To reveal the gravitational erosion process in the headstream area of Jiangjia Ravine, continuous observation was conduced duing the rainy season. The observation and research show that the change of water content of ...To reveal the gravitational erosion process in the headstream area of Jiangjia Ravine, continuous observation was conduced duing the rainy season. The observation and research show that the change of water content of the bank slope lags the precipitation process, the infiltration water concentrates mainly in the shallow layer of the bank slope, also the bank slope was unsaturated, the floods and debris flows in the gully down cut the gully bed, and scour the foot of the bank slope. These results in many collapses, which is the main type of gravitational erosion process, and it provides large amounts of loose solid materials for the eruption of debris flows.展开更多
Rare earth elements (REE) were used to study the temporal and spatial processes of soil erosion from different depths and sections of a slope. Two simulated rainfall events were applied to a prepared plot with a slope...Rare earth elements (REE) were used to study the temporal and spatial processes of soil erosion from different depths and sections of a slope. Two simulated rainfall events were applied to a prepared plot with a slope of 22°. The total runoff and sediment yield were collected every minute during the rainfall events. During the first twenty minutes of the first rainfall event, the average rate of rill erosion and the accumulated sediment yield due to rill erosion was 0.5 and 0.3 times higher than for sheet erosion. During this time, most of the erosion occurred on the lower one third of the plot. After 20 min, rill erosion became the dominant process on the slope. The average acceleration in the rate of rill erosion, the rate of rill erosion and the accumulated sediment yield due to rill erosion were 42, 6 and 4 times higher than that of sheet erosion, respectively. During the first 35 minutes of the second rainfall event, the average acceleration in the rate of rill erosion was 6～9 times higher than that of sheet erosion. Afterwards, the slope became nearly stable with little change in either rill or sheet erosion rates. Initially, most of the rill erosion occurred in the lower third of the slope but later the preexisting rillhead in the middle section of the slope became reactivated and erosion in this section of the slope increased rapidly. These results indicate that REE tracer technology is a valuable tool for quantifying spatial and temporal changes in erosion from a soil slope.展开更多
Meadow degradation provides a major indication of increased soil erosion in alpine regions.Serious soil erosion is observed during the spring in particular because soil thawing coincides with the period of snowmelt an...Meadow degradation provides a major indication of increased soil erosion in alpine regions.Serious soil erosion is observed during the spring in particular because soil thawing coincides with the period of snowmelt and the meadow coverage is very low at this time.Studies relating to soil erosion caused by spring meltwater are,however,limited and controversial.Therefore,a field experimental study was conducted in a typical meadow in the Binggou watershed on the northern edge of the Tibetan Plateau to assess the impact of multiple factors on spring meltwater erosion on an alpine meadow slope.The multiple factors included three flow rates(1,2,and 3 L/min),four slope gradients(10°,15°,20°,and 25°),and three underlying surface conditions(meadow,disturbed meadow,and alluvial soil).An equal volume of concentrated meltwater flow was used in all experiments.The results showed that rapid melting at a high flow rate could accelerate soil erosion;as the flow rate increased from 1 to 3 L/min,the total surface runoff increased by a factor of 0.7 and the total sediment yield increased by more than 6-fold.The in-fluence of the slope gradient on the amount of runoff was positively linear and the influence was relatively low;when the slope increased from 10°to 25°,the total runoff only increased by 16%.However,the slope gradient had a strong impact on soil erosion.The total sediment yield doubled when the slope increased from 10°to 20°and then slightly decreased at 25°.The meadow could effectively reduce soil erosion,although when the meadow was disturbed,the total runoff increased by 60%and the sediment yield by a factor of 1.5.The total runoff from the alluvial soil doubled in comparison to the meadow,while the sediment yield increased nearly 7-fold.The findings of this study could be helpful to understand the characteristics and impact of multiple controlling factors of spring meltwater erosion.It also aims to provide a scientific basis for an improved management of alpine meadows as well as water and soil conservation activities in high-altitude cold regions.展开更多
The soil surface roughness and hydraulic roughness coefficient are important hydraulic resistance characteristic parameters. Precisely estimating the hydraulic roughness coefficient is important to understanding mecha...The soil surface roughness and hydraulic roughness coefficient are important hydraulic resistance characteristic parameters. Precisely estimating the hydraulic roughness coefficient is important to understanding mechanisms of overland flow. Four tillage practices, including cropland raking, artificial hoeing, artificial digging, and straight slopes, were considered based on the local agricultural conditions to simulate different values of soil surface roughness in the Loess Plateau. The objective of this study was to investigate the relationship between the soil surface roughness and hydraulic roughness coefficient on sloping farmland using artificial rainfall simulation. On a slope with a gradient of 10°, a significant logarithmic function was developed between the soil surface roughness and Manning＇s roughness coefficient, and an exponential function was derived to describe the relationship between the soil surface roughness and Reynolds number. On the slope with a gradient of 15°, a significant power function was developed to reflect the relationship between the soil surface roughness and Manning＇s roughness coefficient, and a linear function was derived to relate the soil surface roughness to the Reynolds number. These findings can provide alternative ways to estimate the hydraulic roughness coefficient for different types of soil surface roughness.展开更多
Morphometric analysis and flash floods assessment were conducted for the watersheds of Ras En Naqb escarpment, south Jordan. The study area comprises of twelve small watersheds occupying the faulted-erosional slopes, ...Morphometric analysis and flash floods assessment were conducted for the watersheds of Ras En Naqb escarpment, south Jordan. The study area comprises of twelve small watersheds occupying the faulted-erosional slopes, and the dip slopes. The drainage network shows that dendritic and sub-dendritic patterns dominated the dip slopes, whereas trellis pattern characterized the faulted-erosional slopes. Stream orders range from fourth to sixth order. The mean bifurcation ratios vary between 4.2 and 5.38 for the dip slope basins, and between 3.5 and 5.0 for the faulted-erosional slope watersheds, indicating a noticeable influence of structural disturbances (i.e., faulting and uplifting), and rejuvenation of drainage networks. All watersheds have short basin lengths, ranging from 23.8 km to 42.2 km for the dip slope basins, and between 15.3 km and 45.4 km for the faulted-erosional slope catchments. This is indicative of high flooding susceptibility associated with heavy rainstorms of short duration. The circularity ratios range from 0.177 to 0.704 which denote that the catchments are moderately circular on the faulted-erosional slopes, and to some extent elongated on the dip slopes. The length of overland flow values ranges from 0.854 to 0.924 for the dip slope catchments, whereas L<sub>O</sub> values for the faulted-erosional slopes vary from 0.793 to 0.945 denoting steep slopes and shorter paths on both dip slope and faulted-erosional slope watersheds. Values of stream frequency range from 1.509 to 1.692 for the dip slope, and from 1.688 to 2.0 for the faulted-erosional slope catchments. F<sub>S</sub> values are also indicative of slope steepness, low infiltration rate, and high flooding potential. The watersheds of the dip slopes show lower values of form factor varying from 0.079 to 0.364, indicating elongated shape and suggesting a relatively flat hydrograph peak for longer duration. Similarly, values of D<sub>d</sub> are high for catchments on the dip slope basins (1.709 - 1.85) and the faulted-erosional slope watersheds (1.587 - 2.0) indicating highly dissected topography, high surface runoff, low infiltration rate, and consequently high flooding potential. Furthermore, high relief values exist, ranging from 388 m to 714 m for the dip slope basins, and from 421 m to 846 m for the faulted-erosional slope catchments indicting high relief and steep slopes. Morphometric analysis, and flash flood assessment suggest that ten watersheds (83.3%) are categorized under high and intermediate flooding susceptibility, and the faulted-erosional slope catchments are more hazardous in terms of flooding. Thus the protection of Ma’an, El Jafr rural Bedouin settlements, and Amman-Aqaba highway from recurrent flooding is essential to ensure sustainable future development in Ras En Naqb-Ma’an area.展开更多
文摘To reveal the gravitational erosion process in the headstream area of Jiangjia Ravine, continuous observation was conduced duing the rainy season. The observation and research show that the change of water content of the bank slope lags the precipitation process, the infiltration water concentrates mainly in the shallow layer of the bank slope, also the bank slope was unsaturated, the floods and debris flows in the gully down cut the gully bed, and scour the foot of the bank slope. These results in many collapses, which is the main type of gravitational erosion process, and it provides large amounts of loose solid materials for the eruption of debris flows.
文摘Rare earth elements (REE) were used to study the temporal and spatial processes of soil erosion from different depths and sections of a slope. Two simulated rainfall events were applied to a prepared plot with a slope of 22°. The total runoff and sediment yield were collected every minute during the rainfall events. During the first twenty minutes of the first rainfall event, the average rate of rill erosion and the accumulated sediment yield due to rill erosion was 0.5 and 0.3 times higher than for sheet erosion. During this time, most of the erosion occurred on the lower one third of the plot. After 20 min, rill erosion became the dominant process on the slope. The average acceleration in the rate of rill erosion, the rate of rill erosion and the accumulated sediment yield due to rill erosion were 42, 6 and 4 times higher than that of sheet erosion, respectively. During the first 35 minutes of the second rainfall event, the average acceleration in the rate of rill erosion was 6～9 times higher than that of sheet erosion. Afterwards, the slope became nearly stable with little change in either rill or sheet erosion rates. Initially, most of the rill erosion occurred in the lower third of the slope but later the preexisting rillhead in the middle section of the slope became reactivated and erosion in this section of the slope increased rapidly. These results indicate that REE tracer technology is a valuable tool for quantifying spatial and temporal changes in erosion from a soil slope.
基金This study was financially supported by the National Natural Science Foundation of China(Grant 41571274)
文摘Meadow degradation provides a major indication of increased soil erosion in alpine regions.Serious soil erosion is observed during the spring in particular because soil thawing coincides with the period of snowmelt and the meadow coverage is very low at this time.Studies relating to soil erosion caused by spring meltwater are,however,limited and controversial.Therefore,a field experimental study was conducted in a typical meadow in the Binggou watershed on the northern edge of the Tibetan Plateau to assess the impact of multiple factors on spring meltwater erosion on an alpine meadow slope.The multiple factors included three flow rates(1,2,and 3 L/min),four slope gradients(10°,15°,20°,and 25°),and three underlying surface conditions(meadow,disturbed meadow,and alluvial soil).An equal volume of concentrated meltwater flow was used in all experiments.The results showed that rapid melting at a high flow rate could accelerate soil erosion;as the flow rate increased from 1 to 3 L/min,the total surface runoff increased by a factor of 0.7 and the total sediment yield increased by more than 6-fold.The in-fluence of the slope gradient on the amount of runoff was positively linear and the influence was relatively low;when the slope increased from 10°to 25°,the total runoff only increased by 16%.However,the slope gradient had a strong impact on soil erosion.The total sediment yield doubled when the slope increased from 10°to 20°and then slightly decreased at 25°.The meadow could effectively reduce soil erosion,although when the meadow was disturbed,the total runoff increased by 60%and the sediment yield by a factor of 1.5.The total runoff from the alluvial soil doubled in comparison to the meadow,while the sediment yield increased nearly 7-fold.The findings of this study could be helpful to understand the characteristics and impact of multiple controlling factors of spring meltwater erosion.It also aims to provide a scientific basis for an improved management of alpine meadows as well as water and soil conservation activities in high-altitude cold regions.
基金supported by the National Natural Science Foundation of China(Grant No40901138)the Project of the State Key Laboratory of Earth Surface Processes and Resource Ecology(Grant No 2008-KF-05)the Project of the State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau(Grant No10501-283)
文摘The soil surface roughness and hydraulic roughness coefficient are important hydraulic resistance characteristic parameters. Precisely estimating the hydraulic roughness coefficient is important to understanding mechanisms of overland flow. Four tillage practices, including cropland raking, artificial hoeing, artificial digging, and straight slopes, were considered based on the local agricultural conditions to simulate different values of soil surface roughness in the Loess Plateau. The objective of this study was to investigate the relationship between the soil surface roughness and hydraulic roughness coefficient on sloping farmland using artificial rainfall simulation. On a slope with a gradient of 10°, a significant logarithmic function was developed between the soil surface roughness and Manning＇s roughness coefficient, and an exponential function was derived to describe the relationship between the soil surface roughness and Reynolds number. On the slope with a gradient of 15°, a significant power function was developed to reflect the relationship between the soil surface roughness and Manning＇s roughness coefficient, and a linear function was derived to relate the soil surface roughness to the Reynolds number. These findings can provide alternative ways to estimate the hydraulic roughness coefficient for different types of soil surface roughness.
文摘Morphometric analysis and flash floods assessment were conducted for the watersheds of Ras En Naqb escarpment, south Jordan. The study area comprises of twelve small watersheds occupying the faulted-erosional slopes, and the dip slopes. The drainage network shows that dendritic and sub-dendritic patterns dominated the dip slopes, whereas trellis pattern characterized the faulted-erosional slopes. Stream orders range from fourth to sixth order. The mean bifurcation ratios vary between 4.2 and 5.38 for the dip slope basins, and between 3.5 and 5.0 for the faulted-erosional slope watersheds, indicating a noticeable influence of structural disturbances (i.e., faulting and uplifting), and rejuvenation of drainage networks. All watersheds have short basin lengths, ranging from 23.8 km to 42.2 km for the dip slope basins, and between 15.3 km and 45.4 km for the faulted-erosional slope catchments. This is indicative of high flooding susceptibility associated with heavy rainstorms of short duration. The circularity ratios range from 0.177 to 0.704 which denote that the catchments are moderately circular on the faulted-erosional slopes, and to some extent elongated on the dip slopes. The length of overland flow values ranges from 0.854 to 0.924 for the dip slope catchments, whereas L<sub>O</sub> values for the faulted-erosional slopes vary from 0.793 to 0.945 denoting steep slopes and shorter paths on both dip slope and faulted-erosional slope watersheds. Values of stream frequency range from 1.509 to 1.692 for the dip slope, and from 1.688 to 2.0 for the faulted-erosional slope catchments. F<sub>S</sub> values are also indicative of slope steepness, low infiltration rate, and high flooding potential. The watersheds of the dip slopes show lower values of form factor varying from 0.079 to 0.364, indicating elongated shape and suggesting a relatively flat hydrograph peak for longer duration. Similarly, values of D<sub>d</sub> are high for catchments on the dip slope basins (1.709 - 1.85) and the faulted-erosional slope watersheds (1.587 - 2.0) indicating highly dissected topography, high surface runoff, low infiltration rate, and consequently high flooding potential. Furthermore, high relief values exist, ranging from 388 m to 714 m for the dip slope basins, and from 421 m to 846 m for the faulted-erosional slope catchments indicting high relief and steep slopes. Morphometric analysis, and flash flood assessment suggest that ten watersheds (83.3%) are categorized under high and intermediate flooding susceptibility, and the faulted-erosional slope catchments are more hazardous in terms of flooding. Thus the protection of Ma’an, El Jafr rural Bedouin settlements, and Amman-Aqaba highway from recurrent flooding is essential to ensure sustainable future development in Ras En Naqb-Ma’an area.
