To quantify the impacts of native vegetation on the spatial and temporal variations in hydraulic properties of bank gully concentrated flows,a series of in situ flume experiments in the bank gully were performed at th...To quantify the impacts of native vegetation on the spatial and temporal variations in hydraulic properties of bank gully concentrated flows,a series of in situ flume experiments in the bank gully were performed at the Yuanmou Gully Erosion and Collapse Experimental Station in the dry-hot valley region of the Jinsha River,Southwest China.This experiment involved upstream catchment areas withone-and two-year native grass(Heteropogon contortus)and bare land drained to bare gully headcuts,i.e.,Gullies 1,2 and 3.In Gully 4,Heteropogon contortus and Agave sisalana were planted in the upstream catchment area and gully bed,respectively.Among these experiments,the sediment concentration in runoff in Gully 3 was the highest and that in Gully 2 was the lowest,clearly indicating that the sediment concentration in runoff obviously decreased and the deposition of sediment obviously increased as the vegetation cover increased.The concentrated flows were turbulent in response to the flow discharge.The concentrated flows in the gully zones with native grass and bare land were sub-and supercritical,respectively.The flow rate and shear stress in Gully 3 upstream catchment area were highest among the four upstream catchment areas,while the flow rate and shear stress in the gully bed of Gully 4 were lowest among the four gully beds,indicating that native grass notably decreased the bank gully flow rate and shear stress.The Darcy–Weisbach friction factor(resistance f)and flow energy consumption in the gully bed of Gully 4 were notably higher than those in the other three gully beds,clearly indicating that native grass increased the bank gully surface resistance and flow energy consumption.The Reynolds number(Re),flow rate,shear stress,resistance f,and flow energy consumption in the gully beds and upstream areas increased over time,while the sediment concentration in runoff and Froude number(Fr)decreased.Overall,increasing vegetation cover in upstream catchment areas and downstream gully beds of the bank gully is essential for gully erosion mitigation.展开更多
Scale effects exist in the whole process of rainfall-3-runoff-3-soil erosion-3-sediment transport in river basins. The differences of hydrographs and sediment graphs in different positions in a river basin are treated...Scale effects exist in the whole process of rainfall-3-runoff-3-soil erosion-3-sediment transport in river basins. The differences of hydrographs and sediment graphs in different positions in a river basin are treated as basic scale effects, which are more complex in the gullied Loess Plateau, a region notorious for high intensity soil erosion and hyper-concentrated sediment-laden flow. The up-scaling method of direct extrapolation that maintains dynamical mechanism effective in large scale application was chosen as the methodology of this paper. Firstly, scale effects of hydrographs and sediment graphs were analyzed by using field data, and key sub-processes and their mechanisms contributing to scale effects were clearly defined. Then, the Digital Yellow River Model that integrates sub-models for the subprocesses was used with high resolution to simulate rainfall-3-runoff-3-soil erosion-3-sediment transport response in Chabagou watershed, and the distributed results representing scale effects were obtained. Finally, analysis on the simulation results was carried out. It was shown that gravitational erosion and hyper-concentrated flow contribute most to the spatial variation of hydrographs and sediment graphs in the spatial scale. Different spatial scale distributions and superposition of different sub-processes are the mechanisms of scale effects.展开更多
The European Commission's Thematic Strategy for Soil Protection(COM(2012)46)identified soil erosion as an important threat to European Union's(EU)soil resources.Gully erosion is an important but hitherto poorl...The European Commission's Thematic Strategy for Soil Protection(COM(2012)46)identified soil erosion as an important threat to European Union's(EU)soil resources.Gully erosion is an important but hitherto poorly understood component of this threat.Here we present the results of an unprecedented attempt to monitor the occurrence of gully erosion across the EU and UK.We integrate a soil erosion module into the 2018 LUCAS Topsoil Survey,which was conducted to monitor the soil health status across the EU and to support actions to prevent soil degradation.We discuss and explore opportunities to further improve this method.The 2018 LUCAS Topsoil Survey consisted of soil sampling(0-20 cm depth)and erosion observations conducted in ca.10%(n=24,759)of the 238,077 Land Use/Cover Area frame Survey(LUCAS)2018 in-field survey sites.Gully erosion channels were detected for ca.1%(211 sites)of the visited LUCAS Topsoil sites.Commission(false positives,2.5%)and omission errors(false negatives,5.6%)were found to be low and at a level that could not compromise the representativeness of the gully erosion survey.Overall,the findings indicate that the tested 2018 LUCAS Topsoil in-field gully erosion monitoring system is effective for detecting the incidence of gully erosion.The morphogenesis of the mapped gullies suggests that the approach is an effective tool to map permanent gullies,whereas it appears less effective to detect short-lived forms like ephemeral gullies.Spatial patterns emerging from the LUCAS Topsoil field observations provide new insights on typical gully formation sites across the EU and UK.This can help to design further targeted research activities.An extension of this approach to all LUCAS sites of 2022 would significantly enhance our understanding of the geographical distribution of gully erosion processes across the EU.Repeated every three years,LUCAS soil erosion surveys would contribute to assess the state of gully erosion in the EU over time.It will also enable monitoring and eventually predicting the dynamics of gully erosion.Data collected were part of the publicly available Gully Erosion LUCAS visual assessment(GE-LUCAS v1.0)inventory.展开更多
基金supported by the National Key Research and Development Program of China(2017YFC0505102)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP,No.2019QZKK0307)the Major Science and Technology Program for Water Pollution Control and Treatment(2017ZX07101-001)。
文摘To quantify the impacts of native vegetation on the spatial and temporal variations in hydraulic properties of bank gully concentrated flows,a series of in situ flume experiments in the bank gully were performed at the Yuanmou Gully Erosion and Collapse Experimental Station in the dry-hot valley region of the Jinsha River,Southwest China.This experiment involved upstream catchment areas withone-and two-year native grass(Heteropogon contortus)and bare land drained to bare gully headcuts,i.e.,Gullies 1,2 and 3.In Gully 4,Heteropogon contortus and Agave sisalana were planted in the upstream catchment area and gully bed,respectively.Among these experiments,the sediment concentration in runoff in Gully 3 was the highest and that in Gully 2 was the lowest,clearly indicating that the sediment concentration in runoff obviously decreased and the deposition of sediment obviously increased as the vegetation cover increased.The concentrated flows were turbulent in response to the flow discharge.The concentrated flows in the gully zones with native grass and bare land were sub-and supercritical,respectively.The flow rate and shear stress in Gully 3 upstream catchment area were highest among the four upstream catchment areas,while the flow rate and shear stress in the gully bed of Gully 4 were lowest among the four gully beds,indicating that native grass notably decreased the bank gully flow rate and shear stress.The Darcy–Weisbach friction factor(resistance f)and flow energy consumption in the gully bed of Gully 4 were notably higher than those in the other three gully beds,clearly indicating that native grass increased the bank gully surface resistance and flow energy consumption.The Reynolds number(Re),flow rate,shear stress,resistance f,and flow energy consumption in the gully beds and upstream areas increased over time,while the sediment concentration in runoff and Froude number(Fr)decreased.Overall,increasing vegetation cover in upstream catchment areas and downstream gully beds of the bank gully is essential for gully erosion mitigation.
基金Supported by the National Basic Research Program of China ("973") (Grant No. 2007CB714100)the National Natural Science Foundation of China (Grant Nos. 50849003, 50809028)China Postdoctoral Science Foundation (Grant No. 20080440392)
文摘Scale effects exist in the whole process of rainfall-3-runoff-3-soil erosion-3-sediment transport in river basins. The differences of hydrographs and sediment graphs in different positions in a river basin are treated as basic scale effects, which are more complex in the gullied Loess Plateau, a region notorious for high intensity soil erosion and hyper-concentrated sediment-laden flow. The up-scaling method of direct extrapolation that maintains dynamical mechanism effective in large scale application was chosen as the methodology of this paper. Firstly, scale effects of hydrographs and sediment graphs were analyzed by using field data, and key sub-processes and their mechanisms contributing to scale effects were clearly defined. Then, the Digital Yellow River Model that integrates sub-models for the subprocesses was used with high resolution to simulate rainfall-3-runoff-3-soil erosion-3-sediment transport response in Chabagou watershed, and the distributed results representing scale effects were obtained. Finally, analysis on the simulation results was carried out. It was shown that gravitational erosion and hyper-concentrated flow contribute most to the spatial variation of hydrographs and sediment graphs in the spatial scale. Different spatial scale distributions and superposition of different sub-processes are the mechanisms of scale effects.
基金Pasquale Borrelli was funded by the EcoSSSoil Project,Korea Environmental Industry&Technology Institute(KEITI),Korea(Grant No.2019002820004).
文摘The European Commission's Thematic Strategy for Soil Protection(COM(2012)46)identified soil erosion as an important threat to European Union's(EU)soil resources.Gully erosion is an important but hitherto poorly understood component of this threat.Here we present the results of an unprecedented attempt to monitor the occurrence of gully erosion across the EU and UK.We integrate a soil erosion module into the 2018 LUCAS Topsoil Survey,which was conducted to monitor the soil health status across the EU and to support actions to prevent soil degradation.We discuss and explore opportunities to further improve this method.The 2018 LUCAS Topsoil Survey consisted of soil sampling(0-20 cm depth)and erosion observations conducted in ca.10%(n=24,759)of the 238,077 Land Use/Cover Area frame Survey(LUCAS)2018 in-field survey sites.Gully erosion channels were detected for ca.1%(211 sites)of the visited LUCAS Topsoil sites.Commission(false positives,2.5%)and omission errors(false negatives,5.6%)were found to be low and at a level that could not compromise the representativeness of the gully erosion survey.Overall,the findings indicate that the tested 2018 LUCAS Topsoil in-field gully erosion monitoring system is effective for detecting the incidence of gully erosion.The morphogenesis of the mapped gullies suggests that the approach is an effective tool to map permanent gullies,whereas it appears less effective to detect short-lived forms like ephemeral gullies.Spatial patterns emerging from the LUCAS Topsoil field observations provide new insights on typical gully formation sites across the EU and UK.This can help to design further targeted research activities.An extension of this approach to all LUCAS sites of 2022 would significantly enhance our understanding of the geographical distribution of gully erosion processes across the EU.Repeated every three years,LUCAS soil erosion surveys would contribute to assess the state of gully erosion in the EU over time.It will also enable monitoring and eventually predicting the dynamics of gully erosion.Data collected were part of the publicly available Gully Erosion LUCAS visual assessment(GE-LUCAS v1.0)inventory.
