Pub Date : 2023-10-09DOI: 10.5194/esurf-11-995-2023
Sam Anderson, Nicole Gasparini, Joel Johnson
Abstract. We explore how rock properties and channel morphology vary with rock type in Last Chance Canyon, Guadalupe Mountains, New Mexico, USA. The rocks here are composed of horizontally to near-horizontally interbedded carbonate and sandstone. This study focuses on first- and second-order channel sections, where the streams have a lower channel steepness index (ksn) upstream and transition to higher ksn values downstream. We hypothesize that differences in bed thickness and rock strength influence ksn values, both locally by influencing bulk bedrock strength and also nonlocally through the production of coarse sediment. We collected discontinuity intensity data (the length of bedding planes and fractures per unit area), Schmidt hammer rebound measurements, and measured the largest boulder at every 12.2 m elevation contour to test this hypothesis. Bedrock and boulder mineralogy were determined using a lab-based carbonate dissolution method. High-resolution orthomosaics and digital surface models (DSMs) were generated from drone and ground-based photogrammetry. The orthomosaics were used to map channel sections with exposed bedrock. The United States Geological Survey (USGS) 10 m digital elevation models (DEMs) were used to measure channel slope and hillslope relief. We find that discontinuity intensity is negatively correlated with Schmidt hammer rebound values in sandstone bedrock. Channel steepness tends to be higher where reaches are primarily incising through more thickly bedded carbonate bedrock and lower where more thinly bedded sandstone is exposed. Bedrock properties also influence channel morphology indirectly, through coarse sediment input from adjacent hillslopes. Thickly bedded rock layers on hillslopes erode to contribute larger colluvial sediment to adjacent channels, and these reaches have higher ksn values. Larger and more competent carbonate sediment armors both the carbonate and the more erodible sandstone and reduces steepness contrasts across rock types. We interpret that in the relatively steep, high-level ksn downstream channel sections, the slope is primarily controlled by the coarse alluvial cover. We further posit that the upstream low-level ksn reaches have a base level that is fixed by the steep downstream reaches, resulting in a stable configuration, where channel slopes have adjusted to lithologic differences and/or sediment armor.
{"title":"Building a bimodal landscape: bedrock lithology and bed thickness controls on the morphology of Last Chance Canyon, New Mexico, USA","authors":"Sam Anderson, Nicole Gasparini, Joel Johnson","doi":"10.5194/esurf-11-995-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-995-2023","url":null,"abstract":"Abstract. We explore how rock properties and channel morphology vary with rock type in Last Chance Canyon, Guadalupe Mountains, New Mexico, USA. The rocks here are composed of horizontally to near-horizontally interbedded carbonate and sandstone. This study focuses on first- and second-order channel sections, where the streams have a lower channel steepness index (ksn) upstream and transition to higher ksn values downstream. We hypothesize that differences in bed thickness and rock strength influence ksn values, both locally by influencing bulk bedrock strength and also nonlocally through the production of coarse sediment. We collected discontinuity intensity data (the length of bedding planes and fractures per unit area), Schmidt hammer rebound measurements, and measured the largest boulder at every 12.2 m elevation contour to test this hypothesis. Bedrock and boulder mineralogy were determined using a lab-based carbonate dissolution method. High-resolution orthomosaics and digital surface models (DSMs) were generated from drone and ground-based photogrammetry. The orthomosaics were used to map channel sections with exposed bedrock. The United States Geological Survey (USGS) 10 m digital elevation models (DEMs) were used to measure channel slope and hillslope relief. We find that discontinuity intensity is negatively correlated with Schmidt hammer rebound values in sandstone bedrock. Channel steepness tends to be higher where reaches are primarily incising through more thickly bedded carbonate bedrock and lower where more thinly bedded sandstone is exposed. Bedrock properties also influence channel morphology indirectly, through coarse sediment input from adjacent hillslopes. Thickly bedded rock layers on hillslopes erode to contribute larger colluvial sediment to adjacent channels, and these reaches have higher ksn values. Larger and more competent carbonate sediment armors both the carbonate and the more erodible sandstone and reduces steepness contrasts across rock types. We interpret that in the relatively steep, high-level ksn downstream channel sections, the slope is primarily controlled by the coarse alluvial cover. We further posit that the upstream low-level ksn reaches have a base level that is fixed by the steep downstream reaches, resulting in a stable configuration, where channel slopes have adjusted to lithologic differences and/or sediment armor.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135094101","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-09DOI: 10.5194/esurf-11-979-2023
Jens M. Turowski, Gunnar Pruß, Anne Voigtländer, Andreas Ludwig, Angela Landgraf, Florian Kober, Audrey Bonnelye
Abstract. Bedrock incision by rivers is commonly driven by the impacts of moving bedload particles. The speed of incision is modulated by rock properties, which is quantified within a parameter known as erodibility that scales the erosion rate to the erosive action of the flow. Although basic models for the geotechnical controls on rock erodibility have been suggested, large scatter and trends in the remaining relationships indicate that they are incompletely understood. Here, we conducted dedicated laboratory experiments measuring erodibility using erosion mills. In parallel, we measured uniaxial compressive strength, tensile strength, Young's modulus, bulk density, and the Poisson's ratio for the tested lithologies. We find that under the same flow conditions, erosion rates of samples from the same lithology can vary by a factor of up to 60. This indicates that rock properties that may vary over short distances within the same rock can exert a strong control on its erosional properties. The geotechnical properties of the tested lithologies are strongly cross-correlated, preventing a purely empirical determination of their controls on erodibility. The currently prevailing model predicts that erosion rates should scale linearly with Young's modulus and inversely with the square of the tensile strength. We extend this model using first-principle physical arguments, taking into account the geotechnical properties of the impactor. The extended model provides a better description of the data than the existing model. Yet, the fit is far from satisfactory. We suggest that the ratio of mineral grain size to the impactor diameter presents a strong control on erodibility that has not been quantified so far. We also discuss how our laboratory results upscale to real landscapes and long timescales. For both a revised stream power incision model and a sediment-flux-dependent incision model, we suggest that long-term erosion rates scale linearly with erodibility and that, within this theoretical framework, relative laboratory measurements of erodibility can be applied at the landscape scale.
{"title":"Geotechnical controls on erodibility in fluvial impact erosion","authors":"Jens M. Turowski, Gunnar Pruß, Anne Voigtländer, Andreas Ludwig, Angela Landgraf, Florian Kober, Audrey Bonnelye","doi":"10.5194/esurf-11-979-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-979-2023","url":null,"abstract":"Abstract. Bedrock incision by rivers is commonly driven by the impacts of moving bedload particles. The speed of incision is modulated by rock properties, which is quantified within a parameter known as erodibility that scales the erosion rate to the erosive action of the flow. Although basic models for the geotechnical controls on rock erodibility have been suggested, large scatter and trends in the remaining relationships indicate that they are incompletely understood. Here, we conducted dedicated laboratory experiments measuring erodibility using erosion mills. In parallel, we measured uniaxial compressive strength, tensile strength, Young's modulus, bulk density, and the Poisson's ratio for the tested lithologies. We find that under the same flow conditions, erosion rates of samples from the same lithology can vary by a factor of up to 60. This indicates that rock properties that may vary over short distances within the same rock can exert a strong control on its erosional properties. The geotechnical properties of the tested lithologies are strongly cross-correlated, preventing a purely empirical determination of their controls on erodibility. The currently prevailing model predicts that erosion rates should scale linearly with Young's modulus and inversely with the square of the tensile strength. We extend this model using first-principle physical arguments, taking into account the geotechnical properties of the impactor. The extended model provides a better description of the data than the existing model. Yet, the fit is far from satisfactory. We suggest that the ratio of mineral grain size to the impactor diameter presents a strong control on erodibility that has not been quantified so far. We also discuss how our laboratory results upscale to real landscapes and long timescales. For both a revised stream power incision model and a sediment-flux-dependent incision model, we suggest that long-term erosion rates scale linearly with erodibility and that, within this theoretical framework, relative laboratory measurements of erodibility can be applied at the landscape scale.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135141960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-06DOI: 10.5194/esurf-11-961-2023
Koji Ohata, Hajime Naruse, Norihiro Izumi
Abstract. Plane beds develop under flows in fluvial and marine environments; they are recorded as parallel lamination in sandstone beds, such as those found in turbidites. However, whereas turbidites typically exhibit parallel lamination, they rarely feature dune-scale cross-lamination. Although the reason for the scarcity of dune-scale cross-lamination in turbidites is still debated, the formation of dunes may be dampened by suspended loads. Here, we perform, for the first time, linear-stability analysis to show that flows with suspended loads facilitate the formation of plane beds. For a fine-grained bed, a suspended load can promote the formation of plane beds and dampen the formation of dunes. These results of theoretical analysis were verified with observational data of plane beds under open-channel flows. Our theoretical analysis found that suspended loads promote the formation of plane beds, which suggests that the development of dunes under turbidity currents is suppressed by the presence of suspended loads.
{"title":"Linear-stability analysis of plane beds under flows with suspended loads","authors":"Koji Ohata, Hajime Naruse, Norihiro Izumi","doi":"10.5194/esurf-11-961-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-961-2023","url":null,"abstract":"Abstract. Plane beds develop under flows in fluvial and marine environments; they are recorded as parallel lamination in sandstone beds, such as those found in turbidites. However, whereas turbidites typically exhibit parallel lamination, they rarely feature dune-scale cross-lamination. Although the reason for the scarcity of dune-scale cross-lamination in turbidites is still debated, the formation of dunes may be dampened by suspended loads. Here, we perform, for the first time, linear-stability analysis to show that flows with suspended loads facilitate the formation of plane beds. For a fine-grained bed, a suspended load can promote the formation of plane beds and dampen the formation of dunes. These results of theoretical analysis were verified with observational data of plane beds under open-channel flows. Our theoretical analysis found that suspended loads promote the formation of plane beds, which suggests that the development of dunes under turbidity currents is suppressed by the presence of suspended loads.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134944030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-05DOI: 10.5194/esurf-11-933-2023
Eva P. S. Eibl, Kristin S. Vogfjörd, Benedikt G. Ófeigsson, Matthew J. Roberts, Christopher J. Bean, Morgan T. Jones, Bergur H. Bergsson, Sebastian Heimann, Thoralf Dietrich
Abstract. Subglacial floods cause seismic tremors that can be located and tracked in space and time using a seismic array. Here, we shed light on the generating mechanisms of the seismic signals observed during the largest measured flood from the eastern Skaftá cauldron in the Vatnajökull ice cap, Iceland. We track the propagation of the flood in 2015 using two seismic arrays and a local seismic network in combination with GPS, hydrological, and geochemical data. We find that as the water drained from the subglacial lake beneath the cauldron, families of icequakes were generated in the area around the cauldron, while the glacier surface gradually subsided by more than 100 m. We detected a several-hours-long, non-harmonic tremor and high-frequency transient events migrating downglacier, following the subglacial flood front. We suggest that this tremor is composed of repeating, closely spaced icequakes that were generated as the glacier was being lifted, cracked, and deformed, thus enabling the subglacial water flow. When the lake had largely drained, the pressure within the underlying hydrothermal system dropped. At this time, we recorded minute-long tremor bursts emanating from the cauldron area, followed by an hour-long harmonic tremor each. We interpret these as being caused by hydrothermal explosions in the geothermal system within the cauldron and as being vigorous boiling in the crustal rocks, respectively, which is an interpretation corroborated by floodwater geochemical signals. Finally, the flood also led to detectable tremor due to more energetic flow in the rapids near Sveinstindur in the Skaftá river. We conclude that the flood generated five different seismic signal types that can be associated with five different geophysical processes, including the wide spectrum from brittle failure and explosions to boiling and turbulent flow.
{"title":"Subaerial and subglacial seismic characteristics of the largest measured jökulhlaup from the eastern Skaftá cauldron, Iceland","authors":"Eva P. S. Eibl, Kristin S. Vogfjörd, Benedikt G. Ófeigsson, Matthew J. Roberts, Christopher J. Bean, Morgan T. Jones, Bergur H. Bergsson, Sebastian Heimann, Thoralf Dietrich","doi":"10.5194/esurf-11-933-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-933-2023","url":null,"abstract":"Abstract. Subglacial floods cause seismic tremors that can be located and tracked in space and time using a seismic array. Here, we shed light on the generating mechanisms of the seismic signals observed during the largest measured flood from the eastern Skaftá cauldron in the Vatnajökull ice cap, Iceland. We track the propagation of the flood in 2015 using two seismic arrays and a local seismic network in combination with GPS, hydrological, and geochemical data. We find that as the water drained from the subglacial lake beneath the cauldron, families of icequakes were generated in the area around the cauldron, while the glacier surface gradually subsided by more than 100 m. We detected a several-hours-long, non-harmonic tremor and high-frequency transient events migrating downglacier, following the subglacial flood front. We suggest that this tremor is composed of repeating, closely spaced icequakes that were generated as the glacier was being lifted, cracked, and deformed, thus enabling the subglacial water flow. When the lake had largely drained, the pressure within the underlying hydrothermal system dropped. At this time, we recorded minute-long tremor bursts emanating from the cauldron area, followed by an hour-long harmonic tremor each. We interpret these as being caused by hydrothermal explosions in the geothermal system within the cauldron and as being vigorous boiling in the crustal rocks, respectively, which is an interpretation corroborated by floodwater geochemical signals. Finally, the flood also led to detectable tremor due to more energetic flow in the rapids near Sveinstindur in the Skaftá river. We conclude that the flood generated five different seismic signal types that can be associated with five different geophysical processes, including the wide spectrum from brittle failure and explosions to boiling and turbulent flow.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134976419","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-28DOI: 10.5194/esurf-11-917-2023
Patrick Boyden, Paolo Stocchi, Alessio Rovere
Abstract. The warmest peak of the Last Interglacial (ca. 128–116 ka) is considered a process analogue and is often studied to better understand the effects of a future warmer climate on the Earth's system. In particular, significant efforts have been made to better constrain ice sheet contributions to the peak Last Interglacial sea level through field observation of paleo relative sea level indicators. Along tropical coastal margins, these observations are predominantly based on fossil shallow coral reef sequences, which also provide the possibility of gathering reliable U-series chronological constraints. However, the preservation of many Pleistocene reef sequences is often limited to a series of discrete relative sea level positions within the interglacial, where corals suitable for dating were preserved. This, in turn, limits our ability to understand the continuous evolution of paleo relative sea level through an entire interglacial, also affecting the possibility of unraveling the existence and pattern of sub-stadial sea level oscillations. While the interpretation of lithostratigraphic and geomorphologic properties is often used to overcome this hurdle, geological interpretation may present issues related to subjectivity when dealing with missing facies or incomplete sequences. In this study, we try to step back from a conventional approach, generating a spectrum of synthetic Quaternary subtropical fringing reefs for a site in southwestern Madagascar (Indian Ocean). We use the Dionisos forward stratigraphic model (from Beicip-Franlab) to build a fossil reef at this location. In each model run, we use distinct Greenland and Antarctica ice sheet melt scenarios produced by a coupled ANICE–SELEN glacial isostatic adjustment model. The resulting synthetic reef sequences are then used test these melt scenarios against the stratigraphic record. We propose that this sort of stratigraphic modeling may provide further quantitative control when interpreting Last Interglacial reef sequences.
{"title":"Refining patterns of melt with forward stratigraphic models of stable Pleistocene coastlines","authors":"Patrick Boyden, Paolo Stocchi, Alessio Rovere","doi":"10.5194/esurf-11-917-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-917-2023","url":null,"abstract":"Abstract. The warmest peak of the Last Interglacial (ca. 128–116 ka) is considered a process analogue and is often studied to better understand the effects of a future warmer climate on the Earth's system. In particular, significant efforts have been made to better constrain ice sheet contributions to the peak Last Interglacial sea level through field observation of paleo relative sea level indicators. Along tropical coastal margins, these observations are predominantly based on fossil shallow coral reef sequences, which also provide the possibility of gathering reliable U-series chronological constraints. However, the preservation of many Pleistocene reef sequences is often limited to a series of discrete relative sea level positions within the interglacial, where corals suitable for dating were preserved. This, in turn, limits our ability to understand the continuous evolution of paleo relative sea level through an entire interglacial, also affecting the possibility of unraveling the existence and pattern of sub-stadial sea level oscillations. While the interpretation of lithostratigraphic and geomorphologic properties is often used to overcome this hurdle, geological interpretation may present issues related to subjectivity when dealing with missing facies or incomplete sequences. In this study, we try to step back from a conventional approach, generating a spectrum of synthetic Quaternary subtropical fringing reefs for a site in southwestern Madagascar (Indian Ocean). We use the Dionisos forward stratigraphic model (from Beicip-Franlab) to build a fossil reef at this location. In each model run, we use distinct Greenland and Antarctica ice sheet melt scenarios produced by a coupled ANICE–SELEN glacial isostatic adjustment model. The resulting synthetic reef sequences are then used test these melt scenarios against the stratigraphic record. We propose that this sort of stratigraphic modeling may provide further quantitative control when interpreting Last Interglacial reef sequences.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135386436","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-19DOI: 10.5194/esurf-11-881-2023
Jessica Droujko, Srividya Hariharan Sudha, Gabriel Singer, Peter Molnar
Abstract. Measurement of suspended sediment concentration (SSC) at a basin outlet yields a basin-integrated picture of sediment fluxes; however, it does not give a full spatial perspective on possible sediment pathways within the catchment. Spatially resolved estimates of SSC along river networks are needed to identify sediment sources and sinks, to track erosion gradients, and quantify anthropogenic effects on catchment-scale sediment production, e.g., by dam construction or erosion control. Here we explore the use of high-resolution Sentinel-2 satellite images for this purpose in narrow and morphologically complex mountain rivers, combined with ground station turbidity sensing for calibration and supported by a Lagrangian kayak-derived river profile measurement. The study is carried out on the Vjosa River in Albania, which is one of the last intact large river systems in Europe. We developed a workflow to estimate river turbidity profiles from Sentinel-2 images including atmospheric, cloud cover, and deepwater corrections for the period May 2019 to July 2021 (106 images). In situ turbidity measurements from four turbidity sensors located along the Vjosa River provided ground truthing. A multivariate linear regression model between turbidity and reflectance was fitted to this data. The extracted longitudinal river turbidity profiles were qualitatively validated with two descents of the river with a turbidity sensor attached to a kayak. The satellite-derived river profiles revealed variability in turbidity along the main stem with a strong seasonal signal, with the highest mean turbidity in winter along the entire length of the river. Most importantly, sediment sources and sinks could be identified and quantified from the river turbidity profiles, both for tributaries and within the reaches of the Vjosa. The river basin and network acted as a sediment source most of the time and significant sediment sinks were rare. Sediment sources were mostly tributaries following basin-wide rainfall, but within-reach sources in river beds and banks were also possible. Finally, we used the data to estimate the mean annual fine sediment yield at Dorez at ∼2.5±0.6 Mt yr−1, in line with previous studies, which reveals the importance of the Vjosa River as an important sediment source of the Adriatic Sea. This work presents a proof of concept that open-access high-resolution satellite data have potential for suspended sediment quantification not only in large waterbodies but also in smaller rivers. The potential applications are many, including identifying erosion hotspots, sediment activation processes, local point sources, glacial sediment inputs, and sediment fluxes in river deltas, with a necessary future research focus on improving accuracy and reducing uncertainty in such analyses.
摘要在流域出口测量悬沙浓度(SSC)，可以得到流域整体的泥沙通量图;然而，它并没有给出流域内可能的沉积物路径的完整空间视角。需要对河网沿线的SSC进行空间分辨估计，以确定沉积物来源和汇，跟踪侵蚀梯度，并量化人类对流域尺度沉积物产生的影响，例如大坝建设或侵蚀控制。在这里，我们探索在狭窄和地形复杂的山地河流中使用高分辨率Sentinel-2卫星图像，结合地面站浊度传感进行校准，并通过拉格朗日皮划艇衍生的河流剖面测量来支持。这项研究是在阿尔巴尼亚的Vjosa河上进行的，这是欧洲最后一个完整的大型河流系统之一。我们开发了一个工作流程，从2019年5月至2021年7月(106张图像)的Sentinel-2图像中估计河流浊度概况，包括大气、云层和深水校正。位于Vjosa河沿岸的四个浊度传感器的现场浊度测量提供了地面真实情况。在浊度和反射率之间建立了多元线性回归模型。提取的纵向河流浊度剖面定性验证与河流的两个下降与浑浊度传感器连接到一个皮艇。卫星获取的河流剖面揭示了沿干流的浊度变化，具有强烈的季节性信号，整个河流的冬季平均浊度最高。最重要的是，沉积物来源和汇可以从河流的浑浊度剖面中识别和量化，包括支流和Vjosa河段。大部分时间，流域和河网作为泥沙源区，显著的泥沙汇很少。沉积物来源主要是全流域降雨后的支流，但河床和河岸内的沉积物来源也是可能的。最后，我们利用这些数据估计了Dorez的年平均细沙产量为~ 2.5±0.6 Mt yr - 1，这与之前的研究结果一致，揭示了Vjosa河作为亚得里亚海重要沉积物来源的重要性。这项工作提出了一个概念证明，即开放获取的高分辨率卫星数据不仅在大型水体中，而且在较小的河流中都有可能用于悬浮沉积物的量化。潜在的应用有很多，包括确定河流三角洲的侵蚀热点、泥沙活化过程、局部点源、冰川沉积物输入和泥沙通量，未来的研究重点是提高这些分析的准确性和减少不确定性。
{"title":"Sediment source and sink identification using Sentinel-2 and a small network of turbidimeters on the Vjosa River","authors":"Jessica Droujko, Srividya Hariharan Sudha, Gabriel Singer, Peter Molnar","doi":"10.5194/esurf-11-881-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-881-2023","url":null,"abstract":"Abstract. Measurement of suspended sediment concentration (SSC) at a basin outlet yields a basin-integrated picture of sediment fluxes; however, it does not give a full spatial perspective on possible sediment pathways within the catchment. Spatially resolved estimates of SSC along river networks are needed to identify sediment sources and sinks, to track erosion gradients, and quantify anthropogenic effects on catchment-scale sediment production, e.g., by dam construction or erosion control. Here we explore the use of high-resolution Sentinel-2 satellite images for this purpose in narrow and morphologically complex mountain rivers, combined with ground station turbidity sensing for calibration and supported by a Lagrangian kayak-derived river profile measurement. The study is carried out on the Vjosa River in Albania, which is one of the last intact large river systems in Europe. We developed a workflow to estimate river turbidity profiles from Sentinel-2 images including atmospheric, cloud cover, and deepwater corrections for the period May 2019 to July 2021 (106 images). In situ turbidity measurements from four turbidity sensors located along the Vjosa River provided ground truthing. A multivariate linear regression model between turbidity and reflectance was fitted to this data. The extracted longitudinal river turbidity profiles were qualitatively validated with two descents of the river with a turbidity sensor attached to a kayak. The satellite-derived river profiles revealed variability in turbidity along the main stem with a strong seasonal signal, with the highest mean turbidity in winter along the entire length of the river. Most importantly, sediment sources and sinks could be identified and quantified from the river turbidity profiles, both for tributaries and within the reaches of the Vjosa. The river basin and network acted as a sediment source most of the time and significant sediment sinks were rare. Sediment sources were mostly tributaries following basin-wide rainfall, but within-reach sources in river beds and banks were also possible. Finally, we used the data to estimate the mean annual fine sediment yield at Dorez at ∼2.5±0.6 Mt yr−1, in line with previous studies, which reveals the importance of the Vjosa River as an important sediment source of the Adriatic Sea. This work presents a proof of concept that open-access high-resolution satellite data have potential for suspended sediment quantification not only in large waterbodies but also in smaller rivers. The potential applications are many, including identifying erosion hotspots, sediment activation processes, local point sources, glacial sediment inputs, and sediment fluxes in river deltas, with a necessary future research focus on improving accuracy and reducing uncertainty in such analyses.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135014589","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-19DOI: 10.5194/esurf-11-899-2023
Matan Ben-Asher, Florence Magnin, Sebastian Westermann, Josué Bock, Emmanuel Malet, Johan Berthet, Ludovic Ravanel, Philip Deline
Abstract. Water takes part in most physical processes that shape mountainous periglacial landscapes and initiation of mass-wasting processes. An observed increase in rockfall activity in high mountain regions was previously linked to permafrost degradation, and water that infiltrates into rock fractures is one of the likely drivers of processes related to thawing and destabilization. However, there is very little knowledge of the quantity and timing of water availability for infiltration into steep rock slopes. This knowledge gap originates from the complex meteorological, hydrological, and thermal processes that control snowmelt, as well as challenging access and data acquisition in extreme alpine environments. Here we use field measurements and numerical modeling to simulate the energy balance and hydrological fluxes on a steep high-elevation permafrost-affected rock slope at Aiguille du Midi (3842 m a.s.l, France), in the Mont Blanc massif. Our results provide new information about water balance at the surface of steep rock slopes. Model results suggest that only ∼ 25 % of the snowfall accumulates in our study site; the remaining ∼ 75 % is likely transported downslope by wind and gravity. The snowpack thickness was found to decrease with surface slopes between 40 and 70∘. We found that among all water fluxes, sublimation is the main process of snowpack mass loss at our study site. Snowmelt occurs between spring and late summer, but most of it may not reach the rock surface due to refreezing and the formation of an impermeable ice layer at the base of the snowpack, which was observed at the field site. The annual snowmelt that is available for infiltration (i.e., effective snowmelt) is highly variable in the simulated years 1959–2021, and its onset occurs mostly between May and August and ends before October. By applying the model to a range of altitudes, we show that effective snowmelt is the main source of water for infiltration above 3600 m a.s.l.; below, direct rainfall on the snow-free surface is the dominant source. This change from snowmelt- to rainfall-dominated water input leads to an abrupt, nonlinear increase in water availability at altitudes below 3600 m a.s.l and may point to higher sensitivity of permafrost-affected rock slopes to climate change at these altitudes.
摘要水参与了形成山区冰缘景观和开始大规模消耗过程的大多数物理过程。先前观测到的高山地区岩崩活动增加与永久冻土退化有关，而渗入岩石裂缝的水是与融化和不稳定有关的过程的可能驱动因素之一。然而，对于渗入陡峭岩石边坡的水量和时间，人们知之甚少。这种知识差距源于控制融雪的复杂气象、水文和热过程，以及在极端高山环境中具有挑战性的获取和数据采集。在这里，我们利用野外测量和数值模拟模拟了勃朗峰地块Aiguille du Midi(海拔3842 m a.s.l.，法国)高海拔受永久冻土影响的陡峭岩石斜坡的能量平衡和水文通量。我们的研究结果提供了关于陡峭岩石边坡表面水分平衡的新信息。模式结果表明，只有~ 25%的降雪在我们的研究地点积累;剩下的75%可能通过风和重力向下坡输送。我们发现积雪厚度随地表坡度在40到70°之间而减小。我们发现，在所有的水通量中，升华是我们研究地点积雪质量损失的主要过程。融雪发生在春季和夏末之间，但大部分融雪可能不会到达岩石表面，这是在实地观察到的，因为再冻结和积雪底部形成了不透水的冰层。1959-2021年模拟年可入渗的年融雪量(即有效融雪量)变化很大，其开始时间主要在5 - 8月之间，结束于10月之前。将模型应用于一定的海拔高度，结果表明:在海拔3600m以上，有效融雪是入渗的主要水源;在地下，无雪地表的直接降雨是主要来源。这种从融雪为主到以降雨为主的水输入的变化导致海拔3600米以下的可用水量突然非线性增加，并可能表明这些海拔高度受永久冻土影响的岩石斜坡对气候变化的敏感性更高。
{"title":"Estimating surface water availability in high mountain rock slopes using a numerical energy balance model","authors":"Matan Ben-Asher, Florence Magnin, Sebastian Westermann, Josué Bock, Emmanuel Malet, Johan Berthet, Ludovic Ravanel, Philip Deline","doi":"10.5194/esurf-11-899-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-899-2023","url":null,"abstract":"Abstract. Water takes part in most physical processes that shape mountainous periglacial landscapes and initiation of mass-wasting processes. An observed increase in rockfall activity in high mountain regions was previously linked to permafrost degradation, and water that infiltrates into rock fractures is one of the likely drivers of processes related to thawing and destabilization. However, there is very little knowledge of the quantity and timing of water availability for infiltration into steep rock slopes. This knowledge gap originates from the complex meteorological, hydrological, and thermal processes that control snowmelt, as well as challenging access and data acquisition in extreme alpine environments. Here we use field measurements and numerical modeling to simulate the energy balance and hydrological fluxes on a steep high-elevation permafrost-affected rock slope at Aiguille du Midi (3842 m a.s.l, France), in the Mont Blanc massif. Our results provide new information about water balance at the surface of steep rock slopes. Model results suggest that only ∼ 25 % of the snowfall accumulates in our study site; the remaining ∼ 75 % is likely transported downslope by wind and gravity. The snowpack thickness was found to decrease with surface slopes between 40 and 70∘. We found that among all water fluxes, sublimation is the main process of snowpack mass loss at our study site. Snowmelt occurs between spring and late summer, but most of it may not reach the rock surface due to refreezing and the formation of an impermeable ice layer at the base of the snowpack, which was observed at the field site. The annual snowmelt that is available for infiltration (i.e., effective snowmelt) is highly variable in the simulated years 1959–2021, and its onset occurs mostly between May and August and ends before October. By applying the model to a range of altitudes, we show that effective snowmelt is the main source of water for infiltration above 3600 m a.s.l.; below, direct rainfall on the snow-free surface is the dominant source. This change from snowmelt- to rainfall-dominated water input leads to an abrupt, nonlinear increase in water availability at altitudes below 3600 m a.s.l and may point to higher sensitivity of permafrost-affected rock slopes to climate change at these altitudes.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135014991","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-18DOI: 10.5194/esurf-11-865-2023
Gregory A. Ruetenik, John D. Jansen, Pedro Val, Lotta Ylä-Mella
Abstract. By simulating erosion and deposition, landscape evolution models (LEMs) offer powerful insights into Earth surface processes and dynamics. Stream-power-based LEMs are often constructed from parameters describing drainage area (m), slope (n), substrate erodibility (K), hillslope diffusion (D), and a critical drainage area (Ac) that signifies the downslope transition from hillslope diffusion to advective fluvial processes. In spite of the widespread success of such models, the parameter values are highly uncertain mainly because the advection and diffusion equations amalgamate physical processes and material properties that span widely differing spatial and temporal scales. Here, we use a global catalogue of catchment-averaged cosmogenic 10Be-derived denudation rates with the aim to optimise a set of LEMs via a Monte Carlo-based parameter search. We consider three model scenarios: advection-only, diffusion-only, and an advection–diffusion hybrid. In each case, we search for a parameter set that best approximates denudation rates at the global scale, and we directly compare denudation rates from the modelled scenarios with those derived from 10Be data. We find that optimised ranges can be defined for many LEM parameters at the global scale. In the absence of diffusion, n∼1.3, and with increasing diffusivity the optimal n increases linearly to a global maximum of n∼2.3. Meanwhile, we find that the diffusion-only model yields a slightly lower misfit when comparing model outputs with observed erosion rates than the advection-only model and is optimised when the concavity parameter is raised to a power of 2. With these examples, we suggest that our approach provides baseline parameter estimates for large-scale studies spanning long timescales and diverse landscape properties. Moreover, our direct comparison of model-predicted versus observed denudation rates is preferable to methods that rely upon catchment-scale averaging or amalgamation of topographic metrics. We also seek to optimise the K and D parameters in LEMs with respect to precipitation and substrate lithology. Despite the potential bias due to factors such as lithology, these optimised models allow us to effectively control for topography and specifically target the relationship between denudation and precipitation. All models suggest a general increase in exponents with precipitation in line with previous studies. When isolating K under globally optimised models, we observe a positive correlation between K or D and precipitation > 1500 mm yr−1, plus a local maximum at ∼300 mm yr−1, which is compatible with the long-standing hypothesis that semi-arid environments are among the most erodible.
摘要通过模拟侵蚀和沉积，景观演化模型(LEMs)提供了对地球表面过程和动力学的有力见解。基于水流动力的LEMs通常由以下参数构建:流域面积(m)、坡度(n)、基材可蚀性(K)、山坡扩散(D)和临界流域面积(Ac)，该区域表示从山坡扩散到平流河流过程的下坡过渡。尽管这些模型取得了广泛的成功，但参数值具有高度的不确定性，主要是因为平流和扩散方程合并了跨越广泛不同空间和时间尺度的物理过程和材料特性。在这里，我们使用全球流域平均宇宙起源10be的剥蚀率目录，目的是通过基于蒙特卡洛的参数搜索来优化一组lem。我们考虑了三种模型情景:仅平流、仅扩散和平流-扩散混合。在每一种情况下，我们寻找一个最接近全球尺度剥蚀率的参数集，并直接将模拟情景的剥蚀率与来自10Be数据的剥蚀率进行比较。我们发现可以在全局尺度上定义许多LEM参数的优化范围。在没有扩散的情况下，n ~ 1.3，随着扩散率的增加，最优n线性增加，达到全局最大值n ~ 2.3。与此同时，我们发现，当将模型输出与观测到的侵蚀率进行比较时，仅扩散模型的失配程度略低于仅平流模型，并且当凹凸度参数提高到2次幂时，该模型得到了优化。通过这些例子，我们认为我们的方法为跨越长时间尺度和不同景观特性的大规模研究提供了基线参数估计。此外，我们对模型预测和观测到的剥蚀率的直接比较比依赖于流域尺度平均或地形指标合并的方法更可取。我们还寻求优化lem中关于沉淀和衬底岩性的K和D参数。尽管由于岩性等因素可能存在偏差，但这些优化模型使我们能够有效地控制地形，并专门针对剥蚀与降水之间的关系。所有模式都表明，与以前的研究一致，指数随降水普遍增加。当在全局优化模式下分离K时，我们观察到K或D与降水>之间呈正相关;1500 mm yr - 1，加上约300 mm yr - 1的局部最大值，这与长期以来的假设相符，即半干旱环境是最易侵蚀的环境之一。
{"title":"Optimising global landscape evolution models with <sup>10</sup>Be","authors":"Gregory A. Ruetenik, John D. Jansen, Pedro Val, Lotta Ylä-Mella","doi":"10.5194/esurf-11-865-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-865-2023","url":null,"abstract":"Abstract. By simulating erosion and deposition, landscape evolution models (LEMs) offer powerful insights into Earth surface processes and dynamics. Stream-power-based LEMs are often constructed from parameters describing drainage area (m), slope (n), substrate erodibility (K), hillslope diffusion (D), and a critical drainage area (Ac) that signifies the downslope transition from hillslope diffusion to advective fluvial processes. In spite of the widespread success of such models, the parameter values are highly uncertain mainly because the advection and diffusion equations amalgamate physical processes and material properties that span widely differing spatial and temporal scales. Here, we use a global catalogue of catchment-averaged cosmogenic 10Be-derived denudation rates with the aim to optimise a set of LEMs via a Monte Carlo-based parameter search. We consider three model scenarios: advection-only, diffusion-only, and an advection–diffusion hybrid. In each case, we search for a parameter set that best approximates denudation rates at the global scale, and we directly compare denudation rates from the modelled scenarios with those derived from 10Be data. We find that optimised ranges can be defined for many LEM parameters at the global scale. In the absence of diffusion, n∼1.3, and with increasing diffusivity the optimal n increases linearly to a global maximum of n∼2.3. Meanwhile, we find that the diffusion-only model yields a slightly lower misfit when comparing model outputs with observed erosion rates than the advection-only model and is optimised when the concavity parameter is raised to a power of 2. With these examples, we suggest that our approach provides baseline parameter estimates for large-scale studies spanning long timescales and diverse landscape properties. Moreover, our direct comparison of model-predicted versus observed denudation rates is preferable to methods that rely upon catchment-scale averaging or amalgamation of topographic metrics. We also seek to optimise the K and D parameters in LEMs with respect to precipitation and substrate lithology. Despite the potential bias due to factors such as lithology, these optimised models allow us to effectively control for topography and specifically target the relationship between denudation and precipitation. All models suggest a general increase in exponents with precipitation in line with previous studies. When isolating K under globally optimised models, we observe a positive correlation between K or D and precipitation > 1500 mm yr−1, plus a local maximum at ∼300 mm yr−1, which is compatible with the long-standing hypothesis that semi-arid environments are among the most erodible.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135109996","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-08DOI: 10.5194/esurf-11-849-2023
Andy Margason, Alison M. Anders, Robert J. C. Conrick, Gerard H. Roe
Abstract. Glaciers are sensitive to temporal climate variability. Glacier sensitivity to spatial variability in climate has been much less studied. The Olympic Mountains of Washington state, USA, experience a pronounced orographic precipitation gradient, with modern annual precipitation ranging between ∼6500 and ∼500 mm water equivalent. In the Quinault valley, on the wet side of the range, a glacier extended onto the coastal plain, reaching a maximum position during the Early Wisconsin glaciation. On the dry side of the range, in the Elwha valley, there is no evidence of a large paleo-glacier during the Wisconsin glaciation. We hypothesize that asymmetry in the past glacier extent was driven by spatial variability in precipitation. To evaluate this hypothesis, we constrain the past precipitation gradient and model the glacier extent. We explore variability in observed and modeled precipitation gradients over timescales from 6 h to ∼100 yr. Across three datasets, basin-averaged precipitation in the Elwha is 54 % of that in the Quinault. Our analysis overwhelmingly indicates spatially coherent variability in precipitation across the peninsula. We conclude that the past precipitation gradient was likely similar to the modern gradient. We use a one-dimensional glacier flowline model, driven by sea level summer temperature and annual precipitation to approximate the glacier extent in the Quinault and Elwha valleys. We find several equilibrium states for the Quinault glacier at the mapped maximum position within paleoclimate constraints for cooling and drying, relative to present-day conditions. Assuming stable precipitation gradients, we model the Elwha glacier extent for the climates of these equilibria. At the warm end of the paleoclimate constraint (July average sea level temperature of 10.5 ∘C), a small valley glacier occurs in the high headwaters of the Elwha valley. Yet, for the cooler end of the allowable paleoclimate (July average sea level temperature of 7 ∘C), the Elwha glacier advances to a narrow notch in the valley, thickens, and rapidly extends far beyond the likely true maximum extent. Therefore, we suggest that the Early Wisconsin period was more likely to have been relatively warm because our models of the glacial extent are consistent with the past record of glaciation in both the Quinault valley and Elwha valley for warm conditions but inconsistent for cooler conditions. Alternatively, spatially variable drivers of ablation, including differences in cloudiness, could have contributed to past asymmetry in the glacier extent. Future research to constrain past precipitation gradients and evaluate their impact on glacier dynamics is needed to better interpret the climatic significance of past glaciation and to predict the future response of glaciers to climate change.
{"title":"Spatially coherent variability in modern orographic precipitation produces asymmetric paleo-glacier extents in flowline models: Olympic Mountains, USA","authors":"Andy Margason, Alison M. Anders, Robert J. C. Conrick, Gerard H. Roe","doi":"10.5194/esurf-11-849-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-849-2023","url":null,"abstract":"Abstract. Glaciers are sensitive to temporal climate variability. Glacier sensitivity to spatial variability in climate has been much less studied. The Olympic Mountains of Washington state, USA, experience a pronounced orographic precipitation gradient, with modern annual precipitation ranging between ∼6500 and ∼500 mm water equivalent. In the Quinault valley, on the wet side of the range, a glacier extended onto the coastal plain, reaching a maximum position during the Early Wisconsin glaciation. On the dry side of the range, in the Elwha valley, there is no evidence of a large paleo-glacier during the Wisconsin glaciation. We hypothesize that asymmetry in the past glacier extent was driven by spatial variability in precipitation. To evaluate this hypothesis, we constrain the past precipitation gradient and model the glacier extent. We explore variability in observed and modeled precipitation gradients over timescales from 6 h to ∼100 yr. Across three datasets, basin-averaged precipitation in the Elwha is 54 % of that in the Quinault. Our analysis overwhelmingly indicates spatially coherent variability in precipitation across the peninsula. We conclude that the past precipitation gradient was likely similar to the modern gradient. We use a one-dimensional glacier flowline model, driven by sea level summer temperature and annual precipitation to approximate the glacier extent in the Quinault and Elwha valleys. We find several equilibrium states for the Quinault glacier at the mapped maximum position within paleoclimate constraints for cooling and drying, relative to present-day conditions. Assuming stable precipitation gradients, we model the Elwha glacier extent for the climates of these equilibria. At the warm end of the paleoclimate constraint (July average sea level temperature of 10.5 ∘C), a small valley glacier occurs in the high headwaters of the Elwha valley. Yet, for the cooler end of the allowable paleoclimate (July average sea level temperature of 7 ∘C), the Elwha glacier advances to a narrow notch in the valley, thickens, and rapidly extends far beyond the likely true maximum extent. Therefore, we suggest that the Early Wisconsin period was more likely to have been relatively warm because our models of the glacial extent are consistent with the past record of glaciation in both the Quinault valley and Elwha valley for warm conditions but inconsistent for cooler conditions. Alternatively, spatially variable drivers of ablation, including differences in cloudiness, could have contributed to past asymmetry in the glacier extent. Future research\u0000to constrain past precipitation gradients and evaluate their impact on\u0000glacier dynamics is needed to better interpret the climatic significance of past glaciation and to predict the future response of glaciers to climate\u0000change.\u0000","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"38 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2023-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88958148","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-09-05DOI: 10.5194/esurf-11-835-2023
K. Leary, Leah Tevis, M. Schmeeckle
Abstract. Despite a rich history of studies investigating fluid dynamics over bedforms and dunes in rivers, the spatiotemporal patterns of sub-bedform bedload transport remain poorly understood. Previous experiments assessing the effects of flow separation on downstream fluid turbulent structures and bedload transport suggest that localized, intermittent, high-magnitude transport events (i.e., permeable splat events) play an important role in both downstream and cross-stream bedload transport near flow reattachment. Here, we report results from flume experiments that assess the combined effects of flow separation–reattachment and flow re-acceleration over fixed two-dimensional bedforms (1.7 cm high; 30 cm long). A high-speed camera observed bedload transport along the entirety of the bedform at 250 frames per second. Grain trajectories, grain velocities, and grain transport directions were acquired from bedload images using semiautomated particle-tracking techniques. Downstream and vertical fluid velocities were measured 3 mm above the bed using laser Doppler velocimetry (LDV) at 15 distances along the bedform profile. Mean downstream fluid velocity increases nonlinearly with increasing distance along the bedform. However, observed bedload transport increases linearly with increasing distance along the bedform, except at the crest of the bedform, where both mean downstream fluid velocity and bedload transport decrease substantially. Bedload transport time series and manual particle-tracking data show a zone of high-magnitude, cross-stream transport near flow reattachment, suggesting that permeable splat events play an essential role in the region downstream of flow reattachment.
{"title":"Spatiotemporal bedload transport patterns over two-dimensional bedforms","authors":"K. Leary, Leah Tevis, M. Schmeeckle","doi":"10.5194/esurf-11-835-2023","DOIUrl":"https://doi.org/10.5194/esurf-11-835-2023","url":null,"abstract":"Abstract. Despite a rich history of studies investigating fluid dynamics over bedforms and dunes in rivers, the spatiotemporal patterns of sub-bedform bedload transport remain poorly understood. Previous experiments assessing the effects of flow separation on downstream fluid turbulent structures and bedload transport suggest that localized, intermittent, high-magnitude transport events (i.e., permeable splat events) play an important role in both downstream and cross-stream bedload transport near flow reattachment. Here, we report results from flume experiments that assess the combined effects of flow separation–reattachment and flow re-acceleration over fixed two-dimensional bedforms (1.7 cm high; 30 cm long). A high-speed camera observed bedload transport along the entirety of the bedform at 250 frames per second. Grain trajectories, grain velocities, and grain transport directions were acquired from bedload images using semiautomated particle-tracking techniques. Downstream and vertical fluid velocities were measured 3 mm above the bed using laser Doppler velocimetry (LDV) at 15 distances along the bedform profile. Mean downstream fluid velocity increases nonlinearly with increasing distance along the bedform. However, observed bedload transport increases linearly with increasing distance along the bedform, except at the crest of the bedform, where both mean downstream fluid velocity and bedload transport decrease substantially. Bedload transport time series and manual particle-tracking data show a zone of high-magnitude, cross-stream transport near flow reattachment, suggesting that permeable splat events play an essential role in the region downstream of flow reattachment.\u0000","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"50 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2023-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85799008","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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