2种典型黄土坡面侵蚀特征分析及物理意义解释

研究土壤性质对侵蚀特征的影响可为深刻理解土壤侵蚀机理,以及优化评估模型参数提供重要理论支持。基于此,本研究采用室内模拟降雨试验,在90 mm/h降雨强度及4个坡度(5°、7.5°、10°和15°)条件下,分析黄土丘陵沟壑区2种典型黄土的侵蚀特征,并结合数学关系和物理意义对其侵蚀机制进行解释。结果表明:1)相对于土壤A,土壤B产流快,径流量高,更易发育细沟,侵蚀也更严重,土壤B的总径流量和总侵蚀量分别是土壤A的1.26~1.51倍和3.74~57倍。2)总体来看产流初始阶段侵蚀量、片蚀量和细沟侵蚀阶段侵蚀量均随坡度而增加,片蚀阶段土壤B的含沙量是土壤A的1.09~4.47倍,细沟侵蚀阶段前者是后者2.01倍。土壤B在细沟侵蚀阶段的侵蚀量可达总侵蚀量的98%以上,平均含沙量是片蚀阶段的7.09~32.39倍,相应情况下土壤A分别是96%和10.49倍。3)2种土壤的产沙量与含沙量的关系可用y=ax+b表示,经过优化处理,线性关系的R 2可达0.98及以上,斜率a可用以表征径流的侵蚀能力,截距b用来表征可搬运物质类型及丰富程度。本研究对于深入理解土壤质地在坡面侵蚀中的作用,以及为生态保护提供理论支持具有重要的理论与实践意义。

降雨条件下风速对迎风坡坡面细沟侵蚀特征的影响

[目的]为明确风力作用下迎风坡坡面细沟侵蚀特征。[方法]采用人工模拟风驱雨试验,研究在不同风速条件(0,3,5,7 m/s)下迎风坡坡面水沙过程变化规律及细沟形态特征。[结果]与无风坡面相比,迎风坡面产流时间和跌坎出现时间分别增加20.59%~47.06%和33.10%~137.78%,坡面平均流速减小12.86%~22.53%;产流率和产沙率随风速的增加而显著减少(p<0.05),不同风速条件下,迎风坡面产流率变化趋势相近,随着降雨进行产流率逐渐增加,一段时间后保持稳定,不同风速下的阶段性无明显差异。产沙率随降雨历时的延长整体呈先迅速增加后缓慢下降并趋于稳定趋势,产沙率发生变化的节点与跌坎出现时间基本一致。细沟宽度、深度及其波动程度随着风速的增加而减小;细沟宽度、深度及其波动程度随着风速增加而减小;细沟宽深比和细沟倾斜度分别为1.40~1.69和13.47°~14.76°,均随着风速的增加而增大;不同风速条件下,细沟体积、细沟割裂度和细沟密度分别为4.39×10^(3)~10.27×10^(3)cm^(3),0.024~0.042,2.03~2.92 m/m^(2),三者均随风速的增加而减小。[结论]细沟体积、细沟密度和割裂度与坡面侵蚀量均呈极显著正相关关系,是表征迎风坡坡面细沟形态的优选指标。

基于三维激光扫描技术的冻结黑土细沟发育模拟

为探究融雪径流与冻结状态对黑土细沟网络发育的影响,该研究开展了冻结与非冻结处理黑土坡面的融雪径流模拟冲刷试验,利用三维激光扫描技术获取多次定时径流冲刷并直至侵蚀形态稳定的坡面点云,结合数字表面模型差异(digital surface model of difference,DoD)微地形变化监测方法与点云逆向工程,获取细沟网络发育过程的侵蚀面积、侵蚀体积、细沟长度和细沟密度等侵蚀参数。结果表明,冻结因素与温度变化对细沟网络发育过程与程度有重要影响:1)冻结处理的黑土坡面更容易发展出细沟网络,达到坡面侵蚀形态基本稳定后的侵蚀面积、侵蚀体积以及侵蚀细沟长度是非冻结处理黑土坡面的291%、557%和437%。2)冻结处理与非冻结处理沿坡面细沟截面形态变化差异明显。冻结坡面细沟交叉时宽深比RW/D快速减小,下切速度加快,随后宽度与深度呈比例稳定增加;非冻结坡面汇水处的R_(W/D)随冲刷次数增加而增大,侧蚀速度加快,其他截面R_(W/D)随着冲刷次数的增加而减小,下切速度加快。3)采用ArcGIS与点云逆向工程模型联合获取的冻结状态下细沟形态参数与发育过程DoD相对误差范围为-12.70%~4.42%,提取精度在95%以上。该联合方法在冻结土体条件下获取细沟参数具有较高精度,可作为土壤侵蚀参数高精度提取的一种手段。

仿生非光滑原理及其在金刚石钻头中的应用

仿生非光滑原理与孕镶金刚石钻头结合起来,并将生物非光滑表面的耐磨、减阻等特性引用到钻头的设计中,使钻头也具有这样的特性,研究一种新型的仿生孕镶金刚石钻头,以此来提高钻头的效率和寿命。通过Φ75 mm仿生钻头的野外钻进试验可知,仿生钻头的钻进效率较普通钻头至少提高10%,钻头寿命提高30%。该研究为提高深部地质钻探关键工具的性能提供了新的思路,具有一定的现实意义。

旧桥拼接钻孔植筋技术研究

以青兰高速某特大桥拼接工程为例,阐述了钻孔植筋施工工艺,分析了旧桥拼接施工过程中钻孔植筋存在的问题,并提出解决方案,通过研究相关技术,同时提高此类工程施工水平,以期为后续类似工程施工提供经验。

A Review on Rill Erosion Process and Its Influencing Factors

Rills are frequently observed on slope farmlands and rill erosion significantly contributes to sediment yields. This paper focuses on reviewing the various factors affecting rill erosion processes and the threshold conditions of rill initiation. Six factors, including rainfall, runoff, soil, topography, vegetation and tillage system, are discussed. Rill initiation and network are explored. Runoff erosivity and soil erodibility are recognized as two direct factors affecting rill erosion and other types of factors may have indirect influences on rill erosion through increasing or decreasing the effects of the direct factors. Certain conditions are necessary for rill initiation and the critical conditions are different with different factors. Future studies should be focused on 1) the dynamic changes of rill networks; 2) the combined effect of multiple factors; and 3) the relationships of threshold values with other related factors.

Rainfall and inflow effects on soil erosion for hillslopes dominated by sheet erosion or rill erosion in the Chinese Mollisol region

Erosion agents and patterns profoundly affect hillslope soil loss characteristics. However, few attempts have been made to analyze the effects of rainfall and inflow on soil erosion for hillslopes dominated by sheet erosion or rill erosion in the Chinese Mollisol region. The objective of this study was to discuss the erosive agent(rainfall or inflow), hillslope erosion pattern(sheet erosion or rill erosion) and slope gradient effects on runoff and soil losses. Two soil pans(2.0 m long, 0.5 m wide and 0.5 m deep) with 5° and 10° slopes were subjected to rainfall(0 and 70 mm h–1) and inflow(0 and 70 mm h–1) experiments. Three experimental combinations of rainfall intensity(RI) and inflow rate(IR) were tested using the same water supply of 70 mm by controllingthe run time. A flat soil surface and a soil bed with a straight initial rill were prepared manually, and represented hillslopes dominated by sheet erosion and rill erosion, respectively. The results showed that soil losses had greater differences among treatments than total runoff. Soil losses decreased in the order of RI70+IR70 > RI70+IR0 > RI0+IR70. Additionally, soil losses for hillslopes dominated by rill erosion were 1.7-2.2 times greater at 5° and 2.5-6.9 times greater at 10° than those for hillslopes dominated by sheet erosion. The loss of <0.25 mm soil particles and aggregates varying from 47.72%-99.60% of the total soil loss played a dominant role in the sediment. Compared with sheet erosion hillslopes, rill erosion hillslopes selectively transported more microaggregates under a relatively stable rill development stage, but rills transported increasinglymore macroaggregates under an active rill development stage. In conclusion, eliminating raindrop impact on relatively gentle hillslopes and preventing rill development on relatively steep hillslopes would be useful measures to decrease soil erosion and soil degradation in the Mollisol region of northeastern China.

A Preliminary Study of Rill Marks in the Yellow River Delta

In recent years, the flow of the Yellow River has often been interrupted, which has resulted in exposure of channel bars and point bars, and even extensive exposure of the riverbed. Consequently, a large number of rill marks have developed. They are diverse in morphology. According to the hydrodynamic types of their formation, they can be grouped into 6 categories, i. e. the wave eroded, backwash, seepage, rain eroded, water drainage and runoff rill marks. Morphologically, they can be divided into more than ten types: the linear, tooth shaped, comb shaped, fence like, ear like, braided, branched, leaf like, flower like, root like, dendritic, net like, radial etc. Their cross sections include the broad u type (the width/depth ratio is over 2, and may reach 10—20), U type (width/depth ratio from 1 to 2), V type, Ω type and ( type. Their occurrences may be attributed to the variations in composition, grain size, color, fabric and morphology. They have 5 scales: the micro scale (length and width within 1 cm), small scale (length and width within 10 cm), medium scale (length and width ranging from 10—100cm), large scale (length and width 1—5 m) and giant-scale (length or width over 5 m).

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.

Assessment of Rill Erosion Development during Erosive Storms at Angereb Watershed, Lake Tana Sub-basin in Ethiopia

Application of simple and locally based erosion assessment methods that fit to the local condition is necessary to improve the performance and efficiency of soil conservation practices. In this study, rill erosion formation and development was investigated on the topo-sequence of three catchments （300-500 m slope length）; and on agricultural fields （6 m and 24 m slope lengths） with different crop-tillage surfaces during erosive storms. Rill density and rill erosion rates were measured using rill cross section survey and close range digital photogrammetry. Rill formation and development was commonly observed on conditions where there is wider terrace spacing, concave slope shapes and unstable stone terraces on steep slopes. At field plot level, rill development was controlled by the distribution and abrupt change in the soil surface roughness and extent of slope length. At catchment scale, however, rill formation and development was controlled by landscape structures, and concavity and convexity of the slope. Greater rill cross sections and many small local rills were associated to the rougher soil surfaces. For instance, relative comparison of crop tillage practices have showed that faba-bean tillage management was more susceptible to seasonal rill erosion followed by Teff and wheat tillage surfaces under no cover condition. Surface roughness and landscape structures played a net decreasing effect on the parallel rill network development. This implies that spatial and temporal variability of the rill prone areas was strongly associated with the nature and initial size of surface micro-topography or tillage roughness. Thus, it is necessary to account land management practices, detail micro-topographic surfaces and landscape structures for improved prediction of rill prone areas under complex topographic conditions. Application of both direct rill cross section survey and close range digital photogrammetric techniques could enhance field erosion assessment for practical soil conservation improvement.

Rill flow velocity affected by the subsurface water flow depth of purple soil in Southwest China

Subsurface water flow above the weakly permeable soil layer commonly occurs on purple soil slopes.However,it remains difficult to quantify the effect of subsurface water flow on the surface flow velocity.Laboratory experiments were performed to measure the rill flow velocity on purple soil slopes containing a subsurface water flow layer with the electrolyte tracer method considering 3 subsurface water flow depths(SWFDs:5,10,and 15 cm),3 flow rates(FRs:2,4,and 8 L min^(-1)),and 4 slope gradients(SGs:5°,10°,15°,and 20°).As a result,the pulse boundary model fit the electrolyte transport processes very well under the different SWFDs.The measured rill flow velocities were 0.202 to 0.610 m s^(-1) under the various SWFDs.Stepwise regression results indicated a positive dependence of the flow velocity on the FR and SG but a negative dependence on the SWFD.The SWFD had notable effects on the rill flow velocity.Decreasing the SWFD from 15 to 5 cm increased the flow velocity.Moreover,the flow velocities under the 10-and 15-cm SWFDs were 89%and 86%,respectively,of that under the 5-cm SWFD.The flow velocity under the 5-,10-and 15-cm SWFDs was decreased to 89%,80%,and 77%,respectively,of that on saturated soil slopes.The results will enhance the understanding of rill flow hydrological processes under SWFD impact.

A Preliminary Study on Traditional Level-trench Method to Prevent Rill Initiation in the Three Gorges Region,China

The level-trench method is a traditional tillage operation to develop a drainage system on slope land in the Three Gorges region. Before crops are planted, farmers prepare the land with level trenches spaced 3-1o m apart, depending on the slope gradient： steeper slopes require shorter distances. Little scientific analysis has been done on the use of traditional level trenches for soil conservation. We conducted a field investigation and simulation experiments, and present a comparison between the spacing of level trenches and the slope length required for rill initiation. The results indicate that the spacing of level trenches in farmland is close to the slope length required for rill initiation in the experimental plots, and regression models of trench spacing with the gradient and the slope length required for rill initiation with the gradient have similar formats; the coefficients of determination （R2） for the two equations are 0.99 and 0.88, respectively. There were some differences between the field survey and experiments, but we conclude that the traditional level-trench method has an important role in preventing rill initiation.

Developments of Rill Networks: An Experimental Plot Scale Study

Enumerating the relative proportions of soil losses due to rill erosion processes during monsoon and post-monsoon season is a significant factor in predicting total soil losses and sediment transport and deposition. Present study evaluated the rill network with simulated experiment of treatments on varying slope and rainfall intensity to find out the rill erosion processes and sediment discharge in relation to slope and rainfall intensity. Results showed a significant relationship between the rainfall intensity and sediment yield (r = 0.75). Our results illustrated that due to increase in rainfall intensity represent the development of efficient rill network while, no rill was found with a slope of 20° and a rainfall intensity of 60 mm·h-1. The highest rill length was observed in plot E with 20° slope and 120 mm·h-1 rainfall intensity at 360 minutes. Positive and strong correlation (R2 = 0.734, P 0.001) was observed between the cumulative rainfall intensity and sediment discharge. A longitudinal profile was delineated and showed that the depth and numbers of depressions amplified with time and were more prominent for escalating rainfall intensity for its steeper slopes. Information derived from the study could be applied to estimate longer-term erosion stirring over larger areas possessing parallel landforms.

Gorilla Thriller More Chinese tourists keen to encounter mountain gorillas

The majestic mountain gorilla has a very secluded home,living exclusively in the tropical forests of the Democratic Republic of the Congo(DRC),Rwanda and Uganda.According to the World Wildlife Fund for Nature(WWF),there are more than 1,000 mountain goril las living in the world,less than a half of which live in the Virunga Mountains on the border of the DRC and Rwanda,with the remainder calling tlie Bwindi Impeneti able National Park in Uganda home.

降雨过程中黄土坡面微地形因子与侵蚀关系研究

以断续降雨过程中不同阶段的黄土坡面栅格单元地形信息为研究对象,通过12段30 min、60 mm/h雨强的降雨进行模拟降雨试验,对微坡度、微坡向与黄土坡面侵蚀过程、细沟形态演变的相互影响进行研究。研究结果表明:坡面微坡度与微坡向的变化主要集中在降雨初始阶段(0~30 min),后续阶段(30~360 min)变化幅度较小,微坡度和微坡向变化与坡面时段侵蚀量显著正相关。细沟网络形成后,微坡度<15°区间和45°以上区间栅格占比缓慢上升,且主要产生于细沟内部,细沟内部在发育过程中会产生泥沙堆积的平台和坡度较大的陡坎。细沟的发育过程是细沟内径流的剥蚀和边壁不稳定土体的坍塌共同作用的非均匀发育过程,径流的剥蚀和土体的坍塌互相促进,加速了细沟的发育过程,从而造成了侵蚀量的波动。细沟侵蚀过程中坡面微坡向以坡面坡向为主导,坡面坡向栅格占比在30 min后保持不变,而细沟总表面积逐渐增加,说明微坡向与坡面同向的细沟栅格数增加。细沟会产生有一定宽度的沟底,沟道的横截面由“V”形向“U”形过渡。除北向外,其余微坡向栅格数变化与细沟密度、细沟割裂度、细沟复杂度、细沟累计长度和细沟平均宽度显著相关,微坡向栅格数能够较好地反映坡面细沟形态变化。

基于CT扫描技术的土柱孔隙结构及其抗侵蚀能力研究——以种植百喜草为例

[目的]分析百喜草土柱孔隙结构与土壤抗侵蚀能力之间的联系,为水土保持植物措施的优化布设以及效益评估提供科学依据。[方法]依托植物土柱长期微区试验,通过CT扫描技术研究种植百喜草的土柱孔隙指标(孔隙长度密度、体积密度、表面积密度和孔隙数密度),开展边坡水槽冲刷试验。设置3个坡度(10°,20°和30°)和5个流量(0.8,1.6,2.4,3.2,4.0 L/s)组合量化土壤抗侵蚀能力,分析孔隙指标与抗侵蚀能力因子之间的关系。[结果]百喜草土柱孔隙发育程度随生长时间不断增强,而随土层深度减弱;4个孔隙结构指标在0—5 cm土层的数值远大于5—10 cm土层,且表层0—5 cm的平均土壤细沟可蚀性(0.026 s/m)和临界水流剪切力(7.0 Pa)分别是下层5—10 cm的0.33,1.54倍。[结论]植物根系发育的孔隙指标能够表征土壤抗侵蚀能力变化,CT扫描获取的4个孔隙结构指标与细沟可蚀性等因子显著相关,其中孔隙表面积密度与土壤抗侵蚀能力指标关系最为密切。

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。

不同降雨强度及坡度条件下饱和紫色土坡面细沟形态特征

坡面细沟形态特征的定量分析是研究细沟侵蚀的基础。通过设计3种降雨强度(30,60,90 mm/h)和5种坡度(2°,5°,10°,15°,20°)组合条件下的人工降雨模拟试验,定量研究饱和紫色土坡面降雨强度及坡度对细沟形态及其空间变化特征的影响。结果表明:饱和紫色土坡面细沟平均宽度、深度和细沟宽深比分别为3.44~9.64 cm、1.01~8.14 cm和1.18~3.87,细沟宽度和深度沿坡面从上至下整体均表现出先增大后减小的趋势,细沟宽深比沿坡面表现为上坡<中坡<下坡的变化特征。整体来看,坡面细沟宽度和深度均与降雨强度和坡度呈正相关关系,且降雨强度和坡度对坡面细沟宽度的影响相近,而坡度对细沟深度的影响较降雨强度更显著;细沟宽深比与降雨强度和坡度呈负相关关系,且坡度对坡面细沟宽深比的影响显著大于降雨强度的影响。研究结果对认识饱和土壤坡面细沟侵蚀形态变化规律、进一步探究坡面细沟发育过程具有重要参考价值。

丹江口库区典型小流域生物结皮驱动土壤性质变化及分离响应

为探究生物结皮发育驱动下土壤水蚀特征及机理,选取苔藓发育为优势种的退耕样地,设计5个盖度等级(1%~20%,20%~40%,40%~60%,60%~80%,80%~100%),以裸地为对照,在不同水流剪切力(6.12~19.64 Pa)下进行冲刷试验。结果表明:结皮发育显著影响土壤养分含量,且高盖度结皮覆盖下养分表聚效应更加明显。生物结皮发育显著影响土壤分离能力,裸地土壤分离能力[1.4656 kg/(m^(2)·s)]为生物结皮[0.0042~0.4682 kg/(m^(2)·s)]的3.58~348.95倍,裸地细沟可蚀性(0.2935 s/m)为生物结皮(0.0010~0.0822 s/m)的3.57~293.50倍。相对土壤分离能力及细沟可蚀性均随结皮盖度增加呈指数函数衰减,结皮冲破时间随结皮盖度增加呈指数函数增长;非线性回归分析表明,土壤分离能力可用水流剪切力、生物结皮盖度和土壤黏结力进行模拟(NSE=0.749)。综上,生物结皮发育显著提升土壤抗侵蚀性能,研究结果可为半湿润区水土流失防治及生物结皮管理利用提供理论参考。

基于无人机贴近摄影测量的坡面细沟侵蚀及形态演化研究

[目的]寻求效率和精度均高且适应性强的坡面细沟侵蚀测量技术手段,克服传统测量方法效率低,成本高,适用性差等问题,为坡面细沟侵蚀演变过程及定量化研究提供新的思路和技术手段。[方法]利用无人机通过贴近摄影测量获取连续6场人工模拟降雨下坡面细沟发育的高分辨率影像及模型,经定位精度、模型精度和侵蚀模拟3个方面验证,定量揭示坡面细沟侵蚀及形态演化过程的可行性。[结果](1)三维实景模型地理配准均方根误差RMSE_(3D)=1.5 cm,像控点平面误差RMSE_(H)=0.42 cm,高程误差RMSE_(V)=0.88 cm,模型细节及纹理清晰,分辨率达到毫米级。(2)多期模型能够清晰刻画细沟发育经历的雨滴溅蚀—片蚀—小跌水—断续细沟—连续细沟5个阶段。坡面细沟平均沟宽、沟深、密度分别从最初的1.25 cm,0.82 cm,0.05发展到最终的3.27 cm,4.75 cm,0.23,最大沟长236 cm,最大沟深14.23 cm。(3)细沟土壤侵蚀量模拟值随着降雨历时的增加不断接近真实值并趋于稳定,平均误差在10%以内。[结论]无人机贴近摄影测量技术能较好地反映细沟发育演化过程,作业效率及便利性较传统测量方法具有显著优势。