Pub Date : 2024-04-29DOI: 10.5194/esurf-12-581-2024
Anuska Narayanan, Sagy Cohen, John R. Gardner
Abstract. The Amazon experiences thousands of square kilometers of deforestation annually with recent rates increasing to levels unseen since the late 2000s. These increased rates of deforestation within the basin have led to changes in sediment concentration within its river systems, with potential impacts on ecological functioning, freshwater availability, and fluvial and coastal geomorphic processes. The relationship between deforestation and fluvial sediment dynamics in the Amazon has not been extensively studied using a basin-wide, comparative approach primarily due to lack of data. In this study, we utilize a novel remote-sensing-derived sediment concentration dataset to analyze the impact of deforestation from 2001 to 2020 on suspended sediment in large rivers (>50 m wide) across the Amazon River basin. These impacts are studied using a lag-based approach to quantify the spatiotemporal relationships between observed suspended sediment and changes in land cover over time. The results show that large-scale deforestation of the Amazon during the 2001–2020 period are associated with significant changes in sediment concentration in the eastern portion of the basin. In the heavily deforested eastern regions, the hydrogeomorphic response to deforestation occurs relatively rapidly (within a year), whereas the less disturbed western areas exhibit delays of 1 to 2 years before responses are observable. Moreover, we observe that deforestation must be substantial enough to overcome the collective influences of human activities and natural sediment variations to result in a discernible impact on sediment concentration in large rivers. In 69 % of Amazonian major tributary basins with an immediate response, more than 5 % of the basin was deforested during the 2001–2020 period, while in 85 % of basins with lagged responses, less than 5 % of the land was cleared. These findings suggest severe implications for future sediment dynamics across the Amazon if deforestation is to further expand into the basin.
{"title":"Riverine sediment response to deforestation in the Amazon basin","authors":"Anuska Narayanan, Sagy Cohen, John R. Gardner","doi":"10.5194/esurf-12-581-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-581-2024","url":null,"abstract":"Abstract. The Amazon experiences thousands of square kilometers of deforestation annually with recent rates increasing to levels unseen since the late 2000s. These increased rates of deforestation within the basin have led to changes in sediment concentration within its river systems, with potential impacts on ecological functioning, freshwater availability, and fluvial and coastal geomorphic processes. The relationship between deforestation and fluvial sediment dynamics in the Amazon has not been extensively studied using a basin-wide, comparative approach primarily due to lack of data. In this study, we utilize a novel remote-sensing-derived sediment concentration dataset to analyze the impact of deforestation from 2001 to 2020 on suspended sediment in large rivers (>50 m wide) across the Amazon River basin. These impacts are studied using a lag-based approach to quantify the spatiotemporal relationships between observed suspended sediment and changes in land cover over time. The results show that large-scale deforestation of the Amazon during the 2001–2020 period are associated with significant changes in sediment concentration in the eastern portion of the basin. In the heavily deforested eastern regions, the hydrogeomorphic response to deforestation occurs relatively rapidly (within a year), whereas the less disturbed western areas exhibit delays of 1 to 2 years before responses are observable. Moreover, we observe that deforestation must be substantial enough to overcome the collective influences of human activities and natural sediment variations to result in a discernible impact on sediment concentration in large rivers. In 69 % of Amazonian major tributary basins with an immediate response, more than 5 % of the basin was deforested during the 2001–2020 period, while in 85 % of basins with lagged responses, less than 5 % of the land was cleared. These findings suggest severe implications for future sediment dynamics across the Amazon if deforestation is to further expand into the basin.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140811124","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 : 2024-04-29DOI: 10.5194/esurf-12-621-2024
Steven Y. J. Lai, David Amblas, Aaron Micallef, Hervé Capart
Abstract. Tectonics play a significant role in shaping the morphology of submarine canyons, which form essential links in source-to-sink (S2S) systems. It is difficult, however, to investigate the resulting morphodynamics over the long term. For this purpose, we propose a novel experimental approach that can generate submarine canyons and hanging-wall fans on continuously evolving active faults. We utilize morphometric analysis and morphodynamic models to understand the response of these systems to fault slip rate (Vr) and inflow discharge (Q). Our research reveals several key findings. Firstly, the fault slip rate controls the merging speed of submarine canyons and hanging-wall fans, which in turn affects their quantity and spacing. Additionally, the long profile shapes of submarine canyons and hanging-wall fans can be decoupled into a gravity-dominated breaching process and an underflow-dominated diffusion process, which can be described using a constant-slope relationship and a morphodynamic diffusion model, respectively. Furthermore, both experimental and simulated submarine canyon–hanging-wall fan long profiles exhibit strong self-similarity, indicating that the long profiles are scale independent. The Hack's scaling relationship established through morphometric analyses serves as an important link between different scales in S2S systems, bridging laboratory-scale data to field-scale data and submarine-to-terrestrial relationships. Lastly, for deep-water sedimentary systems, we propose an empirical formula to estimate fan volume using canyon length, and the data from 26 worldwide S2S systems utilized for comparison show a strong agreement. Our geomorphic experiments provide a novel perspective for better understanding of the influence of tectonics on deep-water sedimentary processes. The scaling relationships and empirical formulas we have established aim to assist in estimating volume information that is difficult to obtain during long-term landscape evolution processes.
{"title":"Evolution of submarine canyons and hanging-wall fans: insights from geomorphic experiments and morphodynamic models","authors":"Steven Y. J. Lai, David Amblas, Aaron Micallef, Hervé Capart","doi":"10.5194/esurf-12-621-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-621-2024","url":null,"abstract":"Abstract. Tectonics play a significant role in shaping the morphology of submarine canyons, which form essential links in source-to-sink (S2S) systems. It is difficult, however, to investigate the resulting morphodynamics over the long term. For this purpose, we propose a novel experimental approach that can generate submarine canyons and hanging-wall fans on continuously evolving active faults. We utilize morphometric analysis and morphodynamic models to understand the response of these systems to fault slip rate (Vr) and inflow discharge (Q). Our research reveals several key findings. Firstly, the fault slip rate controls the merging speed of submarine canyons and hanging-wall fans, which in turn affects their quantity and spacing. Additionally, the long profile shapes of submarine canyons and hanging-wall fans can be decoupled into a gravity-dominated breaching process and an underflow-dominated diffusion process, which can be described using a constant-slope relationship and a morphodynamic diffusion model, respectively. Furthermore, both experimental and simulated submarine canyon–hanging-wall fan long profiles exhibit strong self-similarity, indicating that the long profiles are scale independent. The Hack's scaling relationship established through morphometric analyses serves as an important link between different scales in S2S systems, bridging laboratory-scale data to field-scale data and submarine-to-terrestrial relationships. Lastly, for deep-water sedimentary systems, we propose an empirical formula to estimate fan volume using canyon length, and the data from 26 worldwide S2S systems utilized for comparison show a strong agreement. Our geomorphic experiments provide a novel perspective for better understanding of the influence of tectonics on deep-water sedimentary processes. The scaling relationships and empirical formulas we have established aim to assist in estimating volume information that is difficult to obtain during long-term landscape evolution processes.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140812701","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 : 2024-04-29DOI: 10.5194/esurf-12-601-2024
Sarah Hautekiet, Jan-Eike Rossius, Olivier Gourgue, Maarten Kleinhans, Stijn Temmerman
Abstract. Tidal marshes provide highly valued ecosystem services, which depend on variations in the geometric properties of the tidal channel networks dissecting marsh landscapes. The development and evolution of channel network properties are controlled by both abiotic (dynamic flow–landform feedbacks) and biotic processes (e.g. vegetation–flow–landform feedbacks). However, the relative role of biotic and abiotic processes, and under which condition one or the other is more dominant, remains poorly understood. In this study, we investigated the impact of spatio-temporal plant colonization patterns on tidal channel network development through flume experiments. Four scaled experiments mimicking tidal landscape development were conducted in a tidal flume facility: two control experiments without vegetation, a third experiment with hydrochorous vegetation colonization (i.e. seed dispersal via the tidal flow), and a fourth with patchy colonization (i.e. by direct seeding on the sediment bed). Our results show that more dense and efficient channel networks are found in the vegetation experiments, especially in the hydrochorous seeding experiment with slower vegetation colonization. Further, an interdependency between abiotic and biotic controls on channel development can be deduced. Whether biotic factors affect channel network development seems to depend on the force of the hydrodynamic energy and the stage of the system development. Vegetation–flow–landform feedbacks are only dominant in contributing to channel development in places where intermediate hydrodynamic energy levels occur and mainly have an impact during the transition phase from a bare to a vegetated landscape state. Overall, our findings suggest a zonal domination of abiotic processes at the seaward side of intertidal basins, while biotic processes have an additional effect on system development more towards the landward side.
{"title":"On the relative role of abiotic and biotic controls in channel network development: insights from scaled tidal flume experiments","authors":"Sarah Hautekiet, Jan-Eike Rossius, Olivier Gourgue, Maarten Kleinhans, Stijn Temmerman","doi":"10.5194/esurf-12-601-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-601-2024","url":null,"abstract":"Abstract. Tidal marshes provide highly valued ecosystem services, which depend on variations in the geometric properties of the tidal channel networks dissecting marsh landscapes. The development and evolution of channel network properties are controlled by both abiotic (dynamic flow–landform feedbacks) and biotic processes (e.g. vegetation–flow–landform feedbacks). However, the relative role of biotic and abiotic processes, and under which condition one or the other is more dominant, remains poorly understood. In this study, we investigated the impact of spatio-temporal plant colonization patterns on tidal channel network development through flume experiments. Four scaled experiments mimicking tidal landscape development were conducted in a tidal flume facility: two control experiments without vegetation, a third experiment with hydrochorous vegetation colonization (i.e. seed dispersal via the tidal flow), and a fourth with patchy colonization (i.e. by direct seeding on the sediment bed). Our results show that more dense and efficient channel networks are found in the vegetation experiments, especially in the hydrochorous seeding experiment with slower vegetation colonization. Further, an interdependency between abiotic and biotic controls on channel development can be deduced. Whether biotic factors affect channel network development seems to depend on the force of the hydrodynamic energy and the stage of the system development. Vegetation–flow–landform feedbacks are only dominant in contributing to channel development in places where intermediate hydrodynamic energy levels occur and mainly have an impact during the transition phase from a bare to a vegetated landscape state. Overall, our findings suggest a zonal domination of abiotic processes at the seaward side of intertidal basins, while biotic processes have an additional effect on system development more towards the landward side.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140810810","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 : 2024-04-26DOI: 10.5194/esurf-12-559-2024
Jacob Hardt, Tim P. Dooley, Michael R. Hudec
Abstract. Salt structures and their surroundings can play an important role in the energy transition related to a number of storage and energy applications. Thus, it is important to assess the current and future stability of salt bodies in their specific geological settings. We investigate the influence of ice sheet loading and unloading on subsurface salt structures using physical models based on the geological setting of northern Germany, which was repeatedly glaciated by the Scandinavian Ice Sheet during the Pleistocene. Apparent spatial correlations between subsurface salt structures in northern Germany and Weichselian ice marginal positions have been observed before, and the topic is a matter of ongoing debate. Recently described geomorphological features – termed surface cracks – have been interpreted as a direct result of ice-sheet-induced salt movement resulting in surface expansion. The spatial clustering and orientation of these surface cracks has not been well understood so far, owing to only a limited number of available studies dealing with the related salt tectonic processes. Thus, we use four increasingly complex physical models to test the basic loading and unloading principle, to analyze flow patterns within the salt source layer and within salt structures, and to examine the influence of the shape and orientation of the salt structures with respect to a lobate ice margin in a three-dimensional laboratory environment. Three salt structures of the northern German basin were selected as examples that were replicated in the laboratory. Salt structures were initially grown by differential loading and buried before loading. The ice load was simulated by a weight that was temporarily placed on a portion of the surface of the models. The replicated salt structures were either completely covered by the load, partly covered by the load, or situated outside the load extent. In all scenarios, a dynamic response of the system to the load could be observed; while the load was applied, the structures outside the load margin started to rise, with a decreasing tendency with distance from the load margin, and, at the same time, the structures under the load subsided. After the load was removed, a flow reversal set in, and previously loaded structures started to rise, whereas the structures outside the former load margin began to subside. The vertical displacements during the unloading stage were not as strong as during the load stage, and thus the system did not return to its pre-glaciation status. Modeled salt domes that were located at distance from the load margin showed a comparably weak reaction. A more extreme response was shown by modeled salt pillows whose margins varied from sub-parallel to sub-perpendicular to the load margin and were partly covered by the load. Under these conditions, the structures showed a strong reaction in terms of strain and vertical displacement. The observed strain patterns at the surface were influenced by the
{"title":"Physical modeling of ice-sheet-induced salt movements using the example of northern Germany","authors":"Jacob Hardt, Tim P. Dooley, Michael R. Hudec","doi":"10.5194/esurf-12-559-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-559-2024","url":null,"abstract":"Abstract. Salt structures and their surroundings can play an important role in the energy transition related to a number of storage and energy applications. Thus, it is important to assess the current and future stability of salt bodies in their specific geological settings. We investigate the influence of ice sheet loading and unloading on subsurface salt structures using physical models based on the geological setting of northern Germany, which was repeatedly glaciated by the Scandinavian Ice Sheet during the Pleistocene. Apparent spatial correlations between subsurface salt structures in northern Germany and Weichselian ice marginal positions have been observed before, and the topic is a matter of ongoing debate. Recently described geomorphological features – termed surface cracks – have been interpreted as a direct result of ice-sheet-induced salt movement resulting in surface expansion. The spatial clustering and orientation of these surface cracks has not been well understood so far, owing to only a limited number of available studies dealing with the related salt tectonic processes. Thus, we use four increasingly complex physical models to test the basic loading and unloading principle, to analyze flow patterns within the salt source layer and within salt structures, and to examine the influence of the shape and orientation of the salt structures with respect to a lobate ice margin in a three-dimensional laboratory environment. Three salt structures of the northern German basin were selected as examples that were replicated in the laboratory. Salt structures were initially grown by differential loading and buried before loading. The ice load was simulated by a weight that was temporarily placed on a portion of the surface of the models. The replicated salt structures were either completely covered by the load, partly covered by the load, or situated outside the load extent. In all scenarios, a dynamic response of the system to the load could be observed; while the load was applied, the structures outside the load margin started to rise, with a decreasing tendency with distance from the load margin, and, at the same time, the structures under the load subsided. After the load was removed, a flow reversal set in, and previously loaded structures started to rise, whereas the structures outside the former load margin began to subside. The vertical displacements during the unloading stage were not as strong as during the load stage, and thus the system did not return to its pre-glaciation status. Modeled salt domes that were located at distance from the load margin showed a comparably weak reaction. A more extreme response was shown by modeled salt pillows whose margins varied from sub-parallel to sub-perpendicular to the load margin and were partly covered by the load. Under these conditions, the structures showed a strong reaction in terms of strain and vertical displacement. The observed strain patterns at the surface were influenced by the ","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140798132","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 : 2024-04-25DOI: 10.5194/egusphere-2024-1153
Jon D. Pelletier, Robert G. Hayes, Olivia Hoch, Brendan Fenerty, Luke A. McGuire
Abstract. The intersection of two non-parallel planes is a line. Howard (1990), following Horton (1932), proposed that the orientation and slope of a fluvial valley within a tributary network are geometrically constrained by the orientation and slope of the line formed by the intersection of planar approximations to the topography upslope from the tributary junction along the two tributary directions. Previously published analyses of junction-angle data support this geometric model, yet junction angles have also been proposed to be controlled by climate and/or optimality principles (e.g., minimum-power expenditure). In this paper, we document a test of the Howard (1990) model using ~107 fluvial network junctions in the conterminous U.S. and a portion of the Loess Plateau, China. Junction angles are consistent with the predictions of the Howard (1990) model when the orientations and slopes are computed using drainage basins rather than in the traditional way using valley-bottom segments near tributary junctions. When computed in the traditional way, junction angles are a function of slope ratios (as the Howard (1990) model) predicts, but data deviate from the Howard (1990) model in a manner that we propose is the result of valley-bottom meandering/tortuosity. We map the mean junction angles computed along valley bottoms within each 2.5 km x 2.5 km pixel of the conterminous U.S.A. and document lower mean junction angles in incised late-Cenozoic alluvial piedmont deposits compared to those of incised bedrock/older deposits. To understand how this finding relates to the geometric model of Howard (1990), we demonstrate that, for an idealized model of an initially unincised landform, i.e., a tilted plane with random microtopography, lower ratios of the mean microtopographic slope to the large-scale slope/tilt are associated with lower mean junction angles compared to landforms with higher such ratios. Using modern analogs, we demonstrate that unincised late-Cenozoic alluvial piedmonts likely had ratios of mean microtopographic slope to large-scale slope/tilt that were lower (i.e., ~1) prior to tributary drainage network development than the same ratios of bedrock/older deposits (≫1). This finding provides a means of understanding how the geometric model of Howard (1990) results in incised late Cenozoic alluvial piedmont deposits with lower mean tributary fluvial network junction angles, on average, compared to those of incised bedrock/older deposits. This work demonstrates that the topography of a landscape prior to fluvial incision exerts a key constraint on tributary fluvial network junction angles via a fundamental geometric principle that is independent of any climate- or optimality-based principle.
{"title":"Geometric constraints on tributary fluvial network junction angles","authors":"Jon D. Pelletier, Robert G. Hayes, Olivia Hoch, Brendan Fenerty, Luke A. McGuire","doi":"10.5194/egusphere-2024-1153","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1153","url":null,"abstract":"<strong>Abstract.</strong> The intersection of two non-parallel planes is a line. Howard (1990), following Horton (1932), proposed that the orientation and slope of a fluvial valley within a tributary network are geometrically constrained by the orientation and slope of the line formed by the intersection of planar approximations to the topography upslope from the tributary junction along the two tributary directions. Previously published analyses of junction-angle data support this geometric model, yet junction angles have also been proposed to be controlled by climate and/or optimality principles (e.g., minimum-power expenditure). In this paper, we document a test of the Howard (1990) model using ~10<sup>7</sup> fluvial network junctions in the conterminous U.S. and a portion of the Loess Plateau, China. Junction angles are consistent with the predictions of the Howard (1990) model when the orientations and slopes are computed using drainage basins rather than in the traditional way using valley-bottom segments near tributary junctions. When computed in the traditional way, junction angles are a function of slope ratios (as the Howard (1990) model) predicts, but data deviate from the Howard (1990) model in a manner that we propose is the result of valley-bottom meandering/tortuosity. We map the mean junction angles computed along valley bottoms within each 2.5 km x 2.5 km pixel of the conterminous U.S.A. and document lower mean junction angles in incised late-Cenozoic alluvial piedmont deposits compared to those of incised bedrock/older deposits. To understand how this finding relates to the geometric model of Howard (1990), we demonstrate that, for an idealized model of an initially unincised landform, i.e., a tilted plane with random microtopography, lower ratios of the mean microtopographic slope to the large-scale slope/tilt are associated with lower mean junction angles compared to landforms with higher such ratios. Using modern analogs, we demonstrate that unincised late-Cenozoic alluvial piedmonts likely had ratios of mean microtopographic slope to large-scale slope/tilt that were lower (i.e., ~1) prior to tributary drainage network development than the same ratios of bedrock/older deposits (≫1). This finding provides a means of understanding how the geometric model of Howard (1990) results in incised late Cenozoic alluvial piedmont deposits with lower mean tributary fluvial network junction angles, on average, compared to those of incised bedrock/older deposits. This work demonstrates that the topography of a landscape prior to fluvial incision exerts a key constraint on tributary fluvial network junction angles via a fundamental geometric principle that is independent of any climate- or optimality-based principle.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140798135","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 : 2024-04-25DOI: 10.5194/egusphere-2024-579
Julius Reich, Axel Winterscheid
Abstract. Precise and reliable information about bedforms, regarding geometry and dynamics, is relevant for many applications – like ensuring safe conditions for navigation along the waterways, parameterizing the roughness of the riverbed in numerical models, or improving bedload measurement and monitoring techniques. There are many so-called dunetracking tools to extract this information from bathymetrical data. However, most of these tools require the setting of various input parameters, which in turn influence the resulting bedform characteristics. How to set the values for these parameters and what influence they have on the calculations has not yet been comprehensively investigated. This is why we introduce a new dunetracking tool, which is able to quantify the influence of varying input parameter settings by performing a Monte Carlo Simulation. The core of the tool is a combination of the two existing applications Bedforms-ATM (Guitierrez, 2018) and RhenoBT (Frings et al., 2012), which have been extended by adding additional features. A wavelet analysis has been adapted from Bedforms-ATM while a zerocrossing procedure and a cross correlation analysis have been implemented based on RhenoBT. The combination of both tools enables a more accurate and sound procedure, as the results of the first step are required input parameters in the second step. By performing a Monte Carlo Simulation, comprehensive sensitivity analyses can be carried out and the possible range of results is revealed. At the same time, the high degree of automation allows the processing of large amounts of data. By applying the tool to a test dataset, it was found that bedform parameters react with different sensitivity to varying input parameter settings. Bedform lengths appeared to be more sensitive (uncertainties up to 50 % were identified) than bedform heights. The setting of a window size in the zerocrossing procedure (especially for the upper layer of bedforms in case secondary bedforms are present) was identified to be the most decisive input parameter. Here, however, the wavelet analysis offers orientation by providing a range of plausible input window sizes and thus allows a reduction of uncertainties. By choosing values outside this range, divergence behavior could be observed for several resulting bedform parameters. Concurrently, the time interval between two successive measurements has proven to have a significant influence on the determination of bedform dynamics. For the test dataset, the faster migrating secondary bedforms were no longer traceable for intervals longer than two hours. At the same time, they contributed to up to 90 % of the total bedload transport, highlighting the need for measurements in high temporal resolution in order to avoid a severe underestimation.
{"title":"A new dunetracking tool to support input parameter selection and uncertainty analyses using a Monte Carlo approach","authors":"Julius Reich, Axel Winterscheid","doi":"10.5194/egusphere-2024-579","DOIUrl":"https://doi.org/10.5194/egusphere-2024-579","url":null,"abstract":"<strong>Abstract.</strong> Precise and reliable information about bedforms, regarding geometry and dynamics, is relevant for many applications – like ensuring safe conditions for navigation along the waterways, parameterizing the roughness of the riverbed in numerical models, or improving bedload measurement and monitoring techniques. There are many so-called dunetracking tools to extract this information from bathymetrical data. However, most of these tools require the setting of various input parameters, which in turn influence the resulting bedform characteristics. How to set the values for these parameters and what influence they have on the calculations has not yet been comprehensively investigated. This is why we introduce a new dunetracking tool, which is able to quantify the influence of varying input parameter settings by performing a Monte Carlo Simulation. The core of the tool is a combination of the two existing applications Bedforms-ATM (Guitierrez, 2018) and RhenoBT (Frings et al., 2012), which have been extended by adding additional features. A wavelet analysis has been adapted from Bedforms-ATM while a zerocrossing procedure and a cross correlation analysis have been implemented based on RhenoBT. The combination of both tools enables a more accurate and sound procedure, as the results of the first step are required input parameters in the second step. By performing a Monte Carlo Simulation, comprehensive sensitivity analyses can be carried out and the possible range of results is revealed. At the same time, the high degree of automation allows the processing of large amounts of data. By applying the tool to a test dataset, it was found that bedform parameters react with different sensitivity to varying input parameter settings. Bedform lengths appeared to be more sensitive (uncertainties up to 50 % were identified) than bedform heights. The setting of a window size in the zerocrossing procedure (especially for the upper layer of bedforms in case secondary bedforms are present) was identified to be the most decisive input parameter. Here, however, the wavelet analysis offers orientation by providing a range of plausible input window sizes <span>and thus allows a reduction of uncertainties. By choosing values </span>outside this range, divergence behavior could be observed for several resulting bedform parameters. Concurrently, the time interval between two successive measurements has proven to have a significant influence on the determination of bedform dynamics. For the test dataset, the faster migrating secondary bedforms were no longer traceable for intervals longer than two hours. At the same time, they contributed to up to 90 % of the total bedload transport, highlighting the need for measurements in high temporal resolution in order to avoid a severe underestimation.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140798087","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 : 2024-04-22DOI: 10.5194/esurf-12-537-2024
Peter Arlinghaus, Corinna Schrum, Ingrid Kröncke, Wenyan Zhang
Abstract. Benthos has long been recognized as an important factor influencing local sediment stability, deposition, and erosion rates. However, its role in long-term (annual to decadal scale) and large-scale coastal morphological change remains largely speculative. This study aims to derive a quantitative understanding of the importance of benthos in the morphological development of a tidal embayment (Jade Bay) as representative of tidal coastal regions. To achieve this, we first applied a machine-learning-aided species abundance model to derive a complete map of benthos (functional groups, abundance, and biomass) in the study area, based on abundance and biomass measurements. The derived data were used to parameterize the benthos effect on sediment stability, erosion rates and deposition rates, erosion and hydrodynamics in a 3-dimensional hydro-eco-morphodynamic model, which was then applied to Jade Bay to hindcast the morphological and sediment change for 2000–2009. Simulation results indicate significantly improved performance with the benthos effect included. Simulations including benthos show consistency with measurements regarding morphological and sediment changes, while abiotic drivers (tides, storm surges) alone result in a reversed pattern in terms of erosion and deposition contrary to measurement. Based on comparisons among scenarios with various combinations of abiotic and biotic factors, we further investigated the level of complexity of the hydro-eco-morphodynamic models that is needed to capture long-term and large-scale coastal morphological development. The accuracy in the parameterization data was crucial for increasing model complexity. When the parameterization uncertainties were high, the increased model complexity decreased the model performance.
{"title":"Benthos as a key driver of morphological change in coastal regions","authors":"Peter Arlinghaus, Corinna Schrum, Ingrid Kröncke, Wenyan Zhang","doi":"10.5194/esurf-12-537-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-537-2024","url":null,"abstract":"Abstract. Benthos has long been recognized as an important factor influencing local sediment stability, deposition, and erosion rates. However, its role in long-term (annual to decadal scale) and large-scale coastal morphological change remains largely speculative. This study aims to derive a quantitative understanding of the importance of benthos in the morphological development of a tidal embayment (Jade Bay) as representative of tidal coastal regions. To achieve this, we first applied a machine-learning-aided species abundance model to derive a complete map of benthos (functional groups, abundance, and biomass) in the study area, based on abundance and biomass measurements. The derived data were used to parameterize the benthos effect on sediment stability, erosion rates and deposition rates, erosion and hydrodynamics in a 3-dimensional hydro-eco-morphodynamic model, which was then applied to Jade Bay to hindcast the morphological and sediment change for 2000–2009. Simulation results indicate significantly improved performance with the benthos effect included. Simulations including benthos show consistency with measurements regarding morphological and sediment changes, while abiotic drivers (tides, storm surges) alone result in a reversed pattern in terms of erosion and deposition contrary to measurement. Based on comparisons among scenarios with various combinations of abiotic and biotic factors, we further investigated the level of complexity of the hydro-eco-morphodynamic models that is needed to capture long-term and large-scale coastal morphological development. The accuracy in the parameterization data was crucial for increasing model complexity. When the parameterization uncertainties were high, the increased model complexity decreased the model performance.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140635765","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 : 2024-04-22DOI: 10.5194/egusphere-2024-1138
Alexander B. Prescott, Jon D. Pelletier, Satya Chataut, Sriram Ananthanarayan
Abstract. Calculating contributing area (often used as a proxy for surface water discharge) within a Digital Elevation Model (DEM) or Landscape Evolution Model (LEM) is a fundamental operation in geomorphology. Here we document that a commonly used multiple-flow-direction algorithm for calculating contributing area, i.e., D∞ of Tarboton (1997), is sufficiently biased along the cardinal and ordinal directions that it is unsuitable for some standard applications of flow-routing algorithms. We revisit the purported excess dispersion of the MFD algorithm of Freeman (1991) that motivated the development of D∞ and demonstrate that MFD is superior to D∞ when tested against analytic solutions for the contributing areas of idealized landforms and the predictions of the shallow-water-equation solver FLO-2D for more complex landforms in which the water-surface slope is closely approximated by the bed slope. We also introduce a new flow-routing algorithm entitled IDS (in reference to the iterative depth-and-slope-dependent nature of the algorithm) that is more suitable than MFD for applications in which the bed and water-surface slopes differ substantially. IDS solves for water flow depths under steady hydrologic conditions by distributing the discharge delivered to each grid point from upslope to its downslope neighbors in rank order of elevation (highest to lowest) and in proportion to a power-law function of the square root of the water-surface slope and the five-thirds power of the water depth, mimicking the relationships among water discharge, depth, and surface slope in Manning’s equation. IDS is iterative in two ways: 1) water depths are added in small increments so that the water-surface slope can gradually differ from the bed slope, facilitating the spreading of water in areas of laterally unconfined flow, and 2) the partitioning of discharge from high to low elevations can be repeated, improving the accuracy of the solution as the water depths of downslope grid points become more well approximated with each successive iteration. We assess the performance of IDS by comparing its results to those of FLO-2D for a variety of real and idealized landforms and to an analytic solution of the shallow-water equations. We also demonstrate how IDS can be modified to solve other fluid-dynamical nonlinear partial differential equations arising in Earth-surface processes, such as the Boussinesq equation for the height of the water table in an unconfined aquifer.
{"title":"An evaluation of flow-routing algorithms for calculating contributing area on regular grids","authors":"Alexander B. Prescott, Jon D. Pelletier, Satya Chataut, Sriram Ananthanarayan","doi":"10.5194/egusphere-2024-1138","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1138","url":null,"abstract":"<strong>Abstract.</strong> Calculating contributing area (often used as a proxy for surface water discharge) within a Digital Elevation Model (DEM) or Landscape Evolution Model (LEM) is a fundamental operation in geomorphology. Here we document that a commonly used multiple-flow-direction algorithm for calculating contributing area, i.e., D∞ of Tarboton (1997), is sufficiently biased along the cardinal and ordinal directions that it is unsuitable for some standard applications of flow-routing algorithms. We revisit the purported excess dispersion of the MFD algorithm of Freeman (1991) that motivated the development of D∞ and demonstrate that MFD is superior to D∞ when tested against analytic solutions for the contributing areas of idealized landforms and the predictions of the shallow-water-equation solver FLO-2D for more complex landforms in which the water-surface slope is closely approximated by the bed slope. We also introduce a new flow-routing algorithm entitled IDS (in reference to the iterative depth-and-slope-dependent nature of the algorithm) that is more suitable than MFD for applications in which the bed and water-surface slopes differ substantially. IDS solves for water flow depths under steady hydrologic conditions by distributing the discharge delivered to each grid point from upslope to its downslope neighbors in rank order of elevation (highest to lowest) and in proportion to a power-law function of the square root of the water-surface slope and the five-thirds power of the water depth, mimicking the relationships among water discharge, depth, and surface slope in Manning’s equation. IDS is iterative in two ways: 1) water depths are added in small increments so that the water-surface slope can gradually differ from the bed slope, facilitating the spreading of water in areas of laterally unconfined flow, and 2) the partitioning of discharge from high to low elevations can be repeated, improving the accuracy of the solution as the water depths of downslope grid points become more well approximated with each successive iteration. We assess the performance of IDS by comparing its results to those of FLO-2D for a variety of real and idealized landforms and to an analytic solution of the shallow-water equations. We also demonstrate how IDS can be modified to solve other fluid-dynamical nonlinear partial differential equations arising in Earth-surface processes, such as the Boussinesq equation for the height of the water table in an unconfined aquifer.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140635134","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 : 2024-04-18DOI: 10.5194/egusphere-2024-1036
W. Marijn van der Meij
Abstract. Soil erosion is one of the main threats to agricultural food production due to the loss of fertile soil. Determination of erosion rates is essential to quantify the degree of land degradation, but it is inherently challenging to determine temporally dynamic erosion rates over agricultural time scales. Optically Stimulated Luminescence (OSL) dating can provide temporally-resolved deposition rates by determining the last moment of daylight exposure of buried colluvial deposits. However, these deposition rates may differ substantially from the actual hillslope erosion rates. In this study, OSL-based deposition rates were converted to hillslope erosion rates through inverse modelling with soil-landscape evolution model ChronoLorica. This model integrates geochronological tracers into the simulations of soil mixing and redistribution. The model was applied to a kettle hole catchment in north-eastern Germany, which has been affected by tillage erosion over the last 5000 years. The initial shape of the landscape and the land use history are well-constrained, enabling accurate simulations of the landscape evolution that incorporate uncertainties in the model inputs. The calibrated model reveals an increase in erosion rates of almost to orders of magnitude from pre-historic ard ploughing up to recent intensive land management. The simulated rates match well with independent age controls from the same catchment. Uncertainty in the reconstructed initial landscape and land use histories had a minor influence of 12–16 % on the simulated rates. The simulations showed that the deposition rates were on average 1.5 higher than the erosion rates due to the ratio of erosional and depositional area. Recent artificial drainage and land reclamation have increased deposition rates up to five times the erosion rates, emphasizing the need of cautious interpretation of deposition rates as erosion proxies. This study demonstrates the suitability of ChronoLorica for upscaling experimental geochronological data to better understand landscape evolution in agricultural settings.
{"title":"Translating deposition rates into erosion rates with landscape evolution modelling","authors":"W. Marijn van der Meij","doi":"10.5194/egusphere-2024-1036","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1036","url":null,"abstract":"<strong>Abstract.</strong> Soil erosion is one of the main threats to agricultural food production due to the loss of fertile soil. Determination of erosion rates is essential to quantify the degree of land degradation, but it is inherently challenging to determine temporally dynamic erosion rates over agricultural time scales. Optically Stimulated Luminescence (OSL) dating can provide temporally-resolved deposition rates by determining the last moment of daylight exposure of buried colluvial deposits. However, these deposition rates may differ substantially from the actual hillslope erosion rates. In this study, OSL-based deposition rates were converted to hillslope erosion rates through inverse modelling with soil-landscape evolution model ChronoLorica. This model integrates geochronological tracers into the simulations of soil mixing and redistribution. The model was applied to a kettle hole catchment in north-eastern Germany, which has been affected by tillage erosion over the last 5000 years. The initial shape of the landscape and the land use history are well-constrained, enabling accurate simulations of the landscape evolution that incorporate uncertainties in the model inputs. The calibrated model reveals an increase in erosion rates of almost to orders of magnitude from pre-historic ard ploughing up to recent intensive land management. The simulated rates match well with independent age controls from the same catchment. Uncertainty in the reconstructed initial landscape and land use histories had a minor influence of 12–16 % on the simulated rates. The simulations showed that the deposition rates were on average 1.5 higher than the erosion rates due to the ratio of erosional and depositional area. Recent artificial drainage and land reclamation have increased deposition rates up to five times the erosion rates, emphasizing the need of cautious interpretation of deposition rates as erosion proxies. This study demonstrates the suitability of ChronoLorica for upscaling experimental geochronological data to better understand landscape evolution in agricultural settings.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140629824","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 : 2024-04-17DOI: 10.5194/esurf-12-515-2024
Prakash Pokhrel, Mikael Attal, Hugh D. Sinclair, Simon M. Mudd, Mark Naylor
Abstract. Sediment grains are progressively rounded during their transport down a river. For more than a century, Earth scientists have used the roundness of pebbles within modern sediment, and of clasts within conglomerates, as a key metric to constrain the sediment's transport history and source area(s). However, the current practices of assessment of pebble roundness are mainly qualitative and based on time-consuming manual measurement methods. This qualitative judgement provides the transport history only in a broad sense, such as classifying distance as “near” or “far”. In this study, we propose a new model that quantifies the relationship between roundness and the transport distance. We demonstrate that this model can be applied to the clasts of multiple lithologies including modern sediment, as well as conglomerates, deposited by ancient river systems. We present field data from two Himalayan catchments in Nepal. We use the normalized isoperimetric ratio (IRn), which relates a pebble's area (A) to its perimeter (P), to quantify roundness. The maximum analytical value for IRn is 1, and IRn is expected to increase with transport distance. We propose a non-linear roundness model based on our field data, whereby the difference between a grain's IRn and the maximum value of 1 decays exponentially with transport distance, mirroring Sternberg's model of mass loss or size reduction by abrasion. This roundness model predicts an asymptotic behaviour for IRn, and the distance over which IRn approaches the asymptote is controlled by a rounding coefficient. Our field data suggest that the roundness coefficient for granite pebbles is 9 times that of quartzite pebbles. Using this model, we reconstruct the transport history of a Pliocene paleo-river deposit preserved at the base of the Kathmandu intermontane basin. These results, along with other sedimentary evidence, imply that the paleo-river was much longer than the length of the Kathmandu Basin and that it must have lost its headwaters through drainage capture. We further explore the extreme rounding of clasts from Miocene conglomerate of the Siwalik zone and find evidence of sediment recycling.
{"title":"Downstream rounding rate of pebbles in the Himalaya","authors":"Prakash Pokhrel, Mikael Attal, Hugh D. Sinclair, Simon M. Mudd, Mark Naylor","doi":"10.5194/esurf-12-515-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-515-2024","url":null,"abstract":"Abstract. Sediment grains are progressively rounded during their transport down a river. For more than a century, Earth scientists have used the roundness of pebbles within modern sediment, and of clasts within conglomerates, as a key metric to constrain the sediment's transport history and source area(s). However, the current practices of assessment of pebble roundness are mainly qualitative and based on time-consuming manual measurement methods. This qualitative judgement provides the transport history only in a broad sense, such as classifying distance as “near” or “far”. In this study, we propose a new model that quantifies the relationship between roundness and the transport distance. We demonstrate that this model can be applied to the clasts of multiple lithologies including modern sediment, as well as conglomerates, deposited by ancient river systems. We present field data from two Himalayan catchments in Nepal. We use the normalized isoperimetric ratio (IRn), which relates a pebble's area (A) to its perimeter (P), to quantify roundness. The maximum analytical value for IRn is 1, and IRn is expected to increase with transport distance. We propose a non-linear roundness model based on our field data, whereby the difference between a grain's IRn and the maximum value of 1 decays exponentially with transport distance, mirroring Sternberg's model of mass loss or size reduction by abrasion. This roundness model predicts an asymptotic behaviour for IRn, and the distance over which IRn approaches the asymptote is controlled by a rounding coefficient. Our field data suggest that the roundness coefficient for granite pebbles is 9 times that of quartzite pebbles. Using this model, we reconstruct the transport history of a Pliocene paleo-river deposit preserved at the base of the Kathmandu intermontane basin. These results, along with other sedimentary evidence, imply that the paleo-river was much longer than the length of the Kathmandu Basin and that it must have lost its headwaters through drainage capture. We further explore the extreme rounding of clasts from Miocene conglomerate of the Siwalik zone and find evidence of sediment recycling.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":null,"pages":null},"PeriodicalIF":3.4,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140613606","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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