Effects of soil crust on the collapsing erosion of colluvial deposits with granite residual soil

Collapsing erosion is a unique phenomenon commonly observed on the granite residue hillslopes in the tropical and subtropical regions of southern China,characterized by its abrupt occurrence and significant erosion volumes.However,the impacts of soil crust conditions on the erosion of colluvial deposits with granite residual soils have only been studied to a limited extent.To address this issue,this study investigates the impacts of three soil crust conditions(i.e.,without crust,10-minute crust,and 20-minute crust)on gully morphology,rainfall infiltration,and runoff and sediment yield during slope erosion of colluvial deposits with granite residues(classified as Acrisols)in Yudu County,Ganzhou City,Jiangxi Province,China,using simulated rainfall tests and photographic methods.The results showed that as the strength of the soil crust increased,the capacity of moisture infiltration and the width and depth of the gully as well as the sediment concentration and yield ratio decreased;at the same time,the runoff ratio increased.The sediment yield in the without-crust test was found to be 1.24 and 1.43 times higher than that observed in the 10-minute crust and 20-minute crust tests,respectively.These results indicate that soil crusts can effectively prevent slope erosion and moisture infiltration,while providing valuable insights for the management of soil erosion in natural environments.

Observation and Research on Gravitational Erosion Process of Bank Slopes in Headstream Area of Jiangjia Ravine, Yunnan, China

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.

Study of Spatial and Temporal Processes of Soil Erosion on Sloping Land Using Rare Earth Elements As Tracers

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.

Changes in SOC and Nutrients under Intensive Tillage in Two Types of Slope Landscapes

The net effect of tillage erosion on soil properties would be associated with the spatial variation in soil constituents,and therefore plays an important role in ecological agriculture.We conducted a consecutive tillage by hoeing 15 times during a period with no rainfall in the two slope landscapes(a linear slope and complex slope) of the Yangtze Three Gorges reservoir areas,to examine the relationship between soil erosion rates and the variations in soil chemical properties and compare the effects of soil redistribution on SOC and nutrients between the linear and complex slopes.After the simulated tillage,notable changes in 137 Cs inventories of the soil occurred in the summit and toeslope positions on the linear slope,while there were significant changes in 137 Cs inventories at convex and concave positions on the complex slope.Soil profile disappeared at the summit slope boundary,with the exposure area of 16.0% and 7.6% of the experimental plot,respectively,for the linear and complex slopes due to no soil replacement.Soil organic C and nutrients were completely depleted with the disappearance of soil profiles at soil eroding zones,whereas a remarkable increase in SOC,total N and available nutrient concentrations of the post-tillage surface soil and a decrease in total nutrient concentrations(P and K) were found at depositional zones on the linear slope.For the complex slope,however,changes in SOC and nutrient concentrations of the post-tillage surface soil exhibited a patterndifferent from that on the linear slope,which showed a remarkable decrease in SOC and total nutrient concentrations but a slight increase in available nutrient concentrations after tillage in the toeslope position.Due to the gradual increase in soil depth from top to bottom of the slope,SOC and nutrient inventories in the soil profiles were significantly correlated with soil redistribution rates on both the linear and complex slopes.Tillage causes remarkable changes of soil chemical properties in the surface soil layer and soil profile,and increases SOC and nutrient inventories for the soil profile downslope in steeply sloping landscapes.

The characteristics of rill development and their effects on runoff and sediment yield under different slope gradients

Rill formation is the predominant erosion process in slope land in the Loess Plateau, China. This study was conducted to investigate rill erosion characteristics and their effects on runoff and sediment yielding processes under different slope gradients at a rate of 10°, 15°, 20° and 25° with rainfall intensity of 1.5 mm min-1 in a laboratory setting. Results revealed that mean rill depth and rill density has a positive interrelation to the slope gradient. To the contrary, width-depth ratio and distance of the longest rill to the top of the slope negatively related to slope gradient. All these suggested that increasing slope steepness could enhance rill headward erosion, vertical erosion and the fragmentation of the slope surface. Furthermore,total erosion tended to approach a stable maximum value with increasing slope, which implied that there is probably a threshold slope gradient where soil erosion begins to weaken. At the same time, the correlation analysis showed that there was a close connection between slope gradient and the variousindices of soil erosion: the correlation coefficients of slope gradient with maximal rill depth, number of rills and the distance of the longest rill from the top of the slope were 0.98, 0.97 and-0.98, respectively,indicating that slope gradient is the major factor of affecting the development of rills. Furthermore,runoff was not sensitive to slope gradient and rill formation in this study. Sediment concentration,however, is positively related to slope gradient and rill formation, the sediment concentrations increased rapidly after rill initiation, especially. These results may be essential for soil loss prediction.

Wind Tunnel Study of Multiple Factors Affecting Wind Erosion from Cropland in Agro-pastoral Area of Inner Mongolia,China

In this paper,the process of wind erosion on two kinds of soil from the agro-pastoral area of Inner Mongolia are studied using wind tunnel experiments,considering the wind speed,blown angle of wind and soil moisture content.The results showed that the modulus of soil wind erosion increases with an increase of wind speed.When the wind speed exceeds a critical value,the soil wind erosion suddenly increases.The critical speed for both kinds of soil is within the range of 7-8m·s-1.For a constant wind speed,the rate of soil wind erosion changes from increasing to falling at a critical soil slope.The critical slope of loam soil and sandy loam soil is 20° and 10°,respectively.Soil moisture content has a significant effect on wind erosion.Soil wind erosion of both soils decreases with an increase of the soil water content in two treatments,however,for treatment two,the increasing trends of wind erosion for two soils with the falling of soil water content are no significant,especially for the loam soil,and in the same soil water content,the wind erosion of two soils in treatment one is significantly higher than treatment two,this indicates reducing the disturbance of soil surface can evidently control the soil wind erosion.

几种土壤的细沟侵蚀过程及其影响因素

通过间隔为11h的二次人工模拟降雨和冲蚀槽试验研究了10种土壤的侵蚀过程,发现在第2次降雨中大多数土壤出现了细沟侵蚀形式。采样微形态观察发现,在第1次降雨中形成结皮的土壤在第2次降雨中出现了细沟侵蚀;产流产沙观测发现所有出现细沟侵蚀的土壤在第1次降雨中径流含沙量逐渐减少,而第2次降雨中有一个先剧增后减少的过程。土壤理化分析及多元逐步回归分析结果表明,土壤颗粒组成、有机质含量、铁铝含量等因素对细沟侵蚀的影响表现不明显,而与土壤团聚体有关结构指标、细沟侵蚀、产流产沙速率及总量呈显著相关关系。分析表明,团聚体分散度、崩解速率与渗透系数之比两个指标能较好地预测细沟侵蚀发生的可能性,同时也能很好地预测侵蚀产沙量。

斜坡带低位扇砂岩体岩性油气藏勘探方法——以埕岛潜山披覆构造东部斜坡带为例

针对隐蔽油气藏成因和分布规律复杂、勘探技术要求高的特点 ,把层序地层学方法应用于陆相湖盆隐蔽油气藏的勘探。在高分辨率层序地层研究的基础上 ,对沉积体系进行精细的解剖分析 ,研究沉积作用发生和演化的机制 ,探讨隐蔽油藏 (圈闭 )分布的边界条件 ,进而形成了关于斜坡带低位扇砂岩体隐蔽油藏 (圈闭 )分布与预测的地质方法和技术 ,初步提出了湖相盆地“低位扇”和“坡折带”的理论。以埕岛地区东部斜坡带为例 ,介绍了斜坡带低位扇砂体岩性油气藏的勘探思路和方法 ,使该类砂体油藏预测的成因类型和分布规律更加清楚 ,有效地指导了对该类油气藏的勘探。

Experimental study on the effects of multiple factors on spring meltwater erosion on an alpine meadow slope

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.

舟山岛马岙岸段海岸演变与水下岸坡冲淤动态

利用不同年份的水深地形资料进行冲淤计算,结合实测水文泥沙、现场岸滩沉积地貌观察、新老海堤分布位置及以往浅地层探测和考古等资料综合分析发现,岸滩地貌形态从大约距今7 000 a前的一个古基岩港湾经受细颗粒泥沙长期不断地充填、淤积转化为近乎平直的岸段.在自然和人类活动的共同作用下,近370 a来海岸线以5.3 m/a的速度向海推移,潮滩以0.25 cm/a的速率沉积.近40余年来水下岸坡平均冲淤速率为-3.8～2.4 cm/a,横向冲淤调整有类似砂质海岸剖面塑造的特性,泥沙经受了在横向剖面“上部微淤、下部微冲”和纵向总体“东侧微冲、中西部微淤”的交替重复调整过程,目前朝着“上部微淤、下部微冲”的均衡剖面调整方向发展.

上方来水来沙的异位侵蚀效应研究进展

上方来水来沙作为上下不同地貌部位之间水流能量传递的媒介和泥沙输移的载体,对下游侵蚀产沙过程具有重要影响,是土壤侵蚀研究的关键环节。以往研究多侧重于小流域泥沙来源以及上方来水来沙的异位沉积效应,对上方来水来沙的异位侵蚀效应研究相对较少。本文回顾了上方来水来沙异位侵蚀效应的研究方法,在总结归纳前人研究成果的基础上,首次提出了"异位侵蚀"的概念,从异位径流特征、侵蚀产沙等方面,分析了裸露坡面上方来水来沙的异位侵蚀效应,并对水土保持措施异位减蚀作用的研究进展进行了综述。在此基础上,进一步探讨了异位侵蚀研究中的热点和难点问题,提出可从明确异位侵蚀效应概念、探索异位侵蚀影响因素及其机理、阐明上方来水来沙异位侵蚀过程中水沙和能量传递特征、量化水土保持措施异位减蚀作用等4个方面进一步深入研究上方来水来沙的异位侵蚀效应。

Relationship between soil surface roughness and hydraulic roughness coefficient on sloping farmland

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.

Morphometric Analysis and Flash Floods Assessment for Drainage Basins of the Ras En Naqb Area, South Jordan Using GIS

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 LO 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. FS 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 Dd 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.

黄土生态护坡优化措施研究及水土流失治理效果预测

The large-scale management of ditches and implementation of land projects in loess areas have increased the arable land area but have caused considerable engineering issues, resulting in severe soil erosion. In this study, field tests were performed at different time scales, a control group was established, organic material–plant joint restoration technology was proposed as an optimized management measure, and the erosion control mechanism and restoration mode of organic material–plant joint restoration technology were analyzed. Based on the obtained experimental data, a Water Erosion Prediction Project(WEPP)-based hydraulic erosion model was constructed, sensitivity parameters were calibrated, and the soil erosion intensity and corresponding spatial distribution in the watershed of the study area were simulated via the geo-spatial interface for WEPP(GeoWEPP) after organic material–plant joint restoration technology was adopted to predict the effect of optimized management measures. The results showed that among the slopes with different restoration measures, organic material–plant joint restoration technology effectively controlled loess slope erosion, and the average erosion modulus of the organic material–grass and shrub transplantation slope reached only 23.37 t/km^(2), which is a decrease of 97.68% relative to the traditional grass–shrub protection slope. Moreover, the sand content of the joint restoration slope was reduced by 392.41 g/L relative to the bare slope, reaching only 0.29 g/L, and the runoff yield was reduced by 8.88 L/min. The GeoWEPP modeling results revealed that the total runoff yield and average annual erosion modulus of the watershed were lower after joint restoration than during the prerestoration period. Similarly, the total runoff yield of the watershed was 4.6%, the simulated 10-year average annual total sand production reached 2048.3 t,and the average annual erosion modulus was 582.75 t/km^(2), which is 52.15% lower than that under untreated conditions. This study provides a new strategy for solving soil erosion problems and restoring the ecology of slopes after managing ditches and implementing land projects.

准噶尔盆地玛湖凹陷P-T转换期层序结构、坡折发育及油气地质意义

对应晚二叠世—早三叠世地球系统转换期(简称P—T转换期),准噶尔盆地玛湖凹陷P_(3)-T_(1)经历了从前陆冲断向整体拗陷的转变,发育T_(1)/P、P_(3)w/P_(2)w_(2)期大型不整合及上乌尔禾组(P_(3)w)、百口泉组(T_(1)b)_(2)套退覆型低位沉积,形成了一批大型—特大型砾岩油田。针对T_(1)/P和P_(3)w/P_(2)w_(2)个三级层序界面,识别出与构造挠曲和侵蚀作用相关的2类坡折带:构造挠曲坡折带受控于持续性古隆起,控制层序界面之上地层向斜坡高部位逐层“单向超覆”,侵蚀坡折带受控于古残丘,控制层序界面之上地层向古残丘“双向超覆”或沿下切沟谷低位充填。2类坡折带均控制地层沉积变化,有利于形成上倾超覆型、低位充填型和地层削截型岩性地层圈闭。研究成果对于指导古地貌背景坡折控制下的大型岩性地层油气藏勘探具有重要意义。