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Vito Ferro - One of the best experts on this subject based on the ideXlab platform.
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comment on rill erosion processes on steep colluvial deposit slope under heavy rainfall in flume experiments with artificial rain by f jiang et al
Catena, 2020Co-Authors: Vito Ferro, Alessio NicosiaAbstract:Abstract Since rill flows are characterized by small water depths and steeply sloping channels, the corresponding hydraulic conditions are very different to those which are typically found in channels of streams and rivers. Furthermore, limited information is currently available on the effect of rainfall on flow resistance. The objective of this comment was to investigate the applicability of a recently theoretically deduced rill flow resistance equation, based on a power-velocity profile, using measurements carried out by Jiang et al. for both different slope steepness conditions and rainfall intensity. The relationship between the velocity profile parameter Γ, the channel slope and the flow Froude number was calibrated using the data by Jiang et al. The theoretical approach and the measurements carried out in the investigated conditions allowed to state that a) the Darcy-Weisbach Friction Factor can be accurately estimated using the proposed theoretical approach, b) the data were supportive of the slope independence hypothesis of rill velocity stated by Govers and c) the Darcy-Weisbach Friction Factor varies with rainfall intensity.
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assessing flow resistance law in vegetated channels by dimensional analysis and self similarity
Flow Measurement and Instrumentation, 2019Co-Authors: Vito FerroAbstract:Abstract In this paper experimental data collected by Kouwen et al., Wilson and Horrit, Raffaelli et al. and Carollo et al., using straight flumes having a bed covered by grass-like vegetation with different stem concentrations, were used to analyze flow resistance for flexible submerged elements. At first, the dimensional analysis and the incomplete self-similarity hypothesis was applied to deduce the flow velocity distribution and the resulting theoretical expression of the Darcy-Weisbach Friction Factor. Then, a relationship between the Γ function of the velocity profile and the biomechanical characteristics of vegetation, the channel slope, the Reynolds number and the flow Froude number was empirically deduced by the available measurements. This relationship was established distinguishing between the low stem concentration values and the highest values for which a quasi-smooth skimming flow occurs. Finally, the analysis showed that, in comparison with previous results, a more accurate Darcy-Weisbach Friction Factor estimate can be obtained by the theoretical approach based on a power-velocity profile.
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assessing dye tracer technique for rill flow velocity measurements
Catena, 2018Co-Authors: Costanza Di Stefano, Vincenzo Palmeri, Vito Ferro, Vincenzo PampaloneAbstract:Abstract Rill erosion is considered one of the most important processes affecting soil because of the large amount of soil loss. The rill network acts as sediment source and is able to transport both rill flow-detached particles and those delivered from the interrill areas. Small flow depth in a rill and steep slope values of its bed affect significantly flow hydraulics. When rill flow velocity is measured using a dye-tracing method, the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction Factor. The main uncertainty of the dye-tracing technique stands in the relationship between mean and surface flow velocity. In this paper, this relationship was firstly tested using the measured data pairs available from literature and then the influence of the adopted relationship on the estimate of the Darcy Weisbach Friction Factor was examined. The developed analysis showed that the applied estimate criteria of the correction Factor do not affect the estimate performances of the theoretical flow resistance equation. Finally a new flow resistance equation for rill flows which can be directly calibrated by surface velocity measurements was deduced. The proposed procedure for estimating the Friction Factor was calibrated by rill data available from literature and was positively tested by the rill velocity measurements carried out in this investigation.
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assessing flow resistance in gravel bed channels by dimensional analysis and self similarity
Catena, 2018Co-Authors: Vito FerroAbstract:Abstract In this paper a new flow resistance equation for open channel flow, based on the integration of a power velocity profile, was tested for gravel bed channels. First this flow resistance equation, theoretically deduced by dimensional analysis and incomplete self-similarity condition, was reported. Then a relationship between the Γ function of the velocity profile, the channel slope and the Froude number was calibrated by the available laboratory measurements of flow velocity, water depth and bed slope carried out in 416 flume experimental runs with a gravel bed. Then the relationship for estimating Γ function and the theoretical resistance equation was tested by 83 independent flume measurements. The analysis also showed that the proposed flow resistance equation allows an estimate of the Darcy-Weisbach Friction Factor which is more reliable and accurate than that obtained by a semi-logarithmic flow resistance law or a variable-power resistance equation, calibrated with the same gravel bed measurements. For testing the applicability of the proposed Γ function (Eq. (17)), whose coefficients were estimated by flume measurements, available fields measurements were used. The analysis demonstrated that a scale Factor (equal to 0.7611) is necessary to convert Γ values obtained by flume measurements into those corresponding to gravel bed rivers. The similitude between flow resistance in a gravel bed flume and in a gravel bed river is governed by the Γ function and a scale Factor, equal to 1.6, is required to upscale the Darcy-Weisbach Friction Factor values obtained by flume measurements to the river case. In conclusion, the analysis showed that the Darcy-Weisbach Friction Factor for gravel bed channels can be accurately estimated by the proposed theoretical approach based on a power-velocity profile.
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flow resistance in gravel bed channels with large scale roughness
Earth Surface Processes and Landforms, 2003Co-Authors: Vito FerroAbstract:A previously published mixing length (ML) model for evaluating the Darcy–Weisbach Friction Factor for a large-scale roughness condition (depth to sediment height ratio ranging from 1 to 4) is briefly reviewed and modified (MML). Then the MML model and a modified drag (MD) model are experimentally tested using laboratory measurements carried out for gravel-bed channels and large-scale roughness condition. This analysis showed that the MML gives accurate estimates of the Darcy–Weisbach coefficient and for Froude number values greater than 0·5 the MML model coincides with the ML one. Testing of the MD model shows limited accuracy in estimating flow resistance. Finally, the MML and MD models are compared with the performance of a quasi-theoretical (QT) model deduced applying the P-theorem of the dimensional analysis and the incomplete self-similarity condition for the depth/sediment ratio and the Froude number. Using the experimental gravel-bed data to calibrate the QT model, a constant value of the exponent of the Froude number is determined while two relationships are proposed for estimating the scale Factor and the exponent of the depth/sediment ratio. This indirect estimate procedure of the coefficients (b0, b1 and b2) of the QT model can produce a negligible overestimation or underestimation of the Friction Factor. Copyright © 2003 John Wiley & Sons, Ltd.
Yifan Dong - One of the best experts on this subject based on the ideXlab platform.
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the influences of mass failure on the erosion and hydraulic processes of gully headcuts based on an in situ scouring experiment in dry hot valley of china
Catena, 2019Co-Authors: Donghong Xiong, Yifan Dong, Su Zhang, Zhengan Su, Xingwu Duan, Xiaoning Lu, Yong YuanAbstract:Abstract Gully headcut retreat (GHR) is an important processes in gully development, and previous studies have tried to predict GHR rates based on flow hydraulic parameters during runoff scouring, but other dynamics such as gravity also affect GHR processes in addition to flow hydraulics. The aim of this study is to examine the influences of mass failures due to gravity on the erosion and hydraulics processes of gully headcuts during runoff scouring. A flow scouring experiment including 11 tests with two discharges (i.e., 7 tests with 83.3 l min−1 and 4 tests with 166.7 l min−1) was conducted on 5 in situ gully head plots with similar initial topographies. Totally 36 mass failure events were observed of all the 5 gully heads during the experiment, and 63.9% of the events were occurred during the first 10 min of the tests after drying-rewetting cycles. The tests were classified into two series according to whether the mass failure occurred during the scouring. The tests with mass failures (Series I) contributed 81.7% of the total soil loss of GHR, and the average GHR rates by mass (GHRm) was about 5 times higher than that of the tests without mass failures (Series II). The mass failure clearly influenced the flow resistances on gully beds by increasing the surfaces roughness and the sediment load to gully beds, and the average Darcy–Weisbach Friction Factor (f) and Manning coefficient (n) of Series I were clearly higher than those of Series II. Compared to the previous studies without significant soil collapse from gully heads, the logarithmic growth relationship between GHRm and the energy consumption (ΔEt) was quite weak in this study, but the R2 between GHRm and ΔEt increased for longer time scales. The results indicated that for individual runoff events, GHR rates could not be predicted by flow hydraulics alone because mass failures due to gravity made great contribution, but on longer time scales, the influence of soil collapse is reduced, and flow hydraulics become the key Factor impacting GHR processes.
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Effect of grass basal diameter on hydraulic properties and sediment yield processes in gully beds in the dry-hot valley region of Southwest China
CATENA, 2017Co-Authors: Dan Yang, Donghong Xiong, Yifan Dong, Su Zhang, Baojun Zhang, Guo Min, Liang XiaoAbstract:Vegetation is an important Factor impacting the hydrodynamic processes of gully beds and further affecting the headward erosion of gullies. Gully erosion is one of the major contributors to severe land degradation in the Yuanmou dry-hot valley region of Southwest China where soil erosion rates are estimated ranging from 8000 to 20,000 t·km− 2·a− 1, with a mean gully distribution density ranging from 3 to 5 km·km− 2. However, few studies have been performed in this area which focused on the influence of the aboveground part of grass on soil erosion under natural conditions in gullies. To quantify the temporal variation of hydraulic properties (i.e., shear stress (τ), Darcy–Weisbach Friction Factor (resistance f) and Sediment Concentration (SC) and analyse the change trends of hydraulic properties and SC in gully bed along with the downslope direction under different grass basal diameters, a series of in situ scouring experiments were conducted in development areas of gully erosion in the Yuanmou dry-hot valley region. With the grass basal diameter increased from 0 (no grass) to 17 to 43 to 70 to 98 mm in gully beds, the mean shear stress of concentrated flow increased slightly (4.03 to 4.49 Pa) and then decreased obviously (4.49 to 3.45 Pa). On the other hand, increasing trends were observed in temporal variations of shear stress for every grass basal diameter and the increase rate varied from 0.05 to 0.18. Whereas no notable regular changes in shear stress were detected in the downslope direction for grass basal diameters of 0 to 43 mm, obviously increasing trends were observed for the grass basal diameters of 70 mm and 98 mm. The resistance f experienced a notable increase with increasing grass basal diameter in this study. A logarithmic growth of resistance f was observed in the gully bed as the experiment progressed (f = a ln (t + b), P < 0.01), and increasing trends were detected for the resistance f in the downslope direction of the gully bed for all grass basal diameters although regression equation could only be fitted for grass basal diameter of 98 mm (f98 = 2.438 ln (DOH98 − 2.643), P < 0.01). However, the SC showed an exponential decline with the scouring time. And the SC showed an increasing trend along with the downslope direction of the gully bed in all experiments. In addition, a negative correlation could be detected between SC and resistance f in all five grass basal diameter experiments. In this study, only the disposal for grass basal diameter of 98 mm was clearly more effective than other disposals in conserving gully bed, which might because grass basal diameter (≥ 98 mm) that could cover a relatively large section of gully bed could exert apparent impact on reducing runoff shear stress, increasing resistance coefficient and then further decline the sediment yield. In contrast, when grass basal diameter was < 98 mm, the reduction effect for soil erosion was very limited due to overland concentrated flow could detour around the grass base and erode the gully bed.
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influence of bare soil and cultivated land use types upstream of a bank gully on soil erosion rates and energy consumption for different gully erosion zones in the dry hot valley region southwest china
Natural Hazards, 2015Co-Authors: Donghong Xiong, Yifan Dong, Dan Yang, Su Zhang, Baojun Zhang, Xueyong Zheng, Jianhui Zhang, Liangtao ShiAbstract:This study assessed temporal variation in soil erosion rates in response to energy consumption of flow (DE). It employed an in situ bank gully field flume experiment with upstream catchment areas with bare (BLG) or cultivated land (CLG) that drained down to bare gully headcuts. Water discharge treatments ranged from 30 to 120 L Min(-1). Concentrated flow discharge clearly affected bank gully soil erosion rates. Excluding minimal discharge in the CLG upstream catchment area (30 L min(-1)), a declining power function trend (p <= 0.1) was observed with time in soil erosion rates for both BLG and CLG upstream catchment areas and downstream gully beds. Non-steady state soil erosion rates were observed after an abrupt collapse along the headcut slope after prolonged scouring treatments. However, as the experiment progressed, Delta E and energy consumption of flow per unit soil loss (Delta Eu) exhibited a logarithmic growth trend (p < .1) at each BLG and CLG position. Although similar temporal trends in soil erosion and infiltration rates were observed, values clearly differed between BLG and CLG upstream catchment areas. Furthermore, Darcy-Weisbach Friction Factor (f) values in the CLG upstream catchment area were higher than the corresponding BLG area. In contrast to the BLG upstream catchment area, lower Delta Eu and higher soil erosion rates were observed in the CLG upstream catchment area as a result of soil disturbances. This indicated that intensive land use changes accelerate soil erosion rates in upstream catchment areas of bank gullies and increase soil sediment transport to downstream gullies. Accordingly, reducing tillage disturbances and increasing vegetation cover in upstream catchment areas of bank gullies are essential in the dry-hot valley region of Southwest China.
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influence of bare soil and cultivated land use types upstream of a bank gully on soil erosion rates and energy consumption for different gully erosion zones in the dry hot valley region southwest china
Natural Hazards, 2015Co-Authors: Zhengan Su, Donghong Xiong, Yifan Dong, Dan Yang, Su Zhang, Baojun Zhang, Xueyong Zheng, J H ZhangAbstract:This study assessed temporal variation in soil erosion rates in response to energy consumption of flow (ΔE). It employed an in situ bank gully field flume experiment with upstream catchment areas with bare (BLG) or cultivated land (CLG) that drained down to bare gully headcuts. Water discharge treatments ranged from 30 to 120 L Min −1 . Concentrated flow discharge clearly affected bank gully soil erosion rates. Excluding minimal discharge in the CLG upstream catchment area (30 L min −1 ), a declining power function trend (p ≤ 0.1) was observed with time in soil erosion rates for both BLG and CLG upstream catchment areas and downstream gully beds. Non-steady state soil erosion rates were observed after an abrupt collapse along the headcut slope after prolonged scouring treatments. However, as the experiment progressed, ΔE and energy consumption of flow per unit soil loss (ΔEu) exhibited a logarithmic growth trend (p > 0.1) at each BLG and CLG position. Although similar temporal trends in soil erosion and infiltration rates were observed, values clearly differed between BLG and CLG upstream catchment areas. Furthermore, Darcy–Weisbach Friction Factor (f) values in the CLG upstream catchment area were higher than the corresponding BLG area. In contrast to the BLG upstream catchment area, lower ΔEu and higher soil erosion rates were observed in the CLG upstream catchment area as a result of soil disturbances. This indicated that intensive land use changes accelerate soil erosion rates in upstream catchment areas of bank gullies and increase soil sediment transport to downstream gullies. Accordingly, reducing tillage disturbances and increasing vegetation cover in upstream catchment areas of bank gullies are essential in the dry-hot valley region of Southwest China. Copyright Springer Science+Business Media Dordrecht 2015
Su Zhang - One of the best experts on this subject based on the ideXlab platform.
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the influences of mass failure on the erosion and hydraulic processes of gully headcuts based on an in situ scouring experiment in dry hot valley of china
Catena, 2019Co-Authors: Donghong Xiong, Yifan Dong, Su Zhang, Zhengan Su, Xingwu Duan, Xiaoning Lu, Yong YuanAbstract:Abstract Gully headcut retreat (GHR) is an important processes in gully development, and previous studies have tried to predict GHR rates based on flow hydraulic parameters during runoff scouring, but other dynamics such as gravity also affect GHR processes in addition to flow hydraulics. The aim of this study is to examine the influences of mass failures due to gravity on the erosion and hydraulics processes of gully headcuts during runoff scouring. A flow scouring experiment including 11 tests with two discharges (i.e., 7 tests with 83.3 l min−1 and 4 tests with 166.7 l min−1) was conducted on 5 in situ gully head plots with similar initial topographies. Totally 36 mass failure events were observed of all the 5 gully heads during the experiment, and 63.9% of the events were occurred during the first 10 min of the tests after drying-rewetting cycles. The tests were classified into two series according to whether the mass failure occurred during the scouring. The tests with mass failures (Series I) contributed 81.7% of the total soil loss of GHR, and the average GHR rates by mass (GHRm) was about 5 times higher than that of the tests without mass failures (Series II). The mass failure clearly influenced the flow resistances on gully beds by increasing the surfaces roughness and the sediment load to gully beds, and the average Darcy–Weisbach Friction Factor (f) and Manning coefficient (n) of Series I were clearly higher than those of Series II. Compared to the previous studies without significant soil collapse from gully heads, the logarithmic growth relationship between GHRm and the energy consumption (ΔEt) was quite weak in this study, but the R2 between GHRm and ΔEt increased for longer time scales. The results indicated that for individual runoff events, GHR rates could not be predicted by flow hydraulics alone because mass failures due to gravity made great contribution, but on longer time scales, the influence of soil collapse is reduced, and flow hydraulics become the key Factor impacting GHR processes.
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Effect of grass basal diameter on hydraulic properties and sediment yield processes in gully beds in the dry-hot valley region of Southwest China
CATENA, 2017Co-Authors: Dan Yang, Donghong Xiong, Yifan Dong, Su Zhang, Baojun Zhang, Guo Min, Liang XiaoAbstract:Vegetation is an important Factor impacting the hydrodynamic processes of gully beds and further affecting the headward erosion of gullies. Gully erosion is one of the major contributors to severe land degradation in the Yuanmou dry-hot valley region of Southwest China where soil erosion rates are estimated ranging from 8000 to 20,000 t·km− 2·a− 1, with a mean gully distribution density ranging from 3 to 5 km·km− 2. However, few studies have been performed in this area which focused on the influence of the aboveground part of grass on soil erosion under natural conditions in gullies. To quantify the temporal variation of hydraulic properties (i.e., shear stress (τ), Darcy–Weisbach Friction Factor (resistance f) and Sediment Concentration (SC) and analyse the change trends of hydraulic properties and SC in gully bed along with the downslope direction under different grass basal diameters, a series of in situ scouring experiments were conducted in development areas of gully erosion in the Yuanmou dry-hot valley region. With the grass basal diameter increased from 0 (no grass) to 17 to 43 to 70 to 98 mm in gully beds, the mean shear stress of concentrated flow increased slightly (4.03 to 4.49 Pa) and then decreased obviously (4.49 to 3.45 Pa). On the other hand, increasing trends were observed in temporal variations of shear stress for every grass basal diameter and the increase rate varied from 0.05 to 0.18. Whereas no notable regular changes in shear stress were detected in the downslope direction for grass basal diameters of 0 to 43 mm, obviously increasing trends were observed for the grass basal diameters of 70 mm and 98 mm. The resistance f experienced a notable increase with increasing grass basal diameter in this study. A logarithmic growth of resistance f was observed in the gully bed as the experiment progressed (f = a ln (t + b), P < 0.01), and increasing trends were detected for the resistance f in the downslope direction of the gully bed for all grass basal diameters although regression equation could only be fitted for grass basal diameter of 98 mm (f98 = 2.438 ln (DOH98 − 2.643), P < 0.01). However, the SC showed an exponential decline with the scouring time. And the SC showed an increasing trend along with the downslope direction of the gully bed in all experiments. In addition, a negative correlation could be detected between SC and resistance f in all five grass basal diameter experiments. In this study, only the disposal for grass basal diameter of 98 mm was clearly more effective than other disposals in conserving gully bed, which might because grass basal diameter (≥ 98 mm) that could cover a relatively large section of gully bed could exert apparent impact on reducing runoff shear stress, increasing resistance coefficient and then further decline the sediment yield. In contrast, when grass basal diameter was < 98 mm, the reduction effect for soil erosion was very limited due to overland concentrated flow could detour around the grass base and erode the gully bed.
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influence of bare soil and cultivated land use types upstream of a bank gully on soil erosion rates and energy consumption for different gully erosion zones in the dry hot valley region southwest china
Natural Hazards, 2015Co-Authors: Donghong Xiong, Yifan Dong, Dan Yang, Su Zhang, Baojun Zhang, Xueyong Zheng, Jianhui Zhang, Liangtao ShiAbstract:This study assessed temporal variation in soil erosion rates in response to energy consumption of flow (DE). It employed an in situ bank gully field flume experiment with upstream catchment areas with bare (BLG) or cultivated land (CLG) that drained down to bare gully headcuts. Water discharge treatments ranged from 30 to 120 L Min(-1). Concentrated flow discharge clearly affected bank gully soil erosion rates. Excluding minimal discharge in the CLG upstream catchment area (30 L min(-1)), a declining power function trend (p <= 0.1) was observed with time in soil erosion rates for both BLG and CLG upstream catchment areas and downstream gully beds. Non-steady state soil erosion rates were observed after an abrupt collapse along the headcut slope after prolonged scouring treatments. However, as the experiment progressed, Delta E and energy consumption of flow per unit soil loss (Delta Eu) exhibited a logarithmic growth trend (p < .1) at each BLG and CLG position. Although similar temporal trends in soil erosion and infiltration rates were observed, values clearly differed between BLG and CLG upstream catchment areas. Furthermore, Darcy-Weisbach Friction Factor (f) values in the CLG upstream catchment area were higher than the corresponding BLG area. In contrast to the BLG upstream catchment area, lower Delta Eu and higher soil erosion rates were observed in the CLG upstream catchment area as a result of soil disturbances. This indicated that intensive land use changes accelerate soil erosion rates in upstream catchment areas of bank gullies and increase soil sediment transport to downstream gullies. Accordingly, reducing tillage disturbances and increasing vegetation cover in upstream catchment areas of bank gullies are essential in the dry-hot valley region of Southwest China.
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influence of bare soil and cultivated land use types upstream of a bank gully on soil erosion rates and energy consumption for different gully erosion zones in the dry hot valley region southwest china
Natural Hazards, 2015Co-Authors: Zhengan Su, Donghong Xiong, Yifan Dong, Dan Yang, Su Zhang, Baojun Zhang, Xueyong Zheng, J H ZhangAbstract:This study assessed temporal variation in soil erosion rates in response to energy consumption of flow (ΔE). It employed an in situ bank gully field flume experiment with upstream catchment areas with bare (BLG) or cultivated land (CLG) that drained down to bare gully headcuts. Water discharge treatments ranged from 30 to 120 L Min −1 . Concentrated flow discharge clearly affected bank gully soil erosion rates. Excluding minimal discharge in the CLG upstream catchment area (30 L min −1 ), a declining power function trend (p ≤ 0.1) was observed with time in soil erosion rates for both BLG and CLG upstream catchment areas and downstream gully beds. Non-steady state soil erosion rates were observed after an abrupt collapse along the headcut slope after prolonged scouring treatments. However, as the experiment progressed, ΔE and energy consumption of flow per unit soil loss (ΔEu) exhibited a logarithmic growth trend (p > 0.1) at each BLG and CLG position. Although similar temporal trends in soil erosion and infiltration rates were observed, values clearly differed between BLG and CLG upstream catchment areas. Furthermore, Darcy–Weisbach Friction Factor (f) values in the CLG upstream catchment area were higher than the corresponding BLG area. In contrast to the BLG upstream catchment area, lower ΔEu and higher soil erosion rates were observed in the CLG upstream catchment area as a result of soil disturbances. This indicated that intensive land use changes accelerate soil erosion rates in upstream catchment areas of bank gullies and increase soil sediment transport to downstream gullies. Accordingly, reducing tillage disturbances and increasing vegetation cover in upstream catchment areas of bank gullies are essential in the dry-hot valley region of Southwest China. Copyright Springer Science+Business Media Dordrecht 2015
Donghong Xiong - One of the best experts on this subject based on the ideXlab platform.
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the influences of mass failure on the erosion and hydraulic processes of gully headcuts based on an in situ scouring experiment in dry hot valley of china
Catena, 2019Co-Authors: Donghong Xiong, Yifan Dong, Su Zhang, Zhengan Su, Xingwu Duan, Xiaoning Lu, Yong YuanAbstract:Abstract Gully headcut retreat (GHR) is an important processes in gully development, and previous studies have tried to predict GHR rates based on flow hydraulic parameters during runoff scouring, but other dynamics such as gravity also affect GHR processes in addition to flow hydraulics. The aim of this study is to examine the influences of mass failures due to gravity on the erosion and hydraulics processes of gully headcuts during runoff scouring. A flow scouring experiment including 11 tests with two discharges (i.e., 7 tests with 83.3 l min−1 and 4 tests with 166.7 l min−1) was conducted on 5 in situ gully head plots with similar initial topographies. Totally 36 mass failure events were observed of all the 5 gully heads during the experiment, and 63.9% of the events were occurred during the first 10 min of the tests after drying-rewetting cycles. The tests were classified into two series according to whether the mass failure occurred during the scouring. The tests with mass failures (Series I) contributed 81.7% of the total soil loss of GHR, and the average GHR rates by mass (GHRm) was about 5 times higher than that of the tests without mass failures (Series II). The mass failure clearly influenced the flow resistances on gully beds by increasing the surfaces roughness and the sediment load to gully beds, and the average Darcy–Weisbach Friction Factor (f) and Manning coefficient (n) of Series I were clearly higher than those of Series II. Compared to the previous studies without significant soil collapse from gully heads, the logarithmic growth relationship between GHRm and the energy consumption (ΔEt) was quite weak in this study, but the R2 between GHRm and ΔEt increased for longer time scales. The results indicated that for individual runoff events, GHR rates could not be predicted by flow hydraulics alone because mass failures due to gravity made great contribution, but on longer time scales, the influence of soil collapse is reduced, and flow hydraulics become the key Factor impacting GHR processes.
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Effect of grass basal diameter on hydraulic properties and sediment yield processes in gully beds in the dry-hot valley region of Southwest China
CATENA, 2017Co-Authors: Dan Yang, Donghong Xiong, Yifan Dong, Su Zhang, Baojun Zhang, Guo Min, Liang XiaoAbstract:Vegetation is an important Factor impacting the hydrodynamic processes of gully beds and further affecting the headward erosion of gullies. Gully erosion is one of the major contributors to severe land degradation in the Yuanmou dry-hot valley region of Southwest China where soil erosion rates are estimated ranging from 8000 to 20,000 t·km− 2·a− 1, with a mean gully distribution density ranging from 3 to 5 km·km− 2. However, few studies have been performed in this area which focused on the influence of the aboveground part of grass on soil erosion under natural conditions in gullies. To quantify the temporal variation of hydraulic properties (i.e., shear stress (τ), Darcy–Weisbach Friction Factor (resistance f) and Sediment Concentration (SC) and analyse the change trends of hydraulic properties and SC in gully bed along with the downslope direction under different grass basal diameters, a series of in situ scouring experiments were conducted in development areas of gully erosion in the Yuanmou dry-hot valley region. With the grass basal diameter increased from 0 (no grass) to 17 to 43 to 70 to 98 mm in gully beds, the mean shear stress of concentrated flow increased slightly (4.03 to 4.49 Pa) and then decreased obviously (4.49 to 3.45 Pa). On the other hand, increasing trends were observed in temporal variations of shear stress for every grass basal diameter and the increase rate varied from 0.05 to 0.18. Whereas no notable regular changes in shear stress were detected in the downslope direction for grass basal diameters of 0 to 43 mm, obviously increasing trends were observed for the grass basal diameters of 70 mm and 98 mm. The resistance f experienced a notable increase with increasing grass basal diameter in this study. A logarithmic growth of resistance f was observed in the gully bed as the experiment progressed (f = a ln (t + b), P < 0.01), and increasing trends were detected for the resistance f in the downslope direction of the gully bed for all grass basal diameters although regression equation could only be fitted for grass basal diameter of 98 mm (f98 = 2.438 ln (DOH98 − 2.643), P < 0.01). However, the SC showed an exponential decline with the scouring time. And the SC showed an increasing trend along with the downslope direction of the gully bed in all experiments. In addition, a negative correlation could be detected between SC and resistance f in all five grass basal diameter experiments. In this study, only the disposal for grass basal diameter of 98 mm was clearly more effective than other disposals in conserving gully bed, which might because grass basal diameter (≥ 98 mm) that could cover a relatively large section of gully bed could exert apparent impact on reducing runoff shear stress, increasing resistance coefficient and then further decline the sediment yield. In contrast, when grass basal diameter was < 98 mm, the reduction effect for soil erosion was very limited due to overland concentrated flow could detour around the grass base and erode the gully bed.
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influence of bare soil and cultivated land use types upstream of a bank gully on soil erosion rates and energy consumption for different gully erosion zones in the dry hot valley region southwest china
Natural Hazards, 2015Co-Authors: Donghong Xiong, Yifan Dong, Dan Yang, Su Zhang, Baojun Zhang, Xueyong Zheng, Jianhui Zhang, Liangtao ShiAbstract:This study assessed temporal variation in soil erosion rates in response to energy consumption of flow (DE). It employed an in situ bank gully field flume experiment with upstream catchment areas with bare (BLG) or cultivated land (CLG) that drained down to bare gully headcuts. Water discharge treatments ranged from 30 to 120 L Min(-1). Concentrated flow discharge clearly affected bank gully soil erosion rates. Excluding minimal discharge in the CLG upstream catchment area (30 L min(-1)), a declining power function trend (p <= 0.1) was observed with time in soil erosion rates for both BLG and CLG upstream catchment areas and downstream gully beds. Non-steady state soil erosion rates were observed after an abrupt collapse along the headcut slope after prolonged scouring treatments. However, as the experiment progressed, Delta E and energy consumption of flow per unit soil loss (Delta Eu) exhibited a logarithmic growth trend (p < .1) at each BLG and CLG position. Although similar temporal trends in soil erosion and infiltration rates were observed, values clearly differed between BLG and CLG upstream catchment areas. Furthermore, Darcy-Weisbach Friction Factor (f) values in the CLG upstream catchment area were higher than the corresponding BLG area. In contrast to the BLG upstream catchment area, lower Delta Eu and higher soil erosion rates were observed in the CLG upstream catchment area as a result of soil disturbances. This indicated that intensive land use changes accelerate soil erosion rates in upstream catchment areas of bank gullies and increase soil sediment transport to downstream gullies. Accordingly, reducing tillage disturbances and increasing vegetation cover in upstream catchment areas of bank gullies are essential in the dry-hot valley region of Southwest China.
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influence of bare soil and cultivated land use types upstream of a bank gully on soil erosion rates and energy consumption for different gully erosion zones in the dry hot valley region southwest china
Natural Hazards, 2015Co-Authors: Zhengan Su, Donghong Xiong, Yifan Dong, Dan Yang, Su Zhang, Baojun Zhang, Xueyong Zheng, J H ZhangAbstract:This study assessed temporal variation in soil erosion rates in response to energy consumption of flow (ΔE). It employed an in situ bank gully field flume experiment with upstream catchment areas with bare (BLG) or cultivated land (CLG) that drained down to bare gully headcuts. Water discharge treatments ranged from 30 to 120 L Min −1 . Concentrated flow discharge clearly affected bank gully soil erosion rates. Excluding minimal discharge in the CLG upstream catchment area (30 L min −1 ), a declining power function trend (p ≤ 0.1) was observed with time in soil erosion rates for both BLG and CLG upstream catchment areas and downstream gully beds. Non-steady state soil erosion rates were observed after an abrupt collapse along the headcut slope after prolonged scouring treatments. However, as the experiment progressed, ΔE and energy consumption of flow per unit soil loss (ΔEu) exhibited a logarithmic growth trend (p > 0.1) at each BLG and CLG position. Although similar temporal trends in soil erosion and infiltration rates were observed, values clearly differed between BLG and CLG upstream catchment areas. Furthermore, Darcy–Weisbach Friction Factor (f) values in the CLG upstream catchment area were higher than the corresponding BLG area. In contrast to the BLG upstream catchment area, lower ΔEu and higher soil erosion rates were observed in the CLG upstream catchment area as a result of soil disturbances. This indicated that intensive land use changes accelerate soil erosion rates in upstream catchment areas of bank gullies and increase soil sediment transport to downstream gullies. Accordingly, reducing tillage disturbances and increasing vegetation cover in upstream catchment areas of bank gullies are essential in the dry-hot valley region of Southwest China. Copyright Springer Science+Business Media Dordrecht 2015
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Effect of grass basal diameter on hydraulic properties and sediment yield processes in gully beds in the dry-hot valley region of Southwest China
CATENA, 2017Co-Authors: Dan Yang, Donghong Xiong, Yifan Dong, Su Zhang, Baojun Zhang, Guo Min, Liang XiaoAbstract:Vegetation is an important Factor impacting the hydrodynamic processes of gully beds and further affecting the headward erosion of gullies. Gully erosion is one of the major contributors to severe land degradation in the Yuanmou dry-hot valley region of Southwest China where soil erosion rates are estimated ranging from 8000 to 20,000 t·km− 2·a− 1, with a mean gully distribution density ranging from 3 to 5 km·km− 2. However, few studies have been performed in this area which focused on the influence of the aboveground part of grass on soil erosion under natural conditions in gullies. To quantify the temporal variation of hydraulic properties (i.e., shear stress (τ), Darcy–Weisbach Friction Factor (resistance f) and Sediment Concentration (SC) and analyse the change trends of hydraulic properties and SC in gully bed along with the downslope direction under different grass basal diameters, a series of in situ scouring experiments were conducted in development areas of gully erosion in the Yuanmou dry-hot valley region. With the grass basal diameter increased from 0 (no grass) to 17 to 43 to 70 to 98 mm in gully beds, the mean shear stress of concentrated flow increased slightly (4.03 to 4.49 Pa) and then decreased obviously (4.49 to 3.45 Pa). On the other hand, increasing trends were observed in temporal variations of shear stress for every grass basal diameter and the increase rate varied from 0.05 to 0.18. Whereas no notable regular changes in shear stress were detected in the downslope direction for grass basal diameters of 0 to 43 mm, obviously increasing trends were observed for the grass basal diameters of 70 mm and 98 mm. The resistance f experienced a notable increase with increasing grass basal diameter in this study. A logarithmic growth of resistance f was observed in the gully bed as the experiment progressed (f = a ln (t + b), P < 0.01), and increasing trends were detected for the resistance f in the downslope direction of the gully bed for all grass basal diameters although regression equation could only be fitted for grass basal diameter of 98 mm (f98 = 2.438 ln (DOH98 − 2.643), P < 0.01). However, the SC showed an exponential decline with the scouring time. And the SC showed an increasing trend along with the downslope direction of the gully bed in all experiments. In addition, a negative correlation could be detected between SC and resistance f in all five grass basal diameter experiments. In this study, only the disposal for grass basal diameter of 98 mm was clearly more effective than other disposals in conserving gully bed, which might because grass basal diameter (≥ 98 mm) that could cover a relatively large section of gully bed could exert apparent impact on reducing runoff shear stress, increasing resistance coefficient and then further decline the sediment yield. In contrast, when grass basal diameter was < 98 mm, the reduction effect for soil erosion was very limited due to overland concentrated flow could detour around the grass base and erode the gully bed.
