StyleC. Gabriel David; Torsten Schlurmann. 2020. "Hydrodynamic Drivers and Morphological Responses on Small Coral Islands—The Thoondu Spit on Fuvahmulah, the Maldives." Frontiers in Marine Science 7, no. : 1.
Reconstructing the topography of shallow underwater environments using Structure-from-Motion – Multi View Stereo (SfM-MVS) techniques applied to aerial imagery from Unmanned Aerial Vehicles (UAVs) is a challenging problem, as it involves non-linear distortions caused by water refraction. This study presents an experiment with aerial photographs collected with a consumer-grade UAV on the shallow-water reef of Fuvahmulah, the Maldives. Under conditions of rising tide, we surveyed the same portion of the reef in ten successive flights. For each flight, we used SfM-MVS to reconstruct the Digital Elevation Model (DEM) of the reef, and used the flight at low tide (where the reef is almost entirely dry) to compare the performance of DEM reconstruction under higher water levels. Our results show that differences with the reference DEM increase with increasing depth, but are substantially larger if no underwater ground control points are taken into account in the processing. Correcting our imagery with algorithms that account for refraction did not improve the overall accuracy of reconstruction. We conclude that reconstructing shallow-water reefs (less than 1 m depth) with consumer-grade SfM-MVSs and SfM-MVS is possible, but its precision is limited and strongly correlated with water depth. The best results are achieved when ground control points were placed both above and underwater and no refraction correction is used in our processing.
C. Gabriel David; Nina Kohl; Elisa Casella; Alessio Rovere; Pablo Ballesteros; Torsten Schlurmann. Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry. 2020, 1 .
AMA StyleC. Gabriel David, Nina Kohl, Elisa Casella, Alessio Rovere, Pablo Ballesteros, Torsten Schlurmann. Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry. . 2020; ():1.
Chicago/Turabian StyleC. Gabriel David; Nina Kohl; Elisa Casella; Alessio Rovere; Pablo Ballesteros; Torsten Schlurmann. 2020. "Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry." , no. : 1.
River deltas and estuaries are disproportionally-significant coastal landforms that are inhabited by nearly 600 M people globally. In recent history, rapid socio-economic development has dramatically changed many of the World's mega deltas, which have typically undergone agricultural intensification and expansion, land-use change, urbanization, water resources engineering and exploitation of natural resources. As a result, mega deltas have evolved into complex and potentially vulnerable socio-ecological systems with unique threats and coping capabilities. The goal of this research was to establish a holistic understanding of threats, resilience, and adaptation for four mega deltas of variable geography and levels of socio-economic development, namely the Mekong, Yellow River, Yangtze, and Rhine deltas. Compiling this kind of information is critical for managing and developing these complex coastal areas sustainably but is typically hindered by a lack of consistent quantitative data across the ecological, social and economic sectors. To overcome this limitation, we adopted a qualitative approach, where delta characteristics across all sectors were assessed through systematic expert surveys. This approach enabled us to generate a comparative assessment of threats, resilience, and resilience-strengthening adaptation across the four deltas. Our assessment provides novel insights into the various components that dominate the overall risk situation in each delta and, for the first time, illustrates how each of these components differ across the four mega deltas. As such, our findings can guide a more detailed, sector specific, risk assessment or assist in better targeting the implementation of risk mitigation and adaptation strategies.
Claudia Kuenzer; Valentin Heimhuber; John Day; Olli Varis; Tom Bucx; Fabrice Renaud; Liu Gaohuan; Vo Quoc Tuan; Torsten Schlurmann; William Glamore. Profiling resilience and adaptation in mega deltas: A comparative assessment of the Mekong, Yellow, Yangtze, and Rhine deltas. Ocean & Coastal Management 2020, 198, 105362 .
AMA StyleClaudia Kuenzer, Valentin Heimhuber, John Day, Olli Varis, Tom Bucx, Fabrice Renaud, Liu Gaohuan, Vo Quoc Tuan, Torsten Schlurmann, William Glamore. Profiling resilience and adaptation in mega deltas: A comparative assessment of the Mekong, Yellow, Yangtze, and Rhine deltas. Ocean & Coastal Management. 2020; 198 ():105362.
Chicago/Turabian StyleClaudia Kuenzer; Valentin Heimhuber; John Day; Olli Varis; Tom Bucx; Fabrice Renaud; Liu Gaohuan; Vo Quoc Tuan; Torsten Schlurmann; William Glamore. 2020. "Profiling resilience and adaptation in mega deltas: A comparative assessment of the Mekong, Yellow, Yangtze, and Rhine deltas." Ocean & Coastal Management 198, no. : 105362.
The hydro- and morphodynamic processes within the Vietnamese Mekong Delta are heavily impacted by human activity, which in turn affects the livelihood of millions of people. The main drivers that could impact future developments within the delta are local stressors like hydropower development and sand mining, but also global challenges like climate change and relative sea level rise. Within this study, a hydro-morphodynamic model was developed, which focused on a stretch of the Tien River and was nested into a well-calibrated model of the delta’s hydrodynamics. Multiple scenarios were developed in order to assess the projected impacts of the different drivers on the river’s morphodynamics. Simulations were carried out for a baseline scenario (2000–2010) and for a set of plausible scenarios for a future period (2050–2060). The results for the baseline scenario indicate that the Tien River is already subject to substantial erosion under present-day conditions. For the future period, hydropower development has the highest impact on the local erosion and deposition budget, thus amplifying erosional processes, followed by an increase in sand mining activity and climate change-related variations in discharge. The results also indicate that relative sea level rise only has a minimal impact on the local morphodynamics of this river stretch, while erosional tendencies are slowed by a complete prohibition of sand mining activity. In the future, an unfavourable combination of drivers could increase the local imbalance between erosion and deposition by up to 89%, while the bed level could be incised by an additional 146%.
Christian Jordan; Jan Visscher; Nguyen Viet Viet Dung; Heiko Apel; Torsten Schlurmann. Impacts of Human Activity and Global Changes on Future Morphodynamics within the Tien River, Vietnamese Mekong Delta. Water 2020, 12, 2204 .
AMA StyleChristian Jordan, Jan Visscher, Nguyen Viet Viet Dung, Heiko Apel, Torsten Schlurmann. Impacts of Human Activity and Global Changes on Future Morphodynamics within the Tien River, Vietnamese Mekong Delta. Water. 2020; 12 (8):2204.
Chicago/Turabian StyleChristian Jordan; Jan Visscher; Nguyen Viet Viet Dung; Heiko Apel; Torsten Schlurmann. 2020. "Impacts of Human Activity and Global Changes on Future Morphodynamics within the Tien River, Vietnamese Mekong Delta." Water 12, no. 8: 2204.
The progressive expansion of offshore wind energy towards greater water depths demands for an optimization of foundation structure designs to a wider range of load conditions. In offshore waters, wind driven wave irregularity and directionality become important aspects of realistic sea states. To further improve the scour prediction in marine environment a novel experimental study was conducted to investigate the influence of directionally spread (3D) irregular waves on the scouring process. The tests were carried out in the 3D wave basin of the Ludwig-Franzius-Institute, Leibniz University Hannover, Germany. A monopile structure was simulated by a transparent pile made of acrylic glass. The study was set up to progress understanding and explore dissimilarities of scour development and patterns induced by directionally spread (3D) and unidirectional (2D) waves. The model tests were complemented by tests with superimposed oblique currents. Despite identical total wave energy in terms of m0 between the directionally spread and unidirectional wave spectra, minor but distinct differences in scour depth and rate could be observed, which inevitably can only be attributed to the presence and role of the wave spread. For wave-only conditions final scour depths S/D induced by directionally spread waves were on average 33% smaller than those for unidirectional waves. Furthermore, final scour depths decreased with increasing wave spreading and displayed a growing dependency on KC numbers with increasing wave spreading. In combined wave and current conditions of up to Ucw < 0.62 scour depths were found to be slightly larger and scour progression over time faster for directionally spread than for unidirectional waves. Differences regarding the scouring rates and depths have been found to decline with flow conditions further approaching current dominated regime. A prediction approach to estimate the maximum scour depth induced by either directionally spread or unidirectional random waves is proposed. Reasonable results and insights of the present study help advancing the understanding of scour development under more realistic, i.e. natural sea-state, conditions for a more reliable design of marine and offshore infrastructure.
Alexander Schendel; Mario Welzel; Torsten Schlurmann; Tai-Wen Hsu. Scour around a monopile induced by directionally spread irregular waves in combination with oblique currents. Coastal Engineering 2020, 161, 103751 .
AMA StyleAlexander Schendel, Mario Welzel, Torsten Schlurmann, Tai-Wen Hsu. Scour around a monopile induced by directionally spread irregular waves in combination with oblique currents. Coastal Engineering. 2020; 161 ():103751.
Chicago/Turabian StyleAlexander Schendel; Mario Welzel; Torsten Schlurmann; Tai-Wen Hsu. 2020. "Scour around a monopile induced by directionally spread irregular waves in combination with oblique currents." Coastal Engineering 161, no. : 103751.
The tidally influenced shipyard Elsflether Werft, Germany, has experienced a large increase in siltation and short periods of refilling since the 2000s. Its navigational depth was reduced by over 2 m in 2017 and by 0.5 m within only 4 months in 2014. A comprehensive field study was conducted in 2016 employing a time-lapse camera, multiparameter probes, sediment traps, vessel-based measurements, and unmanned aerial observations. Measurements show a strong shear flow along the dock entrance, as well as distinct turbidity signal spikes during regular and neap tides, which are drowned during spring tides. Deploying an unmanned aerial system (UAS), sediment plumes entering the dock were observed. Introducing a biodegradable tracer into the dock, a vortex structure was monitored by the UAS and orthophoto sequences processed by particle image velocimetry yielding time-averaged surface flow patterns and magnitudes, which correlate well with other measurements. Contextual data revealed a cross-sectional widening and river-bed geometry changes, which indicate increased siltation rates attributable to a retention basin effect.
Oliver Lojek; Jan Tiede; Jan Visscher; Remo Cossu; Torsten Schlurmann. Spatiotemporal Investigation of Event-Driven Sedimentation in a Tidally Influenced Shipyard by Air and Waterborne Observations. Journal of Waterway, Port, Coastal, and Ocean Engineering 2020, 146, 05020001 .
AMA StyleOliver Lojek, Jan Tiede, Jan Visscher, Remo Cossu, Torsten Schlurmann. Spatiotemporal Investigation of Event-Driven Sedimentation in a Tidally Influenced Shipyard by Air and Waterborne Observations. Journal of Waterway, Port, Coastal, and Ocean Engineering. 2020; 146 (4):05020001.
Chicago/Turabian StyleOliver Lojek; Jan Tiede; Jan Visscher; Remo Cossu; Torsten Schlurmann. 2020. "Spatiotemporal Investigation of Event-Driven Sedimentation in a Tidally Influenced Shipyard by Air and Waterborne Observations." Journal of Waterway, Port, Coastal, and Ocean Engineering 146, no. 4: 05020001.