鄂尔多斯高原清代风灾     

罗小庆  赵景波 《中国沙漠》2016,36(3):787-791

根据历史文献资料,利用数理统计等方法研究了鄂尔多斯高原清代的风灾。结果表明:鄂尔多斯高原清代发生风灾51次,平均每5.3 a发生1次。其中轻度风灾16次、中度风灾34次、大风灾1次,分别占风灾总数的31.3%、66.7%、2.0%。研究区清代风灾变化可分为3个阶段。第1阶段为1644-1783年,发生风灾24次,平均每5.8 a发生1次,为风灾频次居中的多发阶段。第2阶段为1784-1843年,发生风灾4次,平均每15 a发生1次,为风灾频次最少的低发阶段。第3阶段为1844-1911年,发生风灾23次,平均每3.0 a发生1次,为风灾频次最高的多发阶段。从清代早期到晚期,鄂尔多斯高原风灾频次呈上升趋势。鄂尔多斯高原清代有4次风灾爆发期,分别为公元1708-1710年、1851-1853年、1878-1884年和1908-1910年。在1878-1910年间有2次风灾爆发期,对应于中国东部和北半球的低温期。鄂尔多斯高原清代风灾有6 a左右的短周期和23 a左右的长周期,其中23 a的周期是第一主周期。该区风灾发生的主要原因是强冬季风的活动,在气候寒冷期或干旱期发生频率较高。  相似文献   

不同砾石覆盖度戈壁床面风蚀速率定量模拟   总被引：2，自引：2，他引：0  

谭立海  张伟民  屈建军  殷代英  安志山  边凯 《中国沙漠》2016,36(3):581-588

通过风洞实验,利用称重传感器自动记录风蚀观测样方重量变化过程,对供沙条件下不同砾石覆盖度戈壁床面风蚀速率进行了定量模拟研究。结果表明:砾石覆盖度是影响戈壁风蚀速率的关键因子,戈壁床面风蚀速率随砾石覆盖度增加按指数规律递减。各实验风速下,砾石覆盖度>50%时,戈壁床面风蚀速率随砾石覆盖度增加而减小量有限,甚至无风蚀发生;而盖度从10%到50%时,风蚀速率显著减小。因此,两种实验粒径砾石(3 cm与4 cm)至少在50%盖度时才能达到较好的风蚀防治效果。戈壁风蚀防护机理主要是砾石覆盖度的增加增大了砾石间沙粒的临界起动剪切风速,而且减少了作用在砾石间可蚀地表的剪切压。与沙质对照床面相比,10%~90%砾石盖度戈壁床面沙粒临界起动剪切风速增大了0.8~3.4倍,只有0.5％~28%的剪切压作用在砾石间可蚀地表。  相似文献   

内蒙古中部四子王旗大庙岩体时代及成因   总被引：21，自引：8，他引：13  

章永梅  张华锋  刘文灿  周志广 《岩石学报》2009,25(12):3165-3181

华北北缘的内蒙古中部地区出露大量晚古生代-早中生代花岗岩类,在空间上构成一条巨大的东西向花岗岩带.四子王旗大庙岩体作为一个典型的代表,以花岗闪长岩为主,其内部普遍发育暗色微粒包体(MMEs),是认识花岗岩岩石成因和演化的关键.本文对包体及寄主岩进行了同位素测年、岩相学、矿物化学、全岩主量元素和微量元素分析.寄主岩石中的锆石LA-ICPMS U-Pb年龄平均为265±7Ma(2σ),包体中单颗粒黑云母Rb-Sr年龄为253±5Ma(MSWD=0.85),属晚二叠世-早三叠世岩浆活动的产物.包体具塑性外形及岩浆结构,存在多种不平衡矿物组合;MME中的斜长石An组分及黑云母斑晶中MgO成分呈多期震荡,同时总体上均显示出幔部高于核、边部的特征,暗示斑晶可能为围岩捕虏晶,这种相似的成分变化指示包体与寄主岩相互作用引起的结晶环境改变,标志着岩浆成分的变化,是岩浆混合的标志之一;主量和微量数据进一步证明岩体的岩浆混合成因.Rb/Sr-K/Rb变化关系反映包体非结晶分异或黑云母堆晶的产物,而Ce/Pb-Ce、Ba-δEu和P_2O_5-δEu图及其他微量元素比值图等均表明花岗闪长岩体发生了岩浆混合作用,这也得到岩浆物理化学条件的支持.岩浆底侵和岩浆混合作用是该区岩体形成的主要机制和方式.岩石地球化学特征表明该岩体不同于加厚地壳和俯冲洋壳熔融的TTG和埃达克质岩石,而黑云母矿物化学和岩石地球化学显示其构造背景很可能为同碰撞环境.  相似文献   

CMW工法在隧道基坑支护工程中的应用          下载免费PDF全文

柳孝荣  罗兴 《探矿工程》2009,36(3):60-62

在南京市城市快速内环北线二期隧道基坑支护工程的粉细砂复杂地层中首次成功应用了CMW工法,与钻孔灌注桩、钢板桩、地下连续墙、土钉墙和SMW工法等相比,具有污染小、造价低、速度快和施工质量好等优点。结合该工程实例,介绍了CMW工法施工的优点、工艺流程、设备选择、施工方法、安全管理要求和使用效果等。  相似文献   

Research on wind-induced responses of a large-scale membrane structure   总被引：1，自引：1，他引：0  

Zhou Xuanyi  Han Zhihui  Gu Ming  Zhang An-an  Zhang Weiyu  Fang Wei 《地震工程与工程振动(英文版)》2013,12(2):297-305

The wind-induced responses of a large-scale membrane structure, Expo Boulevard, are evaluated in this study. To obtain the wind pressure distribution on the roof surface, a wind tunnel test is performed. A brief analysis of wind pressure on the membrane roof is conducted first and then an analysis of the wind-induced responses of the structure is carried out using a numerical integral method in the time domain. In the process of calculation, the geometrical nonlinearity is taken into account. Results indicate that mean, RSM and peak values of the structure responses increase nonlinearly while the approaching flow velocity increases. Strong nonlinear characteristics are observed in the displacement responses, whereas the responses of nodal stress and cable axial force show minimal nonlinear properties when the membrane structure is subjected to wind loads. Different values of the damping ratio only have a minimal impact on the RSM response of the structure because the background component is a dominant part of the total dynamic response and the resonant component is too small. As the damping ratio increases from 0.02 to 0.05, the RMS responses of vertical displacement, nodal stress and cable axial force decrease by 8.1%, 6.7% and 17.9%, respectively. Since the mean component plays a significant role in the wind-induced response, the values of the gust response factor are not high for Expo Boulevard.  相似文献   

Trend analysis of reference evapotranspiration in Northwest China: The roles of changing wind speed and surface air temperature   总被引：2，自引：0，他引：2  

Xiaomang Liu  Dan Zhang 《水文研究》2013,27(26):3941-3948

Reference evapotranspiration (ET₀) is an important element in the water cycle that integrates atmospheric demands and surface conditions, and analysis of changes in ET₀ is of great significance for understanding climate change and its impacts on hydrology. As ET₀ is an integrated effect of climate variables, increases in air temperature should lead to increases in ET₀. However, this effect could be offset by decreases in vapor pressure deficit, wind speed, and solar radiation which lead to the decrease in ET₀. In this study, trends in the Penman–Monteith ET₀ at 80 meteorological stations during 1960–2010 in the driest region of China (Northwest China) were examined. The results show that there was a change point for ET₀ series around the year 1993 based on the Pettitt's test. For the region average, ET₀ decreased from 1960 to 1993 by ?2.34 mm yr^?2, while ET₀ began to increase since 1994 by 4.80 mm yr^?2. A differential equation method based on the Food and Agriculture Organization Penman–Monteith formula was used to attribute the change in ET₀. The attribution results show that the significant decrease in wind speed dominated the change in ET₀, which offset the effect of increasing air temperature and led to the decrease in ET₀ from 1960 to 1993. However, wind speed began to increase, and the amplitude of increase in air temperature also rose significantly since the mid‐1990s. Increases in air temperature and wind speed together reversed the trend in ET₀ and led to the increase in ET₀ since 1994. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Soil organic carbon enrichment of dust emissions: magnitude,mechanisms and its implications for the carbon cycle     

Nicholas P. Webb  Craig L. Strong  Adrian Chappell  Samuel K. Marx  Grant H. McTainsh 《地球表面变化过程与地形》2013,38(14):1662-1671

Soil erosion is an important component of the global carbon cycle. However, little attention has been given to the role of aeolian processes in influencing soil organic carbon (SOC) flux and the release of greenhouse gasses, such as carbon dioxide (CO₂), to the atmosphere. Understanding the magnitude and mechanisms of SOC enrichment in dust emissions is necessary to evaluate the impact of wind erosion on the carbon cycle. This research examines the SOC content and enrichment of dust emissions measured using Big Spring Number Eight (BSNE) wind‐vane samplers across five land types in the rangelands of western Queensland, Australia. Our results show that sandy soils and finer particulate quartz‐rich soils are more efficient at SOC emission and have larger SOC dust enrichment than clay‐rich aggregated soils. The SOC enrichment ratios of dusts originating from sites with sand‐rich soil ranged from 2·1–41·9, while the mean enrichment ratio for dusts originating from the clay soil was 2·1. We hypothesize that stronger inter‐particle bonds and the low grain density of the aggregated clay soil explain its reduced capacity to release SOC during saltation, relative to the particulate sandy soils. We also show that size‐selective sorting of SOC during transport may lead to further enrichment of SOC dust emissions. Two dust samples from regional transport events were found to contain 15–20% SOC. These preliminary results provide impetus for additional research into dust SOC enrichment processes to elucidate the impact of wind erosion on SOC flux and reduce uncertainty about the role of soil erosion in the global carbon cycle. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Spatial and temporal dust source variability in northern China identified using advanced remote sensing analysis   总被引：1，自引：0，他引：1  

A. Taramelli  M. Pasqui  J. Barbour  D. Kirschbaum  L. Bottai  C. Busillo  F. Calastrini  F. Guarnieri  C. Small 《地球表面变化过程与地形》2013,38(8):793-809

The aim of this research is to provide a detailed characterization of spatial patterns and temporal trends in the regional and local dust source areas within the desert of the Alashan Prefecture (Inner Mongolia, China). This problem was approached through multi‐scale remote sensing analysis of vegetation changes. The primary requirements for this regional analysis are high spatial and spectral resolution data, accurate spectral calibration and good temporal resolution with a suitable temporal baseline. Landsat analysis and field validation along with the low spatial resolution classifications from MODIS and AVHRR are combined to provide a reliable characterization of the different potential dust‐producing sources. The representation of intra‐annual and inter‐annual Normalized Difference Vegetation Index (NDVI) trend to assess land cover discrimination for mapping potential dust source using MODIS and AVHRR at larger scale is enhanced by Landsat Spectral Mixing Analysis (SMA). The combined methodology is to determine the extent to which Landsat can distinguish important soils types in order to better understand how soil reflectance behaves at seasonal and inter‐annual timescales. As a final result mapping soil surface properties using SMA is representative of responses of different land and soil cover previously identified by NDVI trend. The results could be used in dust emission models even if they are not reflecting aggregate formation, soil stability or particle coatings showing to be critical for accurately represent dust source over different regional and local emitting areas. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Vertical velocity distributions through and above submerged,flexible vegetation     

《水文科学杂志》2013,58(4):905-920

Abstract

A one-dimensional steady-state model was constructed and used to study vertical profiles of longitudinalvelocities in open channel flows through, and above, submerged vegetation. The eddy viscosity was evaluated by using the analogue of the mixing length theory. The model of water velocity profiles takes into account the surface roughness of the channel bottom and the drag exerted by submerged flexible stems. The verification of the calculated velocity profiles was carried out based on data obtained in laboratory experiments. The proportionality coefficients for the analogue of the mixing length formulae in both layers—within homogenous flexible stems and above them—were determined.  相似文献   

Use of artificial flood events to demonstrate the invalidity of simple mixing models / Utilisation de crues artificielles pour prouver l'invalidité des modèles de mélange simple     

ANDREAS KREIN  RENAAT DE SUTTER 《水文科学杂志》2013,58(4):611-622

Abstract

The whole of a basin responds to a precipitate on event. The resulting flood wave introduces a complex pattern of interrelated processes which occur in the vegetation, soil, bedrock, human facilities, channel and in the different parts of the basin. The main advantage of field experiments is that it becomes possible to exclude several governing factors or sources and to control others by the experimental design. In a small brook near Trier (Germany), artificial flood events are created. In-channel transport processes of sediment are investigated without taking into account the interference of soil erosion and runoff. It is demonstrated that kinematic waves-describing the translation of flow with limited hydraulic dispersion or diffusion-also occur in small basins. The kinematic waves-travelling only a few hundred meters-have a large impact on the relationship between the hydrograph and dissolved or particle-bound substances. Consequently, classifications and simple mixing models between those components are impeded.  相似文献