Measuring rill erosion at plot scale by a drone‐based technology

The traditional direct method (i.e. metric ruler and rillmeter) of monitoring rill erosion at plot scale is time consuming and invasive because it modifies the surface of the rilled area. Measuring rill features using a drone‐based technology is considered a non‐invasive method allowing a fast field relief. In the experimental Sparacia area a survey by a quadricopter Microdrones md4‐200 was carried out, and this relief allowed the generation of a Digital Elevation Model (DEM), with a mesh size of 1 cm and a resolution elevation equal to 2 mm, for three plots (L, G and C) affected by rill erosion. At first for the experimental L plot, which is 44 m long, the rill features were surveyed by a ‘manual’ method which was carried out by drawing on the PC screen the rill paths obtained by a visual orthophoto interpretation. This manual method was not applicable for the plots in which rills of limited depth occurred and were not detectable. Then, for both L plot and the other experimental plots having a length ranging from 22 to 44 m, an ‘automatic’ extraction method of rills from DEM was applied. Using an appropriate calculation routine, a vector coverage of transects orthogonal to the main flow direction (i.e. the maximum slope steepness path) was generated. The intersection of each plot DEM with the transect coverage allowed to obtain both the cross sections and the main rill morphological features. For the L plot the comparison between the rill morphological features obtained by the two different methods (manual, automatic) was carried out. Finally, the length–volume relationship and a dimensionless relationship proposed in literature were tested for all studied experimental plots. Copyright © 2015 John Wiley & Sons, Ltd.     

The hydrogeomorphic influences on alluvial gully erosion along the Mitchell River fluvial megafan

Hydrogeomorphic processes influencing alluvial gully erosion were evaluated at multiple spatial and temporal scales across the Mitchell River fluvial megafan in tropical Queensland, Australia. Longitudinal changes in floodplain inundation were quantified using river gauge data, local stage recorders and HEC‐RAS modelling based on LiDAR topographic data. Intra‐ and interannual gully scarp retreat rates were measured using daily time‐lapse photographs and annual GPS surveys. Erosion was analysed in response to different water sources and associated erosion processes across the floodplain perirheic zone, including direct rainfall, infiltration‐excess runoff, soil‐water seepage, river backwater and overbank flood inundation. The frequency of river flood inundation of alluvial gullies changed longitudinally according to river incision and confinement. Near the top of the megafan, flood water was contained within the macrochannel up to the 100‐year recurrence interval, but river backwater still partially inundated adjacent gullies eroding into Pleistocene alluvium. In downstream Holocene floodplains, inundation of alluvial gullies occurred beyond the 2‐ to 5‐year recurrence interval and contributed significantly to total annual erosion. However, most gully scarp retreat at all sites was driven by direct rainfall and infiltration‐excess runoff, with the 24‐h rainfall total being the most predictive variable. The remaining variability can be explained by seasonal vegetative conditions, complex cycles of soil wetting and drying, tension crack development, near‐surface pore‐water pressure, soil block undermining from spalling and overland flow, and soil property heterogeneity. Implications for grazing management impacts on soil surface and perennial grass conditions include effects on direct rainfall erosion, water infiltration, runoff volume, water concentration along tracks, and the resistance of highly dispersible soils to gully initiation or propagation under intense tropical rainfall. Copyright © 2012 John Wiley & Sons, Ltd.     

内蒙古准格尔旗丘陵沟壑区退耕还林(草)模式

根据准格尔旗的自然环境特点,社会经济状况,以及水土流失及沙漠化灾害的特点,总结出适用上述条件下的退耕还林(草)的几种模式,恢复生态,发展经济。     

岷江上游大白杨沟泥石流特征及成因

大白杨沟流域位于岷江上游四川省茂县境内,处于叠溪镇较场山字型构造北端。该沟曾于1935年和1991年暴发过两次较大规模泥石流灾害,其中1935年暴发的泥石流受1933年叠溪7.5级地震影响,规模很大,其泥石流峰值流量达到557 m3/s。通过对大白杨沟流域两条支沟(小沟、大沟)的地形条件、水源条件及物源条件的特征分析,得出两条支沟具有形成泥石流的充分条件:(1)大沟沟道平均纵比降275‰,小沟为398‰,相对高差达2 023 m;(2)大沟拥有的物源总量为29.21万m3,小沟达到42.01万m3,物源丰富。这些条件很好地解释了小沟泥石流的强活动性。对后期泥石流的形成机制进行分析,大沟以"消防水管效应"形成泥石流为主,小沟则以"消防水管效应"和堰塞体溃决两种方式形成泥石流。最后,通过泥痕法还原了历史泥石流流量,并对后期泥石流流量做了较合理的预测,为大白杨沟泥石流灾害防治提供可靠的数据。     

矿山泥石流沟谷形态的分形分维

以2个区域的矿山泥石流为背景,利用分形理论分析了矿山泥石流沟谷形态特征,并与4个区域的自然泥石流沟谷形态进行比较研究。沟谷形态的分形维数具有相同的地学意义:维数越小,该要素对沟道及泥石流的发育和形成的影响越大。沟道比降、汇水面积和沟道长度3个沟谷形态要素中,汇水面积影响最为显著;但矿山泥石流沟谷具有汇水面积少、沟谷尺度小,沟谷比降陡的特点;在此基础上提出了自然—矿山型泥石流的概念。     

硬岩裂纹起裂强度和损伤强度取值方法探讨

岩石裂纹起裂强度σci和损伤强度σcd的研究对探讨岩石渐进破坏过程和脆性破坏机制,建立岩石的起裂强度和长期强度准则具有重要意义。鉴于此,系统总结了岩石起裂强度和损伤强度的4种计算方法,包括裂纹应变模型计算法,声发射参数取值法,侧向应变、体积应变曲线观察法和移动点回归法,并以大理岩和花岗岩在单轴压缩条件下为例,详细描述了用不同方法计算σci和σcd时存在的问题。研究结果表明,裂纹应变模型法物理意义明确,可以方便和准确地确定岩石的σci和σcd;声发射撞击率可以定性或半定量了解岩石的渐进破坏和损伤过程,但无法准确定量确定σci和σcd;移动点回归法计算体积应变刚度时受取值点间隔影响较大,而且加载过程中不同阶段的特征并不明显,难以确定起裂强度值。研究结论可为加深对岩石裂纹起裂强度和损伤强度的重要意义的认识,了解两个强度值的计算方法并合理选取其计算方法提供有益的参考。     

Origin of the Zedang and Luobusa Ophiolites,Tibet

The Zedang and Luobusa ophiolites are located in the eastern section of the Yalung Zangbo ophiolite belt,and they share similar geological tectonic setting and age.Thus,an understanding of their origins is very important for discussion of the evolution of the Eastern Tethys Ocean.There is no complete ophiolite assemblage in the Zedang ophiolite.The Zedang ophiolite is mainly composed of mantle peridotite and a suite of volcanic rocks as well as siliceous rocks,with some blocks of olivinepyroxenite.The mantle peridotite mainly consists of Cpx-harzburgite,harzburgite,some lherzolite,and some dunite.A suite of volcanic rocks is mainly composed of caic-aikaline pyroclastic rocks and secondly of tholeiitic pillow lavas,basaltic andesites,and some boninitic rocks with a lower TiO2 content （TiO2 ＜ 0.6％）.The pyroclastic rocks have a LREE-enriched REE pattern and a LILE-enriched （compared to HFSE） spider diagram,demonstrating an island-arc origin.The tholeiitic volcanic rock has a LREE-depleted REE pattern and a LILE-depleted （compared to HFSE） spider diagram,indicative of an origin from MORB.The boninitic rock was generated from fore-arc extension.The Luobusa ophiolite consists of mantle peridotite and mafic-ultramaflc cumulate units,without dike swarms and volcanic rocks.The mantle peridotite mainly consists of dunite,harzburgite with low-Opx （Opx ＜ 25％）,and harzburgite （Opx ＞ 25％）,which can be divided into two facies belts.The upper is a dunite-harzburgite （Opx ＜ 25％） belt,containing many dunite lenses and a large-scale chromite deposit with high Cr203; the lower is a harzburgite （Opx ＞25％） belt with small amounts of dunite and lherzolite.The Luobusa mantle peridotite exhibits a distinctive vertical zonation of partial melting with high melting in the upper unit and low melting in the lower.Many mantle peridotites are highly depleted,with a characteristic U-shaped REE pattern peculiar to fore-arc peridotite.The Luobusa cumulates are composed of wehrlite and olivine-pyroxenite,of the P-P-G ophiolite series.This study indicates that the Luobusa ophiolite was formed in a fore-arc basin environment on the basis of the occurrence of highly depleted mantle peridotite,a high-Cr2O3 chromite deposit,and cumulates of the P-P-G ophiolite series.We conclude that the evolution of the Eastern Tethys Ocean involved three stages：the initial ocean stage （formation of MORB volcanic rock and dikes）,the forearc extension stage （formation of high-Cr203 chromite deposits and P-P-G cumulates）,and the islandarc stage （formation of caic-alkaline pyroclastic rocks）.     

基于指数滤波法估算沟道根区土壤水分

为更加有效获取黄土高原沟道地形根区土壤水分信息,基于表层（0~20cm）土壤水分观测值,采用指数滤波法在样带和沟道尺度对根区（20~80cm）土壤水分进行估算。结果表明,指数滤波法能够较准确估算沟道根区土壤水分,但随着土层深度增加估算误差逐渐增大。当有根区土壤水分初始值时,估算精度明显提高,但主要集中在时间序列前期。指数滤波法关键参数特征时长T的最优值（T_opt）随土层深度增加而增大,呈现每增加20cm,T_opt值较20~40cm增加1倍的变化规律。对于根区某一土层,不同空间位置（样带）和尺度T_opt交换使用没有明显降低土壤水分估算精度,表明指数滤波法对T_opt的空间敏感性较弱。需注意黄土高原区域尺度土壤性质具有极强空间异质性,指数滤波法在更大尺度上对T_opt的敏感性需进一步深入研究。     

陕北黄土高原水蚀沟谷多维度侵蚀特征量化研究

沟谷地是黄土高原地貌形态特征变化最明显的区域,其发育对整个黄土高原地貌发育具有重要的控制性作用。论文基于5 m分辨率的DEM数据,在陕北黄土高原遴选包含15种地貌类型的42个样区,以沟谷密度、水平逼近度与切割深度作为纵向、横向与垂向3个维度的代表因子,分析了沟谷的多维发育进程、特征、空间分异及影响因素。研究结果显示：陕北黄土高原南北方向上沟谷发育呈现由溯源侵蚀主导转向横向溯源侵蚀主导、溯源下切侵蚀主导到横向溯源侵蚀主导,54.8%的样区各维度对整体发育进程的影响程度相近,且86.4%处于陕北黄土高原中部地区,即中部地区多维度发育均衡,南北两端以溯源侵蚀与横向侵蚀为主。结合面积—高程积分分析发现沟谷发育可划分为3个阶段：发育初期以溯源侵蚀为主,带动下切侵蚀伴有横向侵蚀;发育中期以溯源侵蚀为主,伴有持续性横向侵蚀与较强下切侵蚀;发育晚期以横向侵蚀为主,伴有一定程度的溯源侵蚀与轻微下切侵蚀。黄土厚度对沟谷系统垂向下切侵蚀的影响最大(Cv=0.164),土地利用类型对沟谷系统横向侵蚀的影响较大(Cv=0.0681),林地对于维护各个维度的抗侵蚀能力最强,生长茂密的草地和灌木林及作物次之,生长稀疏的牧草和作物较差。     

Rehabilitation effects on gully sediment yields and vegetation in a savanna rangeland

Gully rehabilitation can contribute to catchment management by stabilizing erosion and reducing downstream sediment yields, yet the globally observed responses are variable. Developing the technical basis for gully rehabilitation and establishing guidelines for application requires studies that evaluate individual rehabilitation measures in specific environments. An eight-year field experiment was undertaken to evaluate sediment yield and vegetation responses to several gully rehabilitation measures. The rehabilitation measures aimed to reduce surface runoff into gully head cuts, trap sediment on gully floors and increase vegetation cover on gully walls and floors. The study occurred in a savanna rangeland in northeast Australia. Two gullies were subject to treatments while four gullies were monitored as untreated controls. A runoff diversion structure reduced headcut erosion from 4.3 to 1.2 m² yr⁻¹. Small porous check dams and cattle exclusion reduced gully total sediment yields by more than 80%, equivalent to a reduction of 0.3 to 2.4 t ha⁻¹ yr⁻¹, but only at catchment areas less than 10 ha. Fine sediment yields (silt and clay) were reduced by 7 and 19% from the two treated gullies, respectively. The porous check dam deposits contained a lower percentage of the fine fraction than the parent soil. Significant regeneration of gully floor vegetation occurred, associated with trapping of organic litter and fine sediment. Increases in vegetation cover and biomass were comprised of native perennial grasses, trees and shrubs. In variable climates, long-term gully rehabilitation will progress during wetter periods, and regress during droughts. Understanding linkages between rehabilitation measures, their hydrologic, hydraulic and vegetation effects and gully sediment yields is important to defining the conditions for their success.