一个理想河口中拦门沙的存在对河口羽流扩展的影响     

吴文森  张昊丹  刘嘉欢  龚文平 《海洋与湖沼》2024,55(1):37-50

河口羽流是河口冲淡水在陆架中扩展的主要形式, 其扩展受到诸多动力与地形因素的影响, 口门拦门沙就是其中之一。以一个理想化的河口为例, 采用区域海洋模型(regional ocean modelling system, ROMS), 研究口门拦门沙对河口羽流扩展的影响, 具体包括拦门沙对羽流的出流状态、扩展范围以及远场区沿岸流淡水输运的影响。研究结果表明, 拦门沙增加了口门处的水体分层, 减小了羽流出流速度, 增大了羽流凸出体的半径, 减小了远场区沿岸流宽度, 并进而减少了沿岸流中的淡水输送。本项研究对地形因素对河口羽流的扩展研究以及陆源物质的向海输运等均具有重要意义。  相似文献   

长春岭油田C107区块扶余油层密井网曲流河储层构型分析          下载免费PDF全文

孙天建  李胜利  许磊  李顺利 《地学前缘》2012,19(2):126-132

以长春岭油田C107区块扶余油层为例,综合应用岩心、录井、动态及测试等资料,按层次分析的思路对曲流河储层进行了构型分析。在井上单河道砂体识别的基础上,采用相控对比方法进行了单河道砂体的井间对比。基于现代沉积,提出了"S"型、同向式、背向式和切割式4类点坝砂体的组合模式,结合点坝砂体厚度特征以及与其紧邻废弃河道分布特征,在研究区识别出8个点坝砂体,单个点坝砂体面积在0.02～0.16km2。综合录井、岩心和测井等资料,在单井侧积层识别的基础上,结合对子井分析法,计算出侧积层的倾角为5°左右,侧积体的宽度为25～70m,建立了点坝砂体内部构型定量模式。应用曲流河构型分析成果,指导了热采动态分析。  相似文献   

Anatomy of a laterally migrating tidal bar in front of a delta system: Esdolomada Member,Roda Formation,Tremp‐Graus Basin,Spain     

MARIANA I. OLARIU  CORNEL OLARIU  RONALD J. STEEL  ROBERT W. DALRYMPLE  ALLARD W. MARTINIUS 《Sedimentology》2012,59(2):356-378

The first sandstone unit of the Esdolomada Member of the Roda Formation (hereafter referred to as ‘Esdolomada 1’) was formed by a laterally‐migrating, shelf tidal bar. This interpretation is based on detailed mapping of the bedding surfaces on the digital terrain model of the outcrop built from light detection and ranging data and outcrop photomosaics combined with vertical measured sections. The Esdolomada 1 sandbody migrated laterally (i.e. transverse to the tidal currents) towards the south‐west along slightly inclined (1.6° to 4.6°) master bedding surfaces. The locally dominant tidal current flowed to the north‐west. This current direction is indicated by the presence of stacked sets of high‐angle (average 21°) cross‐stratification formed by dunes that migrated in this direction, apparently in an approximately coast‐parallel direction. The tidal bar contains sets and cosets of medium‐grained cross‐stratified sandstone that stack to reach a thickness of about 5·5 m. Individual cross‐bed sets average about 50 cm thick (with a range of 10 to 70 cm) and have lengths of ca 130 to 250 m in a direction perpendicular to the palaeocurrent. Set thickness decreases in the direction of migration, towards the south‐west, and the degree of bioturbation increases, so that the cross‐bedded sandstones gradually change into highly bioturbated finer‐grained and thinner‐bedded sandstones lacking any cross‐stratification. The rate of thinning of individual dune sets as they are traced down any obliquely‐accreting master surface is some 40 cm per 100 m (0·004) for the older, thicker sandstones, whereas the younger, thinner beds thin at a rate of 15 cm over 100 m (0·0015). The tidal bar has a sharp base and top and is encased in finer‐grained bioturbated, marine sandstones. The Esdolomada bar crest was oriented north‐west to south‐east, parallel to the tidal palaeocurrents and to the nearby palaeoshoreline, but built by lateral accretion towards the south‐west. Lateral outbuilding generated a flat‐topped bar with a measured width of about 1700 m, and a preserved height of 5·5 m. The bar, disconnected from a genetically related south‐westward prograding delta some 2 km to the north‐east, developed during the transgressive phase of a sedimentary cycle. The tidal bar was most probably initiated as a delta‐attached bar at the toesets of the delta front and during transgression evolved into a detached tidal bar.  相似文献   

River channel and bar patterns explained and predicted by an empirical and a physics‐based method     

Maarten G. Kleinhans  Jan H. van den Berg 《地球表面变化过程与地形》2011,36(6):721-738

Our objective is to understand general causes of different river channel patterns. In this paper we compare an empirical stream power‐based classification and a physics‐based bar pattern predictor. We present a careful selection of data from the literature that contains rivers with discharge and median bed particle size ranging over several orders of magnitude with various channel patterns and bar types, but no obvious eroding or aggrading tendency. Empirically a continuum is found for increasing specific stream power, here calculated with pattern‐independent variables: mean annual flood, valley gradient and channel width predicted with a hydraulic geometry relation. ‘Thresholds’, above which certain patterns emerge, were identified as a function of bed sediment size. Bar theory predicts nature and presence of bars and bar mode, here converted to active braiding index (B_i). The most important variables are actual width–depth ratio and nonlinearity of bed sediment transport. Results agree reasonably well with data. Empirical predictions are somewhat better than bar theory predictions, because the bank strength is indirectly included in the empirical prediction. In combination, empirical and theoretical prediction provide partial explanations for bar and channel patterns. Increasing potential‐specific stream power implies more energy to erode banks and indeed correlates to channels with high width–depth ratio. Bar theory predicts that such rivers develop more bars across the width (higher B_i). At the transition from meandering to braiding, weakly braided rivers and meandering rivers with chutes are found. Rivers with extremely low stream power and width–depth ratios hardly develop bars or dynamic meandering and may be straight or sinuous or, in case of disequilibrium sediment feed, anastomosing. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Evolution and sedimentology of a channel fill in the sandy braided South Saskatchewan River and its comparison to the deposits of an adjacent compound bar     

PHILIP J. ASHWORTH  GREGORY H. SAMBROOK SMITH  JAMES L. BEST  JOHN S. BRIDGE  STUART N. LANE  IAN. A. LUNT  ARNOLD J. H. REESINK  CHRISTOPHER J. SIMPSON  ROBERT E. THOMAS 《Sedimentology》2011,58(7):1860-1883

The depositional stratigraphy of within‐channel deposits in sandy braided rivers is dominated by a variety of barforms (both singular ‘unit’ bars and complex ‘compound’ bars), as well as the infill of individual channels (herein termed ‘channel fills’). The deposits of bars and channel fills define the key components of facies models for braided rivers and their within‐channel heterogeneity, knowledge of which is important for reservoir characterization. However, few studies have sought to address the question of whether the deposits of bars and channel fills can be readily differentiated from each other. This paper presents the first quantitative study to achieve this aim, using aerial images of an evolving modern sandy braided river and geophysical imaging of its subsurface deposits. Aerial photographs taken between 2000 and 2004 document the abandonment and fill of a 1·3 km long, 80 m wide anabranch channel in the sandy braided South Saskatchewan River, Canada. Upstream river regulation traps the majority of very fine sediment and there is little clay (< 1%) in the bed sediments. Channel abandonment was initiated by a series of unit bars that stalled and progressively blocked the anabranch entrance, together with dune deposition and stacking at the anabranch entrance and exit. Complete channel abandonment and subsequent fill of up to 3 m of sediment took approximately two years. Thirteen kilometres of ground‐penetrating radar surveys, coupled with 18 cores, were obtained over the channel fill and an adjacent 750 m long, 400 m wide, compound bar, enabling a quantitative analysis of the channel and bar deposits. Results show that, in terms of grain‐size trends, facies proportions and scale of deposits, there are only subtle differences between the channel fill and bar deposits which, therefore, renders them indistinguishable. Thus, it may be inappropriate to assign different geometric and sedimentological attributes to channel fill and bar facies in object‐based models of sandy braided river alluvial architecture.  相似文献   

苏北盆地溱潼凹陷殷庄—台兴区块阜宁组三段沉积特征及砂体展布          下载免费PDF全文

吴展 《江苏地质》2011,35(1):28-32

苏北盆地溱潼凹陷殷庄—台兴区块阜宁组三段自上而下分为Ⅰ、Ⅱ、Ⅲ、Ⅳ4个砂组,沉积相组合为三角洲前缘相——包括前缘近端坝、远端坝、分流间湾相砂体夹浅湖—半深湖相泥岩互层。各砂组在分布上具有不同的形态。广山、殷庄、台兴、戴南地区发育的三角洲前缘近端坝和远端坝为有利储集相带。  相似文献   

Flow resistance adjustments of channel and bars in the middle reaches of the Yangtze River in response to the operation of the Three Gorges Dam     

Hu  Yong  Deng  Jinyun  Li  Yitian  Liu  Congcong  He  Zican 《地理学报(英文版)》2022,32(10):2013-2035

Journal of Geographical Sciences - Since the Three Gorges Dam (TGD) was put into operation, the flood water level at an identical discharge rate has not displayed a decreasing trend along the...  相似文献   

Form and growth of bars in a wandering gravel‐bed river     

Michael Church  Stephen P. Rice 《地球表面变化过程与地形》2009,34(10):1422-1432

The changing form of developing alluvial river bars has rarely been studied in the field, especially in the context of the fixed, compound, mainly alternate gravel bars that are the major morphological feature of the wandering style. Century scale patterns of three‐dimensional growth and development, and the consequent scaling relations of such bars, are examined along the gravel‐bed reach of lower Fraser River, British Columbia, Canada. A retrospective view based on maps and aerial photographs obtained through the twentieth century shows that individual bars have a life history of about 100 years, except in certain, protected positions. A newly formed gravel bar quickly assumes its ultimate thickness and relatively quickly approaches its equilibrium length. Growth continues mainly by lateral accretion of unit bars, consistent with the lateral style of instability of the river. Bar growth is therefore allometric. Mature bars approach equilibrium dimensions and volume that scale with the overall size of the channel. Accordingly, the bars conform with several published criteria for the ultimate dimensions of alternate barforms. Sand bars, observed farther downstream, have notably different morphology. Fraser River presents a typical wandering channel planform, exhibiting elements of both meandered and low‐order braided channels. Hydraulic criteria to which the Fraser bars conform illustrate why this planform develops and persists. The modest rate of bed material transfer along the channel – typical of the wandering type – determines a century‐length time scale for bar development. This time scale is consistent with estimates that have been made for change of the macroform elements that determine the overall geometry of alluvial channels. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

多孔砖、粉煤灰砌块、火山渣砌块配筋墙体抗震性能试验研究   总被引：4，自引：0，他引：4  

丁世文  夏敬谦  陈惠民 《地震工程与工程振动》2000,20(2):76-84

本文根据普通粘土砖墙体配置水平钢筋的研究成果,在空心多孔砖、粉煤灰砌块、火山渣混凝土砌块墙体中配置少量水平钢筋,研究它们在水平往复荷载及竖向荷载共同作用下的宏观破坏模式、抗剪强度、变形能力、钢筋效应等,为砌块承重房屋的抗震设计提供科学依据。  相似文献   

黄河三角洲河道沉积规律研究Ⅰ.建林边滩的形成与演化   总被引：1，自引：1，他引：0  

陈彰榕  范德江 《中国海洋大学学报(自然科学版)》2000,30(4):673-678

通过对建林边滩形态、沉积物的实地调查 ,查明了建林边滩的形态及沉积物分布特征 ,从河流沉积动力学角度探讨了边滩的形成与演化。建林边滩发育呈“二元结构”,沉积物下粗上细 ,侧向地质作用与垂向地质作用是塑造边滩的根本动力。  相似文献