Symmetric　Stability　of　Rotation　and　Boussinesq　Fluid　in　Bounded　Domain　by　Using　Normal　Mode　Method     

Ren Shuzhan 《大气科学进展》1994,11(3):291-295

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滇东黔西晚二叠世早期辫状河三角洲沉积体系及其聚煤特征   总被引：5，自引：2，他引：5  

邵龙义  张鹏飞  陈代钊  罗忠 《沉积学报》1994,(4)

滇东黔西上二叠统底部发育着一套玄武岩质砾岩，本文针对云南富源和贵州盘县一带的底砾岩进行综合研究，认为这套砾岩为辫状河三角洲沉积，并进一步识别出砾质辫状河道、砂质辫状河道、砾质河口坝、砂质河口坝等沉积类型。文中还对该辫状河三角洲的沉积序列、发育背景以及与聚煤作用关系等问题做了一定分析，认为三角洲朵体之间地区以及在衰退的三角洲朵体之上成煤较好。  相似文献   

Simulation of flow over pool-riffle topography: A consideration of the velocity reversal hypothesis     

P. A. Carling  N. Wood 《地球表面变化过程与地形》1994,19(4):319-332

Computer flow simulations using the HEC-2 step-backwater routine are used to demonstrate the effect of systematically varying river channel width, riffle spacing and channel roughness on the shear velocity, section-mean velocity and energy slope in fixed-bed pool-riffle sequences. Initial scaling is obtained by utilizing published information on hydraulic parameters within reaches of the River Severn. Subsequently this restriction is relaxed and the effect of varying parameter combinations within realistic limits is explored. The purpose of this exercise is to isolate those scenarios which may preclude or promote the occurrence of a competence ‘reversal’, such that pools scour at high flow whilst deposition occurs on riffles. It is concluded that rivers in which pools are hydraulically rougher than riffles are likely to demonstrate a competence reversal. For prescribed conditions, the critical discharge at which a reversal occurs is a negative function of riffle spacing and riffle width relative to pool width. Downstream variation in hydraulic roughness also has implications for the phase relationship of shear velocity maxima and minima in relation to the extremes in pool-riffle topography.  相似文献   

Channel and floodplain response to recent abrupt climate change: The tyne basin,Northern England     

Barbara T. Rumsby  Mark G. Macklin 《地球表面变化过程与地形》1994,19(6):499-515

This paper examines the timing, nature and magnitude of river response in upland, piedmont and lowland reaches of the Tyne basin, northern England, to high-frequency (20–30 year) changes in climate and flood regime since 1700 AD. Over this period fluvial activity has been characterized by alternating phases of river-bed incision and stability coinciding with non-random, decadal-scale fluctuations in flood frequency and hydroclimate that appear to be linked to changes in large-scale upper atmospheric circulation patterns. Episodes of widespread channel bed incision (1760–1799, 1875–1894, 1955–1969) result from a higher frequency of large floods (> 20 year return period) and cool, wet climate under meridional circulation regimes. Phases of more moderate floods (5–20 year return period), corresponding to zonal circulation types (1820–1874, 1920–1954), are characterized by enhanced lateral reworking and sediment transfer in upper reaches of the catchment, and channel narrowing and infilling downstream. Rates of fluvial activity are reduced in intermediate periods (1800–1819, 1895–1919) with no dominant circulation regime associated with lower flood frequency and magnitude. The results of this study provide a valuable guide for forecasting probable drainage basin and channel response to future climate change.  相似文献   

厦漳泉地区外向型经济发展的条件与特征分析     

侯晓虹  姚士谋 《热带地理》1994,14(4):336-344

本文分析厦漳泉地区外向型经济发展的基本条件、发展过程，以及近十几年来利用外资的主要特征。在此基础上，对本区进一步加快发展外向型经济的潜在优势进行评述。  相似文献   

长江三峡地区经济开发条件分析     

杨定国  陈治谏 《山地学报》1994,(1)

长江三峡地区区域地理位置重要，区位优势明显，开发意义重大；区内农业、水能、矿产和旅游等优势自然资源丰富，组合配置良好，开发潜力巨大；区域经济开发的交通、能源、出入通道等基础条件已基本具备。  相似文献   

论水土保持与金沙江农业综合开发：以云南省为例   总被引：1，自引：0，他引：1  

陈循谦 《云南地理环境研究》1994,6(2):61-67

金沙江流域光、热、土地等自然资源丰富，已经引起各方面的关注，正在进行农业综合开发。由于特殊的地质构造和特定的自然地理环境，其开发必须搞好水土保持。水土保持是金沙江农业综合开发的基础和环境保护的重要内容，水土保持型生态农业是金沙江农业综合开发的道路。  相似文献   

钱塘江涌潮简析与预报   总被引：3，自引：0，他引：3  

周黔生 《水文》1994,(6):12-16

根据１９９１年观测资料，仑前潮位站出现涌潮１８４次，涌潮次数多少与江道地形变迁及上游下泄流量大小有关。涌潮高度在１．２－２．２ｍ之间，与涨潮潮差成正比。涌潮潮时预报方法有传播时间法和隔日滞后时间法。涌潮高度的预报，可根据当天涌潮高度预测后一天涌潮高度，也可根据下游站的涌潮高度预报上游站的涌潮高度。  相似文献   

淮北煤田早二叠世化石植物古生态     

杜美利 《中国煤田地质》1994,6(4):21-25

淮北煤田早二叠世化石植物丰富，其形成于炎热多雨的热带滨海三角洲沉积体系中。下三角洲平原是该区化石植物最宜生长的地方。早二叠世该区化石植物常形成四类植物群落：森林沼泽植物群落、沿岸水生植物群落、高地植物群落、三角洲平原真蕨及种子蕨混生植物群落（早期）、树蕨－大羽羊齿类雨林植物群落（晚期）。随着时间的推移，这四类植物群落的结构及面貌发生着不断的变化；其演替显示，早二叠世晚期该区气侯更加湿热，雨林气侯更为普遍。  相似文献   

中国南方下寒武统石煤的特征,沉积,环境和成因   总被引：4，自引：0，他引：4  

姜月华  岳文浙 《中国煤田地质》1994,6(4):26-31

在早寒武世，中国南方存在着四种类型的含石煤地层一南岭型、扬子型、江南型和华南型，其中的石煤在量和质的方面均各不用问，据研究，这主要与当时的沉积背景（一个浅水台地、一个深水盆地和三个深水大陆斜坡）差异有关。作者通过对石煤的分布、厚度、物质组分、岩石类型、物理化学性质和伴生元素的讨论，认为其形成机理为：海平面上升，由上升洋流携带富养海水在沉积速率缓慢和少泥的条件下，促使菌藻类大量发育，并由此引起海底缺氧环境；菌藻类死亡后沉积在海底，经过复杂的成岩变质作用就形成了石煤。  相似文献