共查询到19条相似文献，搜索用时 125 毫秒
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宽浅陡槽水流试验研究表明,浅层急流的阻力大、稳定性差。当陡槽(B/h<40,hk>1.04 m)末端水流呈"马鞍型"动量横向分布时,水流具有较强的稳定性;而当陡槽(B/h>40,hk<1.04 m)末端水流呈"椭圆型"动量横向分布时,就缺乏抗干扰能力,导致下游形成平面涡旋并挤压水跃。基于"介入式"方法,提出了采用潜没式三角翼体来调控浅层急流。利用三角翼对两翼底层水流产生的扰动产生两翼优势流,从而使水体能够抑制边界微小扰动的"多米诺骨牌"累加递增效应,提高了水流整体稳定性,改善了下游水流的衔接消能,效果良好。在此基础上,对三角翼体调控水流动量分布的机理进行了分析,探讨了三角翼体型设计原则及量纲一体型因子k的确定方法。 相似文献
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为解决下游深尾水工程中常规底流式消力池内由于消能紊动不足引起出池水流二次水跃、冲刷下游天然河床等一系列工程难题,结合物理模型和数值模拟对比研究平尾墩、常规宽尾墩以及非完全宽尾墩下游消力池内流场差异。研究结果表明:非完全宽尾墩利用平尾墩闸室与相邻宽尾墩闸室入池水流横向水位落差和纵向流速梯度,迫使雍高射流入池水流呈弧形横向扩散、碰撞,显著增强剪切紊动,促使消力池上游区域形成由底至表不断发展壮大的立轴旋滚,提升消力池内能量紊动耗散、降低出池水流流速,完全解决常规底流式消力池中易出现的二次水跃、消能不充分等问题。 相似文献
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综述了10a来利用高含沙水流特性治理黄河下游河道的研究进展,其中包括黄河水沙变化趋势,高含沙洪水的输沙特性,阻力特性,河槽形态调整变化规律,河道特性与来水来沙之间的关系;改造下游宽浅河道的最优水沙组合,水库调水调沙运用原则,及治理前景等内容.如能实现,下游河道淤积可大幅度减少,输沙用水可大量节省,黄河水资源可得到充分利用,并能形成窄深稳定的新河槽. 相似文献
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均衡状态时的基岩河道纵剖面表现为平滑形态，然而自然界的河道纵剖面常因地球各种内外动力作用的影响而呈现出以裂点为特征的不均衡状态，因此不均衡的河道剖面及裂点的特征可以用于指示外界环境的扰动。位于青藏高原东缘造山带的岷江上游流域水系普遍呈现不均衡的特征，且广泛发育有裂点。文章基于数字高程模型，提取裂点空间分布特征，通过裂点成因分析后发现，这些裂点的形成受到岩性、冰川作用、构造等因素的影响：因岩性形成的裂点主要位于花岗岩与其他地层的交界线上；而高海拔裂点主要受到冰川作用的控制，位于地形起伏度较低的区域；流域内低海拔区域成层分布的坡断型裂点可能主要因多期次区域构造隆升而形成；岷江上游下段流域的阶梯状垂阶型裂点则主要因地震滑坡形成。这一结果增进了对岷江流域的河流地貌发育及其影响因素的理解。此外，研究结果也说明在对河道纵剖面分析时有必要更多考虑到滑坡及冰川等因素对现代河道纵剖面产生的重要影响，为进一步理解造山带地貌演化及控制因素提供了参考视角。 相似文献
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Flow and sediment dynamics in a low sinuosity, braided river: Calamus River, Nebraska Sandhills 总被引：1，自引：0，他引：1
The interaction between channel geometry, flow, sediment transport and deposition associated with a midstream island was studied in a braided to meandering reach of the Calamus River, Nebraska Sandhills. Hydraulic and sediment transport measurements were made over a large discharge range using equipment operated from catwalk bridges. The relatively low sinuosity channel on the right-hand side of the island carries over 70% of the water discharge at high flow stages and 50–60% at low flow stages. As a result, mean velocity, depth, bed shear stress and sediment transport rate tend to be greater here than in the more strongly curved left-hand channel. The loci of maximum flow velocity, depth and bed shear stress are near the centre of the channel upstream of the island, but then split and move towards the outer banks of both channels downstream. Variations in these loci depend on the flow stage. Topographically induced across-stream flows are generally stronger than the weak, curvature-induced secondary circulations. Water surface topography is controlled mainly by centrifugal accelerations and local changes in downstream flow velocity. The averaged water surface slope of the study reach varies very little with discharge, having values between 0·00075 and 0·00090. As bed shear stress generally varies in a similar way to mean velocity, friction coefficients vary little, normally being in the range 0·07–0·13. These values are similar to those in straight channels with sandy dune-covered beds. Bedload is moved mainly as dunes at all flow stages. Grain size is mainly medium sand with coarse sand moved in thalwegs adjacent to the cut banks, and with fine sand at the downstream end of the island. These patterns of flow velocity, depth, water surface topography, bed shear stress, bedload transport rate and mean grain size can be accurately predicted using theoretical models of flow, bed topography and sediment transport rate in single river bends, applied separately to the left and right channels. During high flow stages deposition occurs persistently near the downstream end of the island, and cut banks are eroded. Otherwise, erosion and deposition occurs only locally within the channel as discharge varies. Abandonment and filling of a strongly curved channel segment may occur by migration of an upstream bar into the channel entrance at a high flow stage. 相似文献
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A conceptual model of groundwater and surface-water interactions in areas of minor aquifers has been developed. It assesses the interplay of reach-scale subsurface flow paths (RSSF), controlled by the lateral extent of the alluvial valley, and channel unit-scale hyporheic flow paths (CUSHF), controlled by riffle and run/pool sequences, and their impacts on the spatial variability of riverbed flow and solute exchange. A network of riverbed mini-piezometers and multi-level samplers in different reach- and channel-unit scale settings of the River Don (South Yorkshire, UK) is monitored to: (1) estimate vertical hydraulic gradients (VHGs) and specific discharge; (2) discriminate subsurface flow paths from conservative natural tracers; and (3) deduce biogeochemical processes. In a constrained context (downstream end of the alluvial valley), RSSF discharge favours a homogeneous riverbed hydrochemistry with limited biogeochemical processes and shallow CUSHF. In an unconstrained (open alluvial valley) or asymmetric (bedrock outcropping on one bank) context, low VHGs favour deep CUSHF and a vertical stratification of RSSF. Reducing conditions intensify with depth, and superimpose with mixing in riffles. This good approximation of flow and solute behaviour in minor aquifers provides a practical framework to understand nutrient and contaminant fate and develop cost-effective monitoring programmes across the groundwater/surface-water interface. 相似文献
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阶梯-深潭结构是山区河流中典型的高效消能结构, 以消耗水能、增加阻力的方式提升沟道稳定性。通过水槽试验模拟沟道冲刷, 探究阶梯-深潭结构稳定沟道的机制及效果, 为山区河流消能减灾和稳定河床提供科学和技术参考。结果表明: 阶梯-深潭结构能有效消耗水流能量、抑制泥沙输移和提升水流阻力, 从而有效控制河床下切和边坡破坏; 在阶梯-深潭结构的作用下, 沟道的Darcy-Weisbach系数约增加为无结构条件下的4倍, 时均输沙率降低20%~66%, 但随着流量的增大, 阶梯-深潭稳定沟道的效果降低; 阶梯高度与长度比(0.1)相同时, 结构提升沟道稳定性的效果接近。阶梯-深潭结构自身的稳定是其稳定沟道的关键条件, 实际应用过程中需防止结构发生逐级破坏。 相似文献
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Soil pipes are considered to drain off water from a hillslope and play an important role in the subsurface runoff generation
process, thus reducing the slope failure susceptibility. However, soil pipes are also often detected on the collapsed slope
suggesting that they might act to induce slope instability. To examine how the soil pipes act on pore-water pressure generation
and on a slope failure processes, a numerical model was developed. The model was used to test the response of pore-water pressure
in a hillslope with soil pipes of different cross-sectional areas, lengths, distances from the impermeable bed, roughness,
and hillslope angles. The model was also tested to find the response of open soil pipe if blocked. The study reveals that
pipes reduce pore-water pressure (measured closed to bed) around its upstream end and increase around its downstream end if
compared with no pipe case. Pore-water pressure at downstream end is increased with increase in hillslope angle, pipe cross-sectional
area, pipe length, or depth of soil pipe. Soil pipe, even if it is ended within the hillslope, increases the total discharge
from hillslope. Location of rough soil also affects the discharge and pressure within the hillslope. If the less rough pipe
is close to the source of water, discharge from hillslope matrix is greater regardless of its downstream pipe roughness. Blockage
of small portion of open soil pipe increases the soil pressure around the region but not beyond the case if there is no soil
pipe. However, complete collapse of soil pipe from a point to all along the downstream end of hillslope increases the pore-water
pressure beyond the pressure if there were no soil pipes. Therefore, the position and type of soil pipe collapse might play
an important role in shallow landslide initiation. 相似文献
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研究不同渗流边界条件下粉砂边坡的稳定特性对滑坡安全评价及防灾减灾具有重要意义。开发研制了室内边坡模型试验系统,分别进行了在上部边界入渗、侧向边界入渗和底部边界入渗的边坡失稳模型试验。分析了各试验中边坡内部不同位置体积含水率、孔隙水压力和基质吸力的变化规律以及坡体破坏过程。结果表明,不同入渗边界条件下边坡土体局部由非饱和变为饱和状态,基质吸力消失,最后在坡面形成不稳定区域塌落破坏。上部边界入渗、侧向边界入渗和底部边界入渗所引起的破坏模式根据其特点可分为局部浅层破坏、多级后退式破坏和坡面滑动破坏。通过监测边坡不同位置的体积含水率,可以为渗流引发的边坡失稳预警机制提供参考依据。 相似文献
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Alexander E. Yankovsky Raymond Torres Legna M. Torres-Garcia Kyungho Jeon 《Estuaries and Coasts》2012,35(6):1500-1509
This study was conducted in the freshwater reach of the Santee River approximately 55?±?4?km from the mouth, a transition zone from a fluvial to an estuarine tidal regime. The dataset comprises bathymetric surveys, current profile and bottom pressure measurements at two locations, and time series of discharge. Our data indicate that the transition zone is characterized by strong tidal dissipation and distinctive channel geometry. Tidal dissipation is evident in the rapid decrease of the M2 amplitude to the mean along-channel velocity ratio from 2.1 to 0.9 over a ??6-km distance. Channel cross-sectional area in the transition zone converges at a higher rate than both upstream and downstream while channel depth reveals threefold variations in the form of adjacent shoals and deeps. We hypothesize that the enhanced tidal dissipation is at the same time a cause and a result of strongly convergent bathymetry in the transition zone. 相似文献
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扇三角洲是苏北盆地高邮凹陷戴南组较为发育的一种沉积类型,集中分布在凹陷南部陡坡带一侧,是该区一个重要的勘探领域。根据岩芯、测井、地震、粒度等资料,对高邮凹陷古近系戴南组扇三角洲的沉积特征进行了研究,建立了高邮凹陷戴南组的沉积相模式。根据单井沉积相、连井沉积相分析以及地震剖面反射特征和砂地比图综合分析,确定了戴南组各亚段沉积相的平面展布,编制了戴南组各亚段沉积相分布图。结果表明：高邮凹陷南部陡坡带地形陡,存在扇三角洲发育的条件,也存在反映浅水环境的岩性特点,成分成熟度和结构成熟度低反映了近物源的条件,还发现反映牵引流和重力流共存的沉积构造特点;从地震反射特征上看,反射结构不稳定,并发现向盆地边缘加厚的楔形地震相。在此基础上,重点对戴南组扇三角洲相各微相进行了分析,共划分出扇三角洲平原、扇三角洲前缘和前扇三角洲亚相,并进一步划分出水上分流河道、漫滩沼泽、水下分流河道、分流河道间和席状砂等微相,最后详细阐述了各微相的沉积特征。 相似文献
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含有多层软弱夹层的开挖边坡具有坡体结构复杂、稳定性评价及治理难度大的特点。以黔西地区现场开挖高边坡为研究对象,建立室内物理试验模型,通过不同的工况开挖,呈现变形破坏演化过程,分析变形破坏模型及形成机理,确定失稳破坏范围。结果显示:开挖边坡裂隙产生由表及里,由上及下,由最初的陡倾短小裂隙扩展延伸,最终贯通,形成近似平行岩层的长大裂缝;缓坡度开挖变形破坏为浅表层,整体稳定性较好,失稳范围及规模较小;陡坡度开挖变形破坏规模大,稳定性较差,以滑移-拉裂深层失稳为主;浅层滑坡滑面以层间泥化夹层剪切为主,基本呈直线状;深层滑坡滑面以层间泥化夹层剪切以及陡倾裂隙组合形成阶梯状。该研究成果对于黔西地区的顺层开挖高边坡设计、稳定性评价、治理措施选择等具有重要的指导意义。 相似文献