Sedimentary architecture of submarine channel-lobe systems under different seafloor topography:Insights from the Rovuma Basin offshore East Africa

Seafloor topography plays an important role in the evolution of submarine lobes.However,it is still not so clear how the shape of slope affects the three-dimensional(3-D)architecture of submarine lobes.In this study,we analyze the effect of topography factors on different hierarchical lobe architectures that formed during Pliocene to Quaternary in the Rovuma Basin offshore East Africa.We characterize the shape,size and growth pattern of different hierarchical lobe architectures using 3-D seismic data.We find that the relief of the topographic slope determines the location of preferential deposition of lobe complexes and single lobes.When the topography is irregular and presents topographic lows,lobe complexes first infill these depressions.Single lobes are deposited preferentially at positions with higher longitudinal(i.e.across-slope)slope gradients.As the longitudinal slope becomes higher,the aspect ratio of the single lobes increases.Lateral(i.e.along-slope)topography does not seem to have a strong influence on the shape of single lobe,but it seems to affect the overlap of single lobes.When the lateral slope gradient is relatively high,the single lobes tend to have a larger overlap surface.Furthermore,as the average of lateral slope and longitudinal slope gets greater,the width/thickness ratio of the single lobe is smaller,i.e.sediments tend to accumulate vertically.The results demonstrate that the shape of slopes more comprehensively influences the 3-D architecture of lobes in natural deep-sea systems than previously other lobe deposits and analogue experiments,which helps us better understand the development and evolution of the distal parts of turbidite systems.

Aerodynamic performance analysis of trains on slope topography under crosswinds

This work used the computational fluid dynamics method combined with full-scale train tests to analyze the train aerodynamic performance on special slope topography. Results show that with the increment in the slope gradient, the aerodynamic forces and moment increase sharply. Compared with the flat ground condition, the lateral force, lift force, and overturning moment of the train on the first line increase by 153.2%, 53.4% and 124.7%, respectively, under the slope gradient of 20°. However, with the increment of the windward side's depth, the windbreak effect is improved obviously. When the depth is equal to 10 m, compared with the 0 m, the lateral force, lift force and overturning moment of the train on the first line decrease by 70.9%, 77.0% and 70.6%,respectively. Through analyzing the influence of slope parameters on the aerodynamic performance of the train, the relationships among them are established. All these will provide a basic reference for enhancing train aerodynamic performances under different slope conditions and achieve reasonable train speeds for the operation safety in different wind environments.

New Method for Estimating Daily Global Solar Radiation over Sloped Topography in China

A new scheme for the estimation of daily global solar radiation over sloped topography in China is developed based on the Iqbal model C and MODIS cloud fraction. The effects of topography are determined using a digital elevation model. The scheme is tested using observations of solar radiation at 98 stations in China, and the results show that the mean absolute bias error is 1.51 MJ m-2 d-1 and the mean relative absolute bias error is 10.57%. Based on calculations using this scheme, the distribution of daily global solar radiation over slopes in China on four days in the middle of each season （15 January, 15 April, 15 July and 15 October 2003） at a spatial resolution of 1 km×1 km are analyzed. To investigate the effects of topography on global solar radiation, the results determined in four mountains areas （Tianshan, Kunlun Mountains, Qinling, and Nanling） are discussed, and the typical characteristics of solar radiation over sloped surfaces revealed. In general, the new scheme can produce reasonable characteristics of solar radiation distribution at a high spatial resolution in mountain areas, which will be useful in analyses of mountain climate and planning for agricultural production.

Numerical Simulation of Non-Linear Wave Propagation in Waters of Mildly Varying Topography with Complicated Boundary

In this paper, the characteristics of different forms of mild slope equations for non-linear wave are analyzed, and new non-linear theoretic models for wave propagation are presented, with non-linear terms added to the mild slope equations for non-stationary linear waves and dissipative effects considered. Numerical simulation models are developed of non-linear wave propagation for waters of mildly varying topography with complicated boundary, and the effects are studied of different non-linear corrections on calculation results of extended mild slope equations. Systematical numerical simulation tests show that the present models can effectively reflect non-linear effects.

Slope Instability Analysis of the Qiongdongnan Basin in the Northern Part of the South China Sea:Implications for the Risk Evaluation of Deepwater Drilling

The instability of continental slopes damages marine engineering equipment,such as submarine pipelines,resulting in the generation of tsunamis,which endangers the safety of nearshore personnel.Therefore,research on the instability of continental slopes where submarine landslides usually occur is crucial to the risk evaluation of deepwater drilling.Previous studies were mainly based on simplified 2D and 3D models,which extend the 2D model applied on submarine slopes with complex topography.In this study,a numerical model with bathymetric data from the Qiongdongnan Basin was established.Furthermore,3D slope stability analysis and static and dynamic analyses were conducted.The static analysis found two discussions where slopes are most likely to occur.Through the analysis of different seismic forces,the dynamic result showed that an instability area is added to the two positions where the static analysis is unstable.Topography scatters and transmits seismic waves and controls the accumulation and diffusion of seismic energy.3D calculations and analysis revealed that the direction of slope instability is closely related to terrain inclination,slope,terrain effect,and terrain curvature.Data showed that instability situations could not be derived from a single direction or profile data.Such situations are an important factor in slope stability analysis and are critical to the prediction and evaluation of marine geological disasters.

东沙海域上坡波导声传播实验及其特性分析

针对上坡波导环境对水声传播的影响,在东沙海域开展海上声传播实验,观测到了斜坡顶端声能量急剧下降的现象。通过建立实际波导环境模型,利用抛物方程理论计算声传播损失,验证了斜坡环境对声传播的影响,并利用射线方法对声能量急剧下降机理进行了讨论和分析。结果表明:声波在声速负梯度环境上坡传播过程中,受声源深度、斜坡坡度、斜坡水平距离和海底声速的综合影响,有效传播至斜坡顶端的声能存在显著差异。声源深度越浅、斜坡坡度越大、海底纵波声速越低,传播至斜坡顶端的声能量越弱;此外,与水平波导相比,斜坡波导的水平距离增加同样会加剧声能的衰减。

露天矿台阶对高密度电法勘探影响的实验研究

露天矿边坡稳定性评估是预防边坡事故发生的基本手段之一,物探结论一直作为重要依据被广泛采纳。在露天矿台阶上进行高密度电法勘探时,为研究台阶对勘探结果的影响,本文进行了水槽相似材料模拟实验,研究了待测剖面内的电流场分布。实验结果显示:待测剖面中靠近上下坡面线及清扫平台宽度线的浅部位置电流密度大,且分布均匀;中部位置电流密度变化急剧,且电流密度等高线的形状与台阶形状相似;深部位置电流密度小,变化迟缓;待测剖面上靠近坡底线的位置出现明显的电流聚集效应,台阶地形下的电流密度比在平面地形下的电流密度大,且分布不均匀。这表明应用高密度电法实测时,露天矿台阶会导致中部位置和靠近坡底线位置处的反演成果异常。

山区缓坡堆积体滑坡治理实例分析

文中以某山区高速公路所在的缓坡堆积体滑坡治理为例,结合地质勘察及倾斜摄影、深部位移监测等手段综合分析滑坡范围、变形特性及滑面位置,再结合室内试验和工程类比,综合分析岩土体的参数,利用不平衡推力法进行稳定性分析及滑坡推力计算,最终通过分期治理,使滑坡得到了有效控制。

Effect of Lithology and Structure on Seismic Response of Steep Slope in a Shaking Table Test

Studies on landslides by the 2008 Wenchuan earthquake showed that topography was of great importance in amplifying the seismic shaking, and among other factors, lithology and slope structure controlled the spatial occurrence of slope failures. The present study carried out experiments on four rock slopes with steep angle of 60° by means of a shaking table. The recorded Wenchuan earthquake waves were scaled to excite the model slopes. Measurements from accelerometers installed on free surface of the model slope were analyzed, with much effort on timedomain acceleration responses to horizontal components of seismic shaking. It was found that the amplification factor of peak horizontal acceleration, RPHA, was increasing with elevation of each model slope, though the upper and lower halves of the slope exhibited different increasing patterns. As excitation intensity was increased, the drastic deterioration of the inner structure of each slope caused the sudden increase of RPHA in the upper slope part. In addition, the model simulating the soft rock slope produced the larger RPHA than the model simulating the hard rock slope by a maximum factor of 2.6. The layered model slope also produced the larger RPHA than the homogeneous model slope by a maximum factor of 2.7. The upper half of a slope was influenced more seriously by the effect of lithology, while the lower half was influenced more seriously by the effect of slope structure.

Non-linear Dynamics of Inlet Film Thickness during Unsteady Rolling Process

The inlet film thickness directly affects film and stress distribution of rolling interfaces. Unsteady factors, such as unsteady back tension, may disturb the inlet film thickness. However, the current models of unsteady inlet film thickness lack unsteady disturbance factors and do not take surface topography into consideration. In this paper, based on the hydrodynamic analysis of inlet zone an unsteady rolling film model which concerns the direction of surface topography is built up. Considering the small fluctuation of inlet angle, absolute reduction, reduction ratio, inlet strip thickness and roll radius as the input variables and the fluctuation of inlet film thickness as the output variable, the non-linear relationship between the input and output is discussed. The discussion results show that there is 180° phase difference between the inlet film thickness and the input variables, such as the fluctuant absolute reduction, the fluctuant reduction ratio and non-uniform inlet strip thickness, but there is no phase difference between unsteady roll radius and the output. The inlet angle, the steady roll radius and the direction of surface topography have significant influence on the fluctuant amplitude of unsteady inlet film thickness. This study proposes an analysis method for unsteady inlet film thickness which takes surface topography and new disturbance factors into consideration.

Spatial Variability of Soil Organic Carbon in Different Hillslope Positions in Toshan Area, Golestan Province, Iran: Geostatistical Approaches

Accessibility to organic carbon(OC) budget is required for sustainable agricultural development and ecosystem preservation and restoration. Using geostatistical models to describe and demonstrate the spatial variability of soil organic carbon(SOC) will lead to a greater understanding of this dynamics. The aim of this paper is to present the relationships between the spatial variability of SOC and the topographic features by using geostatistical methods on a loess mountain-slope in Toshan region, Golestan Province, northern Iran. Hence, 234 soil samples were collected in a regular grid that covered different parts of the slope. The results showed that such factors as silt, clay, saturated moisture content, mean weighted diameter(MWD) and bulk density were all correlated to the OC content in different slope positions, and the spatial variability of SOC more to slope positions and elevations. The coefficient of variation(CV) indicated that the variability of SOC was moderate in different slope positions and for the mountain-slope as a whole. However, the higher variability of SOC(CV = 45.6%) was shown in the back-slope positions. Also, the ordinary cokriging method for clay as covariant gave better results in evaluating SOC for the whole slope with the RMSE value 0.2552 in comparison with the kriging and the inverse distance weighted(IDW) methods. The interpolation map of OC for the slope under investigation showed lowering SOC concentrations versus increasing elevation and slope gradient. The spatial correlation ratio was different between various slope positions and related to the topographic texture.

Low-Frequency Waves Forced by Large-scale Topography in the Barotropic Model

A barotropic model containing large-scale topography and zonal mean flow is established to discuss the effects of large-scale topography on the low-frequency waves. The results show that what affects low-frequency waves mostly is maximal height of topography and topographic slope. The former makes frequency of topographic Rossby waves decrease, the latter makes Rossby waves instable. Moreover, when topographic slope is appropriate, it can also make Rossby waves turn into low-frequency waves.

Effect of Point Cloud Data Simplification and Encryption on Micro-Topography Data Analysis

Simplification and encryption are performed on the point cloud data concerning high-relief( 20 cm tillage) and low-relief( raking bare slope) terrain on a different scale of observation. We select three indicators( surface curvature,slope aspect and surface roughness) to evaluate the effect of simplification and encryption on micro-topography data analysis. The results show that simplification and encryption have a significant impact on the curvature of high-relief terrain,but have no significant impact on low-relief terrain. The slope aspect change is not significant after 5,10 mm data simplification and encryption; 1 mm simplification has a regular impact on surface roughness; 5 mm encryption and simplification have a complex impact on high-relief terrain; 10 mm encryption has a complex impact on high-relief terrain roughness change but a regular impact on bare slope change.

An Analytical Solution for Wave Transformation Over Axi-Symmetric Topography

The present study considers wave scattering phenomena around a cylindrical island mounted on a general axisymmetric topography or a general submerged truncated axi-symmetric shoal based on the mild-slope equation. The method of separation of variables and Taylor series expansion are invoked to find the approximate solution to the variable water depth region which varies proportionally to an arbitrary power of radial distance. Validations against the solutions for the combined wave refraction and diffraction around a cylindrical island mounted on a paraboloidal shoal of Liu et al. in 2004 and the scattering and trapping of wave energy by a submerged truncated paraboloidal shoal of Lin and Liu in 2007 show excellent agreements as the power of radial distance being equal to two. For the solutions of wave refraction and diffraction around a cylindrical island mounted on a shoal with depth proportionally to an arbitrary power of radial distance, good agreements with Zhai et al.’s(2013) solutions are demonstrated. Since the robustness of the assumption of a general axi-symmetric geometry based on an arbitrary power variability of the radial distance, the present solution can be very conveniently employed to investigate the effects of bottom topography on wave scattering and trapping patterns.

EXTENDED MILD-SLOPE EQUATION

The Hamiltonian formalism for surface waves and the mild-slope approximation were empolyed in handling the case of slowly varying three-dimensional currents and an uneven bottom, thus leading to an extended mild-slope equation. The bottom topography consists of two components: the slowly varying component whose horizontal length scale is longer than the surface wave length, and the fast varying component with the amplitude being smaller than that of the surface wave. ne frequency of the fast varying depth component is, however, comparable to that of the surface waves. The extended mild-slope equation is more widely applicable and contains as special cases famous mild-slope equations below: the classical mild-slope equation of Berkhoff, Kirby's mild-slope equation with current, and Dingemans's mild-slope equation for rippled bed. The extended shallow water equations for ambient currents and rapidly varying topography are also obtained.

An extended time-dependent numerical model of the mild-slope equation with weakly nonlinear amplitude dispersion

In the present paper, by introducing the effective wave elevation, we transform the extended elliptic mild-slope equation with bottom friction, wave breaking and steep or rapidly varying bottom topography to the simplest time-dependent hyperbolic equation. Based on this equation and the empirical nonlinear amplitude dispersion relation proposed by Li et al. （2003）, the numerical scheme is established. Error analysis by Taylor expansion method shows that the numerical stability of the present model succeeds the merits in Song et al. （2007）＇s model because of the introduced dissipation terms. For the purpose of verifying its performance on wave nonlinearity, rapidly varying topography and wave breaking, the present model is applied to study： （1） wave refraction and diffraction over a submerged elliptic shoal on a slope （Berkhoff et al., 1982）; （2） Bragg reflection of monochromatic waves from the sinusoidal ripples （Davies and Heathershaw, 1985）; （3） wave transformation near a shore attached breakwater （Watanabe and Maruyama, 1986）. Comparisons of the numerical solutions with the experimental or theoretical ones or with those of other models （REF/DIF model and FUNWAVE model） show good results, which indicate that the present model is capable of giving favorably predictions of wave refraction, diffraction, reflection, shoaling, bottom friction, breaking energy dissipation and weak nonlinearity in the near shore zone.

地形对凉山州夏季降雨的影响研究

利用地面区域自动站降水、GMTED2010高程、ERA5再分析等资料,通过三阶反距离平方权差分、卷积计算等求出地形、降雨指标,分析凉山州夏季(5一10月)降雨、地形特征及其复杂地形对降雨的影响。结果表明:凉山州复杂地形下降雨空间分布不均匀,总降雨量1100mm以上大值区及强降雨主要分布在河谷流域,雨日100d以上的大值区主要分布在东部山区;坡向、坡度对大雨及以上量级的强降雨都有显著影响,对中雨及以下降雨影响不明显。高精度坡度、坡向地形指标有助于在凉山州这种复杂地形下更好地评估强降雨过程的雨量,提高灾害预警质量,特别是在地形多样、对降雨敏感的河谷流域作用更加明显。

青藏高原坡度坡长因子(LS)空间格局及影响因素分析

地形是影响土壤侵蚀的主要因素,但目前关于青藏高原地形因子的分布格局和影响因素有待研究。基于1弧秒分辨率的SRTM(shuttle radar topography mission)高程数据,计算坡度、坡长、LS因子(slope length and steepness factors,LS),结合高程积分和Hack剖面等,对青藏高原LS因子的分布格局、统计分布特征和影响因素进行研究,结果表明:(1)坡度、坡长和LS因子这3个地形指标,均表现出高原内部小、四周高山大的格局,内流区与外流区的坡度均值分别为6.55°和14.3°,坡长均值分别为122.9,172.2 m,LS均值分别为4.8和12.7;(2)青藏高原LS因子整体受坡度影响,但高原边缘陡峭地区LS因子主要受坡长影响;(3)青藏高原6条主要河流的Hack剖面都呈上凸形态,该地区地貌演化整体上处于幼年期;(4)青藏高原LS因子的分布特征与土壤侵蚀类型及其组合有对应关系:周边地区的高值对应冰川侵蚀—水蚀,西北部的低值对应水力—冻融侵蚀和风蚀,东南部边缘向高原内部过渡地区的较高值对应水力—重力侵蚀。通过分析LS因子的分布格局和统计特征,可为土壤侵蚀学评价提供理论和数据支撑,对于青藏高原地球系统物质迁移转换研究具有重要意义。

东北黑土区长缓坡耕地横坡垄作与地形对土壤可蚀性的交互作用

【目的】东北黑土区坡耕地土壤侵蚀日益加重,研究横坡垄作与地形对土壤可蚀性K值的交互作用,为东北黑土区坡耕地水土流失的精准防控提供科学依据。【方法】选取黑龙江省北安市红星农场内典型坡耕地为研究对象,在横坡垄作方向与顺坡水线方向共布设25个采样点,并计算相应样点的土壤可蚀性K值,采用单因素方差分析(One-wayANOVA)检验土壤可蚀性K值的差异性,并使用地理探测器模型探讨土壤可蚀性K值的影响因子及其交互作用。【结果】横坡垄作方向,土壤可蚀性K值在垄台呈现从坡顶到坡足逐渐减小的变化趋势,坡足比坡顶减小幅度为6.2%;在垄沟呈现从坡肩到坡足逐渐减小的变化趋势,坡足比坡肩减小幅度为5.8%。顺坡水线方向,由于垄台对地表径流的阻挡作用,垄台和垄沟土壤可蚀性K值沿着坡面并没有明显的变化趋势。地理探测器分析表明,横坡垄作对土壤可蚀性K值的影响最大,其垄台和垄沟的解释率分别达51%和18%以上;横坡垄作与其他因子的交互作用增强了对土壤可蚀性K值的解释能力,特别是横坡垄作与地形的交互作用尤为明显。【结论】黑土区坡耕地土壤可蚀性K值具有明显的空间变异性,横坡垄作与地形对土壤可蚀性的影响存在明显的交互作用,横坡垄作可以显著拦蓄径流,减少土壤侵蚀,但因黑土区坡耕地横坡垄作的坡缓而长,在坡足处易于汇集径流,依然有“断垄”潜在风险。

植物篱防蚀措施对三峡库区坡耕地微地形的影响

本文对位于三峡库区陡坡地4种管理模式长期试验径流小区坡面地形相关参数进行了观测、分析。结果显示,与对照小麦–花生种植模式相比,采用套种紫花苜蓿植物篱、香椿植物篱能够极著降低水土流失,坡面地形沿篱基梯级化显著。而黑麦草–籽粒苋替代模式对水土流失控制效果不稳定,且坡面地形与对照无差异。小麦–花生套种紫花苜蓿、香椿植物篱处理的坡面均形成基于篱带部的篱坎,篱坎下部侵蚀较强,篱带上淤下蚀现象明显。其中小麦–花生套种香椿植物篱小区坡面形成2级植物篱淤积坎,坎宽幅平均达到420.8cm,淤积坎相对高差为40.4cm,平均坡度下降1.4度。小麦–花生套种紫花苜蓿植物篱坡面形成4级篱坎,平均坎宽幅为210.3 cm,平均相对高度为110.6 cm,平均坡长为238.1 cm,平均坡度下降0.3度。说明坡耕地采用植物篱技术能够减蚀截淤,显著改变微地形。针对微地形的变化,套作植物篱的坡耕地在后期宜实行坡改梯或梯级坡地配套完善灌排设施,利用已优选的植物品种设计木本与草本套种的复合植物篱,有望进一步改善土体根系分布,从而稳固篱坎,控制水土流失。该研究为植物篱技术后续管理措施优化提供了参考依据。