Bifurcation modelling in a meandering gravel–sand bed river     

Kees Sloff  Erik Mosselman 《地球表面变化过程与地形》2012,37(14):1556-1566

The Rhine bifurcation at Pannerden forms the major distribution point for water supply in the Netherlands, distributing not only water and sediment but also flooding risks and navigability. Its morphological stability has been a concern for centuries. We present experiences from more than two decades of numerical morphological modelling of this bifurcation with a gravel–sand bed and a meandering planform. Successive computations have shown the importance of upstream approach conditions, the necessity to include physical mechanisms for grain sorting and alluvial roughness, and the need to assume a thicker active layer of the river bed than is suggested by laboratory flume experiments using a constant discharge. The active layer must be thicker in the model to account for river bed variations due to higher‐frequency discharge variations that are filtered out in morphological modelling. We discuss limitations in calibration and verification, but argue that, notwithstanding these limitations, 2D and 3D morphological models are valuable tools, not only for pragmatic applications to engineering problems, but also for revealing the limitations of established knowledge and understanding of the relevant physical processes. The application of numerical models to the Pannerden bifurcation appeared to reveal shortcomings in established model formulations that do not pose particular problems in other cases. This application is therefore particularly useful for setting the agenda for further research. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Diagnosis of river basins as CO2 sources or sinks subject to sediment movement     

Yao Yue  Jinren Ni  Alistair G. L. Borthwick  Chiyuan Miao 《地球表面变化过程与地形》2012,37(13):1398-1406

Sediment movement during erosion, transport and deposition greatly affects the ecosystem of river basins. However, there is presently no consensus as to whether particular river basins act as carbon dioxide (CO₂) sources or sinks related to these processes. This paper introduces a rule‐of‐thumb coordinate system based on sediment delivery ratio (SDR) and soil humin content (SHC) in order to evaluate the net effect of soil erosion, sediment transport and deposition on CO₂ flux in river basins. The SDR–SHC system delineates CO₂ source and sink areas, and further divides the sink into strong and weak areas according to the world‐average line. The Yellow River Basin, most severely suffering soil erosion in the world, only appears to be a weak erosion‐induced CO₂ sink in this system. The average annual CO₂ sequestration is ~0·235 Mt from 1960 to 2008, a relatively small value considering its 3·1% contribution to the World's sediment discharge. The temporal analysis shows that the Yellow River Basin was once a source in the 1960s, but changed its role to become a weak sink in the past 40 years due to both anthropogenic and climatic influences. The spatial analysis identifies the middle sub‐basin as the main source region, and the lower as the main sink. For comparison, sediment‐movement‐related CO₂ fluxes of eight other major basins in four continents are examined. It is found that the six basins considered in the Northern Hemisphere appear to be sinks, while the other two in the Southern Hemisphere act as sources. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

How persistent are hysteresis patterns between suspended sediment concentration and discharge at different timescales?     

《水文科学杂志》2012,57(15):1909-1917

ABSTRACT

This study was conducted to characterize the hysteresis of suspended sediment concentration (SSC) at different timescales for the Educational and Research Forest Watershed of Tarbiat Modares University, Iran. Hysteresis loops were developed between flow discharge and SSC using data for (i) the whole period, (ii) seasonal, (iii) monthly and (iv) storm-event timescales. The data were collected on an hourly basis at daily and storm-event scales from October 2007 to July 2008. The SSC hysteresis for all the events in the whole study period showed a clockwise pattern, with a flushing behaviour pointing to sudden changes in sediment sources. The results further reveal that the study watershed behaves differently from the viewpoint of hysteresis patterns, with different conditions of dilution and flushing between SSC and flow discharge at different timescales. These result from the complex varying effect of governing conditions on the watershed.  相似文献   

A study of suspended sediment concentration in Yangshan deep-water port in Shanghai,China   总被引：1，自引：0，他引：1  

Shu-hua ZUO  Ning-chuan ZHANG  Bei LI  Shen-liang CHEN 《国际泥沙研究》2012,27(1):50-60

Suspended sediment concentration (SSC) plays an important role in the estuarine environment.Its spatial or temporal variations in coastal zones and estuaries indicate that sediments are suspended,trans...  相似文献   

Bed morphology and grain size characteristics around a spur dyke     

Hao ZHANG  Hajime NAKAGAWA  Hideaki MIZUTANI 《国际泥沙研究》2012,27(2):141-155,157,156

This paper presents an experimental study on the local bed morphology and grain size characteristics around an impermeable spur dyke.A series of experiments are conducted with different types of sedime...  相似文献   

垂向悬沙扩散与近岸挟沙力理论研究     

李瑞杰  董德信  郑俊  张伟一  潘锡山 《海洋学报》2012,34(5):169-173

根据垂向二维悬沙扩散方程和谢才公式,假定泥沙垂向扩散系数为常数或为水深和摩阻流速的函数时,从理论上推导得到一个新的不仅适用一般水域,也适用于高含沙水域的挟沙力公式。公式一阶近似形式上与近岸海域常用的刘家驹公式相一致也不显含泥沙沉速,从理论上证明了刘家驹公式的合理性,说明其经验公式在理论上也成立。对更高阶近似,公式显含泥沙沉速,与维利卡诺夫以及张瑞瑾等挟沙力公式相一致,说明了张瑞瑾公式的合理性。分析了导出的公式的物理意义以及与刘家驹公式和张瑞瑾公式的异同。新的挟沙力公式也表明挟沙力公式的近似应是流速平方的多项式,选择低阶项作为近似会有一定的误差。  相似文献   

渤海地区全新世孢粉序列及古环境演化   总被引：2，自引：0，他引：2  

陈金霞  石学法  乔淑卿 《海洋学报》2012,34(3):99-105

通过对取自黄河口外泥质区的BH-264孔的沉积孢粉进行分析,对渤海地区全新世古植被和古环境演化历史进行了恢复。在早全新世(距今9.5~7.6 ka)渤海地区气候温暖湿润,在陆缘海滨地带出现大量沼泽湿地,上面生长着莎草和香蒲等植被,在周围的山地、丘陵和平原地区植被以松属和落叶栎属为主,并伴生着桦木属、榆科、桑科等树种;在中全新世(距今7.6~5.8 ka)温度的升高和海平面上升,使BH-264孔沉积孢粉中松属占主导地位,不利于远距离传播的草本植物花粉含量降为全新世最低值;在距今5.8 ka以后东亚夏季风减弱和降雨量减少导致渤海西部陆源海滨地带植被以旱生草本藜科、蒿属和菊属为主,黄河三角洲的形成缩短了研究区的离岸距离,使这些草本植物花粉易于传播到BH-264孔中沉积。  相似文献   

烟台四十里湾表层沉积物有机质来源及环境意义   总被引：5，自引：3，他引：2  

刘东艳  申旭红  王玉珏  陈颖军  李丽 《海洋学报》2012,34(5):205-212

  相似文献   

辽东湾北部海域沉积物重金属环境质量和污染演化   总被引：6，自引：0，他引：6  

张现荣  张勇  叶青  范德江  毕世普  王亮  张喜林  孔祥淮 《海洋地质与第四纪地质》2012,(2):21-29

基于取自辽东湾北部海域表层沉积物和岩心样品,利用XRF等方法对沉积物中的重金属含量进行系统的测定,结合137 Cs、210Pb年代测定,分析了研究区表层沉积物中重金属分布特征、环境质量状态以及重金属污染历史。结果表明:辽东湾表层沉积物重金属As、Cd、Cr、Cu、Pb、Zn、Hg含量高值区主要分布在葫芦岛附近海域,并且呈现由近岸向远岸递减的趋势;辽东湾海域部分站位表层沉积物已经受到重金属污染,轻度和重度污染率为34.5%,清洁率为65.5%,重度污染站位集中在葫芦岛附近海域;辽东湾沉积物中重金属污染大致出现在1975年,于1997年达到最大,随后,重金属污染开始明显减少。辽东湾沉积物中重金属分布及演化特征与沿海社会经济发展和国家环境保护政策有着密切的联系。  相似文献   

长江口北支强潮河道悬沙运动及输移机制   总被引：6，自引：3，他引：3  

陈炜  李九发  李占海  戴志军  闫虹  徐敏  赵军凯 《海洋学报》2012,34(2):84-91

随着崇明北侧岸滩的自然淤涨和人工圈围,北支河道显著束窄,"喇叭口"顶点位置下移。在新的地形及流域来水来沙变异背景下,作为长江河口的分支强潮汊道,其悬沙运动与输移特点值得探讨。根据2010年4月小潮至大潮连续8 d的半个半月潮水沙观测,结合多年不同河段水沙观测数据得到的含沙量过程曲线显示:整个河道潮流强、含沙量高,含沙量过程曲线呈 "单峰-双峰-单峰"的变化特点;河道悬沙的输移以平流输移和"潮泵输移"为主,以"喇叭口"顶点为界,上游段河道平流输移占主导地位,"潮泵输移"次之;下游段"潮泵输移"占主导,平流输移次之。净输沙总量呈:上段河道向海,下段河道向陆,在"喇叭口"顶点附近存在一个泥沙汇聚的最大浑浊带区域。  相似文献