降雨和径流条件下红壤坡面细沟侵蚀过程

为明确第四纪黏土发育红壤坡面侵蚀过程特征,采用人工模拟降雨和径流冲刷相结合试验,研究坡度、流量和降雨因素对坡面细沟侵蚀过程影响。结果表明:1)坡面侵蚀过程呈现明显阶段性,试验条件下侵蚀前3 min为层状面蚀为主的初始阶段,细沟出现后转变为细沟侵蚀为主的细沟发育阶段。降雨以及增加坡度和流量能加快细沟发育速度和侵蚀速率;2)各侵蚀阶段平均侵蚀速率关系为初始阶段细沟发育阶段细沟稳定阶段。初始阶段侵蚀速率对各水动力学参数响应关系为水流功率坡度水流剪切力单位水流功率=流速流量。细沟发育阶段平均侵蚀速率与水流功率、水流剪切力和坡度关系密切,而细沟稳定阶段侵蚀速率只与坡度和流量相关;3)水流功率是与初始阶段和细沟发育阶段关系最密切的水动力学参数,侵蚀初始阶段的层状面蚀、单独径流冲刷和降雨-径流作用下细沟侵蚀发生的临界水流功率分别为0.091、0.121、?1.691 N/(m·s)。试验在小尺度条件下初步揭示了红壤坡面细沟侵蚀过程特征,为南方红壤丘陵区土壤侵蚀预报模型和侵蚀防治提供理论参考。     

7Be示踪坡耕地次降雨细沟与细沟间侵蚀

对于坡面细沟与细沟间侵蚀过程的了解是建立侵蚀预报模型的基础,但传统方法难以对其进行深入研究。利用7Be示踪技术并结合人工模拟降雨,考虑坡脚沉积作用,研究了25°坡耕地径流小区次降雨过程中细沟与细沟间侵蚀动态。结果表明：根据流出径流小区泥沙7Be含量变化计算坡面明显细沟出现时间,由于坡脚沉积作用使得A、B两试验小区这一时间比实际细沟出现分别延迟了45 min和11 min;根据坡面-侵蚀泥沙中7Be总量守恒和泥沙质量平衡原理,坡面细沟间侵蚀及细沟侵蚀在坡面总侵蚀、坡脚沉积区泥沙及流出径流小区泥沙中的比例被定量区分开;总体上,细沟间侵蚀量在径流泥沙中的比例逐渐减少,而细沟侵蚀量逐渐增加。两试验小区中7Be示踪计算坡面细沟侵蚀量和坡脚沉积量与实测值相比相对误差均较小,因此7Be示踪技术可以对土壤侵蚀进行较为准确地定量研究。     

黄土坡面细沟侵蚀过程

采用具有定流量放水组合小区模拟降雨试验方法,对黄土坡面细沟侵蚀过程进行模拟试验。结果表明：不同坡度和不同降雨强度下,细沟侵蚀率都呈现随径流变化过程的递增而增大的趋势,并且幂函数方程可以较好地模拟出其变化过程,同时在径流变化过程中,不同坡度下细沟侵蚀率随径流过程变化的递增速率总体上大于不同降雨强度下的递增速率;细沟侵蚀模数随坡度及降雨强度的增大皆增大,可分别用对数方程及指数方程很好地描述,坡度及降雨强度对细沟侵蚀模数的综合作用可用二元幂函数方程很好地描述;试验条件下,水流切应力是细沟侵蚀过程发生发展的动力根源。     

黄土高原坡耕地的细沟侵蚀及其防治途径

陕北典型黄土丘陵沟壑区的定位观测、野外调查和室内一系列人工降雨试验资料,表明了细沟侵蚀量占坡面侵蚀量的70%。而细沟侵蚀的发生是在坡面股流的流程上,当径流侵蚀力增大到足以冲刷土块,形成小跌水,进而演化为细沟下切沟头时,细沟侵蚀就开始发生了。下切沟头的下切侵蚀和下切沟头间径流对沟底的冲刷、沟头的溯源侵蚀、沟壁的崩塌形成了断续细沟,而位于一条股流流程上多个断续沟头溯源侵蚀的连接就形成了连续细沟。在这个过程中。由于降雨径流侵蚀力和土壤抗侵蚀力在时空上的强弱对比关系,出现了细沟的分叉、合并及连通现象。所有这些过程不但促进了细沟的发展,而且也造成了严重的细沟侵蚀。降雨径流侵蚀力。土壤抗侵蚀性能,坡度、坡长、坡形和土地管理因素是影响细沟侵蚀的主要因素。因此。防治细沟侵蚀的关键是削弱降雨径流侵蚀力和提高土壤的抗侵蚀性能。而免耕留茬、覆盖、草粮带状间作、水平沟种植及土地的合理利用是防治细沟侵蚀行之有效的措施。     

细沟侵蚀过程与细沟水流水力学参数的关系研究

利用供沙土槽和试验土槽的双土槽径流小区 ,定量研究了在不同降雨强度下上方来水来沙对陡坡地细沟侵蚀产沙过程和细沟水流水力学参数的影响及其细沟水流水力学特征参数与细沟侵蚀产沙量的关系。结果表明 :坡面细沟侵蚀过程以侵蚀—搬运过程为主 ,坡上方来沙不仅被径流全部搬运 ,且上方来水在坡下方引起了另外的侵蚀产沙量 ,其值随上方来水含沙量的减少和降雨强度的增加而增大。上方来水的汇入或降雨强度的增大可使细沟水流流态由层流转化为紊流。上方来水对细沟水流水力学参数 (流速、水力半径、雷诺数、弗劳德数和阻力系数 )有重要影响。定量分析了细沟水流水力学特征参数 (流速、雷诺数和阻力系数 )与上坡来水引起坡下方净侵蚀产沙量的关系 ,建立了净侵蚀产沙量与细沟水流流速、雷诺数和阻力系数统计模型。     

褐土与棕壤坡耕地细沟侵蚀发生的阶段性水沙变化

为深入探究辽西低山丘陵区坡耕地土壤侵蚀机理,以该区的典型土壤类型褐土和棕壤为研究对象,采用室内人工降雨模拟试验,研究3种坡度(5°,10°,15°)和3种降雨强度(40,60,80 mm/h)下细沟侵蚀发生的阶段性水沙变化过程。结果表明:褐土与棕壤坡面侵蚀过程可划分为3个阶段,即细沟侵蚀之前阶段、跌坎发育阶段和细沟侵蚀快速发育阶段;细沟侵蚀之前的面蚀阶段,同一坡度条件下,褐土与棕壤随雨强的增加,坡面流速呈增大趋势,而在同一雨强条件下,坡度对流速的影响并无明显规律;细沟侵蚀阶段,当坡度一定条件下,褐土与棕壤细沟内、细沟间的流速随雨强的增加而增大,当雨强一定时,褐土与棕壤随坡度的增加细沟间流速增加;细沟侵蚀阶段流速表现为细沟内流速坡面流速细沟间流速;细沟侵蚀快速发育阶段2种土壤产生的径流量占总径流量的80%以上,土壤侵蚀量占总侵蚀量均在70%以上,且棕壤对总体侵蚀量的贡献更稳定,更易发生细沟侵蚀。整场降雨的侵蚀方式是面蚀向细沟侵蚀的转变,坡面一旦发生侵蚀,细沟侵蚀对坡面总侵蚀的贡献更大。     

黄土坡面细沟发育及细沟与细沟间侵蚀比率研究

基于室内人工模拟降雨试验,采用三维激光扫描仪对坡面进行监测,研究了黄土坡面不同坡度(10°,15°,20°,25°)和雨强(90,120mm/h)下细沟发育过程、形态特征及细沟与细沟间侵蚀比率变化规律。结果表明:(1)随着坡度、降雨强度增大,坡面产流时间、细沟出现时间有减小趋势,断面流速有增大趋势;(2)黄绵土坡面细沟形态变化受降雨强度影响较小,受坡度影响较大。在10°,15°坡度条件下,受溯源侵蚀及沟道下切作用较强,形成的细沟长、窄,深;在20°,25°条件下,受沟壁坍塌作用影响较大,形成的细沟短、宽、浅;(3)采用多元回归方法对细沟与细沟间侵蚀比率与坡度、雨强、径流的关系进行拟合,拟合函数为幂函数方程,细沟与细沟间侵蚀比率随着坡度、降雨强度增大而增大。     

黄土坡面细沟侵蚀能力的水动力学试验研究

建立以水动力学为基础的侵蚀预报模型,必须解决影响土壤侵蚀发生过程及其强度的各水力要素的合理计算问题。本文通过室内径流冲刷试验,研究了黄土坡国沟侵蚀发生的水动力学机理及其输沙特征,探讨了细沟侵蚀预报模型中,细沟侵蚀民涉衣的土壤及有关径流的水力参数;土壤侵蚀性系数,细沟侵蚀发生的临界切应力,细沟径流的平均流速,Ｍａｎｎｎｉｎｇ糙率系数,以及反映细沟断面形态特征的系数的估算问题。     

细沟侵蚀阶段玉米季坡耕地氮素流失特征

研究紫色土区坡耕地玉米全生育期细沟侵蚀阶段水土及氮素流失规律,以期为研究区氮素流失有效防控提供科学依据。采用人工模拟降雨与野外径流小区相结合的方法,开展降雨强度为1.5mm/min条件下玉米全生育期细沟侵蚀阶段地表径流、壤中流和侵蚀泥沙中氮素流失特征的研究。结果表明:细沟侵蚀阶段,玉米各生育期地表径流量、壤中流量和侵蚀产沙量总体表现为随降雨时间延长呈先增加后平稳的变化趋势。地表径流中总氮、可溶性总氮、硝态氮和侵蚀泥沙中总氮流失量总体呈现先增加后平稳的趋势,而地表径流中铵态氮流失量变化趋势在降雨前期呈现波动性变化,降雨后期逐渐平稳。壤中流中总氮、可溶性总氮、硝态氮、铵态氮流失量则随着降雨时间延长呈现平稳的变化趋势。细沟侵蚀阶段地表径流中氮素流失总量在玉米苗期最大,为628.77mg/m2;壤中流中氮素流失总量在拔节期和抽雄期最大;侵蚀泥沙中氮素流失总量在苗期最大,为144.95mg/m2。壤中流为氮素流失主要途径,硝态氮为氮素流失主要形态。     

黄土坡面细沟侵蚀发育过程与模拟

以坡面细沟侵蚀过程为研究对象,利用人工模拟降雨试验和三维激光扫描技术,研究了同一坡面三场间歇性降雨下细沟侵蚀发生、发展和演化的图形化过程;同时,采用已有细沟侵蚀过程模型(CARill),结合Net Logo软件,将试验结果与模型模拟结果进行对比分析。结果表明:(1)扫描三场降雨图形化过程显示:侵蚀阶段呈现出溅蚀—片蚀—跌坑—断续细沟—连续细沟—细沟崩塌过程,沟长发育迅速,沟宽和沟深发育相对缓慢,细沟沟网形成迅速,降雨结束后侵蚀强度达到22.11 kg m-2,较初期降雨侵蚀增加了22.04倍。(2)CA-Rill模型模拟结果显示,在细沟侵蚀演化图形化过程方面,该模型可较完整地模拟细沟形态发育过程,实现细沟侵蚀的发生、发展以及演化过程中细沟形态的可视化模拟;(3)模型模拟三场降雨细沟侵蚀参数t检验结果发现:最长平均沟深、最大沟深、最长沟平均沟宽模拟效果不好;而细沟平面密度、最长沟长、侵蚀强度模拟效果较好。     

基于7Be示踪和细沟沟网分形维数研究坡面土壤侵蚀

本文试图结合7Be示踪和分形理论定量化描述降雨对坡面的侵蚀过程。7Be示踪结果显示,降雨初期,坡面细沟间侵蚀贡献率高,细沟侵蚀贡献率低,随着降雨的进行,细沟间侵蚀贡献率降低,而细沟侵蚀贡献率增大并处优势,在降雨后期,细沟间侵蚀贡献率又有增大的趋势。整个降雨过程坡面细沟沟网分形维数整体呈增大趋势,在细沟发育中前期增加快,后期增加变缓,中间有波动。细沟沟网分形维数与总侵蚀量和细沟侵蚀量均呈正相关,分维变与相对应总侵蚀量和细沟侵蚀量也均呈正相关,但与细沟侵蚀量的相关性最好,说明细沟沟网分形维数可表征细沟发育过程和坡面侵蚀强度的变化。     

砾石覆盖对土壤水蚀过程影响的研究进展

 土壤中砾石的存在对水蚀过程有着重要的影响,有关砾石特别是表土砾石覆盖对土壤水蚀影响的研究结果表明,表土砾石对溅蚀分散、细沟间及细沟侵蚀等坡面侵蚀过程有重要影响:1)泥沙溅蚀分散量与砾石覆盖度呈负相关关系;2)砾石覆盖与细沟间侵蚀的关系较为复杂,这取决于表土的结构、砾石的位置和大小以及坡度等因素,当砾石嵌入结皮表土时,二者呈负相关关系,当砾石置于表土之上或嵌入具有结构孔隙的表土时,二者呈正相关关系;3)砾石覆盖对细沟间侵蚀产沙的作用效率与砾石粒径呈负相关关系,砾石置于表土之上的表土产沙量总低于砾石嵌入表土的产沙量;4)表土砾石覆盖能抑制细沟的形成,增加细沟糙度,降低细沟径流速率以及径流的侵蚀速率。鉴于砾石对水蚀过程的重要影响,RUSLE、WEPP和EUORSEM等土壤侵蚀模型预报含砾石土壤流失量时对相关参数做了修正。     

坡面细沟发生临界水动力条件初探

通过玻璃水槽试验和土槽放水冲刷试验对坡面细沟侵蚀发生的临界水动力条件进行了初步研究。结果表明 ,坡面径流在顺坡向下流动过程中以滚波形式运动并发生叠加是造成侵蚀方式发生变化的主要原因。由于径流流动过程中发生滚波叠加 ,造成在径流流路上出现局部水深增加 ,导致侵蚀切应力激增 ,当切应力大于该处的土壤抗蚀力时便发生侵蚀 ,并最终造成细沟沟头的出现。通过对土槽冲刷试验的结果分析 ,运用能量守恒原理建立了径流能耗和径流侵蚀产沙率之间的关系 ,给出了给定土壤条件下坡面细沟侵蚀率估算模型。结果表明 ,坡面土壤侵蚀的发生具有一定的临界条件 ,当径流能耗大于 7 3 8(J)时坡面开始有细沟侵蚀发生     

坡耕地细沟侵蚀影响因素的研究

本文利用人工降雨试验和野外调查资料分析研究了黄土高原坡耕地细沟侵蚀发生发展的影响因素.其结果表明:降雨径流能量(尤其是径流能量)、土壤抗侵蚀性能、坡度、坡长、坡形、土地管理是影响细沟侵蚀的主要因素.作者认为防治坡耕地土壤侵蚀的关键是削弱降雨能量和提高土壤的抗侵蚀性能.     

Quantifying spatial distribution of interrill and rill erosion in a loess at different slopes using structure from motion (SfM) photogrammetry

The spatial distribution of interrill and rill erosion is essential for unravelling soil erosion principles and the application of soil and water conservation practices. To quantify interrill and rill erosion and their spatial development, four 30-min rainfalls at 90 mm h^?1 intensity were consecutively simulated on runoff plots packed with a loess at six slopes of 10°, 15°, 20°, 25°, 30° and 35°. The soil surface was measured using the structure from motion (SfM) photogrammetry upon each simulation run, and the runoff and sediment samples were collected and measured at every 10 min. Rills did not develop until the third simulation run. During the initial two runs, the lower third section was more severely eroded than the upper and middle thirds along the slope direction, yet the interrill erosion was statistically uniform from left to right. Rills tended to emerge by both sidewalls and in the lower portion in the third run. The corresponding rill erosion increased with slope from 10° to 20° and then decreased for the slopes steeper, which was consistent with the slope trend of the sediment yield directly measured. The rills expanded substantially primarily via head retreat and to a lesser extent via sideward erosion after receiving another 30-min rainfall. Rill erosion contributed 69.3% of the total erosion loss, and shifted the critical slope corresponding to the maximum loss from 20° to 25°. These findings demonstrate the significance of rill erosion not only in total soil loss but also in its relation to slope, as well as the effectiveness of SfM photogrammetry in quantifying interrill and rill erosion.     

Magnitude of soil erosion on the northern slope of the Uluguru Mountains,Tanzania: Interrill and rill erosion

The magnitude of interrill and rill erosion was determined on the northern slopes of the Uluguru Mountains, Tanzania which is representative for larger areas of East African Arch Mountains, where population pressure is high and land degradation is severe. The aim of the study was to develop a database to support soil conservation in the area. The study was done on two distinct geomorphic units with respect to altitude and hence rainfall distribution pattern: mountain ridges with an altitude ranging from 1000 to 1500 masl and mean annual rainfall of 2300 mm and mountain foothills whose altitude and mean annual rainfall are 550 to 900 masl and 900 mm, respectively. Total soil loss was measured on 36 individual bounded plots measuring 1.2 m × 20 m using Gerlarch troughs on each day with rain from July 2000 to June 2001. The plots were located on six different geopedologic units, nine on mountain ridges and the rest on the mountain foothills. The slope gradient on the terrain ranged from 30% to 70%. The plots were put under maize cultivation as the main crop. Soil loss through rill erosion was estimated by volumetric measurements of rills on each soil erosion plot. The soil loss due to interrill erosion was obtained by subtracting soil loss through rill erosion from the total soil loss measured in the Gerlarch troughs. The results indicate that soil loss due to both interrill and rill erosion was very high with mean soil loss of 69 and 163 t/ha/year, respectively. Rill erosion accounted for about 58% of the total soil loss while interrill erosion contributed to the remaining 42%. Both interrill and rill erosion were higher in the mountain ridges with mean soil loss of 88 t/ha/year and 210 t/ha/year compared to 49 and 116 t/ha/year in the mountain foothills, respectively. Rill erosion was significantly higher (P ≤ 0.001) in all geopedologic units with slope gradient above 40% (mean soil loss ranged between 91 and 258 t/ha/year) compared to interrill erosion with mean soil loss varying from 41 to 115 t/ha/year. In geopedologic units with slope gradient above 60% both interrill and rill erosion were highly active while in geopedologic units with slope gradient below 40% the two processes were less active. The results demonstrate that rill erosion is more important than interrill erosion in the study area particularly where the slope gradient exceeds 40%. The results further show that the major part of the studied area has moderate interrill erosion (10–50 t/ha/year) and severe to very severe (> 100 t/ha/year) rill erosion. This study clarifies the magnitude of interrill and rill erosion which is important for designing soil conservation on agricultural fields.     

Soil resistance to interrill erosion: Model parameterization and sensitivity

Interrill erosion, which is less visible in the landscape than rill and gully erosion, may cause major sediment deposits in the lower part of cultivated fields. It is often associated with runoff resulting from sealing and crusting, and soil properties such as soil detachability or soil aggregate stability have been used to express soil resistance to interrill erosion processes, i.e., interrill erodibility. From a literature review including more than fifteen erosion models, we have identified three main methods used to measure these properties: aggregate stability and splash cup detachability, methods performed in the laboratory using only a few grams of soil, and standard plot methods that are based on field plot measurements. This difference makes the parameters involved in assessing interrill erodibility dependent upon the scale and the hydrological processes involved and difficult to compare. According to the literature, the sensitivity of actual erosion models to interrill erodibility is lower than the sensitivity to hydrological properties and rill erodibility parameters. This numerical study shows that erodibility measurements from the three major assessment methods give different results regarding the contribution of interrill erosion and show that the sensitivity of erosion modeling to interrill erodibility may in fact be greater than shown in the literature on global sensitivity analysis.     

REE示踪坡面侵蚀过程研究

在观测年度气候条件下,坡面产流初始阶段片蚀是坡面侵蚀的主要方式,试验期间的三次降雨片蚀分别占坡面总侵蚀量的71%、48%、49%,表明坡面侵蚀处于片蚀-细沟侵蚀演变的初期阶段;同时随着降雨的进行,细沟侵蚀量在不断增大,表明坡面由片蚀为主逐渐过渡到片蚀向细沟侵蚀转变的阶段。对次降雨条件下坡面不同部位的侵蚀泥沙来源研究表明:无论片蚀绝对量如何变化,坡面表层上段的相对侵蚀量始终不大于10%,表明坡面片蚀的来源主要集中在坡面下部;降雨结束后对不同坡段的细沟相对侵蚀量比较分析后发现,不同坡段的相对侵蚀量结果分别为:距坡脚0~1米坡段16%;2~4米坡段6%;5~9米坡段3%,三段的侵蚀量之比约为5∶2∶1,表明细沟侵蚀的主要来源集中在距坡脚4米段内。     

坡面水土流失比尺模型相似性的试验研究

通过不同比尺的系列模型试验,为坡面水土流失的比尺模型相似性研究,提供了原型和模型的降雨-产沙资料。试验结果表明,坡面产沙浓度随时间的变化有较强的紊动性,因此建议采用经验回归的方法率定降雨产沙的比尺关系;原型和模型的侵蚀产沙量都与雨强成幂函数相关,其雨强系数随模型几何比尺的增大而减小,而雨强指数的大小与坡面几何尺度的大小无关。