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.

Using ^(137)Cs Tracing Methods to Estimate Soil Redistribution Rates and to Construct a Sediment Budget for a Small Agricultural Catchment in the Three Gorges Reservoir Region,China

Soil erosion and associated off-site sedimentation are threatening the sustainable use of the Three Gorges Dam. To initiate management intervention to reduce sediment yields, there is an increasing need for reliable information on soil erosion in the Three Gorges Reservoir Region （TGRR）. The purpose of this study is to use 137Cs tracing methods to construct a sediment budget for a small agricultural catchment in the TGRR. Cores were taken from a pond and from paddy fields, for laTCs measurements. The results show that the average sedimentation rate in the pond since 1963 is 1.50 g cm-2 yr-1 and the corresponding amount of sediment deposited is 1,553 t. The surface erosion rate for the sloping cultivated lands and the sedimentation rate in the paddy fields were estimated to be 3,770 t km-2 yr-1 and 2,600 t km-2 yr^1 respectively. Based on the estimated erosion and deposition rates, and the area of each unit, the post 197o sediment budget for the catchment has been constructed. A sediment delivery ratio of 0.5 has been estimated for the past 42 years. The data indicate that the sloping cultivated lands are the primary sediment source areas, and that the paddy fields are deposition zones. The typical land use pattern （with the upper parts characterized by sloping cultivated land and the lower parts by paddy fields） plays an important role in reducing sediment yield from agricultural catchments in the TGRR. A 137Cs profile for the sediment deposited in a pond is shownto provide an effective means of estimating the land surface erosion rate in the upstream catchment.

Soil reinforcement by a root system and its effects on sediment yield in response to concentrated flow in the loess plateau

The importance of roots in soil conservation has long been underestimated due to a lack of sys-tematic studies conducted to evaluate root dis-tribution patterns and their effects on soil ero-sion. Current knowledge regarding root mor-phology and its impact on soil erosion by water is limited;therefore, detailed analysis of the role that root systems play in controlling soil ero-sion is needed. In this study, stratified runoff scouring at different soil depths in the field was conducted in a grassland area. The results in-dicated that both root biomass and soil wa-ter-stable aggregates decreased as soil depth increased at all three sites, while there was al-most no change in soil bulk density at 1.3g/cm3. Sediment yields under different runoff dis-charge at different sites showed similar trends, and the sediment yield increased as the soil depth increased at all three sites. Further analysis revealed that close relationships ex-isted between root biomass and the amount of water-stable aggregates and soil organic matter content, and that these factors greatly influ-enced soil erosion. Based on the data generated by the experiment, equations describing the relationship between sediment production at different soil depths and root biomass were determined.

Water Yield and Sediment Yield Simulations for Teba Catchment in Spain Using SWRRB Model: Ⅱ. Simulation Results

Simulated results of water yield, sediment yield, surface runoff,subsurface runoff, peak flow, evapo- transipiration, etc., in theTeba catchment, Spain, using SWRRB (Simulator for Water Resources inRural Basins) model are presented and the related problems arediscussed. The results showed that water yield And sediment yieldcould be satisfactorily simulated using SWRRB model. The accuracy ofthe annual water Yield simulation in the Teba catchment was up to83.68/100, which implied that this method could be effectively Usedto predict the annual or inter-annual water yield and to realize thequantification of geographic elements And processes of a river basin.

Impact of Land-Use Practices on Sediment Yield in the Dhrabi Watershed of Pakistan

Soil erosion by water is one of the most important land degradation processes in the sloping rainfed lands in Pakistan. A study was conducted in the Dhrabi watershed of Pakistan to evaluate sediment yield associated with rainfall-runoff under various land-use practices. Five sub-catchments with sizes varying from 1.5 to 350 ha were selected for measurement of rainfall, runoff and sediment yield. Soil conservation techniques were also introduced to reduce the soil erosion. All runoff events occurred in the summer especially during monsoon season （July-September）. Sediment yield of two small gully catchments ranged from 4.79 to 8.34 t/ha/yr in 2009, a relatively dry year. In 2010, the annual sediment yield was 8.15 to 12.31 t/ha. Terraced catchment with arable crops produced annual 4.1 t/ha of sediment as compared to 12.31 t/ha by the adjacent gully catchment showing high potential of terraces in reducing erosion. Runoff coefficients calculated for these catchments vary from 0.09 to 0.75. The macro and micro nutrients present in the sediment indicate that these nutrients are being depleted due to soil erosion.

Soil Erosion on a Slope without Vegetation: a Simulating Experiment on a Bare Land in Mt.Tanakami

In order to understand the process of surface erosion and its changing characteristics, a sprinkling experiment is conducted on a bare slope in Mt. Tanakami. Based on the measurements and analysis of runoff, mean soil erosion depth sediment yield and semiment transport, etc., the characteristics in the process of surface erosion in the experimental area are as follows: the occurrence of sediment discharge is interrupted, with a saturated overland-flow surface runoff; the mean erosion depth is 0.086 2 cm, which is thicker compared with other areas in Mt. Tanakmi; sediment yield is 431. 283 m3·km?2, whose process is detachment-limited, and the type of sediment transport is a sediment flow. Key words runoff - soil erosion depth - sediment yield - sediment transport - Mt. Tanakami CLC number S 157 Biography: ZHAO Wei (1975-), female, Ph. D candidate, Lecturer, now is working in College of Earth Sciences, Jilin University, research dircetion: physical geography, environmental planning and management

A Simulating Experiment in the Process of Soil Erosion on Bare Land in Mt.Tanakami

In order to understand the process of surface erosion and acquire basic data of conditions on hillslope without vegetation, a sprinkling experiment is conducted on a bare slope in Mt.Tanakami in the central part of Japan. Based on the measurements of runoff, mean soil erosion depth, and sediment yield, etc., the results suggest the following characteristics in the process of surface erosion in the experimental area. (1) The occurrence of sediment discharge is interrupted; (2) Surface runoff is a saturated overland flow; (3) The mean soil erosion depth is thick compared with other areas in Mt.Tanakami; (4) Sediment discharge process is detachment-limited.

递增式连续降雨条件下典型山区坡面径流产沙水动力学特征

山区复杂的下垫面条件导致了山区小流域水文响应过程的复杂性,山区坡面作为山区小流域水文响应的基本单元,研究其不同下垫面条件下径流产沙水动力特征具有重要意义。为明晰山区坡面不同下垫面条件下径流水沙水动力特征,该研究选用官山河小流域作为研究对象,基于室内模拟递增式连续降雨试验方法,研究了坡度、土层厚度分布和土层底部透水性等山区坡面下垫面特性共同作用下的坡面径流产沙水动力学特征。结果表明:1)连续降雨条件下,雷诺数、水流剪切力和径流功率随着产流时间和雨强增加呈现增加趋势,Darcy-Weisbach阻力系数呈降低趋势。2)雨强增加使雷诺数均值和径流功率均值显著增加(P<0.05),设计雨强60、90、120 mm/h时的雷诺数均值、径流功率均值分别比30 mm/h的雷诺数均值、径流功率均值增加了130%、276%、366%和171%、328%、435%;坡度增加使水流剪切力均值和径流功率均值显著增加(P<0.05),坡度15°、25°的水流剪切力均值分别比坡度5°的增加了135%和187%,坡度15°、25°的径流功率均值分别比坡度5°的均值增加了224%和357%;土层厚度分布对阻力系数均值和土层底部透水的雷诺数均值、径流功率均值有显著影响(P<0.05),土层底部透水性仅对土层厚度分布为上薄下厚的雷诺数均值和水流剪切力均值有显著影响(P<0.05)。3)雨强是影响坡面产流产沙水动力特征的主导因素,对雷诺数的方差贡献率高达83.11%,水流剪切力主要受到雨强和坡度的影响,累计贡献率达67.64%,径流功率主要受到雨强和坡度的影响,累计贡献率达80.58%。在单一雨强条件下,坡度和土层厚度分布是影响水动力参数的主要因素,土层厚度分布和坡度的交互作用、土层底部透水性和土层厚度分布的交互作用对水动力参数也有一定影响。因此,在研究坡面产流产沙规律时,除考虑雨强和坡度外,还应兼顾考虑土层厚度分布和土层底部透水性及其交互作用的影响。该研究结果可为山区坡面复杂下垫面条件下的坡面产流产沙机理提供一定的理论支撑,并为改进山区小流域水文过程分布式模拟提供参数率定依据。

山区陡坡坡面产流产沙过程的降雨试验研究

为弄清雨强、土层厚度分布和土层底部透水性交互作用对山区陡坡坡面产流产沙过程影响规律,本文基于4种设计土槽进行室内模拟连续降雨试验。结果表明:地表径流率在连续降雨过程中呈明显波动上升趋势,侵蚀速率均值在连续降雨过程中呈现先增加后减小的趋势。地表径流率主要受到雨强的影响,方差贡献率达88.85%,侵蚀速率主要受到雨强以及土层厚度分布和雨强的交互影响,方差贡献率分别为46.13%和20.64%,土层厚度分布和土层底部透水性的交互作用对侵蚀速率也有一定影响,方差贡献率为9.21%。因此,除考虑雨强外,还应兼顾考虑土层厚度分布、土层底部透水性及其交互作用对产流产沙过程的影响。本研究可为山区坡面复杂下垫面条件下的坡面产流产沙机理提供理论支撑。

Soil Erosion and Sediment Control Effects in the Three Gorges Reservoir Region, China

The Three Gorges Reservoir, the world’s largest hydropower reservoir, receives a significant sediment yield from soil erosion. Sloping farmland is the main source, exacerbated by changes in land use from relocating the inhabitants, and from engineering projects related to dam construction. Related geo-hazards, including landsliding of valley-side slopes, will further increase the sediment yield to the completed reservoir. Integrated watershed management, begun extensively in 1989, has effectively controlled soil erosion and sediment delivery to date. What is described here as the Taipinxi Mode of integrated watershed management, based on its application in the 26.14 km2 watershed of that name in Yiling District, has been successful and is recommended for the entire region. The effects of this set of erosion-mitigation measures are assessed, using experienced formulas for soil and water conservation and information from remote sensing. The amount of soil erosion, and of sediment delivery to the reservoir were reduced by 43.75–45.94 × 106 t y-1, and by 12.25–12.86 × 106 t y-1, respectively, by 2005, by which time the project had been operative for 16 years.

Upscaling the use of fallout radionuclides in soil erosion and sediment budget investigations:Addressing the challenge

The application of fallout radionuclides in soil erosion investigations and related sediment budget studies has provided a widely used tool for improving understanding of soil erosion and sediment transfer processes.However,most studies using fallout radionuclides undertaken to date have focussed on small areas.This focus on small areas reflects both the issues addressed and practical constraints associated with sample collection and analysis.Increasing acceptance of the important role of fine sediment in degrading aquatic habitats and in the transfer and fate of nutrients and contaminants within terrestrial and fluvial systems has emphasised the need to consider larger areas and the catchment or regional scale.The need to upscale existing approaches to the use of fallout radionuclides to larger areas represents an important challenge.This contribution provides a brief review of existing and potential approaches to upscaling the use of fallout radionuclides and presents two examples where such approaches have been successfully applied.These involve a national scale assessment of soil erosion rates in England and Wales based on 137Cs measurements and an investigation of the sediment budgets of three small/intermediate-size catchments in southern Italy.

碎石含量对三峡库区坡耕地土壤氮磷流失特征的影响

坡耕地是三峡库区水土流失的主要来源,导致土壤养分的损失,严重影响库区生态环境建设与社会经济可持续发展。库区坡耕地土壤浅薄化和砾质化特征明显,但目前对含碎石坡耕地土壤侵蚀和养分流失特征的研究尚不多见。该研究通过设置3个降雨梯度(60、90、120 mm/h)和4种碎石含量(0、10%、20%、30%),开展人工模拟降雨试验,分析各试验条件下含碎石土壤产流产沙和氮磷流失特征。结果表明:1)碎石主要通过改变土壤结构以增大产流产沙量来促进氮磷流失,而对相应流失速率与流失浓度的变化规律影响较小,不同碎石含量下泥沙产量的变异系数更高,且泥沙中不同碎石含量下的氮磷流失量显著性差异更强(P<0.05);2)泥沙中累计磷流失量略微大于氮流失量,有效磷几乎不随泥沙流失,有效氮约占全氮流失量的15%;径流中氮素流失量几乎为磷素的10倍且以有效氮为主,占总氮流失量的75%,有效磷占总磷流失量的25%;3)不同碎石含量下有效氮流失规律大致相同,径流中硝态氮约占有效氮流失量的70%,而泥沙中则以铵态氮为主,约占65%;4)不同碎石含量下土壤中氮磷元素均以随侵蚀产沙流失为主,累计产沙量与氮磷元素随侵蚀产沙流失量均在20%碎石含量下达到极大值,10%碎石含量下流失量相对较小,因此泥沙库区坡耕地氮磷流失防治应以减少侵蚀产沙为主,注意大雨暴雨多发季节的水质监测与施肥控制。同时可对土中碎石进行清除使其保持在不高于10%水平。研究结果可为三峡库区含碎石坡耕地水土流失防治和氮磷流失治理提供科学参考。

裸露岩石对喀斯特坡地水土流失及水动力特征的影响

[目的]裸露岩石如何影响坡地产流产沙及水动力特征尚需进一步深入研究。[方法]通过室内模拟试验,设置不同岩石裸露率(0,10%,30%,50%,70%)的坡地,开展不同雨强(30,60,90 mm/h)条件下的人工模拟降雨试验,旨在探究雨强与裸露岩石对坡地产流产沙及水动力特征的影响。[结果]坡地地表产流产沙随雨强增大呈增大趋势,而随岩石裸露率的增加呈减小趋势。在不同雨强条件下,0岩石裸露率坡地与10%岩石裸露率坡地的产流产沙差异多呈不显著(p>0.05),而与其他岩石裸露率坡地之间呈显著差异(p<0.05)。低岩石裸露率坡地(10%)与高岩石裸露率坡地(50%及以上)间产流产沙差异显著(p<0.05)。流速(V)、水深(h)、雷诺数(Re)、弗罗德数(Fr)、水流剪切力(τ)及水流功率(w)随雨强增大呈增大趋势,阻力系数(f)随雨强增大呈减小趋势。流速(V)、弗罗德数(Fr)随着岩石裸露率增加呈减小趋势,而水深(h)、阻力系数(f)随着岩石裸露率增加呈增大趋势,雷诺数(Re)、水流剪切力(τ)与水流功率(w)在不同雨强下变化规律有差异。水动力参数变化在不同坡地间具有一定差异性。产沙与水动力参数数量关系以指数函数拟合效果最好,流速(V)(R^(2)=0.819,p<0.05)、水流剪切力(τ)(R^(2)=0.858,p<0.05)及水流功率(w)(R^(2)=0.890,p<0.05)预测坡地产沙效果较好,其中水流功率(w)为最佳预测参数。[结论]研究结果进一步丰富了岩溶坡地土壤侵蚀理论,并可为建立适合于岩石裸露坡地的水蚀预测模型提供参考。

黄河中游典型流域侵蚀产沙特征分析研究

黄河中游多沙粗沙区是黄河泥沙的主要来源地,也是黄土高原土壤侵蚀最为强烈的地区。淤地坝拦截的泥沙赋存了大量侵蚀产沙信息,提供了对缺乏资料地区土壤侵蚀研究的可能。选取黄河中游的窟野河流域为研究对象,对淤地坝沉积特性进行分析,研究坝控流域的侵蚀产沙强度及泥沙来源,模拟流域不同时期土壤侵蚀情况。结果表明,流域产沙模数与降雨量显著相关,年产沙量呈下降趋势,主要泥沙来源为裸地。

A new ecological control method for Pisha sandstone based on hydrophilic polyurethane

The Pisha sandstone-coverd area is among the regions that suffer from the most severe water loss and soil erosion in China and is the main source of coarse sand for the Yellow River. This study demonstrated a new erosion control method using W-OH solution, a type of hydrophilic polyurethane, to prevent the Pisha sandstone from water erosion. We evaluated the comprehensive effects of W-OH on water erosion resistance and vegetation-growth promotion through simulated scouring tests and field demonstrations on the Ordos Plateau of China. The results of simulated scouring tests show that the water erosion resistance of W-OH treated area was excellent and the cumulative sediment yield reduction reached more than 99%. In the field demonstrations, the vegetation coverage reached approximately 95% in the consolidation-green area, and there was almost no shallow trenches on the entire slope in the treated area. In comparison, the control area experienced severe erosion with deep erosion gullies appeared on the slope and the vegetation coverage was less than 30%. This study illustrated that W-OH treatment can protect the Pisha sandstone from erosion and provide the vegetation seeds a chance to grow. Once the vegetation matured, the effects of consolidation-growth mutual promotion can efficiently and effectively improve the water erosion resistance and ecological restoration.

Assessment of Sedimentation Impacts on Small Dams—A Case of Small Reservoirs in the Lotsane Catchment

Sedimentation is a major problem for agricultural dams in Botswana, as it reduces the storage capacity and life span of the reservoirs. The process of sedimentation starts from day one of the impounding of water in any given reservoir. Even though a provision is made for every reservoir during planning for a certain storage capacity, specifically for sediment deposition, called dead storage, a major portion of the sediment gets deposited for many years of the reservoir’s life in areas other than the dead storage, and this trend cannot be reversed at easy cost. This study is aimed at the analysis of prevailing sedimentation processes in the nearby dozens of dams found in the Lotsane catchment located within the Limpopo Basin of Botswana, and focuses on assessment of annual sedimentation rate. A spatial analysis and modelling study was conducted based on the Revised Universal Soil Loss Equation and GIS to determine sediment yield and degree of impact of each reservoir for a given landscape, rainfall and catchment heterogeneity. Field observations and soil sampling were carried out in order to determine the factors that lead to reservoir sedimentation. Spatial data on the dams in Lotsane catchment were also collected from Ministry of Agriculture, which were used for ground-truthing, GIS-based calculations and model validation. The average sediment rate and sediment delivery ratio were found to be 1.74 t/ha/year and 81%, respectively. These are useful parameters to estimate service life of the dams and plan remedial measures related to sedimentation problems.

Sediment Delivery across Multiple Spatio-temporal Scales in an Agriculture Watershed of the Chinese Loess Plateau

There is a consensus that sediment delivery ratio in the Chinese Loess Plateau is close to 1at the inter-annual timescale. However, little information is available about the sediment delivery at finer timescales. We evaluated the sediment delivery from plots to watersheds at the event or intra-annual, annual, and inter-annual timescales within the Wudinghe river basin, a 30,261 km2 basin in the Loess Plateau. We calculated the ratio of sediment output to sediment input and presented the temporal change of the channel morphology to determine whether sediment deposition occurs.Although a single flood event frequently has a sediment yield exceeding 10,000 t km-2, sediment deposition rarely occurs except during some small runoff events(sediment yield < 5000 t km-2) or dry years(sediment yield < 10,000 t km-2) when moving from slopes up to the main channels of the Wudinghe River. This observation suggests a sediment delivery ratio close to 1 even at the event or intra-annual and the annual timescales, but not necessarily at the interannual timescale. Such a high sediment delivery ratio can be related to hyper-concentrated flows, which have very strong sediment transport capacity even at low flow strength. Because hyper-concentrated flows are well-developed in the whole Loess Plateau, a sediment delivery ratio close to 1 below the interannual timescale possibly remains true for other rivers in the Loess Plateau.

基于近20年《中国水土保持公报》的水土流失治理分析

水土保持是生态文明建设的重要组成部分,也是反映经济社会发展与生态环境质量动态平衡的重要综合指标。基于近20 a的《中国水土保持公报》,分析了水土流失现状,总结了水土保持工作进展,深入探究了水土流失动态变化成因及水土保持阶段性成效,研究成果对评价水土保持工作成效具有重要理论意义。研究结果表明:①与20世纪80年代末相比,2020年全国水土流失面积下降了26.6%,相较于20世纪初下降了24.4%;②2011年以前水土流失以中度及以上强度为主,2018年以后轻度流失面积占比超过60%;③水土流失综合治理是水土流失面积降低的主要原因;近20 a来,11条主要江河年总输沙量下降了72.4%,年输沙量与累计水土流失治理面积呈显著的负相关关系(R 2=0.90)。现阶段我国水土流失治理由“面”向“点”纵深推进,水土保持工作迈入高质量发展。研究成果可为我国水土保持工作评价及水土保持高质量发展提供定量数据和理论基础。

黄土高塬沟壑区土壤侵蚀特征分析

黄土高塬沟壑区侵蚀十分严重,是黄河泥沙主要源区,厘清该区域土壤侵蚀特征与治理重点是区域高质量发展的关键。以黄土高塬沟壑区砚瓦川流域为研究区,收集整理1976—2019年实测径流及泥沙资料,采用产流模数及产沙模数等指标体系,系统分析了黄土高塬沟壑区流域侵蚀产沙强度及能力变化。结果表明:砚瓦川流域1976—2019年产流模数与产沙模数均呈下降趋势,二者具有较好的一致性。多年平均产流模数与产沙模数分别为22991 m^(3)/km^(2)和1889 t/km^(2),产流及产沙变化规律一致,二者均于1997年发生突变。相较于突变年份之前,年均产流强度和产沙强度分别减少23.9%和75.8%,表征产流及产沙能力的产流系数和产沙系数则分别降低24.0%和73.0%。1976—2019年,流域的产流量及产沙量呈下降趋势。河流年均含沙量64.5 kg/m^(3),由突变前的98.3 kg/m^(3)减少至突变后的33.6 kg/m^(3),减少了67.0%。黄土高塬沟壑区侵蚀产沙多来自场次降雨,年内最大3 d侵蚀产沙占年总产沙量的50%。突变前,年产流模数与年降雨量的相关关系最优;突变后,年产流模数与日降雨量高于50 mm的年累计降雨量的关系最为密切。研究中进一步明晰了黄土高塬沟壑区水沙过程及其与降雨关系的变化,可为极端事件频发下黄土高塬沟壑区水土保持治理策略的转变提供一定参考。

紫色土坡面细沟形态变化及其对产流产沙的影响

[目的]揭示紫色土坡面细沟形态特征及其对产流产沙的影响,阐明紫色土区影响细沟产流产沙的主控因素,进而为紫色土区水土流失治理提供参考依据。[方法]以紫色土坡耕地为研究对象,设计3个流量(6,8,10 L/min)和5个坡长(1,2,3,4,5 m),利用放水冲刷试验定量分析细沟形态和产流产沙变化特征,探讨细沟形态变化对产流产沙特征的影响。[结果]随流量增加,沟宽和沟深均呈增大趋势,宽深比则呈减小趋势;随坡长增加,沟宽与宽深比呈先减小后增大的趋势,沟深变化规律则相反,且细沟形态在坡长3~4 m存在突变。流量与产流率、产沙率和细沟侵蚀速率呈正相关关系,坡长与产沙率呈正相关关系,而与产流率和细沟侵蚀速率呈负相关关系,其中产流率主要受流量的影响,而产沙率和细沟侵蚀速率受流量和坡长交互作用的影响较大。相关性分析表明,相比于产流(r=0.54,p<0.05),细沟形态与产沙关系更为密切(r>0.67,p<0.01)。通过多元逐步回归分析发现,沟宽是影响细沟侵蚀速率的关键因素(p<0.05),沟深是影响产沙率、累积产沙量的关键因素(p<0.01)。[结论]沟宽与沟深可用于预测紫色土坡面侵蚀程度,其中沟深是表征侵蚀产沙的最佳指标,未来细沟侵蚀防治措施重点应在控制沟深发育方面。