Subsurface Flow Processes in Sloping Cropland of Purple Soil

Subsurface flow is a prominent runoff process in sloping lands of purple soil in the upper Yangtze River basin.However,it remains difficult to identify and quantify.In this study,in situ runoff experimental plots were used to measure soil moisture dynamics using an array of time domain reflectometry(TDR) together with overland flow and subsurface flow using isolated collecting troughs.Frequency of preferential flow during rainfall events and the controls of subsurface flow processes were investigated through combined analysis of soil properties,topography,rainfall intensity,initial wetness,and tillage.Results showed that subsurface flow was ubiquitous in purple soil profiles due to welldeveloped macropores,especially in surface soils while frequency of preferential flow occurrence was very low(only 2 cases in plot C) during all 22 rainfall events.Dry antecedent moisture conditions promoted the occurrence of preferential flow.However,consecutive real-time monitoring of soil moisture at different depths and various slope positions implied the possible occurrence of multiple subsurface lateral flows during intensive storms.Rainfall intensity,tillage operation,and soil properties were recognized as main controls of subsurface flow in the study area,which allows the optimization of management practices for alleviating adverse environmental effects of subsurface flow in the region.

Combined Effect of Infiltration, Capillary Barrier and Sloping Layered Soil on Flow and Solute Transfer in a Heterogeneous Lysimeter

This aim of this paper is to describe a study of the combined effect of infiltration, capillary barrier and sloping layered soil on both flow and solute transport processes in a large, physical model (1 × 1 × 1.6 m3) called LUGH (Lysimeter for Urban Groundwater Hydrology) and a 3D numerical flow model. Sand and a soil composed of a bimodal sand-gravel mixture were placed in the lysimeter to simulate one of the basic structural and textural elements of the heterogeneity observed in the vadose zone under an infiltration basin of Lyon (France). Water and an inert tracer (KBr) were injected from the top of the lysimeter using a specific water sprinkler system and collected at 15 different outlets at the bottom. The outlet flows and the 15 breakthrough curves obtained presented high heterogeneity, emphasising the establishment of preferential flows resulting from both capillary barrier and soil layer dip effects. Numerical modelling led to better understanding of the mechanisms responsible for these heterogeneous transfers and it was also used to perform a sensitivity analysis of the effects of water velocity (water and solute flux fed by the sprinkler) and the slope interface. The results show that decreasing velocity and increasing the slope of the interface can lead to the development of preferential flows. In addition, the offset of the centre of gravity of the flow distribution at the output increases linearly as a function of the slope angle of the layered soil. This paper provides relevant information on the coupling between hydrodynamic processes and pollutant transfer in unsaturated heterogeneous soil and emphasizes the role of the geometry of the interfaces between materials and boundary conditions as key factors for preferential flow.

Relations among Sap Flow, Soil Moisture, Weather, and Soybean Plant Parameters in High Water Demand and Final Growth Stages

The dynamics of sap flow in relation to plant morphology and weather conditions during reproductive growth of soybean (Glycine max. L. Merr.) influence decisions pertaining to efficient irrigation management and other inputs for high yields. Field studies began in 2017 at Marianna, Arkansas to measure moisture dynamics of soybeans during seed fill (R5 to R7) using heat balance stem flow gauges. Sap flow was highly correlated to solar radiation with maximum rates observed during beginning seed fill (R5). A solar radiation efficiency (SRE) value, calculated as hourly sap flow rate per Watt-hour of solar radiation (g/Wh2), is proposed. The SRE relates to crop water demand and hydraulic resistance of the soil-root-stem-leaf-pod-seed pathway. SRE values ranged from 0 - 1.2 g/Wh2. Soil moisture, growth stage, time of day, and weather conditions influenced the SRE, with higher values observed in the morning, late afternoon, and during R5 growth. Peak sap flows of 39 g/h at R5, 25 g/h at R6, and 3 g/h at R7 occurred. The ratio of measured sap flow to estimated crop evapotranspiration was 0.9 to 1.3 during R5 to R6.9 (maximum dry matter), but dropped to 0.2 at R7. Further research is needed to better understand late season reproductive moisture dynamics in soybeans.

Effects of sediment load on the abrasion of soil aggregate and hydraulic parameters in experimental overland flow

The breakdown of soil aggregates under rainfall and their abrasion in overland flow are important processes in water erosion due to the production of more fine and transportable particles and,the subsequent significant effect on the erosion intensity.Currently,little is known about the effects of sediment load on the soil aggregate abrasion and the relationship of this abrasion with some related hydraulic parameters.Here,the potential effects of sediment load on soil aggregate abrasion and hydraulic parameters in overland flow were investigated through a series of experiments in a 3.8-m-long hydraulic flume at the slope gradients of 8.7 and 26.8%,unit flow discharges from 2×10^-3 to 6×10^-3 m^2 s^-1,and the sediment concentration from 0 to 110 kg m-3.All the aggregates from Ultisols developed Quaternary red clay,Central China.The results indicated that discharge had the most significant(P<0.01)effect on the aggregates abrasion with the contributions of 58.76 and 60.34%,followed by sediment feed rate,with contributions of 39.66 and 34.12%at the slope gradients of 8.7 and 26.8%,respectively.The abrasion degree of aggregates was found to increase as a power function of the sediment concentration.Meanwhile,the flow depth,friction factor,and shear stress increased as a power function along with the increase of sediment concentration at different slope gradients and discharges.Reynolds number was obviously affected by sediment concentration and it decreased as sediment concentration increased.The ratio of the residual weight to the initial weight of soil aggregates(Wr/Wi)was found to increase as the linear function with an increasing flow depth(P=0.008)or Reynolds number(P=0.002)in the sediment-laden flow.The Wr/Wi values followed a power function decrease with increasing friction factor or shear stress in the sediment-laden flow,indicating that friction factor is the best hydraulic parameter for prediction of soil aggregate abrasion under different sediment load conditions.The information regarding the soil aggregate abrasion under various sediment load conditions can facilitate soil process-based erosion modeling.

An Efficient Multiple-Dimensional Finite Element Solution for Water Flow in Variably Saturated Soils

Multiple-dimensional water flow in variably saturated soils plays an important role in ecological systems such as irrigation and water uptake by plant roots; its quantitative description is usually based on the Richards＇ equation. Because of the nonlinearity of the Richards＇ equation and the complexity of natural soils, most practical simulations rely on numerical solutions with the nonlinearity solved by iterations. The commonly used iterations for solving the nonlinearity are Picard and Newton methods with the former converging at first-order rate and the later at second-order rate. A recent theoretical analysis by the authors, however, revealed that for solving the diffusive flow, the classical Picard method is actually a chord-Newton method, converging at a rate faster than first order; its linear convergence rate is due to the treatment of the gravity term. To improve computational efficiency, a similar chord-Newton method as for solving the diffusive term was proposed to solve the gravity term. Testing examples for one-dimensional flow showed significant improvement. The core of this method is to produce a diagonally dominant matrix in the linear system so as to improve the iteration-toiteration stability and hence the convergence. In this paper, we develop a similar method for multiple-dimensional flow and compare its performance with the classical Picard and Newton methods for water flow in soils characterised by a wide range of van Genuchten parameters.

Soil Evolution Features of Debris Flow Waste-Shoal Land

The reclamation and utilization of debris flow waste-shoal land plays an important role in the mitigation and control of debris flow hazards, which thus contributes a lot to the exploitation of insufficient land resources in mountainous areas and the reduction of losses caused by debris flow. The aim of this paper is to discuss the features and mechanism of soil evolution of debris flow waste-shoal land so as to search for the available modes of its reclamation and utilization. The Jiangjiagou Ravine, a typical debris flow ravine, was selected to study soil evolution features of debris flow waste-shoal land based on the analysis of soil physicochemical properties and soil microstructure. It was found that the soil evolution rates of debris flow waste-shoal land varied with different modes of reclamation. For the land which had been reclaimed for less than 10 years, soil evolved most rapidly in paddy fields, and more rapidly in dry farmland than in naturally restored waste-shoal land. For the land which had been used for more than 10 years, the soil evolution rates of dry farmland, naturally restored waste-shoal land and paddy farmland decreased in the file. For the same utilization period of time, significant differences were recognized in soil evolution features under different modes of reclamation. Analysis data showed that soil clay content, soil thickness, the psephicity of skeleton particles and contents of microaggregates (<0.02 mm) in paddy farmland were all highest. Soil nutrients and porosity of dry farmland were better than those of paddy farmland and naturally restored waste-shoal land, and those of paddy farmland were superior to those of naturally restored waste-shoal land. Paddy farmland characterized by rapid pedogenesis, stable evolution and high utilizability was the priority candidate for the reclamation and utilization of debris flow waste-shoal land.

薄层水流冲刷条件下斜坡土体的临界起动

斜坡土体侵蚀是丘陵地区和水库岸坡普遍存在的灾害现象,其主要动力因素是降雨或者波浪上爬产生的薄层水流对土体产生的冲刷剪切作用。为探索水流冲刷作用下的斜坡土体临界起动条件,采用自主研发的冲刷起动试验装置,开展斜坡土体的冲刷起动试验和理论研究。通过颗粒染色和高倍数电子显微等技术手段观测无黏性土颗粒的起动现象,确定了无黏性岸坡土体的起动模式与水流流速的相互关系;探索了不同干密度、不同黏粒含量及不同坡度与黏土斜坡临界起动流速的相互关系,土体的黏粒含量、干密度及坡度对黏性土体的起动流速影响较大,与干密度和土体坡度相比,黏粒含量对黏土斜坡的起动流速影响更为明显。验证了无黏性岸坡土体的临界起动方程,其中滚动起动流速方程具有较强的可靠性;基于黏土的起动模式构建了黏土斜坡的起动力学平衡方程,获得了黏土斜坡半经验半理论的起动流速方程,用试验结果求解了起动流速方程的相关参数,最终确定的起动流速公式与试验结果拟合度较好,同时验证了起动流速公式的可靠性。

连续流动-钼酸铵分光光度法测定土壤全磷

利用硫酸-高氯酸湿法消解土壤,采用连续流动分析仪直接测定消解液磷酸根含量,建立了高通量测定土壤全磷的实验方法。方法检测限6.0 mg·kg^(-1),土壤样品的加标回收率为85%~100%。将该方法用于土壤标准物质(GBW07405、GBW07406a)全磷含量测定,结果准确,相对标准偏差(RSD)分别为3.5%、4.5%(n=3)。方法具备无需调节待测液pH值、分析速度快、消耗试剂少、结果准确可靠等优点,适用于大批量土壤全磷的测定分析。

蒸汽浴-流动分析仪法测定土壤有机碳含量的方法

为了准确高效批量测定土壤有机碳含量,采用比色管代替消煮管,蒸汽加热消煮土壤,利用流动分析仪法测定有机碳。并将此方法与重铬酸钾氧化-外加热法(常规通用)进行了比较,探讨方法的可行性。结果表明,蒸汽浴-流动分析仪法测定土壤有机碳含量重复性试验的相对标准偏差为3.19%~9.41%,回收率为92.21%~97.63%。方法精密度及准确性良好。所测结果与重铬酸钾氧化-外加热法无显著性差异(P>0.05),两种方法拟合的回归方程:y(蒸汽浴-流动分析仪法)=0.947x(重铬酸钾氧化-外加热法)+1.621(r^(2)=0.933),两者呈良好的相关性。用两种方法测定200个土壤有机碳,蒸汽浴-流动分析仪法的检测用时是重铬酸钾氧化-外加热法用时的68%,人工操作用时是重铬酸钾氧化-外加热法用时的44%,蒸汽浴-流动分析仪法无需使用硫酸亚铁,重铬酸钾、硫酸和水用量为重铬酸钾氧化-外加热法的40%。蒸汽浴-流动分析仪法省工省时,人员工作强度低,试剂用量少,环境危害降低,检测准确高效,经济安全,可推荐为大批量土壤有机碳含量测定的方法。

考虑非达西渗流的泥浆离心脱水分析

为深入探究离心脱水技术在处理主要由黏性土组成的建筑废弃泥浆时的内在机理及其影响因素,利用分段线性化方法,充分考虑黏性土中渗流的非达西特性以及土体变形的非线性特征,建立在离心作用下能够考虑其非达西渗流特性的泥浆脱水分析模型。通过与已有研究成果及室内试验结果的对比,证明了该模型的有效性。在此基础上,分析了模型参数对脱水过程的影响。研究结果表明:脱水速度和最终土水界面位移量随着电机转速的增大而增大;增加泥浆初始厚度会增大最终土水界面位移量,但会降低初期的土水界面移动速度;压缩指数在初期对土水界面位移的影响并不明显,但其增大会导致最终土水界面位移量的增加;非达西渗流参数的增大会导致土水界面位移的减少,但通过提升电机转速,可以有效地降低非达西渗流对脱水效果的不利影响。研究成果可为离心脱水技术在建筑废弃泥浆处理中的进一步优化与应用提供借鉴和参考。

排渗失效下尾矿库溃坝三维模型试验研究

针对尾矿库渗透破坏模式,为克服二维试验槽边壁效应对模型渗流走向及溃决位置的影响,本文以某尾矿库为原型,基于自主设计的三维尾矿库溃坝模型试验平台,进行了排渗设施失效诱发的尾矿库溃坝模型试验研究,揭示了该尾矿库的溃决模式及溃决机理。结果表明:(1)排渗失效导致的溃坝呈现局部流土破坏-坝体累计变形-深层滑动面发展贯通-整体突发失稳的渐进伴突发型溃决演化模式;(2)坝体孔隙水压力骤变是坝体发生滑动破坏的关键响应指标,预示着坝体将在短时间内由滑动体前后缘局部散浸软化、流土、塌陷转变为大范围溃决,可作为坝体溃决事故的前兆信息;(3)排渗失效导致的尾矿库溃坝过程具有渐进性和突发性的特点,发生散浸与流土破坏的过程时间较长,发生深层滑动和溃决的时间短暂,该特征可为尾矿库渗透破坏隐患治理及坝体溃决应急响应提供参考。研究结果对尾矿库溃坝的灾害预防具有重要的现实意义。

球状风化花岗岩类土质边坡土-岩界面优势流潜蚀特性研究

受降雨作用,球状风化花岗岩类土质边坡的土-岩差异风化界面极易演化为优势渗流通道而发生渗流潜蚀,进而加速该类边坡的变形失稳,然而当前有关其渗流潜蚀作用特征、细颗粒迁移规律等的研究仍鲜见开展。基于多孔介质非饱和渗流理论,综合考虑细颗粒运移、潜蚀启动响应与非饱和渗流的耦合关系,提出一种可准确描述土-岩界面渗流潜蚀过程的数值计算框架。采用有限元方法,构建优势流作用下非饱和花岗岩残积土的渗流潜蚀模型,并以均质土柱的渗流潜蚀过程为参考,系统研究3种典型土-岩界面埋藏状态下的优势流潜蚀特性。结果表明:球状风化花岗岩类土质边坡的土-岩界面与基质渗透性存在高度差异性,湿润锋形成向下凹陷的渗透漏斗,且随着降雨的持续,湿润锋的凹陷程度愈发明显;细颗粒流失程度与土-岩界面的埋藏状态相关,其中下填土体工况的优势流潜蚀最为显著,其界面处甚至出现超孔隙水压力,最不利于该类边坡的稳定性。研究成果可为降雨条件下球状风化花岗岩类土质边坡稳定性的准确评价提供科学依据。

2023年甘肃积石山6.2级地震灾害特征

2023年12月18日,甘肃省临夏州积石山县发生6.2级地震,震源深度10km。此次地震造成了大量人员伤亡。地震强度较大,建筑结构、非结构构件震害严重;生命线系统多见破坏;场地灾害主要表现为土壤液化、山体崩塌、液化流滑,其中以金田村的液化流滑现象尤为突出。与2018年印尼帕鲁7.5级地震、1303年洪洞8.0级地震、1920年海原8.5级地震相比,此次地震液化流滑现象具有低角度、大范围、长距离的显著特征。现场调查分析发现,充分的水利补给、物源区的明显凹陷是导致本次地震液化流滑规模巨大的原因,且此次流滑与2018年帕鲁地震流滑现象有多处相似之处,但两者流滑机理上存在着本质的不同,值得后续深入研究。对于此次地震,美国地质调查局给出的人员伤亡及场地破坏预测偏向保守,急需发展匹配抗震设防能力的震害预测方法。

表层土壤结构对红壤坡耕地产流及产沙过程的影响

针对南方红壤区坡耕地水土流失严重与表层结构退化的现状,采用室内模拟降雨的方法,分析表层土壤结构和雨强对降雨再分配、坡面产流及产沙过程的影响。结果表明:(1)表层土壤结构显著改变降雨的再分配过程,深耕作层可以降低地表径流比例,增加壤中流比例,60和90 mm·h^(-1)雨强下,随耕作层深度增加,地表径流平均比例依次为70.5%,62.9%和56.8%,壤中流平均比例依次提升为7.1%,12.3%和18.1%;(2)土壤流失率随雨强增加而增大,90 mm·h^(-1)雨强下土壤流失率为60 mm·h^(-1)雨强下的4.4倍,土壤流失率随耕作层深度增加而显著减小,依次为36.8、21.1和13.1 g·m^(-2) min^(-1);(3)雨强和表层土壤结构显著影响坡面侵蚀形态的演变,随耕作深度增加坡面侵蚀由细沟侵蚀逐渐转变为面蚀。表层土壤结构显著改变坡耕地降雨-径流关系和侵蚀过程,合理增加耕作层深度,对降低地表侵蚀、促进土壤水分的深层下渗、增加土壤深层持水量具有积极作用。

Re-Examining Field-Surveyed Variations in Elevation and Soil Properties with a 1-m Resolution LiDAR-Generated DEM

This article presents a 2017 LiDAR-DEM guided 1-m resolution examination of field-surveyed elevation and soil property variations (5 × 5 m spacings) conducted in 1977 across a hummocky New Brunswick field used for potato production. This examination revealed that the field incurred minor elevation differences likely due to upslope erosion as revealed through increasing Sand % and CF % with increasing elevation, and increasing Silt % along low-lying areas. Soil moisture, field capacity, permanent wilting and nitrate nitrogen (NO3-N) also increased at downslope locations. Directly as well as indirectly, soil pH, ammonium nitrogen (NH4-N), Caesium137 (Cs137) and Mehlich-3 extracted Ca, Mg, K, Fe, Mn, Cu, and Zn were likewise affected by topographic location. Factor analyzing these variables led to: 1) a Soil Loss Factor that captured 24% of the textural variations;2) a Soil-Cropping Factor accounting for 16% of the N, P, K, Ca, Mg, Mn variations;3) a Soil Organic Matter (SOM) Factor relating 9% of the in-field variations for SOM, Fe, Zn, Cu to via organo-metal complexation and low NO3-N retention. Many of the topographic variations increased or decreased with the metric DEM-projected depth-to-water index (DTW) index. This index was set to 0 along DEM-derived flow channels with minimum upslope flow-accumulation areas of 0.1, 0.25, 0.5, 1 or 4 ha. Among these, the DTW > 4 ha threshold was useful for reproducing the textural variations, while the DTW > 0.25 ha threshold assisted in capturing trends pertaining to moisture retention and elemental concentrations.

膜下滴灌滴水流量对棉花根系分布的影响

为探明膜下滴灌条件下滴水流量对棉花根系分布的影响,采用田间定位试验,设置3组滴水流量,分别为1.69 L·h^(-1)(W169)、3.46 L·h^(-1)(W346)和6.33 L·h^(-1)(W633),分析膜下滴灌土壤水吸力对棉花根系空间分布特征的影响。结果表明:滴水流量越大,膜外裸地和膜内土壤的基质吸力越小,边行棉花根系吸水受到的胁迫程度也越小,W633处理膜下根区土壤水吸力分布均匀且适合棉花生长,棉花根长密度水平分布不论是初期还是后期均呈双峰抛物线分布;棉花根重密度呈现出相同的变化规律,内、边行棉花根重密度在花期、铃期、吐絮期的差值分别为42.26、-0.22、97.40 g·m^(-3)。当滴水流量越小时,膜外裸地的基质吸力大于膜内土壤的基质吸力,致使边行棉花的根系吸水受到较大胁迫,W169处理棉花根长密度水平分布由生育初期的双峰抛物线分布变为后期的单峰抛物线分布;内、边行棉花根重密度在花期、铃期、吐絮期的差值分别为299.70、304.86、369.84 g·m^(-3)。表明随着滴水流量的增加,膜下滴灌行间棉花根系生长更加均匀,研究结果可为棉花膜下滴灌系统设计提供技术参考。

巴基斯坦谢胡普拉农业区优先流三维结构及其影响因素

优先流是水通过土壤中特定路径的运动,而不是水在土壤结构里均匀地流动。由于土壤的异质性,例如裂缝、根通道或虫洞,这些优先流动路径经常形成。这种分形图案使理解和描述首选流动路线的行为变得具有挑战性。为了准确地进行水和溶质的输送,需要花费大量时间来理解和描述优先流路的增长和演变。传统模型需要改进来捕捉优先流的复杂和非线性行为。选取4块120 cm×120 cm样地,对4块样地进行染料示踪实验,以确认溶质和水的优选流动模式。数据已在Origin Lab中进行分析,以创建3D图表,并使用Sketchu p-2021 Pro向每个绘图提供0.50 L亮蓝溶液(5 g/L)。每个地块包含3个垂直的土壤剖面,每个剖面深150 cm,并且剖面墙经过广泛的刀具准备。将亮蓝留在表面24 h以渗透到土壤表面。结果表明:优先流在压实度最小且大孔隙连续性保持的区域最为突出。相反,压实的影响导致压实区域微孔隙率降低和优先流动模式减弱。亮蓝色在土壤中的最大深度可达15.5 cm。FCP的运动取决于不同的因素,如根部、毛孔、裂缝等。亮蓝色在根部可用的地方达到最大深度。在本研究中,通过使用Sketch Pro软件以三维方式显示亮蓝色运动,以便更好地理解它。此外,本研究揭示压实和随后的恢复过程如何影响土壤对水流和地表径流的敏感性。全面的3D表示,这项研究提供了对水流通道的形成和演化的深入理解。根据本研究发现的水流模式,在没有压实作用的较高位置,大孔隙连续性得以保留,择流最强。由于压实作用,微孔隙度下降,且越下侧越弱。该研究可以更好地理解水流通道的创建和演化。该研究增强对优先流及其在自然和农业生态系统中养分和水循环中的作用的了解。从这项研究中获得的见解可以为制定改进的农业用地管理策略提供信息,促进可持续和高效的水资源管理。

12·18甘肃积石山地震诱发泥石流地质灾害成因及建筑物破坏特征分析

2023年12月18日甘肃省临夏州积石山县发生了Ms6.2级地震,地震诱发临近的青海省草滩村至金田村一带泥石流地质灾害,造成了巨大的人员伤亡。通过震后现场调研、物源提取、现状台塬稳定性分析以及泥石流冲击力与砌体结构的相互作用分析,并探讨泥石流成因、类别及泥流与建筑物相互作用机理。结果表明:灾害成因为该区域台塬冬灌后标准冻深内土体震后液化导致台塬滑塌引起,液化后土体呈泥流状随现状沟道运移至沟口,并迅速扩散与建筑物发生强烈的冲击作用,泥石流的作用方向与建筑物受力面夹角为90°,深度达到2.8 m、冲击力达到6.4 kPa时,建筑物即发生剪切破坏而倒塌。

2种土壤地下滴灌滴头流量变化规律及对入渗空腔的响应

为研究入渗空腔对地下滴灌滴头流量和土水势的影响规律,通过土箱试验和数值模拟相结合的方法,对比分析了黏土和壤质砂土2种土壤灌水过程中土壤正压及滴头流量的变化规律,反演了滴头出口处空腔半径,并建立了黏土中空腔半径的计算模型.研究结果表明:相同条件下,壤质砂土中的滴头流量大于黏土中的,但变化幅度小于黏土中的;壤质砂土中土壤正压随时间变化呈上升趋势,黏土中土壤正压随时间变化呈下降趋势,受空腔影响,滴头流量与土壤正压随时间的变化趋势不存在必然关系.模拟中,壤质砂土入渗空腔半径可选择较小值或认为与滴头出口半径相同.黏土中空腔半径随滴头额定流量和容重增大而增大.相对于选用固定值,研究得到的空腔半径可以提高现有计算公式在求解滴头流量和土壤正压的精度,拟合的空腔半径经验模型可以应用于地下滴灌水力设计,同时为土壤水分入渗数值模拟的边界条件设置提供依据.