The morphological characteristics of small-scale bedforms were measured by means of an acoustic profiling sonar on the Dafeng tidal flat, Jiangsu, in 2009, and in the Jiulong Estuary, Xiamen, in 2010, respectively. T...The morphological characteristics of small-scale bedforms were measured by means of an acoustic profiling sonar on the Dafeng tidal flat, Jiangsu, in 2009, and in the Jiulong Estuary, Xiamen, in 2010, respectively. The ＂multi-threshold value＂ method was utilized to reveal the morphological undulations along which bedforms were present. Analyses of the datasets obtained show that： （1） sand ripples can have irregular shapes, and （2） changes in bedform morphology are small within a single tidal cycle but may be significant over several tidal cycles. Fractal and variogram analyses of the seabed roughness revealed the existence of a significant relationship between current speed and the fractal dimension of the seabed roughness. As current speed increases, seabed roughness increases with a trend of smaller-scale bottom structures being replaced by larger-scale structures. Furthermore, the surface of the larger-scale bottom structures can either become smooth due to the absence of smaller-scale features or become rougher due to the presence of superimposed smaller-scale structures.展开更多
A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9 th Chinese Arctic Research Expedit...A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9 th Chinese Arctic Research Expedition(CHINARE-Arc9)in 2018 and previously published data.The new data reveal scours that developed at water depths of 850–1030 m with an orientation of about 75°/255°.The maximum water depth occurs in the southernmost scour and is deeper than that from previous investigations,which showed a maximum scouring depth of about 900 m on the seamount.The topographic and geomorphological characteristics suggest that these scours resulted from erosion by the ice shelf extending from the Chukchi margin and/or Laurentide Ice Sheet that grounded on the crest of the seamount and moved in a NE–SW direction.Other possibilities of their genesis include armadas of large icebergs/multi-keel icebergs calved from the Chukchi Shelf or the Laurentide Ice Sheet.The new data provide new constraints for assessing the extent and volume of the ice sheet in the Chukchi area during glacial maxima.展开更多
The bedform-driven hyporheic exchange plays a crucial role in mass transport within natural aquatic ecosystems like streams and rivers. This study aimed to unveil the impact of geometric features of impermeable discre...The bedform-driven hyporheic exchange plays a crucial role in mass transport within natural aquatic ecosystems like streams and rivers. This study aimed to unveil the impact of geometric features of impermeable discrete bedforms on hyporheic exchange by experimentally measuring quantitative hyporheic exchange flux data and variation characteristics in an annual flume. The experiments encompassed diverse conditions involving the ratio of bedform wavelength (λ) to wave height (h) and relative submergence. The study also analyzed the dependence of the effective diffusion coefficient on the geometric characteristics of bedform composition elements. The experimental results showed that, in comparison to a permeable flat bed, the presence of an impermeable discrete bedform tended to either attenuate or enhance hyporheic exchange, contingent on the geometric characteristics of bedform composition elements. The hyporheic exchange flux exhibited an initially increase followed by a decrease with increasing λ/h, with turbulence penetration emerging as the dominant mechanism governing hyporheic exchange for cases with relatively denser bedform composition elements (e.g., λ/h = 4.0). The effective diffusion coefficient peaked at λ/h around 6.0–8.0, owing to a significant augmentation in the relative contribution of pumping exchange to gross hyporheic exchange. Furthermore, the hyporheic exchange intensity generally increased with decreasing relative submergence, primarily attributed to the augmented relative contribution of pumping exchange to gross hyporheic exchange.展开更多
The South China Sea(SCS),as one of the Earth's largest marginal seas,provides an ideal location for investigating turbidity currents(TC)and turbidites.Frequent TC activities in the area have been evidenced through...The South China Sea(SCS),as one of the Earth's largest marginal seas,provides an ideal location for investigating turbidity currents(TC)and turbidites.Frequent TC activities in the area have been evidenced through in-situ measurements,damage records to seabed infrastructure,and mapping the distribution of plastic litter(Note S1 online).展开更多
This paper investigates the functional and morphological self organization phenomena that occur during the bedform process in river systems. The fluvial process has architecturally functional self organization actio...This paper investigates the functional and morphological self organization phenomena that occur during the bedform process in river systems. The fluvial process has architecturally functional self organization actions that serve to self adjust the river regime. The bedform (or sand waves) process is part of the functional self organization at the middle level of the geometrical scale. By increasing the resistance of the mobile bed and simultaneously decreasing the capacity carrying sediment, the bedform serves to self adjust the river system. The morphological self organization of the bedform process is the basis for the functional self organization. The concept of the water sand interaction region is suggested, and a nonlinear model is constructed to describe the complex interaction among water flow, bed load transport, and local bed deformation, i e , the sand waves. A numerical simulation was developed based upon this model. The primary results show that the model is able to repeat many important phenomena in the bedform process, especially the critical phase transition.展开更多
The bedform evolution in an alluvial river system is studied. A mathematical model is designed to simulate the flow in the water sand region and the bedform processes.The model results in a free boundary problem. ...The bedform evolution in an alluvial river system is studied. A mathematical model is designed to simulate the flow in the water sand region and the bedform processes.The model results in a free boundary problem. Features of the free boundary problem are given.Explicit solutions as well as their physical implications for a few special cases of the free boundary problem are presented.展开更多
In the present study,among six gravel-bed river reaches,two natural gravel-bed river reaches with approximately similar bedforms and flow conditions have been found,one river reach with vegetation on bedforms and the ...In the present study,among six gravel-bed river reaches,two natural gravel-bed river reaches with approximately similar bedforms and flow conditions have been found,one river reach with vegetation on bedforms and the other without vegetation on bedforms.Based on field measurements,the impacts of vegetation over bedforms on flow characteristics have been investigated.Flow velocity,Reynolds stress and turbulence intensity distributions over bedforms with vegetation have been compared with those over gravel bedforms without vegetation.By using the quadrant analysis,the dominant events of turbulent flow structures have been assessed for flows over gravel bedforms with vegetation and without vegetation.Results show that the effect of vegetation enhances the anisotropy in turbulence and generates strong secondary currents,which lead to the occurrence of dip phenomenon at the stoss section and the crest of vegetated bedforms.The change of bed roughness from gravel bed to vegetated bed causes a development of a new boundary layer.This resulted in the different shape of velocity distributions over bedforms with vegetation from those over bedforms without vegetation,which can affect the lives of aquatic animals.Reynolds shear stress at downstream section of gravel bedform without vegetation is much higher than that of vegetated bedform,which shows that the erosion takes place from downstream of vegetated bedforms,while in the bare beds;the deposition is at downstream of bedforms.It is found that the presence of vegetation causes a chaotic distribution pattern of Reynolds shear stress,while it has more orderly pattern at the downstream section of gravel bedform without vegetation.Besides,the distribution of turbulence intensity in the lee side of vegetated bedform has a concave shape and in the stoss section,turbulence is generated in ejections and sweeps near the vegetation cover.These findings are significant to the practice of river ecological restoration.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 40876043,40976051 andJ1103408)Public Science and Technology Research Funds Projects of Ocean (Grant No. 201105001-2)the Priority Academic Program Development of Jiangsu Higher Education Institutions fund
文摘The morphological characteristics of small-scale bedforms were measured by means of an acoustic profiling sonar on the Dafeng tidal flat, Jiangsu, in 2009, and in the Jiulong Estuary, Xiamen, in 2010, respectively. The ＂multi-threshold value＂ method was utilized to reveal the morphological undulations along which bedforms were present. Analyses of the datasets obtained show that： （1） sand ripples can have irregular shapes, and （2） changes in bedform morphology are small within a single tidal cycle but may be significant over several tidal cycles. Fractal and variogram analyses of the seabed roughness revealed the existence of a significant relationship between current speed and the fractal dimension of the seabed roughness. As current speed increases, seabed roughness increases with a trend of smaller-scale bottom structures being replaced by larger-scale structures. Furthermore, the surface of the larger-scale bottom structures can either become smooth due to the absence of smaller-scale features or become rougher due to the presence of superimposed smaller-scale structures.
基金The National Natural Science Foundation of China under contract No.41976079the Chinese Polar Environment Comprehensive Investigation and Assessment Programmes under contract No.CHINARE-03-03。
文摘A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9 th Chinese Arctic Research Expedition(CHINARE-Arc9)in 2018 and previously published data.The new data reveal scours that developed at water depths of 850–1030 m with an orientation of about 75°/255°.The maximum water depth occurs in the southernmost scour and is deeper than that from previous investigations,which showed a maximum scouring depth of about 900 m on the seamount.The topographic and geomorphological characteristics suggest that these scours resulted from erosion by the ice shelf extending from the Chukchi margin and/or Laurentide Ice Sheet that grounded on the crest of the seamount and moved in a NE–SW direction.Other possibilities of their genesis include armadas of large icebergs/multi-keel icebergs calved from the Chukchi Shelf or the Laurentide Ice Sheet.The new data provide new constraints for assessing the extent and volume of the ice sheet in the Chukchi area during glacial maxima.
基金supported by the National Natural Science Foundation of China(Grant No.11472168).
文摘The bedform-driven hyporheic exchange plays a crucial role in mass transport within natural aquatic ecosystems like streams and rivers. This study aimed to unveil the impact of geometric features of impermeable discrete bedforms on hyporheic exchange by experimentally measuring quantitative hyporheic exchange flux data and variation characteristics in an annual flume. The experiments encompassed diverse conditions involving the ratio of bedform wavelength (λ) to wave height (h) and relative submergence. The study also analyzed the dependence of the effective diffusion coefficient on the geometric characteristics of bedform composition elements. The experimental results showed that, in comparison to a permeable flat bed, the presence of an impermeable discrete bedform tended to either attenuate or enhance hyporheic exchange, contingent on the geometric characteristics of bedform composition elements. The hyporheic exchange flux exhibited an initially increase followed by a decrease with increasing λ/h, with turbulence penetration emerging as the dominant mechanism governing hyporheic exchange for cases with relatively denser bedform composition elements (e.g., λ/h = 4.0). The effective diffusion coefficient peaked at λ/h around 6.0–8.0, owing to a significant augmentation in the relative contribution of pumping exchange to gross hyporheic exchange. Furthermore, the hyporheic exchange intensity generally increased with decreasing relative submergence, primarily attributed to the augmented relative contribution of pumping exchange to gross hyporheic exchange.
基金supported by the National Key Research and Development Program of China(2022YFF0800503)the National Natural Science Foundation of China(91028003,41676029,and 41876049).1。
文摘The South China Sea(SCS),as one of the Earth's largest marginal seas,provides an ideal location for investigating turbidity currents(TC)and turbidites.Frequent TC activities in the area have been evidenced through in-situ measurements,damage records to seabed infrastructure,and mapping the distribution of plastic litter(Note S1 online).
文摘This paper investigates the functional and morphological self organization phenomena that occur during the bedform process in river systems. The fluvial process has architecturally functional self organization actions that serve to self adjust the river regime. The bedform (or sand waves) process is part of the functional self organization at the middle level of the geometrical scale. By increasing the resistance of the mobile bed and simultaneously decreasing the capacity carrying sediment, the bedform serves to self adjust the river system. The morphological self organization of the bedform process is the basis for the functional self organization. The concept of the water sand interaction region is suggested, and a nonlinear model is constructed to describe the complex interaction among water flow, bed load transport, and local bed deformation, i e , the sand waves. A numerical simulation was developed based upon this model. The primary results show that the model is able to repeat many important phenomena in the bedform process, especially the critical phase transition.
文摘The bedform evolution in an alluvial river system is studied. A mathematical model is designed to simulate the flow in the water sand region and the bedform processes.The model results in a free boundary problem. Features of the free boundary problem are given.Explicit solutions as well as their physical implications for a few special cases of the free boundary problem are presented.
文摘In the present study,among six gravel-bed river reaches,two natural gravel-bed river reaches with approximately similar bedforms and flow conditions have been found,one river reach with vegetation on bedforms and the other without vegetation on bedforms.Based on field measurements,the impacts of vegetation over bedforms on flow characteristics have been investigated.Flow velocity,Reynolds stress and turbulence intensity distributions over bedforms with vegetation have been compared with those over gravel bedforms without vegetation.By using the quadrant analysis,the dominant events of turbulent flow structures have been assessed for flows over gravel bedforms with vegetation and without vegetation.Results show that the effect of vegetation enhances the anisotropy in turbulence and generates strong secondary currents,which lead to the occurrence of dip phenomenon at the stoss section and the crest of vegetated bedforms.The change of bed roughness from gravel bed to vegetated bed causes a development of a new boundary layer.This resulted in the different shape of velocity distributions over bedforms with vegetation from those over bedforms without vegetation,which can affect the lives of aquatic animals.Reynolds shear stress at downstream section of gravel bedform without vegetation is much higher than that of vegetated bedform,which shows that the erosion takes place from downstream of vegetated bedforms,while in the bare beds;the deposition is at downstream of bedforms.It is found that the presence of vegetation causes a chaotic distribution pattern of Reynolds shear stress,while it has more orderly pattern at the downstream section of gravel bedform without vegetation.Besides,the distribution of turbulence intensity in the lee side of vegetated bedform has a concave shape and in the stoss section,turbulence is generated in ejections and sweeps near the vegetation cover.These findings are significant to the practice of river ecological restoration.
