紫色土坡耕地细沟发育的形态演变

研究细沟发育的形态演变规律是认识细沟发生机理的前提,本研究通过人工降雨与微地貌扫描相结合的方法,调查了紫色土坡耕地细沟发生过程的形态演变特征.采用三维激光扫描仪扫描不同降雨时段坡面,生成高精度坡面DEM图像,统计各时段不同坡段等高线偏离度,量算坡面凹陷区的表面积、周长、直径以及沟头下切深度;结果表明,等高线偏离度越大细沟发育越完全,有细沟发生坡面等高线偏离度是无细沟坡面的1倍以上;凹陷区的表面积、周长、直径相对于单位降雨量的扩展速率均在细沟贯穿时段出现最大值;跌坑位置与坡面水平起伏关系不明显,统计的3条沟头分别发育于水平方向起伏的最高点、中间点和低点;跌坑下切深度及其单位降雨量的扩展速率在跌坑贯穿形成细沟时段出现最大值,之后逐渐降低,说明跌坑的形成是细沟造床的关键.     

山前洪积扇坡面细沟侵蚀跌坑特征的试验研究

跌坑的出现是坡面侵蚀过程中的重要现象,标志着细沟侵蚀正在发育,跌坑的贯穿标志着细沟的形成。采用土槽冲刷模型试验,选取流量、坡度、冲刷时间和坡面形态作为影响跌坑发育的因子结合正交试验调查了不同试验条件下跌坑发育特征及影响因素。结果表明：影响跌坑发育的因素主次为冲刷时间、流量、坡面形态、坡度;跌坑沿坡面连续分布,深度具有波动性,沿坡向下呈现先增大后减小的趋势,最大值一般发育在坡面中部;根据跌坑的发育特征将坡面细沟侵蚀划分为片蚀、细沟雏形、细沟发育和细沟调整四个阶段;坡面细沟侵蚀跌坑深宽积与土壤侵蚀量具有较显著线性关系。研究结果对输油管线水毁及水土流失防治具有一定的参考价值。     

岔巴沟流域次暴雨坡面土壤侵蚀经验模型

坡面土壤流失预测、水保效益评估,无不需要坡面侵蚀模型。本文以岔巴沟流域坡面径流场降雨水文资料为基础,建立了次侵蚀性降雨坡面土壤侵蚀模型、次降雨坡面细沟侵蚀模型,并对各模型的精度进行了分析。结果发现模型具有较好的预报精度,对大侵蚀产沙事件预测很准;坡度、最大10分钟雨强、植被覆盖度是影响次侵蚀性降雨主要因子,坡度、最大10分钟雨强、降雨量是影响细沟侵蚀主要因子,植被覆盖对细沟侵蚀产沙影响很小。     

黄土坡面发育平稳的细沟流水动力学特性

由于天然降雨存在间歇性,常会出现前期降雨已经发育成型的细沟又经历了二次降雨的情况,但目前对这一条件下细沟流水动力学特性的研究还很少。本文采用室内人工模拟降雨的方法,通过间隔24 h两场不同雨强的降雨,研究黄土坡面经过第一场降雨形成比较稳定的细沟之后,在第二场较小雨强降雨过程中,细沟发育平稳时的流水动力学特性。研究结果表明:①细沟流速大小受坡长影响并不显著,相同坡度下不同坡长的细沟流平均流速差别不大;细沟流速受细沟形态影响较大,25°坡面比20°坡面细沟密度大,流速相对较小;②剪切力大小受流量和坡度共同作用;雷诺数与水流剪切力呈显著正相关关系,弗洛德数与水流剪切力则呈显著负相关关系;③随着距坡顶距离的增加,阻力系数呈增大趋势;第二次降雨强度相同,坡度大的坡面上阻力系数也较大,可见阻力系数与径流量和坡度的关系十分紧密;阻力系数与雷诺数之间呈显著正相关关系,雷诺数的增加意味着平均流速增大,水流强度增大导致细沟形态更为复杂,水流受到的阻力增大;虽然雷诺数增加同时也意味着水流深度增大,但从试验结果可见,陡坡条件下阻力系数受流速的影响较大。     

紫色土坡地侵蚀产沙过程的~7Be法初探

利用环境放射性核素示踪技术研究土壤侵蚀是传统土壤侵蚀监测技术的重要补充手段。宇宙成因核素7Be具有半衰期短和在表土分布浅等特点,能够用于指示短时间尺度的坡面侵蚀堆积过程。采用7Be技术与泥沙颗粒分析相结合,定量判读了模拟降雨下紫色土坡面侵蚀过程演变。结果表明,对于20°坡面,7Be法指示的坡面侵蚀方式转折点与侵蚀泥沙颗粒变化得到的结果基本一致。7Be在表征侵蚀过程演变时具有独特的优势,可以将坡面片蚀发育过程随降雨时间的变化明显地识别出来。这对防治坡面侵蚀,特别是细沟侵蚀的发生具有重要意义。     

降雨对泥石流源地土体活动的指数式放大效应

多数泥石流是从坡面活动开始的.坡面的不稳定土体活动,如崩塌、滑坡等,既是泥石流的物质来源,也决定着泥石流的形成方式和规模变化.四川汶川牛圈沟和北川魏家沟泥石流源地坡面人工降雨实验表明,坡面土体活动是间歇、涨落的随机过程,崩塌的时间间隔随着降雨强度的增大呈指数减小,每组实验中的崩塌总数目和雨强的关系如N=CN exp(kN IR);崩塌规模随着降雨强度的增大呈指数增大,每组实验中平均崩塌量与雨强的关系如M=CMexp(kM IR);坡面崩塌的总量可以表示为:V=NM=CNCM exp((kN+kM)IR);受土体颗粒粒径的影响,不同坡面崩塌量随雨强变化的参数不同,研究揭示了大规模泥石流的形成是由于源地土体活动强度随雨强的指数式增强.     

黄土坡面不同侵蚀带侵蚀产沙关系及其机理

黄土梁峁坡面土壤侵蚀具有明显的垂直分带性,不同侵蚀带具有各自的侵蚀产沙特点,且彼此相互影响,坡面侵蚀产沙分配受降雨强度和降雨能量的制约,随着雨强和降雨能量的增加,坡面侵蚀产沙量的最大部位由细沟侵蚀带向浅沟侵蚀带过渡,坡面侵蚀产沙强度变化的本抽为侵蚀方式的演变,坡面复合侵蚀带的径流模数明显小于对应的单一侵蚀带径流模数,而其侵蚀模数则明显大于对应的单一侵蚀带侵蚀模数,溅蚀片蚀带的来水来沙可吏细沟侵蚀带     

紫色土坡面降雨侵蚀试验研究

坡面水蚀的主要侵蚀动力来自降雨及其产生的地表径流,将坡面水蚀过程分为降雨侵蚀和径流侵蚀,可以从侵蚀动力、侵蚀特征差异与侵蚀规律等方面研究坡面水蚀过程与机理。应用人工模拟降雨及微小区测定技术,以大田紫色土为研究对象,模拟和测定不同雨强与不同坡度条件下降雨侵蚀过程和侵蚀量,揭示以降雨为主要动力的土壤降雨侵蚀特征和规律。研究结果表明：(1)小雨强(＜67．26 mm/h)下,紫色土坡面降雨侵蚀率具有稳定性,随着降雨历时的增加变化微小；大雨强(106．57 mm/h)下,降雨侵蚀率随降雨历时增加呈上下波动；(2)紫色土降雨侵蚀率与降雨强度呈线性相关,随降雨强度增加而直线增加；(3)降雨侵蚀率与坡度符合二次抛物线关系,随坡度的增加出现临界坡度,且临界坡度随雨强的变化而改变。在中小雨强(18．06～67．26 mm/h)条件下,临界坡度SK的变化范围在17°～19°。在大雨强条件下,临界坡度有逐渐增大的趋势；(4)当坡度与雨强共同影响产沙效应时,坡度对降雨侵蚀的影响较小,雨强能掩盖坡度对产沙的贡献。     

坡面侵蚀水沙流时间变化特征的模拟实验

多坡段实验模型以黄土丘陵沟壑区垂向上梁峁坡面与沟谷坡面构成的坡沟系统为原型,采用人工降雨模拟实验方法,对坡沟系统土壤侵蚀链内降雨径流产沙随时间变化的规律进行了系统的研究。结果表明:雨强29 7mm/h时36′40″开始产流,60 5mm/h时3′43″产流,90 2mm/h时2′30″产流。雨强29 7mm/h时侵蚀过程以面蚀为主,产沙起伏20min出现一次。60 5mm/h时以面蚀与细沟蚀为主,35°陡坡伴有崩塌、滑塌等重力侵蚀,产沙波动平均12min出现一次。雨强90 2mm/h时坡面上细沟发育充分,有细沟合并及出现浅沟侵蚀现象,35°坡崩塌、滑塌剧烈,产沙过程波动频繁,每10min一次。雨强29 7mm/h时单位流量的产沙量为0 10kg/L;雨强60 5mm/h时为0 30kg/L;雨强90 2mm/h时为0 41kg/L。流量的大小影响了侵蚀方式和形态分异的程度,使产沙过程出现强弱相间的波动性特点。     

紫色土陡坡耕地顺坡垄作条件下的土壤及其流失特征

顺坡垄作是在长江上游特别是紫色土坡耕地上农民普遍采用的耕作模式,以往由于主流思想的影响,没有得到应有的重视。以三峡库区紫色土坡耕地为例,采用野外调查与小区实验相结合,分别采集垄沟和垄坡表层土壤,测试顺坡垄作地块沟、垄土壤容重、粒径分布、有机质含量、TN、TP、土壤含水量等指标,小区实验调查顺坡垄作条件下的土壤流失特征,进而探讨顺坡垄作导致的土壤特性差异与顺坡垄作的水土保持机制。结果表明:与垄沟内土壤相比,垄坡土壤平均含水量、容重分别降低29.74%和16.41%,土壤总孔隙度高20.56%,说明垄坡土壤具有更大的吸持水分的潜力,降雨产流阈值相比于垄沟土壤也更大。相比于垄沟内土壤,粘粒在垄沟内发生富集,垄坡土壤中的有机质、总氮(TN)和总磷(TP)指标分别高18.79%、17.30%和9.31%。侵蚀泥沙中沙粒含量出现明显富集,几乎是垄沟土壤沙粒含量的1倍,而粘粒和粉粒含量则远小于径流小区土壤成分,说明顺坡垄作有利于50μm土壤细颗粒的保持。侵蚀泥沙中有机质和TN远小于径流小区土壤成分,而TP则高于径流小区土壤成分,与侵蚀泥沙颗粒分选现象近似,说明顺坡垄作的肥力指标流失差异同样主要由侵蚀分选导致,也说明顺坡垄作有利于紫色土有机质和氮肥的保持。     

黄土坡面片蚀过程稳定含沙量及其影响因素

黄土高原地区坡面土壤侵蚀具有明显的垂直分带性,溅蚀片蚀带是坡面侵蚀的最上方地带,研究片蚀过程含沙量变化有助于阐明坡面侵蚀规律。本文采用人工模拟降雨试验方法研究了黄土坡面片蚀稳定含沙量及其影响因素;试验处理包括2种质地的黄土(塿土和黑垆土),2个雨强(90和120 mm/h)和4个坡度(10°、15°、20°和25°)。结果表明：在不同质地黄土、降雨强度和坡度条件下,水流含沙量均呈现先减小后平稳的规律;稳定含沙量与土壤颗粒体积分形维数、降雨强度和坡度呈幂函数关系,稳定含沙量随土壤颗粒体积分形维数的增大而减小,随降雨强度和坡度的增大而增大,影响程度依次为土壤颗粒体积分形维数、降雨强度和坡度;所分析的水动力学指标中单位水流功率与稳定含沙量关系最密切,降雨强度对稳定含沙量的影响大于单位水流功率。     

坡面动力侵蚀过程的实验研究进展

本文首先总结了坡面流及坡面动力侵蚀过程的实验设备、技术手段及实验内容方面的进展,然后全面探讨了坡面侵蚀实验方面的国内外研究最新进展,最后作者分析了实验研究方面存在的问题,并提出了前景展望。     

Effects of soil surface components on soil hydrological behaviour in a dry Mediterranean environment (Southern Spain)

Various researchers have studied the spatial pattern of soil surface components such as vegetation, rock fragments, bare soil, litter and surface crusts, as a key factor of hydrological behaviour in Mediterranean settings with heterogeneous patches of vegetation cover and strong human impact. The studies indicate that there is a mosaic of patches that generate run-off or infiltrate overland flow, distributed in various ways along hillslopes. Few of these studies, however, have looked at areas underlain by metamorphic rocks such as phyllites or schists. This study analysed the temporal and spatial variability of the effects of soil surface components on hydrological processes in a small dry Mediterranean catchment underlain by metamorphic rocks. A systematic sampling of multiple sites throughout a hydrological year was carried out.We related the hydrological behaviour of soil surface components to 1) their position along the hillslope, 2) the distance of existing vegetation tussocks from the line of run-off, 3) rainfall intensity and 4) the main physical/chemical soil properties affecting infiltration processes. Statistical analysis was used to check the validity of the relationships. The results show that soil surface components have highly variable effects, in both space and time, on soil hydrological behaviour. These effects particularly depend on the location along the line of maximum slope and the intensity of preceding rainfall, whose interaction defines soil hydrological status. These results are similar to those for other Mediterranean settings with different lithology, in that the succession of contributing patches are hydrologically interconnected along a hillslope. The variables used and the grouping of explanatory variables through principal component analyses were found to be suitable for discussing the spatial distribution of soil surface components in the hydrologically dynamic environment of the study area.     

IMPACTS OF DIFFERENT TYPES OF LAND USE ON PROCESSES OF SOIL AND WATER LOSS OVER PURPLE SOIL SLOPELAND

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人工模拟降雨下细沟与细沟间流速的沿程分布

径流流速不仅是坡面径流的重要水动力学特性,而且是计算其他水力特性及侵蚀产沙的重要参数,本文目的在于研究坡面细沟流和细沟间薄层水流流速沿坡面的变化过程,比较细沟和细沟间径流流速的差别。实验选取1m、2．5m、4m、5．5m、7m、8．5m和10m共7个坡长的小区（均为5。）,装填粉壤土,采用历时2h、总雨量121mm的变...     

Empirical models of rain-spells characteristics – A case study of a Mediterranean-arid climatic transect

Environmental (geomorphological, hydrological and ecological) processes are controlled by rainfall, particularly in the Mediterranean, semi-arid and arid regions. Rainfall was analyzed using the concept of rain-spells, i.e., a period of successive rain days preceded and followed by at least one day without rainfall. Daily data from 13 stations along a climatic transect extending from the Judean Mountains with a Mediterranean climate to the Dead Sea arid region in Israel were studied. Rain-spell characteristics (number, yield and duration), based on these data, are presented for different rainfall thresholds, which might be used for different environmental processes such as rock weathering, soil organic matter dynamics, landslides, overland flow and floods and soil erosion. Three estimation models have been developed in order to predict the mean annual Number of Rain-Spells (NRS), mean Rain-Spell Yield (RSY), and mean Rain-Spell Duration (RSD) for the mean annual rainfall and for any given rainfall threshold. These models can be used for current climatic conditions and for scenarios in which the rainfall total changes.     

Nonlinearity of ecogeomorphic processes along Mediterranean-arid transect

The study was conducted along a climatic transect extending from the Judaean mountains (mean annual rainfall, 700 mm; annual mean temperature, 17 °C) to the Dead Sea (mean annual rainfall, <100 mm; annual mean temperature, 23 °C).A high correlation was found between climatic conditions and factors and processes of the ecogeomorphological system. The values of certain factors and processes, such as soluble salt content and overland flow, increase with increasing aridity, whereas those of others, such as soil organic matter content, clay content, aggregate size and stability and infiltration rate, diminish with increasing aridity. These trends express the long-term effect of the prevailing mean climatic conditions in the research stations, conditions that led to the development of various types of soil and of plant communities.It was also found that for many of the factors and processes examined, such as organic matter content, salt concentration, aggregate stability, infiltration rate and overland flow yield, the rates of change with respect to position along the transect are not linear, and that a climatic threshold value exists in the zone with a mean annual rainfall of about 300 mm and in which the P/T ratio is about 17, which creates a sharp boundary between arid and Mediterranean ecogeomorphological systems. While in arid systems, erosion occurs mainly through physical–mechanical processes, under Mediterranean systems, it is governed mainly by chemical and biological processes.The significance of the existence of a sharp boundary between the arid and the Mediterranean zones is that even a relatively slight increase in the annual mean temperature and/or a slight decrease in the mean annual rainfall is liable to shift the boundary towards the Mediterranean zone and accelerate desertification processes.     

三峡库区紫色土坡地养分状况及养分流失*

紫色土是三峡库区移民安置区的主要坡地土壤。本研究采用典型区域调查,代表性土壤剖面养分分析,结合实验小区人工降雨的方法,初步研究了发育于侏罗纪紫色砂泥岩母质上紫色土的养分状况、养分流失特点、过程及影响养分流失因素。