Mechanisms of riverbank failure along the Arno River,central Italy     

Stefano Dapporto  Massimo Rinaldi  Nicola Casagli  Pietro Vannocci 《地球表面变化过程与地形》2003,28(12):1303-1323

Riverbanks along the Arno River have been investigated with the aims of de?ning the main mechanisms of failure and retreat, their spatial distribution, and their causes. Geomorphological aspects were investigated by a reconnaissance of riverbank processes, for a number (26) of representative sites. Laboratory and in situ tests were then performed on a selected number of riverbanks (15). Based on the material characteristics, six main typologies of riverbanks have been de?ned, with homogeneous ?ne‐grained and composite banks representing the most frequent types. Slab‐type failures are the most frequent mechanism observed on ?ne‐grained banks, while cantilever failures prevail on composite banks. The role of river stage and related pore water pressure distributions in triggering the main observed mechanisms of failure has been investigated using two different types of stability analysis. The ?rst was conducted for 15 riverbanks, using the limit equilibrium method and considering simpli?ed hypotheses for pore water pressure distribution (annulment of negative pore pressures in the portion of the bank between low water stage and peak stage). Stability conditions and predicted mechanisms of failure are shown to be in reasonably good agreement with ?eld observations. Three riverbanks, representative of the main alluvial reaches of the river, were then selected for a more detailed bank stability analysis, consisting of: (a) de?nition of characteristic hydrographs of the reach with different return periods; (b) modelling of saturated and unsaturated ?ow using ?nite element seepage analysis; and (c) stability analysis with the limit equilibrium method, by adopting pore water pressure values derived from the seepage analysis. The results are compared to those obtained from the previous simpli?ed analysis, and are used to investigate the different responses, in terms of stability, to different hydrological and riverbank conditions. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Observed daily large-scale rainfall patterns during BOBMEX-1999     

A. K. Mitra  M. Das Gupta  R. K. Paliwal  S. V. Singh 《Journal of Earth System Science》2003,112(2):223-232

A daily rainfall dataset and the corresponding rainfall maps have been produced by objective analysis of rainfall data. The satellite estimate of rainfall and the raingauge values are merged to form the final analysis. Associated with epochs of monsoon these rainfall maps are able to show the rainfall activities over India and the Bay of Bengal region during the BOBMEX period. The intra-seasonal variations of rainfall during BOBMEX are also seen using these data. This dataset over the oceanic region compares well with other available popular datasets like GPCP and CMAP. Over land this dataset brings out the features of monsoon in more detail due to the availability of more local raingauge stations.  相似文献   

Old inherited origin for the present near-bimodal topography of Africa     

C. Moctar Doucour  Maarten J. de Wit 《Journal of African Earth Sciences》2003,36(4):371-388

Africa’s landscape is dominated by a manifold of second-order epeirogenic structures superimposed on a first-order bimodal topography. Bivariate regression analysis of Africa’s surface topography shows that this is a complexly folded surface with regionally elevated areas in southern and eastern Africa, and a topographically low northern and western Africa. The apparent spatial relationships between these features are analysed using anomaly correlation between surface topography and free-air gravity anomalies. Occurrences of positively correlated features between gravity and topography in Africa are found to be limited to second-order epeirogenic features. Geophysical modelling and geologic evidence indicate that Africa’s bimodal topography is genetically distinct from these second-order features, and linked to sources as deep as the sublithospheric mantle. The age, measured and modelled elevation of the bimodal topography require that topographic uplift of south-central Africa be episodic. We infer from our findings together with relative sea-level changes, that the near-bimodality of Africa’s topography is an ancient feature inherited at least from upper Paleozoic times. Our reconstructed paleotopography suggests that Africa was largely a low-lying continent dominated by its cratons, and that basement distribution disregards the present-day uplift patterns of Africa.  相似文献   

中尺度自忆模式在强降水预报中的应用   总被引：2，自引：0，他引：2       下载免费PDF全文

贾晓静  封国林  曹鸿兴 《大气科学》2003,27(2):265-272

根据大气自忆性原理提出的回溯时间积分格式应用于中尺度格点模式MM5,构建了中尺度自忆模式SMM5并做了短期强降水预报的实验.结果表明,SMM5模式与MM5模式相比,由于使用了多个时刻的场资料,预报精度有了明显的提高, SMM5预报的最大雨区的中心位置与降水量也比MM5更接近实际观测场.  相似文献   

黄河流域夏季分区面雨量预报研究   总被引：6，自引：0，他引：6  

许力  刘强 《南京气象学院学报》2003,26(1):116-123

介绍黄河流域分区夏季面雨量预报的研究成果，精心挑选51个具有较好代表性的测站对黄河流域夏季降水的时空演变特征进行分析，使用K均值动态聚类对黄河流域的夏季降水进行了客观分区，并计算出各流域夏季面雨量。通过对黄河流域夏季雨量与500hPa环流，海温、OLR、中纬阻高，高原积雪，欧亚积雪等重要影响因子的关系分析，结合黄河流域夏季面雨量年降和年代际演变特征的分析，研究出黄河流域分区夏季面雨量预测的基本方法和模型，并通过客观化的数学方法建立黄河流域夏季面雨量预测系统，预测系统十年回报的结果显示出具有较的预测技巧。  相似文献   

广西异常暴雨天气事件之异常指数初探   总被引：3，自引：1，他引：3       下载免费PDF全文

高安宁  陈业国  吴兴国 《气象》2003,29(1):46-48

对广西异常暴雨天气事件之“异常指数”的设置进行了初步探讨，提出暴雨天气事件中过程日最大暴雨范围，过程持续时间，过程强降雨，特强降雨发生范围等四项异常分指数，然后统计同一过程分指数之和，得总指数，在此基础上分别选出了4－10月各月广西异常暴雨天气事件。  相似文献   

“2002.6.30”滇中低涡暴雨的中尺度分析   总被引：4，自引：2，他引：4       下载免费PDF全文

郭荣芬  鲁亚斌 《气象》2003,29(2):29-33

利用MICAPS常规资料和GMS卫星云图，3830—C多普勒雷达观测资料，对2002年6月30日发生于滇中地区的暴雨天气过程进行诊断和分析，发现暴雨过程由中低层低涡切变造成，暴雨区与垂直速度及涡度所表现的强烈上升区对应，并伴有高能高湿条件；同时卫星云图上有中尺度低涡云团发展。多普勒雷达回波资料分析表明，暴雨过程中出现了明显的中尺度系统，如中尺度辐合线、中尺度气旋、逆风区等，具有典型的对流型特征。  相似文献   

用MM5模式Reisner霰方案对华南暴雨的数值模拟   总被引：13，自引：2，他引：13       下载免费PDF全文

孙晶  王鹏云 《气象》2003,29(4):10-13

利用MM5中尺度数值模式对1998年6月8～9日华南暴雨进行了模拟，用Re—isner在方案模拟了可分辨尺度降水，详细分析了暴雨的微物理过程。结果表明，Re—isner在方案对华南暴雨具有较好的模拟能力。在降水最大时段，霰和云水是形成雨水的主要来源，云水的碰冻是产生霰的主要微物理过程。  相似文献   

北极涛动对东亚夏季降水的预测意义   总被引：11，自引：0，他引：11  

龚道溢 《气象》2003,29(6):3-6

分析了春季北极涛动(AO)指数的变化对梅雨—Changma——Baiu带夏季降水年际变化的影响。对观测的东亚10个站的降水长序列资料(1899—1999年)，进行滤波处理，保留10年以下的年际时间尺度的变化，再进行相关分析。结果表明，近百年的5月北极涛动指数与10站夏季平均降水相关最高达—0．45，超过99％信度水平。当北极涛动偏强一个标准差时，整个长江中下游地区到日本南部一带，降水减少平均约8％左右。降水的这种变化与对流层东亚急流的变化密切相关：春季北极涛动强时，随后夏季急流位置通常偏北，雨带位置也北移，从而造成梅雨—Changma——Baiu带降水减少，反之亦然。较强的AO异常对降水的影响更明显，而较弱的AO与降水异常的对应关系并不显著。这对东亚夏季年际降水异常具有一定的预测意义。  相似文献   

2002年7～8月海河流域面雨量预报的误差分析   总被引：2，自引：0，他引：2  

王新龙  胡欣  尤凤春 《气象》2003,29(6):41-45

对天津市气象台和河北省气象台在2002年7—8月的海河流域面雨量24h、48h预报进行了误差对比分析，列举了几种预报误差，并利用模糊数学中的综合评判法，计算了它们的模糊评分。结果表明：海河流域的面雨量预报有一定的可信度，把其作为水文模式的初值，有较高的利用价值；对于各气象台各自辖区内的预报，范围越小，预报越准确；在对面雨量预报效果的评估上，80％(或80)这一数值是客观、可信的。  相似文献