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黄河下游不同河型河道的水沙效应及演变趋势分析 总被引：3，自引：2，他引：1
黄河下游沿程出现的辫状河流（游荡型河流）、弯曲河流（弯曲型河流）、顺直河流（顺直微弯型河流）的转化现象引人关注,并有不同方面的专门研究。本研究针对以往研究的不足,通过对不同河型段的水沙演变、断面形态对流量的响应、河道断面演变、河床沉积速率及能耗率特征等方面,系统分析了不同河型段河道的水沙效应。认为黄河下游沿程出现的三类河型是由河道比降小、河床质细、洪枯水交替、粗泥沙输入少及大堤限制等因素起主导作用。其中顺直河流的出现是人工大堤的胁迫性产物。随着近年来水沙的阶段性减小,顺直河流在大堤的挟持下得以维持;弯曲河段河道的侧向摆动依然、宽度略微变窄,河床加积速率最大,但不会导致整个下游河道比降发生明显变化;辫状河段能耗率相对较大,冲淤强烈,滩槽更替频繁,但随着流量的减小,其能耗率明显减小,其比邻弯曲河流段的河道会逐渐曲流化,表现为弯曲河段的适度上延,但延伸有限。各类治理措施中,以中上游修建水库和淤地坝是最有效的,可拦截大量粗泥沙,从而降低下游河床的加积速率,以延缓悬河的发展。当然,针对决口险情的大堤建设是必要的,但要与不同河型段的河道稳定性相适应。 相似文献
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山溪性强潮河口是中国东南沿海的一种典型河口,水动力强劲、泥沙运动活跃,对人类活动响应迅速。自然条件与人类活动共同驱动下山溪性强潮分汊河道演变机制尚需进一步研究。以径潮流作用下滩槽演变剧烈的瓯江江心屿分汊河段为例,采用实测资料分析与二维水沙数学模型计算的方法,分析了20世纪70年代以前自然演变、70年代至90年代末上村丁顺坝建设影响期、21世纪以来人工采砂等影响下的河道演变机制。结果表明,丁顺坝建设等人类活动改变了该河段自然条件下主支汊周期性交替的演变规律;21世纪以来人工采砂等造成河床大幅下切,近20 a来潮差增大0.5 m、涨潮流量增大约47%,分流与分沙不均匀性分别减弱0.08～0.30和0.28～0.54,涨落潮流速差异减小,有利于减缓支汊萎缩态势,河道演变机制受到自然-人类活动双重因素主导。研究成果可为类似河流演变和保护利用提供借鉴。 相似文献
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青藏高原东北缘循化-贵德地区晚新生代构造活动强烈,同时晚新生代黄河的发育和演化也提供了研究高原构造隆升扩展以及黄河侵蚀下切过程的理想场所。黄河水系通过调整河流纵剖面的形态在垂向上响应不同的构造隆升以及河床岩性的变化。利用数字高程模型数据,提取黄河水系河流纵剖面形态,利用基岩河道河流水力侵蚀模型（stream-power incision model）为依托,尝试揭示晚新生代以来强烈构造活动在黄河水系河流纵剖面形态特征上的表现。分析发现,在循化-贵德地区岩性分布均匀的新生代盆地内部,黄河水系纵剖面在河流水力侵蚀模型坡度-面积双对数图解中大部分表现为上凸特征,即基岩河道的河床随时间的变化为正值,指示了基岩的隆升速率大于河流的下切侵蚀速率。在河流流经盆地内部不同岩性地区,特别是前新生界地层区,河流纵剖面也表现为一定的上凸特征,表明了新生界与前新生界地层岩性差异对河流纵剖面的控制作用。综合来看,青藏高原东北缘循化-贵德地区黄河水系河流纵剖面形态特征是晚新生代强烈构造活动和岩性差异共同控制的结果,揭示了循化-贵德地区造山系统地形发育仍然处于前均衡或接近均衡状态,同时也从侧面表明青藏高原东北缘地区是整个高原隆升扩展的最新和最前缘部位的时空格局特征。 相似文献
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为预测黄河下游游荡性河道大规模整治后对河床演变的作用,基于河流动力学理论,通过物理模型试验的方法,以黄河下游游荡性河道典型河段为对象,研究了河床过程对河道整治的复杂响应关系。研究结果表明,河槽横断面形态的调整与人工边界约束程度、流量变差及含沙量变差有关;只要整治工程体系平面布设合理,整治工程量达到一定规模后,通过河道整治,可使河槽横断面形态趋于窄深方向发展,促使游荡型河道向限制性弯曲型河道转化,同时,河道泄洪输沙能力有所提高;河道整治后,不同河段的比降调整不会平行进行。 相似文献
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末次冰期是距离人类最近的一次冰期,气候异常寒冷且存在高频高幅波动,河流系统如何响应冰期气候的变化值得关注与研究。基于河流系统对气候变化的敏感响应,传统的经典地貌理论认为河流下切在河流阶地形成过程中起着至关重要的作用,河流的下切行为发生在间冰期或者冰期向间冰期的过渡阶段,堆积行为发生于冰期,然而近年来最新的河流地貌研究成果表明,末次冰期河流下切较为普遍。首先对河流阶地形成的传统模式进行总结分析,认为单纯的构造驱动模式存在不合理性,气候也发挥着重要的调节作用;单一的气候变化无法驱动多级且高差较大阶地的形成,地壳抬升往往是必要因素;气候变化是引发河流堆积-下切行为转换形成河流阶地的关键因素。其次通过前人的研究案例总结出末次冰期河流下切行为响应气候变化的三种模式：(1)气候的高度不稳定性引发大规模的洪水事件驱动河流快速下切;(2)快速隆升区气候高频波动叠加构造抬升驱动河流下切;(3)沿海平原地区海平面大幅度下降驱动河流下切。这三种模式对于理解末次冰期河流系统对短尺度高频气候变化的响应以及对河流阶地成因的判断具有十分重要的指导意义。 相似文献
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下切谷及其油气勘探意义 总被引：3，自引：0，他引：3
下切谷是层序地层学中的一个重要术语.在海平面下降时期河流切割早期陆架,从而形成下切谷,下切谷充填发生于海平面上升早期,通常是由若干河道沉积叠加而形成的.下切谷的形成与充填与河流的作用密切相关,不同类型(包括流量、沉积负载等)的河流可以形成不同规模的下切谷,同样不同类型的河流可以形成不同类型的下切谷充填.下切谷的宽度在数公里至数十公里甚至达上百公里,深度从数米至数十米甚至上百米.层序地层学研究表明,下切谷是低位体系域(LST)的重要组成部分,位于低位体系域的上倾部分,在时间上和空间上广泛分布,其内充填有广泛的河流相沉积,因此在油气藏形成过程中既是良好的油气运移通道,又是良好的油气储集场所. 相似文献
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淮干中游河段是淮河河道治理的重点河段。目前，关于中游河道的各项整治工程有的已陆继展开，有的正在加紧规划设计。作为当前规划设计或将来河道演变趋势观测的依据，有关该河段的河道特征及一些基本特征参数的研究越来越受到有关各方的重视。河道造床流量是指其造床作用相当于河段整个水沙过程的综合造床作用的一个流量参数，反映河段内水沙特性和河床边界条件相互作用的综合特征，无疑是河道整治工程、河床演变规律研究中的一个十 相似文献
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Braided rivers exhibit highly variable morphologies, morphodynamic behaviours and resulting depositional records. To evaluate relationships between characteristics of braided-river channel belts and river depth, water discharge and streambed gradient, 39 numerical modelling experiments were conducted with the software Delft3D to simulate braided-river evolution under a broad range of boundary conditions. Data from model outputs were integrated with observations from 63 natural braided rivers differing with respect to river depth and streambed gradient. The modelled rivers each underwent similar evolutions, yet each culminated in markedly different final river morphologies, dependent on discharge and riverbed gradient. The rivers underwent evolutionary stages of: (i) formation of transverse unit bars with limited relief from an initially featureless bed; (ii) channel development around bars and in some cases dissecting transverse unit bars; (iii) formation of relatively simpler compound bars; and (iv) amalgamation of these simpler compound bars into more complex compound bars. Quantitative relationships relating to braided-river channel-belt morphology and organization are established, and the following results are noted: (i) bar elongation (length-to-width ratio) is correlated positively with riverbed gradient; (ii) bar height and area are correlated positively with discharge, and negatively with riverbed gradient; (iii) the river depth is the main predictor of mean braid-bar area; and (iv) the degree of braiding is primarily associated with river width-to-depth ratio and riverbed gradient. Results arising from this research improve our understanding of controls on the morphology and architectures of braided fluvial channel belts; they provide a novel empirical characterization that can be applied for predicting channel depth, bar morphology, streambed gradient, and degree of braiding of modern fluvial systems and of the formative rivers of ancient preserved successions. 相似文献
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Sediment dynamics and hydrodynamics in the lower course of a river highly regulated by dams: the Ebro River 总被引：1，自引：0，他引：1
The lowest part of the Ebro River is a microtidal salt-wedge estuary. Penetration of the salt-wedge is largely controlled by the fluvial discharge and the morphology of the river bed, although sea level variations caused by tides and atmospheric conditions can also play significant roles. The concentration and distribution of suspended particulate matter in this part of the river and the fluvial sediment discharge are strongly influenced by the dynamics of the salt-wedge. Damming of the river has caused sediment to be trapped in reservoirs and has regulated the fluvial discharge. Intrusion of the salt wedge has thus also been regulated. At present, sediment discharge is between 1 and 1·5 × 105 tons per year, which is less than 1% of the sediment that the Ebro River discharged into the sea before construction of the dams. This extreme reduction in sediment supply has allowed marine erosional processes to dominate in the delta. 相似文献
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JAMES R. MAYNARD 《Sedimentology》2006,53(3):515-536
Tectonic deformation of the land surface is known to influence the gradient, water and sediment discharge and the grain-size of modern fluvial systems. Any change in these variables alters the equilibrium of a fluvial system, potentially causing a change in channel morphology. 3D seismic data from the Tertiary (Miocene) age, Upper Frio Formation, Kelsey Field, South Texas, in the US are used to examine changing fluvial channel morphology through time during a period of active growth of a rollover anticline in the hangingwall of a normal fault (the Vicksburg Fault). The studied interval varies between 22 and 47 m thick, and spans several hundred thousand years. It consists of an alternation of fluvial sandstones, overbank mudstones and coal. Seismic extractions show the evolution of sinuous fluvial channels during a phase of growth fault activity. Prior to growth, a single sinuous channel is imaged. During growth, the fluvial system became decapitated by a developing rollover anticline, and a highly sinuous drainage network formed, with frequent avulsion events, headward propagation of streams and related stream capture. Increased channel sinuosity was spatially associated with increased avulsion frequency in the area down dip to the east of the rollover anticline, more than 10 km from the active fault. More than 25 m of relative accommodation developed on the flank of the growing rollover anticline compared with on the crest. The increased channel sinuosity is interpreted as reflecting an increase in longitudinal valley slope analogous to observations made in flume experiments and modern river systems. The increase in avulsion frequency is attributed to increased aggradation as the rivers adjusted back to equilibrium grade following the increase in slope. 相似文献
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河床冲淤相对平衡下的洪水分组含沙量阈值是多泥沙河流水沙调控的重要参数.基于河床演变学的原理,根据黄河下游200余场次洪水实测资料,探讨了洪水分组含沙量阈值和分组来沙系数阈值.研究表明,黄河下游洪水过程中,在一定的分组含沙量及来沙系数条件下,可以使得河床冲淤达到相对平衡.对于悬沙以细泥沙为主的洪水,其河槽冲淤临界含沙量与主槽单宽流量、最大日均流量、花园口以下河段最小平滩流量、床沙中值粒径大于0.05 mm的沙重百分数有关;对于悬沙以中粗泥沙为主的临界含沙量则与粒径大于0.05 mm的沙重百分数无关;对于悬沙以粗泥沙为主的临界含沙量除与细泥沙临界含沙量的因素有关外,还与悬沙中值粒径小于0.025 mm、大于0.05 mm的沙重百分数有关.对于含沙量级相近的洪水,若流量级不同,同样可以产生不同的冲淤结果,即存在着分组来沙系数临界值. 相似文献
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Ágnes Cserkész-Nagy Tamás Tóth 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(2):238-247
We present a case study on how riverbed morphology of the engineered and meandering Tisza River of the Pannonian Basin (Hungary) has changed during post-engineering times. The objectives were (1) mapping the location and morphology of scours and point bars, (2) reconstructing their changes in a 150 year time-scale in response to engineering work, (3) describing the differences of quasi-natural and engineered channels and (4) distinguishing of local and general causes, both natural and anthropogenic.Recent erosion and deposition have been traced on continuous ultrahigh resolution (UHR) seismic profiles. These results were matched up to channel cross-sections and to time-series planimetric and bathymetric maps. The topography of the riverbed is determined primarily by two factors: the plan view geometry of the channel and the lithology of the substratum. As well as naturally developing scours in the river bends, shallower and elongated, slightly refilled ones appear on straight reaches or in engineered channels. Elongated bed scours and extraordinary forms are related to local human effects. However, erosion is observed everywhere in the investigated 102 km long Middle-Tisza region. As a result of cut-offs the gradient increased and, as a consequence, the riverbed became incised.Sedimentation is reflected in accelerated point bar development, which resulted in intensive lateral migration and increasing sinuosity, which is enhanced in the vicinity of human interventions. Changes do not propagate far away. Channel adjustments happened in two phases: rapid incision was followed by a slower sinuosity increase in order to obtain a new dynamic equilibrium. 相似文献
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Palaeocompetence analysis and palaeodischarge estimation techniques are applied to a late Pleistocene–early Holocene gravel terrace in the Mahi River Basin, western India. Terrace sedimentology, comprising gravels overlain by sand lithofacies suggests a gradual change in palaeohydrological conditions marking a switch from braided to meandering fluvial styles. The discharge values for the gravel bedforms based on the clast size and the cross bed set thickness are estimated between ∼150–180 m3 s−1 comparable with the present day observed values albeit with a much higher competence. Results indicate that fluvial aggradation occurred under low discharge conditions with intermittent high discharge events depositing longitudinal gravel bars. The incision of these gravel bars and the formation of terraces can be attributed to the higher discharge regime post 9.2 ka. The study further indicates that whereas the aggradation of the gravel terrace during the early Holocene was controlled by the large sediment influx, the incision that followed was in response to the increase in the discharge and competence of the river flow. 相似文献
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JOANNE MOL 《第四纪科学杂志》1997,12(1):43-60
The last glacial shows large variations in climate, which are reflected in the fluvial record in the Niederlausitz, eastern Germany. The entire sequence resembles the fluvial development in other river basins in northwestern Europe, which show contemporaneous changes in depositional style at the onset of a climatic change. During the Middle and the Late Pleniglacial, permafrost conditions resulted in an episodic river discharge. The presence or absence of vegetation, in combination with such ephemeral stream conditions, determined the type of river during each period. A relatively well-developed vegetation cover on the flood plains during the Middle Pleniglacial resulted in a low sediment yield. In combination with the intermittent discharge, this caused the development of an ephemeral anastomosing river system, a river with stable channels and extensive sandy overbank areas. The decline in vegetation cover at ca. 28 ka BP caused an increase in sediment yield and peak discharges, which resulted in the development of a sandy braided river in adjustment to these new conditions. Following the coldest period at around 20 ka, precipitation was so low that fluvial activity was limited and aeolian deposition took place in the valley. © 1997 by John Wiley & Sons, Ltd. 相似文献
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Lars J. Noorbergen Antonio Turtu Klaudia F. Kuiper Cornelis Kasse Sverre van Ginneken Mark J. Dekkers Wout Krijgsman Hemmo A. Abels Frederik J. Hilgen 《Sedimentology》2020,67(5):2529-2560
Aggradation and fluvial incision controlled by downstream base-level changes at timescales of 10 to 500 kyr is incorporated in classic sequence stratigraphic models. However, upstream climate control on sediment supply and discharge variability causes fluvial incision and aggradation as well. Orbital forcing often regulates climate change at 10 to 500 kyr timescales while tectonic processes such as flexural (un)loading exert a dominant control at timescales longer than 500 kyr. It remains challenging to attribute fluvial incision and aggradation to upstream or downstream processes or disentangle allogenic from autogenic forcing, because time control is mostly limited in fluvial successions. The Palaeocene outcrops of the fluvial Lebo Shale Member in north-eastern Montana (Williston Basin, USA) constitute an exception. This study uses a distinctive tephra layer and two geomagnetic polarity reversals to create a 15 km long chronostratigraphic framework based on the correlation of twelve sections. Three aggradation–incision sequences are identified with durations of approximately 400 kyr, suggesting a relation with long-eccentricity. This age control further reveals that incision occurred during the approach of – or during – a 405 kyr long-eccentricity minimum. A long-term relaxation of the hydrological cycle related to such an orbital phasing potentially exerts an upstream climate control on river incision. Upstream, an expanding vegetation cover is expected because of an increasingly constant moisture supply to source areas. Entrapping by vegetation led to a significantly reduced sediment supply relative to discharge, especially at times of low evapotranspiration. Hence, high discharges resulted in incision. This study assesses the long-eccentricity regulated climate control on fluvial aggradation and incision in a new aggradation–incision sequence model. 相似文献
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Stability of landslide dams and development of knickpoints 总被引：2，自引：0，他引：2
The Wenchuan earthquake triggered many landslides and numerous avalanches and created 100 odd quake lakes. The quake lakes
may be removed or preserved. The removal strategy was applied to several large landslide dams, which were dangerous because
massive amounts of water pooled up in the quake lakes. The dams could eventually fail under the action of dam outburst flooding,
potentially endangering the lives of people in the downstream reaches. This paper studied the stability of landslide dams
and the development of knickpoints by field investigations and experiments, and analyzing satellite images. The study concluded
that if landslide dams were preserved, they would develop into knickpoints and act as a primary control of riverbed incision
and, thus, reduce the potential of new landslide. The stability of landslide dams depends mainly on the development of the
step-pool system and stream power of the flood flow. If a landslide dam consists of many boulders, a step-pool system may
develop on the spillway channel of the dam, which would maximize the resistance, consume most of the flow energy and consequently
protect the dam from incision. The development degree of the step-pool system is represented by a parameter S
p, which was measured with a specially designed instrument. A preservation ratio of landslide dams is defined as the ratio
of preserved height after flood scouring to the original height of the dam. For streams with peak flood discharge lower than
30 m3/s, the preservation ratio is linearly proportional to S
p. For rivers with a peak flood discharge higher than 30 m3/s (30–30,000 m3/s), the minimum S
p value for stable channel increases with log p, in which p is the unit stream power. For a landslide dam with a poorly developed step-pool system, S
p is smaller than the minimum value and the outburst flood incises the spillway channel and causes failure of the dam. For
preserved landslide dams, sediment deposits in the quake lakes. A landslide dam may develop into a knickpoint if it is stabilized
by long-term action of the flow. Large knickpoints can totally change the fluvial processes and river morphology. Uplift of
the Qinghai–Tibetan Plateau has caused extensive channel bed incision along almost all rivers. For many rivers, the incision
has been partly controlled by knickpoints. Upstream reaches of a knickpoint have a new and unchanging base level. This brings
about a transition from degradation to aggradation and from vertical bed evolution to horizontal fluvial process. Multiple
and unstable channels are prominent in the reaches, upstream of the knickpoints. If hundreds of landslide dams occurred simultaneously
on a reach of a mountain river, the potential energy of bank failure and the slope erosion would be greatly reduced and sediment
yield from the watershed may be reduced to nearly zero. The quake lakes may be preserved long term and become beautiful landscapes.
Streams with long-term unfilled quake lakes have good aquatic ecology. 相似文献