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21.
Daniel R. Parsons James L. Best Stuart N. Lane Oscar Orfeo Richard J. Hardy Ray Kostaschuk 《地球表面变化过程与地形》2007,32(1):155-162
Confluence–diffluence units are key elements within many river networks, having a major impact upon the routing of flow and sediment, and hence upon channel change. Although much progress has been made in understanding river confluences, and increasing attention is being paid to bifurcations and the important role of bifurcation asymmetry, most studies have been conducted in laboratory flumes or within small rivers with width:depth (aspect) ratios less than 50. This paper presents results of a field‐based study that details the bed morphology and 3D flow structure within a very large confluence–diffluence in the Río Paraná, Argentina, with a width:depth ratio of approximately 200. Flow within the confluence–diffluence is dominated largely by the bed roughness, in the form of sand dunes; coherent, channel‐scale, secondary flow cells, that have been identified as important aspects of the flow field within smaller channels, and assumed to be present within large rivers, are generally absent in this reach. This finding has profound implications for flow mixing rates, sediment transport rates and pathways, and thus the interpretation of confluence–diffluence morphology and sedimentology. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
22.
Robert I. Ferguson Judith R. Cudden Trevor B. Hoey Stephen P. Rice 《地球表面变化过程与地形》2006,31(9):1149-1166
In alluvial river systems, lateral inputs of water and/or sediment at junctions or undercut hillsides can disrupt what would otherwise be smooth downstream trends in mainstream bed elevation, channel gradient, and bed grain size. Generic styles of mainstream response to lateral inputs are investigated using a one‐dimensional sediment routing model with multiple grain size fractions. Numerical experiments isolate the effects of three para‐meters: ratio of tributary to mainstream water flux (QR), ratio of tributary to mainstream bedload flux (FR), and ratio of tributary to mainstream bedload diameter (DR). The findings are not unduly sensitive to the choice of initial conditions or to approximations made in the model. The primary distinction is between junctions that aggrade, causing local profile convexity with interrupted downstream fining, and junctions that degrade. The immediate effects of aggradation extend further upstream than downstream, whereas degradation is much more subdued and has no upstream impact. Aggradation is typical of coarse inputs (DR > 2), and degradation of fine inputs (DR < 1), but very high ratios of QR to FR also promote degradation. Both aggrading and degrading junctions can lead to a change in mainstream bed grain size well below the junction, with higher ratios of QR to FR producing a coarser distal bed. The effect of a tributary reflects the interplay between additional bed load and additional discharge to transport it. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
23.
祁连山老虎沟流域产汇流特征分析 总被引：1，自引：0，他引：1
为了研究老虎沟流域冰川产汇流特征,根据老虎沟流域2009年消融期4-10月的气象与水文观测资料,采用排除和不排除降水对冰雪消融产流影响的方法,对老虎沟流域融水径流的产流特征、白天和夜晚径流特征、径流的滞后效应进行了分析。结果表明： 5-9月各月流量占到整个消融期流量的比例分别为7%、26%、33%、19%、14%。降水对河流的产流贡献率约为22%,冰雪融水和地下水对河流的产流贡献率为78％。观测期内,除5月外,白天流量全部大于晚上流量,而且6-8月白天和夜晚径流之间的差值较大。老虎沟冰川区以裸冰消融为主,冰面湖较少而且小,汇流较快,储水性能并不明显。5-9月流量峰值和谷值平均分别滞后气温7.0 h、3.5 h、2.5 h、2.5 h和4.5 h,冰川排水系统也随着流量变化经历慢速-快速-慢速的变化过程。 相似文献
24.
基于中国东南沿海冬季强降水的统计分析,采用EOF、REOF、North检验等方法对2011—2016年冬季(12、1、2月)欧洲中期天气预报中心降水资料进行分类,选取位于内陆的第1、第4 REOF模态,对该两模态的降水样本进行合成分析,合成的降水中心与东南沿海福建的多年统计暴雨中心吻合。与强降水相配合,1 000 hPa上有自北向南的渐近线型辐合气流,并伴有锋区,从而形成天气尺度渐近线型锋生辐合线,强降水位于辐合轴线左侧气旋式风切变处。这是一类以前未曾受到关注和讨论的东南沿海地区冬季暴雨系统。利用客观判定方法和建立系统坐标系,以确认并诊断该系统的结构。在冷干少雨、低层盛行偏北风的冬季,此类系统兼有锋区热力抬升与辐合气流动力抬升,在雨区形成旺盛的上升运动;同时,通过辐合线正交风分量将邻近的海面水汽汇集到降水区,与中高层副高边缘偏南气流相向而行,构成较为深厚的交汇式水汽输送层;通过非绝热加热,形成深厚的热力对流不稳定,并通过干区向湿气团下楔入,形成下干上湿的湿动力不稳定,以及假相当位温随高度增加而递减,形成上暖湿、下冷干的对流不稳定层。因此,该系统对冬季强降水的发生发展及落区具有重要影响。通过WRF模式的模拟结果探讨环境热力机制的影响,结果显示,凝结潜热加热可影响辐合线的辐合位置和强度、锋生区的位置及强度,进而影响系统的活跃程度。中层潜热加热抑制平流感热冷却进入暖气团,维持降雨区的热力不稳定和降水强度。渐近线型锋生辐合线有利于东南沿海冬季大范围降水出现暴雨,其中凝结潜热释放具有重要贡献。 相似文献
25.
The Antarctic Intermediate Water (AAIW) exhibits a decadal variability during recent years, i.e., salinification before 1997 and freshening thereafter, with the maximum anomalies locating at the region of Brazil and Malvinas currents confluence. Our study proposed that the local mesoscale eddies may play an important role in triggering this decadal oscillation. The eddy activity intensification (weakening) leads to the increase (decrease) of poleward cross-frontal eddy salinity flux and upward eddy buoyancy flux, which results in the weakening (strengthening) of the subsurface stratification and potential vorticity (PV). The PV anomalies facilitate (block) the poleward transport of warm saline subtropical water, while the stratification weakening favors the further downward transmission of salinity anomalies by processes of eddy flux as well as mean-flow advection (the stratification strengthening inhibits the vertical transport), then initiates the decadal change of the AAIW property. The whole process of the eddy-related propagation of salinity anomalies takes about 4 to 6 years. 相似文献
26.
针对黄河上游干、支流交汇区形成的沙坝淤堵事件,利用野外观测资料,分析了支流高含沙洪水特性及交汇区沙坝淤堵特点,探讨了汇流比(支流流量与干流流量之比)、支流洪水水量、支流洪水沙量等因素对沙坝淤堵形成的影响;根据动量原理建立了交汇区形成沙坝淤堵的判别关系,结合黄河上游干、支流洪水输移特性,得出了基于汇流比与支流洪水水量关系及支流洪水沙量与支流洪水水量关系的沙坝淤堵判别条件。由此,可根据汇流比、支流洪水水量及沙量判断交汇区能否形成沙坝淤堵,可为暴雨洪水期黄河上游交汇区形成沙坝淤堵灾害的预报及防治提供参考。 相似文献
27.
为分析水流交汇区污染物输移扩散规律,开展了交汇区污染物浓度分布规律的实验和数值模拟研究。建立了交汇区污染物扩散的水气两相流数学模型,并采用实验结果进行验证,对交汇区不同流量、动量和交汇角情况进行实验和数值模拟研究。结果表明:含高浓度污染物的支流汇入干流后,在交汇口下游支流侧形成较长的污染带,且支流与干流的交汇角和流量比(动量比)越小,污染带越狭长;在污染带范围内,污染物浓度梯度较大;污染物分布主要受随流输移和扩散的综合作用影响,其中在交汇区污染物的扩散作用明显。 相似文献
28.
Following climate change, changes in precipitation patterns and food security are major challenges faced by humans. However, research on how these changes in precipitation pattern impacts food supply is limited. This study aims to elucidate this impact and response mechanisms using precipitation data of a climate change-sensitive confluence zone of the southwest and southeast monsoons in Yunnan Province from 1988 to 2018. The results revealed that the precipitation pattern could be divided into three periods: abundant precipitation(Stage I, from 1988 to 2004), decreased precipitation(Stage II, from 2005 to 2015), and drought recovery(Stage III, from 2016 to 2018). Following the transition from Stage I to Stage II and from Stage II to Stage III, the area of precipitation changed significantly, accounting for 15.07%, 13.87%, and 16.53% of Yunnan's total area, for Stages I, II, and III, respectively. At the provincial level, a significant positive correlation was observed between precipitation and food production(r = 0.535, P 0.01), and the correlation coefficient between precipitation and grain yield was higher than that between precipitation and meat and milk production. Based on a precipitation–grain yield transect and breakpoint detection method, key precipitation thresholds affecting grain yield were estimated as 700 and 1500 mm, respectively; when precipitation was 700, 700–1500, and ≥1500 mm, the correlation coefficients between precipitation and grain yield were 0.448(P 0.01), 0.370(P 0.01), and –0.229(P 0.05), respectively. Based on the precipitation thresholds, Yunnan Province can be divided into precipitation surplus, precipitation equilibrium, and precipitation deficit regions, corresponding countermeasures to stabilize grain yield were proposed for each of these regions. The threshold effect of precipitation on grain yield is controlled by molecular-level water–crop mechanisms, in which reactive oxygen species, a by-product of plant aerobic metabolism, plays a key regulatory role. 相似文献
29.
泥石流沟道汇流对堆积危险范围影响的数值模拟研究 总被引：1，自引：0，他引：1
利用离散元法和图形处理器（GPU）并行计算手段建立泥石流运动堆积模型,以自然界沟道泥石流汇流后运动堆积特征及危险范围作为模拟参照,利用所构建的泥石流流通槽完成沟道泥石流不同交汇角汇流模拟试验和堆积危险范围预测,实现了泥石流沟道汇流的可视化模拟和数值模拟。试验结果表明,可视化模拟能够模拟出自然界中泥石流自流通区运动汇流后产生堆积的运动特征;数值模拟实现了锐角条件下仅考虑单因素即沟道交汇角对泥石流堆积危险范围影响的模拟试验。此外,利用GPU并行计算的优势可用于模拟大规模泥石流汇流现象,模型的可扩展性为泥石流汇流堆积危险范围分析向更为复杂的地理环境模拟奠定基础。 相似文献
30.
本文以地下水成矿理论，探讨了会理红盆南部爱国─湾子村砂岩型铜银矿点的成矿有利条件，根据构造对该类矿床的控制作用和金属矿物分带形成机制等新认识，阐明该区砂岩型铜矿床的控矿因素． 相似文献