四川省康定市泥石流灾害与降水预报阈值确定

通过对康定市历史泥石流灾害资料与历史气象降雨资料进行统计分析,揭示了康定市泥石流灾害与降雨的关系特征,并在此基础上,研制了康定市1h、3h降雨量诱发泥石流预警指标。结果表明：康定市境内各地均有发生泥石流灾害的可能性,东部地区是泥石流的高易发区。康定市境内泥石流灾害发生与当日降雨量、短时强降雨、前期有效降雨量关系密切。降雨量大且降雨强度强的月份（6~8月）易发生泥石流灾害。短时强降水的强度越大,发生灾害的风险越大,强降水出现频率最高的时段（19:00~02:00）也是泥石流高发时段。当降水强度<10mm/h和20mm/3h时,有出现泥石流的可能性,泥石流灾害气象风险等级为4~5级;当降水强度达到10~20mm/h、21~35mm/3h时,发生泥石流的可能性较大,风险等级为3级;当降水强度达到21~35mm/h、36~50mm/3h时,泥石流发生的可能性大,风险等级为2级;当降水强度>35mm/h、50mm/3h时,泥石流发生的可能性极大,风险等级为1级。     

The effect of wildfire on runoff and erosion in native Eucalyptus forest

Wildfires raise concerns over the risk of accelerated erosion as a result of increased overland flow and decreased protection of the soil by litter and ground vegetation cover. We investigated these issues following the 1994 fires that burnt large areas of native Eucalyptus forest surrounding Sydney, Australia. A review of previous studies identifies the fire and rainfall conditions that are likely to lead to increased runoff and accelerated erosion. We then compare runoff and erosion between burnt and unburnt sites for 10 months after the 1994 fires. At the scale of hillslope plots, the 1994 fire increased runoff by enhancing soil hydrophobicity, and greatly increased sediment transport, mainly through the reduced ground cover, which lowered substantially the threshold for initial sediment movement. However, both runoff and sediment transport were very localized, resulting in little runoff or sediment yield after the fire at the hillslope catchment scale. We identify that after moderately intense fires, rainfall events of greater than one year recurrence interval are required to generate substantial runoff and sediment yield. Such events did not occur during the monitoring period. Past work shows that mild burns have little effect on erosion, and it is only after the most extreme fires that erosion is produced from small, frequent storms. © 1998 John Wiley & Sons, Ltd.     

Effects of groundwater flow on mineral diagenesis, with emphasis on carbonate aquifers

 This article provides a critical synopsis of the effects of groundwater flow on mineral diagenesis. Emphasis is placed on those aspects and processes that change porosity and permeability in carbonate aquifers, because they are of particular importance to human societies as sources of supplies of water for human consumption (drinking, irrigation) and of crude oil and natural gas. Diagenetic settings in carbonates as well as clastics are generally ill defined. This paper proposes a new comprehensive classification of diagenetic settings into near-surface, shallow-, intermediate-, and deep-burial diagenetic settings; hydrocarbon-contaminated plumes; and fractures. These settings are defined on the basis of mineralogy, petroleum, hydrogeochemistry, and hydrogeology. This classification is applicable to all sedimentary basins. Diagenesis is governed by various intrinsic and extrinsic factors that include thermodynamic and kinetic constraints, as well as microstructural factors that may override the others. These factors govern diagenetic processes, such as dissolution, compaction, recrystallization, replacement, and sulfate–hydrocarbon redox-reactions. Processes such as cementation, dissolution, and dolomitization require significant flow of groundwater driven by an externally imposed hydraulic gradient. Other processes, such as stylolitization and thermochemical sulfate reduction, commonly take place without significant groundwater flow in hydrologically nearly or completely stagnant systems that are geochemically "closed." Two major effects of groundwater flow on mineral diagenesis are enhancement and reduction of porosity and permeability, although groundwater flow can also leave these rock properties essentially unchanged. In extreme cases, an aquifer or hydrocarbon reservoir rock can have highly enhanced porosity and permeability due to extensive mineral dissolution, or it can be plugged up due to extensive mineral precipitation. Received, April 1998 · Revised, July 1998 · Accepted, September 1998     

细颗粒对粗颗粒床沙质输沙率影响的初步研究

考虑高含沙紊流涡团中细颗粒絮凝形成网络结构对粗颗粒运动影响后,建立了粗颗粒悬移质泥沙的输沙率计算方法.该方法中包含的细颗粒影响项反映了流域因素对粗颗粒泥沙输沙的影响,证明细颗粒的影响是引起多沙河流中“多来多排”现象的一个重要因素.与黄河实测资料的对比表明,该计算方法能够反映高含沙紊流输沙时随流域细颗粒增多粗颗粒悬移质输沙率相对增大的现象,并具有较好的计算精度     

纬向切变基流中的非线性Rossby波

本文在半地转近似下讨论了纬向切变基流中的非线性正压Ｒｏｓｓｂｙ波，给出了存在波解的切变基流条件。     

青藏高原东南缘热流估算及与地震活动相关性分析

青藏高原东南缘地区内部构造运动强烈,是地热资源发育与地震事件频发的活动地区.大地热流记录了发生在地球深部各种作用过程的热学信息,可以作为地质构造活动和地震活动研究的有效约束,但是大范围的热流数据测量很难实现,因此,本文根据居里面深度结合放射性元素分布等计算了青藏高原东南缘的大地热流分布.首先,通过地表放射性元素的分布计算出地表产热量的分布,然后,利用相关地热参数之间的关系迭代计算出该地区地壳上下层的热导率分布,最终估算出地表热流及地下不同深度处热流值的分布.本文结果表明：（1）青藏高原东南缘的大地热流位于44~108 mW·m^-2之间,平均75 mW·m^-2,符合研究地区西南高、东北低的背景趋势,地壳内部热流值随深度的增加而降低.大部分地区地表热流异常与实际地热带分布相吻合,如川西、藏东南与滇西地区等地为地热高值区,川东和楚雄等地为热流低值区.（2）结合其他地球物理探测结果,总结了地壳内部热流与地震事件的联系：在地热梯度带地区,当两侧地层在一定深度范围内存在明显物性差异时,地震事件高发.

     

1321号台风“蝴蝶”强度变化特征和影响因素分析

利用NCEP/NCAR全球再分析格点资料（空间分辨率1°×1°）、台风实况资料及海南省气象台站观测资料,选取1321号台风＂蝴蝶＂为研究个例,从天气学原理高低空形势及动力、热力学物理量等多角度分析了＂蝴蝶＂强度演变特征及影响因素.研究结果表明,副热带高压与高空西风槽是影响此次台风的主要大尺度天气系统,弱冷空气南侵、南海海温偏高及越赤道气流强盛是＂蝴蝶＂迅速加强的重要原因.西风槽引导弱冷空气南侵使得台风外围环流气压梯度增加,斜压不稳定状态加剧;南海海温达到29℃,海温偏高使台风区域大气层结降低,深热对流发展;105°E越赤道气流强盛为台风提供了充沛水汽和能量.三者共同作用促使台风强度突然增强.另外,低层涡度、高层散度、湿位涡及水汽通量等物理量能够较好地表征＂蝴蝶＂强度变化特征.低层辐合流入、高层辐散流出为台风的加强提供了动力条件;湿位涡下负上正表明大气热力层结不稳定;水汽通量增加表明水汽条件充足.良好的动力条件、热力条件与水汽条件共同作用,使得＂蝴蝶＂在短时间内迅速加强为强台风.     

Response of saturated and nearly saturated porous media: Different formulations and their applicability

The response of saturated porous medium is of significant interest in many fields ranging from geomechanics to biomechanics. Biot was the first to formulate the basic equations governing the process of coupled flow and deformation in porous media. Depending on the nature of loading vis‐à‐vis the characteristics of the media, different formulations (fully dynamic, partly dynamic, quasi‐static) are possible. In this study, analytical solutions are developed for the response of saturated and nearly saturated porous media under plane strain condition. The solutions for different formulations are developed in terms of non‐dimensional parameters. The response is studied for various conditions and the regions of validity for various formulations are identified in a parametric space. An assessment of the needed formulation for few important problems is also presented. Copyright © 2008 John Wiley & Sons, Ltd.     

流域演化与泥石流的系统性——以云南东川蒋家沟为例

以典型的云南东川蒋家沟为例,根据Strahler面积-高程曲线的积分将其分区,揭示了流域的演化差异.证明了泥石流发生在特定的演化区域,并具有特定的物质组成.通过概率模型,定性说明了泥石流在流域的形成和扩张,其结果就表现为间歇性的阵流.阵流的时空特征反过来证明了泥石流的系统性.统计还表明,阵流的流量分布和衰减取决于最大流量;最大流量序列很好继承了作为流域系统行为的动力学特征.最后,可以根据单沟泥石流的过程系统考察区域泥石流活动.泥石流在大尺度水系的分布,从概率过程看,完全等同于泥石流源地小分支在单个流域的分布,而且满足相似的分布特征.     

Deterministic sensitivity analysis for a model for flow in porous media

A deterministic method for sensitivity analysis is developed and applied to a mathematical model for the simulation of flow in porous media. The method is based on the singular value decomposition (SVD) of the Jacobian matrix of the model. It is a local approach to sensitivity analysis providing a hierarchical classification of the directions in both the input space and of those in the output space reflecting the degree of sensitiveness of the latter to the former. Its low computational cost, in comparison with that of statistical approaches, allows the study of the variability of the results of the sensitivity analysis due to the variations of the input parameters of the model, and thus it can provide a quality criterion for the validity of more classical probabilistic global approaches. For the example treated here, however, this variability is weak, and deterministic and statistical methods yield similar sensitivity results.