黄河下游挟沙能力自动调整机理的初步探讨

前言 天然河流的河床形态是流经河床上的水流和泥沙与河床长期相互作用、不断自动调整后形成的。这种自动调整作用的最终结果在于使河流能够保持一定的平衡,这时河床断面、比降、糙率及物质组成正好具有使来自流域的泥沙能够在这样的容重和粘性的水流中输移下泄的流速。     

风蚀水蚀共同作用下沙漠河流泥沙级配特征

以水蚀风蚀区内蒙古河段重要入黄支流西柳沟为研究对象,通过对西柳沟流域产沙地层及河流水文站悬移质泥沙采样分析和激光粒度仪测定,对研究区河道纵向、横向断面沉积的泥沙级配特征进行了分析,揭示了流域沉积泥沙粒径分布变化规律。结果表明：西柳沟流域沉积泥沙的中数粒径从上游丘陵沟壑区到下游农田区逐渐减小;河流右岸泥沙粒径较大,左岸泥沙粒径相对较小,河床泥沙粒径介于二者之间;流域沉积泥沙粒径主要分布在0.125~0.5 mm,而流域出口水文站悬移质泥沙粒径72.5%在0.025 mm以下,说明西柳沟进入黄河干流的泥沙主要为细泥沙。     

长江河口枯季河床沉积物与河床沙波现场观测研究

于2002年3月利用浅地层剖面仪、双频道测深仪、旁侧声纳和ADCP流速剖面仪、ENDECO海流仪、OBS测沙仪在江阴至横沙岛航行150km,取得河床沉积物、河床形态和与此相关的动力因子实测资料。采用沉积学和泥沙运动力学相结合的方法进行研究,结果表明:观测期间该河段河床沉积物颗粒组成以细砂为主,中值粒径为2φ左右,分选较好;河床泥沙以单颗粒群体跳跃运动为主,在河床上形成沙波形态,并发育良好;其河床沙波的形成、发展和消失与河床沉积物颗粒度特征和涨落潮水流强弱息息相关。     

泥沙研究的发展趋势和新课题

根据国内外近年来泥沙运动研究的动向和资料积累,本文探讨了未来泥沙研究的发展趋势和面临的新课题,包括河道运动动力学、河床形态与泥沙输移的关系、非恒定流河床冲刷率、湿地泥沙生态学模拟、河口萎缩和海流输沙、全球产沙和泥沙概算、泥沙造陆、河流自净、土地利用变化的影响、黄河人造高含沙水流输沙入海和人工智能的应用等．     

基于遥感技术的黑龙江上中游河道特征研究

以2000年Landsat-7 ETM+影像、地形图、数字高程数据等为数据源,从河道平面形态及河流纵剖面形态对黑龙江上中游河道特征进行分析。从河流动力特征、流域自然环境条件及人类活动方面探讨其对河道形态特征形成的影响。研究发现:黑龙江上中游河道曲折系数均值为1.20,属于微弯顺直型河道,整体相对稳定,但局部河段河道形态复杂,河流纵剖面形态为下凹型曲线;河流形态的形成遵循一定的河流动力学规律,是水流和河床在自然因素与人类活动影响下相互作用结果。     

大河三角洲河口海岸演化机理模型研究:(I)模式理论与进展

从水沙通量变化对大河三角洲河口海岸建造及地貌演化的影响机理角度,通过研究目前国际上普遍采用的统计模型、几何模型、沉积动力学模型,以及数值模拟模型四种方法在建立大河三角洲河口海岸演化机理模型研究中的各自特点和不足,提出了建立宏观尺度机理模型的初步设想,并对运用Lagrange余流建立海岸演化机理模型所涉及的余流场的尺度转换、总余流场的建立和表达、用长期余流场构建泥沙起动、输运和沉积条件模式以及一线模型与三维动力模式耦合等关键性问题,提出了初步解决方案     

粗糙透水床面明渠水流垂线流速分布的试验研究

冲积河流的粗颗粒河床,具有较大的渗透性,河床渗透对明渠水流运动特性的影响不可忽视．通过水槽试验,研究了河床渗透对垂线流速分布的影响．距试验玻璃水槽进口10m处,设计一个长1．65m、宽0．7m的收缩段,由12层直径1cm的玻璃珠紧密有规则铺成,以模拟粗糙透水床面．其上下游铺上1层相同玻璃珠,形成粗糙度相同但不透水的床面．垂线流速分布通过激光多普勒测速仪及配套的高精度坐标架系统测量．试验施放了3种流量,分别在不透水和透水床面进行垂线流速分布测量．试验结果表明：1）不透水床面的垂线流速分布符合粗糙床面的对数分布公式;2）粗糙透水床面明渠流的垂线流速分布与不透水床面相似;3）相同水流条件下,透水床面的摩阻流速要大于不透水床面;4）透水床面的摩阻流速与积分常数的变化规律有待进一步研究．     

喀斯特地区洞穴壶穴形态的形成与发育

喀斯特洞穴河床壶穴是记录洞穴微地貌演化、洞道走向、水流与地下河床边界条件相互作用的关键性证据之一。通过对贵州绥阳双河洞穴系统,属娄山关组白云岩地下河段108处洞穴壶穴的形态及分布特征进行实地仔细观察和分析发现:该区地下河河床壶穴分为两种形式即跌水壶穴(plunge holes)和旋转流壶穴(eddy holes)。它的规模、形态及分布特征规律性较地表河床壶穴强,主要受水动力、洞道走向控制。由于洞内气候环境长期稳定,洞穴河床壶穴的形成与演化主要是水动力条件、洞道走向、岩性、洪冲积物综合作用的结果。本研究结果将丰富与完善壶穴不同地貌部位、不同岩性特征及成因,为洞穴河床壶穴形态的形成与发育提供科学论证,为洞穴微地貌演化过程及洞穴水动力研究发展提供科学依据。     

中国黄土分布区多沙曲流发育规律

依据中国黄土分布区多沙曲流的水沙资料、河床平面形态和河床大断面测量资料分析认为：多沙河流来水变率影响河床断面形态和曲流发育;由于窄深的河槽是高含沙水流输沙的必要条件和结果,因此随着含沙量的增加,多沙河流河床断面形态首先出现变窄深的趋势,随着含沙量的进一步增加,水流造床能力增大,河槽会向宽浅方向调整;一定的河床冲淤强度有利于曲流的发育,随着含沙量的增加,多沙河流河床曲率存在先增加后减小的规律。     

风-水两相作用区内河床沉积粒度对地貌过程的响应:以内蒙古黑赖沟流域为例（英文）

黑赖沟流域位于内蒙古风-水两相交互侵蚀区域,主河道的泥沙输移特征较为复杂。为了分析河道沉积粒度与地貌过程的关系,文中主要通过探讨粒度参数与外营力特征的关系对沉积粒度的成因机制进行了研究。在分析过程中首先对河床沉积粒度参数、风成颗粒的最大粒径、河流功率和面积-高程积分值沿河道方向的连续变化值进行了计算,分别对不同河段的外营力活动特征进行分析,并以此为基础,将粒度参数作为因变量,其余三者作为自变量,建立了多元回归函数。分析结果显示不同河段外营力对河床沉积物的影响特征不同,其中上游河段河床沉积物主要受径流和风力作用影响;中游河段主要受河流作用影响,沉积颗粒的分选性最差,沉积颗粒的大小与河流功率关系密切,粗质颗粒难以被搬运到下游河段;下游河段受库布齐沙漠影响的可能性较大。就河道整体特征来讲,河道两侧地貌的侵蚀演化特征对河道内的沉积颗粒影响不显著,河床沉积物特征主要受河流和风力作用,其中沉积颗粒的平均粒径主要反映了河流功率的大小,风力作用对沉积颗粒的分选性具有一定影响。河道内的风成颗粒主要来自流域西部,粒径值不会大于0.88Φ,其中下游河段内的风成颗粒比上游河段略粗。总而言之,河流作用对河道沉积粒度特征的影响起主要作用,风力作用次之。     

Impacts of backwater hydrodynamics on fluvial–deltaic stratigraphy

The hydrodynamics of rivers approaching a receiving basin are influenced by the onset of backwater conditions that give rise to decelerating reach-average flow velocity and decreasing boundary shear stress. These changes occur across a spatial gradient over which decreasing sediment transport capacity triggers morphodynamic responses that include sediment deposition at the transition from uniform to nonuniform flow. As a consequence, the channel width-to-depth ratio and bed sediment grain size decrease downstream. While nonuniform flow and associated morphodynamic adjustments have been investigated in modern fluvial–deltaic systems, the impacts to fluvial–deltaic stratigraphy remain relatively unexplored. This represents an important unresolved gap: there are few contributions that link morphodynamic response to nonuniform flow, impacts on sediment deposition and influence on the rock record. This study uses a numerical model to explore how variable channel hydraulics influence long-term (1000s years) patterns of sediment deposition and development of stratigraphy. The model results indicate that: (a) nonuniform flow propagates upstream beyond the backwater transition that is traditionally estimated with a basic backwater length scale relationship. (b) Base-level fluctuations, especially rising, enhance the impact of nonuniform flow. (c) Sediment deposition shows large spatio-temporal variability, which ultimately contributes to unique stacking patterns of fluvial–deltaic stratigraphy. (d) Nonuniform flow imparts spatial variation in flow depth, channel bed slope and sediment grain size over the delta, and these signatures are potentially preserved and recognizable in the rock record.     

甬江河床演变及航道治理

本文分析甬江动力、泥沙、边界及河床演变的基本特征,提出甬江航道整治的原则和措施。     

三峡水库下游弯曲河型演变规律调整及其驱动机制

大型水库的兴建深刻改变了下游水沙输移特点,进而导致河床演变规律显著调整,水库下游弯曲河型对水沙过程改变响应敏感,是水库下游河床演变、航道整治、河势控制等方面研究的关键区域。本文基于1996-2016年的实测水文、地形资料,对长江三峡水库下游弯曲河型的演变规律及其驱动机制开展研究,结果表明：① 三峡水库蓄水前,下荆江存在“凸淤凹冲”、“凸冲凹淤”两类弯曲河型,而三峡水库蓄水后均表现为“凸冲凹淤”的一致性规律;② 在水库拦沙作用的影响下,下荆江河段平滩河槽存在累积性冲刷现象,冲刷部位集中于枯水河槽与基本河槽之间的低滩,冲淤部位调整主要由变化的流量过程所驱动,上游河势、河道边界以及支流入汇等因素均有一定驱动作用;③ 在三峡水库蓄水后缺乏大洪水的情况下,凸岸水流挟沙力随流量增加逐渐增强,水流对凸岸冲蚀力度在平滩流量级附近（20000~25000 m3/s）达到最强,平滩流量附近流量级的持续时间超过20天时,弯曲河道发生凸冲凹淤现象。而悬沙中造床粗沙的减少,增强了水流冲刷强度,加剧了凸岸的冲蚀程度。     

Interacting effects of multiple factors on the morphological evolution of the meandering reaches downstream the Three Gorges Dam

Elucidating the influence of dams on fluvial processes can inform river protection and basin management. However, relatively few studies have focused on how multiple factors interact to affect the morphological evolution of meandering reaches. Using hydrological and topographical data, we analyzed the factors that influence and regulate the meandering reaches downstream the Three Gorges Dam (TGD). Our conclusions are as follows. (1) The meandering reaches can be classified into two types based on their evolution during the pre-dam period: G1 reaches, characterized by convex point bar erosion and concave channel deposition (CECD), and G2 reaches, characterized by convex point bar deposition and concave channel erosion (CDCE). Both reach types exhibited CECD features during the post-dam period. (2) Flow processes and sediment transport are the factors that caused serious erosion of the low beaches located in the convex point bars. However, changes in the river regime, river boundaries and jacking of Dongting Lake do not act as primary controls on the morphological evolution of the meandering reaches. (3) Flood discharges ranging from 20,000 to 25,000 m³/s result in greater erosion of convex point bars. The point bars become scoured if the durations of these flows, which are close to bankfull discharge, exceed 20 days. In addition, the reduction in bedload causes the decreasing of point bar siltation in the water-falling period. (4) During the post-dam period, flood abatement, the increased duration of discharges ranging from 20,000 to 25,000 m³/s, and a significant reduction in sediment transport are the main factors that caused meandering reaches to show CECD features. Our results are relevant to other meandering reaches, where they can inform estimates of riverbed change, river management strategies and river protection.     

多因素对三峡水库下游弯曲河型演变的迭加效应（英文）

Elucidating the influence of dams on fluvial processes can inform river protection and basin management.However,relatively few studies have focused on how multiple factors interact to affect the morphological evolution of meandering reaches.Using hydrological and topographical data,we analyzed the factors that influence and regulate the meandering reaches downstream the Three Gorges Dam(TGD).Our conclusions are as follows.(1)The meandering reaches can be classified into two types based on their evolution during the pre-dam period:G1 reaches,characterized by convex point bar erosion and concave channel deposition(CECD),and G2 reaches,characterized by convex point bar deposition and concave channel erosion(CDCE).Both reach types exhibited CECD features during the post-dam period.(2)Flow processes and sediment transport are the factors that caused serious erosion of the low beaches located in the convex point bars.However,changes in the river regime,river boundaries and jacking of Dongting Lake do not act as primary controls on the morphological evolution of the meandering reaches.(3)Flood discharges ranging from 20,000 to 25,000 m3/s result in greater erosion of convex point bars.The point bars become scoured if the durations of these flows,which are close to bankfull discharge,exceed 20 days.In addition,the reduction in bedload causes the decreasing of point bar siltation in the water-falling period.(4)During the post-dam period,flood abatement,the increased duration of discharges ranging from 20,000 to 25,000 m3/s,and a significant reduction in sediment transport are the main factors that caused meandering reaches to show CECD features.Our results are relevant to other meandering reaches,where they can inform estimates of riverbed change,river management strategies and river protection.     

Embedding reach-scale fluvial dynamics within the CAESAR cellular automaton landscape evolution model

We introduce a new computational model designed to simulate and investigate reach-scale alluvial dynamics within a landscape evolution model. The model is based on the cellular automaton concept, whereby the continued iteration of a series of local process ‘rules’ governs the behaviour of the entire system. The model is a modified version of the CAESAR landscape evolution model, which applies a suite of physically based rules to simulate the entrainment, transport and deposition of sediments. The CAESAR model has been altered to improve the representation of hydraulic and geomorphic processes in an alluvial environment. In-channel and overbank flow, sediment entrainment and deposition, suspended load and bed load transport, lateral erosion and bank failure have all been represented as local cellular automaton rules. Although these rules are relatively simple and straightforward, their combined and repeatedly iterated effect is such that complex, non-linear geomorphological response can be simulated within the model. Examples of such larger-scale, emergent responses include channel incision and aggradation, terrace formation, channel migration and river meandering, formation of meander cutoffs, and transitions between braided and single-thread channel patterns. In the current study, the model is illustrated on a reach of the River Teifi, near Lampeter, Wales, UK.     

Morphodynamics of a pseudomeandering gravel bar reach

A large number of rivers in Tuscany have channel planforms, which are neither straight nor what is usually understood as meandering. In the typical case, they consist of an almost straight, slightly incised main channel fringed with large lateral bars and lunate-shaped embayments eroded into the former flood plain. In the past, these rivers have not been recognised as an individual category and have often been considered to be either braided or meandering. It is suggested here that this type of river planform be termed pseudomeandering.A typical pseudomeandering river (the Cecina River) is described and analysed to investigate the main factors responsible for producing this channel pattern. A study reach (100×300 m) was surveyed in detail and related to data on discharge, channel changes after floods and grain-size distribution of bed sediments. During 18 months of topographic monitoring, the inner lateral bar in the study reach expanded and migrated towards the concave outer bank which, concurrently, retreated by as much as 25 m. A sediment balance was constructed to analyse bar growth and bank retreat in relation to sediment supply and channel morphology. The conditions necessary to maintain the pseudomeandering morphology of these rivers by preventing them from developing a meandering planform, are discussed and interpreted as a combination of a few main factors such as the flashy character of floods, sediment supply (influenced by both natural processes and human impact), the morphological effects of discharges with contrasting return intervals and the short duration of flood events. Finally, the channel response to floods with variable sediment transport capacity (represented by bed shear stress) is analysed using a simple model. It is demonstrated that bend migration is associated with moderate floods while major floods are responsible for the development of chute channels, which act to suppress bend growth and maintain the low sinuosity configuration of the river.     

高含沙型曲流河床形成机理的初步研究

本文描述了在我国黄土高原宽谷中发现的含沙量超过100kg/m^3的曲流河床，并运用高含沙水流的作用对其成因进行了探讨。指出当水流进入高含沙范围时，水流能耗率大幅度降低，挟沙能力大大增加，这是促使河床向弯曲发展的主要原因。由于高含沙水流的稳定输送有赖于边界条件，故边界条件在这种曲流河床的形成中起了重要的作用。文中并讨论了这一地区游荡河型与弯曲河型的判别条件。     

浙江椒江山溪性强潮河口的若干特征

本文从椒江河口的径流、潮流变化,泥沙运移和沉积结构以及河床演变和河口的发育过程探讨了山溪性强潮河口若干特征。     

The mechanism of barrier river reaches in the middle and lower Yangtze River

Alluvial channel has always adjusted itself to the equilibrium state of sediment transport after it was artificially or naturally disturbed. How to maintain the equilibrium state of sediment transport and keep the river regime stable has always been the concerns of fluvial geomorphologists. The channel in the middle and lower reaches of the Yangtze River is characterized by the staggered distribution of the bifurcated river and the single-thread river. The change of river regime is more violently in the bifurcated river than in the single-thread river. Whether the adjustment of the river regime in the bifurcated river can pass through the single-thread river and propagate to the downstream reaches affects the stabilities of the overall river regime. Studies show that the barrier river reach can block the upstream channel adjustment from propagating to the downstream reaches; therefore, it plays a key role in stabilizing the river regime. This study investigates 34 single-thread river reaches in the middle and lower reaches of the Yangtze River. On the basis of the systematic summarization of the fluvial process of the middle and lower reaches of the Yangtze River, the control factors of barrier river reach are summarized and extracted: the planar morphology of single-thread and meandering; with no flow deflecting node distributed in the upper or middle part of the river reach; the hydraulic geometric coefficient is less than 4; the longitudinal gradient is greater than 12‰, the clay content of the concave bank is greater than 9.5%, and the median diameter of the bed sediment is greater than 0.158 mm. From the Navier-Stokes equation, the calculation formula of the bending radius of flow dynamic axis is deduced, and then the roles of these control factors on restricting the migration of the flow dynamic axis and the formation of the barrier river reach are analyzed. The barrier river reach is considered as such when the ratio of the migration force of the flow dynamic axis to the constraint force of the channel boundary is less than 1 under different flow levels. The mechanism of the barrier river reach is such that even when the upstream river regime adjusts, the channel boundary of this reach can always constrain the migration amplitude of the flow dynamic axis and centralize the planar position of the main stream line under different upstream river regime conditions, providing a relatively stable incoming flow conditions for the downstream reaches, thereby blocking the upstream river regime adjustment from propagating to the downstream reaches.