scholarly journals Assessment of land use impact on hydraulic threshold conditions for gully head cut initiation

2016 ◽  
Vol 20 (7) ◽  
pp. 3005-3012 ◽  
Author(s):  
Aliakbar Nazari Samani ◽  
Qiuwen Chen ◽  
Shahram Khalighi ◽  
Robert James Wasson ◽  
Mohammad Reza Rahdari
Keyword(s):  
Land Use ◽  
Shear Stress ◽  
Soil Erosion ◽  
Critical Shear Stress ◽  
Gully Erosion ◽  
Threshold Condition ◽  
Stream Power ◽  
Threshold Phenomenon ◽  
Erosion Models ◽  
Dry Farming

Abstract. A gully as an accelerated erosion process is responsible for land degradation under various environmental conditions and has been known as a threshold phenomenon. Although the effects of gullying processes have been well documented, few soil erosion models have taken into account the threshold condition necessary for gully development. This research was devoted to determining the effects of land use change on hydraulic threshold condition and stream power of water flow through an in situ experimental flume (15 m  ×  0.4 m). Results indicated that head cut initiation and detachment rates showed a better correlation to stream power indices than shear stress (τcr). The threshold unit stream power value (ωu) for head cut initiation in rangeland, abandoned land, and dry farming land was 0.0276, 0.0149, and 4.5  ×  10−5 m s−1, respectively. Moreover, the micro-relief condition of soil surface and surface vegetation affected the flow regime of discharge and velocity. It is seen that the composite hydraulic criteria of Froude number (Fr) and discharge (Q) can clearly discriminate the land uses' threshold. In fact, the remarkable decrease of τcr in dry farming was related to the effect of tillage practice on soil susceptibility and aggregate strength. The findings indicated that using the unit steam power index instead of critical shear stress could increase the models' precision for prediction of head cut development. Compared to the Ephemeral Gully Erosion Model (EGEM) equation for critical shear stress, it is important to point out that for modelling of gully erosion, using single soil attributes can lead to an inaccurate estimation for τcr. In addition, based on the findings of this research, the use of threshold values of τcr  =  35 dyne cm−2 and ωu  =  0.4 cm s−1 in physically based soil erosion models is susceptible to high uncertainty when assessing gully erosion.

scholarly journals Assessment of land use impact on hydraulic threshold conditions for gully head cut initiation

2016 ◽  
Author(s):  
Aliakbar Nazari Samani ◽  
Qiuwen Chen ◽  
Shahram Khalighi ◽  
Robert James Wasson
Keyword(s):  
Land Use ◽  
Shear Stress ◽  
Vegetation Cover ◽  
Agricultural Land ◽  
Gully Erosion ◽  
Soil Conditions ◽  
Shear Stresses ◽  
Soil Response ◽  
Threshold Phenomenon ◽  
Dry Farming

Abstract. Gully erosion is a geomorphic threshold phenomenon controlled by different environmental factors as well as human activities. In this research, we examined the effect of land use on hydraulic flow and the consequent head cut initiation for similar soil conditions using an experimental plot of 15m*0.4m. Results indicated that boundary shear stresses τcr for gully initiation in rangeland, dry farming and abandoned land are 192, 43 and 174, respectively, due to the differences in surface vegetation cover. Moreover, the dyne/cm2 turbulence of flow and soil response to an increase in water depth showed complicated behavior, which could be attributed to the effect of surface micro relief features and land use impacts. Compared to dry farming, the short vegetation cover in the rangeland decreased the effect of ground cover on flow regime. Even after seven years of abandonment, the response of agricultural land to increasing shear stress was similar to that of dry farming, which indicated the low resilience and high erosional susceptibility of soil in dry land was the environments. The main explanation for dramatic (3-4 fold) variations of τcr in dry vegetation cover and soil surface conditions. In fact, the remarkable decrease of τcr farming was related to the effect of tillage practice on soil susceptibility and aggregate used in some strength. The findings indicated that a critical shear stress of 35 dyne/cm2 physically based models for erosion prediction is not appropriate for estimating gully erosion. In addition, the duration of land abandonment has a crucial influence on soil erodibility that has been less considered in erosion models.

scholarly journals Spatiotemporal changes in flow hydraulic characteristics and soil loss during gully headcut erosion under controlled conditions

2021 ◽  
Vol 25 (8) ◽  
pp. 4473-4494
Author(s):  
Mingming Guo ◽  
Zhuoxin Chen ◽  
Wenlong Wang ◽  
Tianchao Wang ◽  
Qianhua Shi ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Energy Consumption ◽  
Soil Erosion ◽  
Soil Loss ◽  
Gully Erosion ◽  
Stream Power ◽  
Spatiotemporal Changes ◽  
Headcut Erosion ◽  
Over Time

Abstract. The spatiotemporal changes in flow hydraulics and energy consumption and their associated soil erosion remain unclear during gully headcut retreat. A simulated scouring experiment was conducted on five headcut plots consisting of upstream area (UA), gully headwall (GH), and gully bed (GB) to elucidate the spatiotemporal changes in flow hydraulic, energy consumption, and soil loss during headcut erosion. The flow velocity at the brink of a headcut increased as a power function of time, whereas the jet velocity entry to the plunge pool and jet shear stress either logarithmically or linearly decreased over time. The jet properties were significantly affected by upstream flow discharge. The Reynolds number, runoff shear stress, and stream power of UA and GB increased as logarithmic or power functions of time, but the Froude number decreased logarithmically over time. The Reynolds number, shear stress, and stream power decreased by 56.0 %, 63.8 %, and 55.9 %, respectively, but the Froude number increased by 7.9 % when flow dropped from UA to GB. The accumulated energy consumption of UA, GH, and GB positions linearly increased with time. In total, 91.12 %–99.90 % of total flow energy was consumed during headcut erosion, of which the gully head accounted for 77.7 % of total energy dissipation, followed by UA (18.3 %), and GB (4.0 %). The soil loss rate of the “UA-GH-GB” system initially rose and then gradually declined and levelled off. The soil loss of UA and GH decreased logarithmically over time, whereas the GB was mainly characterized by sediment deposition. The proportion of soil loss at UA and GH is 11.5 % and 88.5 %, respectively, of which the proportion of deposited sediment on GB reached 3.8 %. The change in soil loss of UA, GH, and GB was significantly affected by flow hydraulic and jet properties. The critical energy consumption initiating soil erosion of UA, GH, and GB is 1.62, 5.79, and 1.64 J s−1, respectively. These results are helpful for deepening the understanding of gully erosion process and hydrodynamic mechanisms and can also provide a scientific basis for the construction of gully erosion model and the design of gully erosion prevention measures.

Experimental study on dynamic mechanism of sheet erosion processes on steep grassland in the loess region of China

2021 ◽  
Author(s):  
Qi Guo ◽  
Zhanli Wang
Keyword(s):  
Shear Stress ◽  
Soil Erosion ◽  
Power Function ◽  
Erosion Rate ◽  
Dynamic Mechanism ◽  
Erosion Process ◽  
Stream Power ◽  
Study Results ◽  
Loess Region ◽  
Sheet Erosion

<p>Sheet erosion has been the major erosion process on steep grassland since the Grain-for-Green project was implemented in 1999 in the Loess Plateau with serious soil erosion, in China. Quantifying sheet erosion rate on steep grassland could improve soil erosion estimation on loess hillslopes and provide scientific support for effectively controlling soil erosion and rationally managing grassland. Simulated rainfall experiments were conducted on grassland plot with vegetation coverage of 40% under complete combination of rainfall intensities of 0.7, 1.0, 1.5, 2.0 and 2.5 mm min<sup>-1</sup> and slope gradients of 7°, 10°, 15°, 20° and 25°. Results showed that sheet erosion rate (<em>SE</em>), varying from 0.0048 to 0.0578 kg m<sup>-2</sup> min<sup>-1</sup>, was well described by binary power function equation (<em>SE</em> = 0.0026 <em>I</em><sup>1.306</sup><em>S</em><sup>0.662</sup>) containing rainfall intensity and slope gradient with <em>R<sup>2</sup></em> = 0.940. The logarithmic equation of shear stress (<em>SE</em> = 0.084 + Ln (<em>τ</em>)) and the power function equation of stream power (<em>SE</em> = 1.141 <em>ɷ</em><sup>1.073</sup>) could be used to predict sheet erosion rate. Stream power (<em>R<sup>2</sup></em> = 0.903) was a better predictor of sheet erosion than shear stress (<em>R<sup>2</sup></em> = 0.882). However, predictions based on flow velocity, unit stream power, and unit energy were unsatisfactory. The stream power was an excellent hydrodynamic parameter for predicting sheet erosion rate. The sheet erosion process of grassland slope was also affected by the raindrop impact except the dynamic action of sheet flow. The combination of stream power and rainfall kinetic energy (<em>KE</em>) among different rainfall physical parameters had the most closely relationship with the sheet erosion rates, which is also better than the stream power only, and a binary power function equation (<em>SE</em> = 0.221 <em>ω</em><sup>0.831</sup><em>KE</em><sup>0.416</sup>) could be used to predict sheet erosion rate on grassland slope with <em>R<sup>2</sup></em> = 0.930. The study results revealed the dynamic mechanism of the sheet erosion process on steep grassland in the loess region of China.</p>

scholarly journals Site-Specific Erodibility in Claypan Soils: Dependence on Subsoil Characteristics

2017 ◽  
Vol 33 (5) ◽  
pp. 705-718 ◽  
Author(s):  
Stacey E. Tucker-Kulesza ◽  
Gretchen F. Sassenrath ◽  
Tri Tran ◽  
Weston Koehn ◽  
Lauren Erickson
Keyword(s):  
Electrical Conductivity ◽  
Shear Stress ◽  
Soil Erosion ◽  
Soil Profile ◽  
Crop Production ◽  
Electrical Resistivity Tomography ◽  
Critical Shear Stress ◽  
Productive Capacity ◽  
Clay Layer ◽  
Resistivity Tomography

Abstract. Soil erosion is a primary factor limiting the productive capacity of many crop production fields and contributing to sediment and nutrient impairments of water bodies. Loss of topsoil is especially critical for areas of limited topsoil depth, such as the claypan area of the central United States. More than a century of conventional agricultural practices have eroded the topsoil and, in places, exposed the unproductive clay layer. This clay layer is impervious, limiting water infiltration and root penetration, and severely restricting agricultural productivity. Previous studies have documented changes in topsoil thickness using apparent electrical conductivity (ECa). However, that methodology is limited by its shallow depth of measurement within the soil profile, and as such cannot adequately explore factors within the soil profile that potentially contribute to topsoil erosion. In this study, we identified areas of limited topsoil depth using crop yields and ECa. Two areas within the production field varying in crop production and ECa were selected for detailed measurements using Electrical Resistivity Tomography. This methodology allowed delineation of soil stratigraphy to a depth of 5.3 m. The erodibility of undisturbed soil samples from the two areas were measured in an Erosion Function Apparatus to obtain the critical shear stress, or the applied stress at which soil begins to erode. Based on resistivity measurement, the highly productive region of the field had a thick (1.0-2.0 m) soil layer of saturated clayey sand soil over a uniform sandy material, with minimal clay layer. This soil had a critical shear stress of 12 Pa. The extent of historical erosion was evident in the poorly-producing area, as only a thin band of topsoil material remained over a thicker clay layer. The unproductive area with exposed clay layer had a critical shear stress of 128 Pa, indicating it was more resistant to erosion than the highly productive region. The clay layer was found to extend to 1.3-1.5 m in depth in the soil profile in the poorly producing area. Below this layer was a layer with similar resistivity to the high-producing region. The data reveal the extent of historical erosion within the crop production field and highlight significant variability in measured soil properties within a field of identical production practices. While spatial variations in topsoil have long been considered in developing management practices to improve soil health and productive capacity, our results indicate the importance of identifying variability of subsoil characteristics to address long-term impacts on soil erosion and productivity. Keywords: Soil erosion, Soil electrical conductivity, Claypan soil, Productive capacity, Electrical resistivity tomography.

scholarly journals A review of the (Revised) Universal Soil Loss Equation ((R)USLE): with a view to increasing its global applicability and improving soil loss estimates

2018 ◽  
Vol 22 (11) ◽  
pp. 6059-6086 ◽  
Author(s):  
Rubianca Benavidez ◽  
Bethanna Jackson ◽  
Deborah Maxwell ◽  
Kevin Norton
Keyword(s):  
Soil Erosion ◽  
Soil Loss ◽  
Gully Erosion ◽  
Data Availability ◽  
Universal Soil Loss Equation ◽  
Soil Productivity ◽  
Temporal Scales ◽  
Erosion Models ◽  
The World ◽  
Soil Loss Equation

Abstract. Soil erosion is a major problem around the world because of its effects on soil productivity, nutrient loss, siltation in water bodies, and degradation of water quality. By understanding the driving forces behind soil erosion, we can more easily identify erosion-prone areas within a landscape to address the problem strategically. Soil erosion models have been used to assist in this task. One of the most commonly used soil erosion models is the Universal Soil Loss Equation (USLE) and its family of models: the Revised Universal Soil Loss Equation (RUSLE), the Revised Universal Soil Loss Equation version 2 (RUSLE2), and the Modified Universal Soil Loss Equation (MUSLE). This paper reviews the different sub-factors of USLE and RUSLE, and analyses how different studies around the world have adapted the equations to local conditions. We compiled these studies and equations to serve as a reference for other researchers working with (R)USLE and related approaches. Within each sub-factor section, the strengths and limitations of the different equations are discussed, and guidance is given as to which equations may be most appropriate for particular climate types, spatial resolution, and temporal scale. We investigate some of the limitations of existing (R)USLE formulations, such as uncertainty issues given the simple empirical nature of the model and many of its sub-components; uncertainty issues around data availability; and its inability to account for soil loss from gully erosion, mass wasting events, or predicting potential sediment yields to streams. Recommendations on how to overcome some of the uncertainties associated with the model are given. Several key future directions to refine it are outlined: e.g. incorporating soil loss from other types of soil erosion, estimating soil loss at sub-annual temporal scales, and compiling consistent units for the future literature to reduce confusion and errors caused by mismatching units. The potential of combining (R)USLE with the Compound Topographic Index (CTI) and sediment delivery ratio (SDR) to account for gully erosion and sediment yield to streams respectively is discussed. Overall, the aim of this paper is to review the (R)USLE and its sub-factors, and to elucidate the caveats, limitations, and recommendations for future applications of these soil erosion models. We hope these recommendations will help researchers more robustly apply (R)USLE in a range of geoclimatic regions with varying data availability, and modelling different land cover scenarios at finer spatial and temporal scales (e.g. at the field scale with different cropping options).

Pressure conditions in the hole erosion test

2015 ◽  
Vol 52 (1) ◽  
pp. 114-119 ◽  
Author(s):  
Jaromír Říha ◽  
Jan Jandora
Keyword(s):  
Shear Stress ◽  
Soil Erosion ◽  
Numerical Study ◽  
Critical Shear Stress ◽  
Technical Note ◽  
Hydraulic Gradient ◽  
Hydraulic Gradients ◽  
Erosion Test ◽  
The Difference

The hole erosion test (HET) is used in the study of soil erosion in the case of what is known as “piping” when concentrated leaks occur. The HET enables the determination of soil erosion characteristics such as the critical shear stress along the pre-formed hole (pipe) and the coefficient of soil erosion. Normally, in the HET, the hydraulic gradient is determined from the difference between the piezometric heads measured at the inflow and outflow chambers (upstream and downstream of the soil specimen). Hydraulic analysis shows that such measurements ignore losses at the entrance and exit of the hole, causing the overestimation of the hydraulic gradient along the length of the hole, and thus the calculated shear stress. In this technical note, the results of preliminary analysis using the Bernoulli principle and of numerical study of the pressure conditions in the HET apparatus are shown. The turbulent flow in the HET apparatus was calculated using ANSYS commercial CFD (computational fluid dynamics) software. The analysis was performed for various hole entrance shapes. The conclusion of this note details the differences between traditionally determined hydraulic gradients and those numerically derived along the length of a hole.

scholarly journals Study on Parameters of Two Widely Used Cohesive Soils Erosion Models

Water ◽  
2021 ◽  
Vol 13 (24) ◽  
pp. 3621
Author(s):  
Qiusheng Wang ◽  
Pengzhan Zhou ◽  
Junjie Fan ◽  
Songnan Qiu
Keyword(s):  
Shear Stress ◽  
Critical Shear Stress ◽  
Cohesive Soils ◽  
Stress Model ◽  
Wilson Model ◽  
Erosion Models ◽  
Erodibility Coefficient ◽  
Proportional Relationship ◽  
Model Equations ◽  
Parameter Values

The erosion rate of cohesive soils was typically modeled with the excess shear stress model and the Wilson model. Several kinds of research have been conducted to determine the erodibility parameters of the two models, but few attempts have been made hitherto to investigate the general trends and range of the erodibility parameter values obtained by the commonly used Erosion Function apparatus. This paper collected a database of 177 erosion function apparatus tests to indicate the variability of all erodibility parameters; the range of erodibility parameters is determined by data statistics and parameter theoretical value derivation. The critical shear stress (τc) and erodibility coefficient (Z0) in the over-shear stress model have a positive proportional relationship when the data samples are sufficient. However, there is no such relationship between the erodibility coefficient (b0) and erodibility coefficient (b1) in the Wilson model. It is necessary to express the soil erosion resistance by considering all erosion parameters in the erosion model. Equations relating erodibility parameters to water content, plasticity index, and median particle size were developed by regression analysis.

scholarly journals Spatial-temporal changes in flow hydraulic characteristics and soil loss during gully headcut erosion

2020 ◽  
Author(s):  
Mingming Guo ◽  
Zhuoxin Chen ◽  
Wenlong Wang ◽  
Tianchao Wang ◽  
Qianhua Shi ◽  
...  
Keyword(s):  
Shear Stress ◽  
Energy Consumption ◽  
Soil Erosion ◽  
Froude Number ◽  
Soil Loss ◽  
Reynold Number ◽  
Stream Power ◽  
Spatial Changes ◽  
Headcut Erosion ◽  
Over Time

Abstract. The temporal-spatial changes in flow hydraulics and energy consumption and their associated soil erosion remain unclear during gully headcut retreat. A simulated scouring experiment was conducted on five headcut plots consisting of upstream area (UA), gully headwall (GH) and gully bed (GB) to elucidate the temporal-spatial changes in flow hydraulic, energy consumption, and soil loss during headcut erosion. The flow velocity at the brink of headcut increased as a power function of time, whereas the jet velocity entry to plunge pool and jet shear stress logarithmically or linearly decreased over time. The jet properties significantly affected by upstream flow discharge. The Reynold number, runoff shear stress, and stream power of UA and GB increased as logarithmic or power functions of time, but the Froude number decreased logarithmically over time. The flow of UA and GB was supercritical and subcritical, respectively, and transformed to turbulent with inflow discharge increased. The Reynold number, shear stress and stream power decreased by 56.0 %, 63.8 % and 55.9 %, respectively, but the Froude number increased by 7.9 % when flow dropped from UA to GB. The accumulated runoff energy consumption of UA, GH and GB positions linearly increased with time, and their proportions of energy consumption are 18.3 %, 77.7 % and 4.0 %, respectively. The soil loss rate of the UA-GH-GB system initially rose and then gradually declined and levelled off. The soil loss of UA and GH decreased logarithmically over time, whereas the GB was mainly characterized by sediment deposition. The proportion of soil loss at UA and GH are 11.5 % and 88.5 %, respectively, of which the proportion of deposited sediment on GB reached 3.8 %. The change in soil loss of UA, GH and GB was significantly affected by flow hydraulic and jet properties. The critical energy consumption initiating soil erosion of UA, GH, and GB are 1.62 J s−1, 5.79 J s−1 and 1.64 J s−1, respectively. These results are helpful to reveal the mechanism of gully headcut erosion and built headcut migration model.

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