1986-2015年小浪底水库运行前后黄河下游主槽调整规律

基于黄河下游1986-2015年的水沙和沿程实测大断面数据等资料,统计分析了小浪底水库运行前后下游主槽断面形态参数（河宽、水深、河相系数）的调整过程。结果表明：1986-1999年小浪底运行前主槽持续淤积萎缩,主槽河宽和水深均减小,河宽与水深调整强度高村以上段河宽大于水深、断面河相系数明显减小,高村以下段河宽小于水深、河相系数小幅增加;2000-2015年小浪底水库运行后主槽持续冲刷,主槽河宽和水深增加,沿程各段水深调整强度均大于河宽,河相系数减小;各段断面形态调整方式淤积期表现为艾山以上游荡段和过渡段既有横向萎缩又有垂向淤高、艾山以下弯曲段以垂向淤高为主,冲刷期游荡段和过渡段为横向展宽和垂向冲深、弯曲段以垂向冲深为主;河宽淤积期减小速率明显大于冲刷期增加速率,水深淤积期减小速率略小于冲刷期增加速率,经过一轮淤积和冲刷后,断面形态向窄深方向发展;主槽断面形态调整规律与水沙条件密切相关,断面河相系数除游荡段淤积期与流量呈正相关、与含沙量呈负相关外,游荡段冲刷期、过渡段和弯曲段淤积与冲刷不同阶段,河相系数与流量呈负相关,与含沙量呈正相关。     

游荡性河流演变规律研究进展及其河型归属探讨

游荡性河道在中国广泛分布,其中以黄河下游上段最为典型,但关于游荡性河型的归属问题尚存在很大争议,国际上多将游荡性河流归属为辫状河型。本文以黄河下游游荡性河道为典型案例,系统总结了游荡性河流的演变特征、主要影响因素和形成机理,并从定义、成因、特征及河道形成过程方面,将游荡与辫状河型的异同点进行对比分析。得到以下启示：游荡性河型是一种重要的河道型态,与辫状河型在许多方面存在较明显差异。特别是游荡河型主要发育于能量小于输沙需求的环境,因而形态呈现不稳定特性,但辫状河型不仅出现在能量较多的环境,而且也常在能量较小的环境中出现,因而一部分具有稳定形态,另一部分则表现出不稳定的特性,因此,有必要对游荡性河道和辫状河道给予区分。最后对未来研究进行了展望,提出应重视河型形成的内在机理,对能量理论进行发展及深化,进一步系统性评价游荡性河道与辫状河道的异同性,以解决游荡性河道的河型归属问题。     

汉江襄■段游荡性河道特征分析及该段河道的整治

汉江是长江最长的支流,全长1507公里,汉江丹江口以上为上游,属山区,河道长890公里;丹江口至钟祥为中游,属丘陵区,河道长240.2公里;钟祥至汉口为下游,属平原区,河道长376.7公里。汉江较大的支流有褒河、任河、洵河、甲河、堵河、丹江、南河和唐白河。襄(氵利)段河道属汉江中游下段,长约110公里,具有河道宽浅,沙洲林立,水流散乱,汊道较多,主支汊易位频繁,主泓摆动幅度大,沙洲变化无常,河道稳定性差的特点,为游荡性河道,以雅口至流水沟、转斗湾至(氵利)河口最为明显。     

黄河下游游荡性河道小水致灾研究

20世纪80年代中期以来,黄河下游游荡性河道的洪水灾害是在下游水量明显减少、洪峰流量也不断减小的情况下发生的。即使是水量比较小的普通洪水,也能造成下游滩区大面积受淹、控导工程决口、桥梁被冲毁、房屋倒塌等严重灾害。小水致灾的形成机理主要是:河道游荡,引发“横河、斜河”;小水淤积,河床抬高,行洪能力下降;人与河床争地,造成滩区阻塞。     

黄河下游孟津——陶城埠河道形态特征及新构造的控制作用

一、河道形态特征 这里所指的河道形态,是指河道宽度、河床坡降、主槽位置的稳定性、河道的弯曲率、大堤间的河道地貌、河流两岸地貌特征等。根据上述特征,可将其分为四段。 (1)孟津——京广铁路桥河段(91公里):黄河出孟津后,河道突然展宽,流势平缓,故在靠近出山口的地方堆积了由粗砂和卵石构造的鸡心滩,再向下游,其沙洲出没无常,河床变换不定,属游荡性河段。     

常流河向季节河转变过程中河床适应性调整及对行洪影响——以黄河和滹沱河为

研究黄河和滹沱河对季节河化的适应性调整,发现季节化程度较高的滹沱河下游床断面和平面形态调整幅度不大,而河床的糙率成倍增加造成下游的小水大灾现象;黄河下游近年流量减小,不断断流,主槽淤积,虽然河槽断面形态在游荡段变得更窄深,但主槽明显变小、变窄、变高,构成下游近年出现的小水大灾现象的主要原因。     

黄河下游河道输沙功能的时间变化及其原因

以输出某一河道的泥沙总量与进入这一河道的泥沙量之比来定义河道输沙功能,以此为指标研究了黄河下游输沙功能的时间变化。研究表明,近50年来黄河下游河道输沙功能表现出随时间而减小的明显趋势。在总的减小趋势中,由于水库运用方式与下游水沙组合的不同,河道输沙功能指标具有明显的差异,可以划分为6个阶段。1986¹997年,由于降水偏少,且人类大量引水,黄河下游进入连续枯水的水文系列,河道萎缩,输沙功能迅速降低,此时段中输沙功能指标的时段平均值为0.62,为有水沙记录以来最低的时期。对于黄河下游输沙功能指标与流域因子和河道特性因子的时间变化系列进行了比较,以揭示输沙功能减小的原因。结果表明,黄河下游河道输沙功能指标与流域平均年降水量、兰州站和三门峡站汛期径流占年径流百分比、游荡段典型断面平滩水位下断面面积、花园口站和高村站水面比降等因子有同步减小的关系,并随流域水土保持面积、人类引水量及其占天然径流量比率的增大而增大,说明这些因子的变化导致了黄河下游输沙功能的减弱。     

常流河向季节河转变过程中河床适应性调整及对行洪影响--以黄河和滹沱河为例

研究黄河和滹沱河对季节河化的适应性调整，发现季节化程度较高的滹沱河下游河床断面和平面形态调整幅度不大，而河床的糙率成倍增加造成下游的小水大灾现象；黄河下游近年流量减小，不断断流，主槽淤积，虽然河槽断面形态在游荡段变得更窄深，但主槽明显变小、变窄、变高，构成下游近年出现的小水大灾现象的主要原因。     

陕西湑水河下游城固段朱鹮游荡期的食物丰富度

于2009年9月和2010年5月,在朱鹮(Nipponia nippon)重要游荡区之一的湑水河下游城固段,对食物丰富度进行了调查。将湑水河城固段约30km长的河道分成上段、中段和下段,并随机选取7个取样点。在每个取样点,采用五点取样法,设置5个1m×1m的样方,并取地表以下10cm的土样,在河岸滩涂调查小型无脊椎动物和两栖动物;采用样线捕尽法来调查鱼类,样线长度为100m。两个季节共采集到鱼类30种,小型无脊椎动物24种和两栖类蝌蚪2种。在各河道段,不同季节的鱼类物种组成和质量密度有显著差异,小型无脊椎动物物种组成和数量密度也有显著差异。总体上,湑水河下游城固段的食物非常丰富,是朱鹮在游荡期的理想觅食地,但是,河流污染和人类活动干扰会对朱鹮的觅食造成不利影响。     

黄河下游游荡段河道平面形态与河势变化趋势预测

黄河下游河道平面形态与河势演变,从20世纪60年代起,地貌界就用地图法和航片资料作过不同程度的研究.随着资料的不断积累,该项研究得到逐步的深化."八五"期间,水利界又对主流线作了深入分析,结果表明:各家所得结论不同,需要作进一步的分析讨论.我们认为:从长远的角度来看,小浪底水库清水下泄期间,黄河下游游荡性河段不对称的河谷形态不会改变;在继承性新构造运动造成的地壳向南掀沉、科氏力和人类活动的综合影响下,主流线总体上仍呈南摆趋势;清水冲刷不会导致河型彻底转化;河道整治工程虽然能够限制主流的摆动幅度和弱化河道的游荡强度,对河势的影响较大,但是根本不可能改变上述河道平面形态的长期演变趋势.     

渭河下游河道调整过程中的复杂响应现象

应用系统复杂响应的原理研究三门峡水库上游渭河河道调整过程,表明上游河道河床形态对基面上升所作出的响应是复杂的,弯曲系数的变化为先减小而后增大,宽深比的变化是先增大后减小,比降由先减小而后增大,最后均趋于稳定.     

Quantifying channel development and sediment transfer following chute cutoff in a wandering gravel-bed river

Three-dimensional morphological adjustment in a chute cutoff (breach) alluvial channel is quantified using Digital Elevation Model (DEM) analysis for a ca. 0.7 km reach of the River Coquet, Northumberland, UK. Following cutoff in January 1999, channel and bar topography was surveyed using a Total Station on five occasions between February 1999 and December 2000. Analysis of planform change coupled with DEM differencing elucidates channel and barform development following cutoff, and enables quantification of sediment transfers associated with morphological adjustment within the reach. This exercise indicates an initial phase of bed scour, followed by a period characterised by extensive bank erosion and lateral channel migration where erosion (including bed scour) totalled some 15,000 m³ of sediment. The channel in the post-cutoff, disequilibrium state is highly sensitive to relatively low-magnitude floods, and provision of accommodation space by bank erosion encouraged extensive lateral bar development. Bar development was further facilitated by infilling of channels abandoned by repeated within-reach avulsion and large-scale aggradation of sediment lobes deposited by higher magnitude floods. Calculations indicate that at least 6600 m³ of sediment was deposited on emerging bars within the reach over the survey period, and >2300 m³ deposited within the channel. Sediment losses from the reach may have exceeded 6500 m³.     

黄河下游游荡段河床调整对于水沙组合的复杂响应

以黄河资料为基础,提示地包括非高含沙水流和高含沙水流在内的河道挟不流的复杂冲淤行为。由于这种复杂冲淤行为的作用和高含沙水流特殊能耗特征的影响,使得河床横断面形态及平面形态对于水沙组合的响应出现非线性特征,这可视为流水地貌系统复杂响应的又一表现形式。这种复杂响应不能用Ｓｃｈｕｍｍ的河床调整来解释,因而需要对这一理论作必要的修正。     

Long-term morphodynamic changes of a desert reach of the Yellow River following upstream large reservoirs' operation

China's Yellow River has experienced its dramatically decreasing trend for the flow discharge since the construction and operation of large reservoirs located upstream. This low flow regulation has triggered a severe aggradation of the Ulan Buh Desert channel of the Yellow River because the declining flow exhibits no capability to scour and carry away large amount input of desert sands from the Ulan Buh Desert. Twenty monitoring cross-sections documented the Ulan Buh Desert channel has experienced its increasing aggradational trend in conjunction with its lateral migration decreasing trend from 1966 to 2005, which is opposite to the normal pattern of aggradation with deepening or symmetrical infilling for a channel located downstream of a reservoir. The channel aggradation can also be identified two stages: slow aggradation and rapid aggradation. Slow aggradation is characterized by the channel bed elevation rising 9.5 cm on average between 1968 and 1985, which responded to the operation of the Liujiaxia reservoir. During this period, the flow discharge was similar to pre-dam flow conditions but the sediment transport reduced to half of its pre-dam value. Because of about 0.24 × 10⁸ t of desert sands entering the channel from the Ulan Buh Desert annually, this dilute flow indicated not to scour the channel as expected, but contrarily to cause the channel aggraded. Rapid aggradation followed completion of the Longyangxia reservoir with the channel bed elevation rising by 73 cm on average between 1986 and 2005. In this period, the combined regulation of Liujiaxia and Longyangxia reservoirs has caused the flow discharge decreasing dramatically, which is more beneficial for accumulation of the desert sands (0.19 × 10⁸ t yr^− 1 on average) in the desert channel, and led to the channel aggradation rate accelerated rapidly.     

Complex channel responses to changes in stream flow and sediment supply on the lower Duchesne River, Utah

Channel responses to flow depletions in the lower Duchesne River over the past 100 years have been highly complex and variable in space and time. In general, sand-bed reaches adjusted to all perturbations with bed-level changes, whereas the gravel-bed reaches adjusted primarily through width changes. Gravel-bed reaches aggraded only when gravel was supplied to the channel through local bank erosion and degraded only during extreme flood events.A 50% reduction in stream flow and an increase in fine sediment supply to the study area occurred in the first third of the 20th century. The gravel-bed reach responded primarily with channel narrowing, whereas bed aggradation and four large-scale avulsions occurred in the sand-bed reaches. These avulsions almost completely replaced a section of sinuous channel about 14 km long with a straighter section about 7 km long. The most upstream avulsion, located near a break in valley slope and the transition from a gravel bed upstream and a sand bed downstream, transformed a sinuous sand-bed reach into a braided gravel-bed reach and eventually into a meandering gravel-bed reach over a 30-year period. Later, an increase in flood magnitudes and durations caused widening and secondary bed aggradation in the gravel-bed reaches, whereas the sand-bed reaches incised and narrowed. Water diversions since the 1950s have progressively eliminated moderate flood events, whereas larger floods have been less affected. The loss of frequent flooding has increased the duration and severity of drought periods during which riparian vegetation can establish along the channel margins. As a result, the channel has gradually narrowed throughout the study area since the late 1960s, despite the occasional occurrence of large floods. No tributaries enter the Duchesne River within the study area, so all reaches have experienced identical changes in stream flow and upstream sediment supply.     

边界条件对水库下游河床演变的影响——以汉江丹江口水库下游河道为例

通过野外考察和室内自然模型试验,本文探讨边界条件在水库下游再造床过程中的作用。从土壤物理力学性质与水流作用力的对比关系出发,建立了河床边界抗冲性的定量指标;采用多元回归分析的方法,建立了调整之后的河床形态与边界条件、水动力条件之间的经验方程;还运用判别分析的方法,得到了区分水库下游河床演变趋势的判别函数。     

Double-thresholds in scour–fill processes and some implications in channel adjustment

Through an analysis of data collected from the Yellow River and its tributaries on the Loess Plateau of China, the phenomenon of double-thresholds in scour–fill processes of wide-range water-sediment two-phase flows has been shown. Thresholds located in non-hyperconcentrated flows may be called the lower threshold, and that in hyperconcentrated flows the upper threshold. This double-threshold phenomenon leads to complicated sediment transport behavior of heavily sediment-laden rivers. With an increase in suspended sediment concentration, the channel sediment delivery ratio increases initially and becomes higher than 1, followed by a decrease and finally becomes lower than 1 again.Controlled by the double-thresholds in the scour–fill processes, channel adjustment of the lower Yellow River is non-linear and complex. When the suspended concentrations were lower than the lower threshold or higher than the upper threshold, scour or bed downcutting was the dominant channel-forming process. Channel shape tends to be narrower and deeper, and the channel thalweg became more sinuous. When the suspended concentrations lay between the lower and upper thresholds, deposition of sediment was the dominant channel-forming process; channel shape tended to be shallower and wider, and channel thalweg became less sinuous.     

Fluvial process and morphology of the Brahmaputra River in Assam, India

The Brahmaputra River finds its origin in the Chema Yundung glacier of Tibet and flows through India and Bangladesh. The slope of the river decreases suddenly in front of the Himalayas and results in the deposition of sediment and a braided channel pattern. It flows through Assam, India, along a valley comprising its own Recent alluvium. In Assam the basin receives 300 cm mean annual rainfall, 66–85% of which occurs in the monsoon period from June through September. Mean annual discharge at Pandu for 1955–1990 is 16,682.24 m³ s^{− 1}. Average monthly discharge is highest in July (19%) and lowest in February (2%). Most hydrographs exhibit multiple flood peaks occurring at different times from June to September. The mean annual suspended sediment load is 402 million tons and average monthly sediment discharge is highest in June (19.05%) and lowest in January (1.02%). The bed load at Pandu was found to be 5–15% of the total load of the river. Three kinds of major geomorphic units are found in the basin. The river bed of the Brahmaputra shows four topographic levels, with increasing height and vegetation. The single first order primary channels of this braided river split into two or more smaller second order channels separated by bars and islands. The second order channels are of three kinds. The maximum length and width of the bars in the area under study are 18.43 km and 6.17 km, respectively. The Brahmaputra channel is characterised by mid-channel bars, side bars, tributary mouth bars and unit bars. The geometry of meandering tributary rivers shows that the relationship between meander wavelength and bend radius is most linear. The Brahmaputra had been undergoing overall aggradation by about 16 cm during 1971 to 1979. The channel of the Brahmaputra River has been migrating because of channel widening and avulsion. The meandering tributaries change because of neck cut-off and progressive shifting at the meander bends. The braiding index of the Brahmaputra has been increasing from 6.11 in 1912–1928 to 8.33 in 1996. During the twentieth century, the total amount of bank area lost from erosion was 868 km². Maximum rate of shift of the north bank to south resulting in erosion was 227.5 m/year and maximum rate of shift of the south bank to north resulting in accretion was 331.56 m/year. Shear failure of upper bank and liquefaction of clayey-silt materials are two main causes of bank erosion.     

长江口横沙通道近岸冲刷地貌形成机制

近岸河床的剧烈冲刷是引起岸坡失稳的主要原因之一。通过SeaBat 7125多波束测深系统对长江口近岸冲刷最为剧烈的横沙通道北口冲刷坑地貌进行测量,同时利用双频ADCP采集区域水流数据,结合历史海图资料,研究该冲刷坑演变过程及形成机制。结果表明：冲刷坑呈椭圆形,长约430 m,宽约150 m,最深处距床面约38 m;1984-2017年期间,冲刷坑附近河床经历了冲—淤—冲的演变模式,整体呈冲刷状态,净冲刷量3.45×10 ⁷ m ³,平均冲深4.68 m;2005年后冲刷坑快速发育,且持续向南延伸。这主要是因为长兴北沿圈围工程的建设减小该处弯道曲率半径,导致了侵蚀加剧。其次,青草沙水库的建设使得北港上中段深泓线发生偏移,横沙通道北口水动力增强,这也是快速冲刷的主要原因之一。另外,长江口深水航道工程、横沙东滩围垦、横沙通道两侧圈围工程及港口码头的建设也一定程度加剧了冲刷之势。由此可见,人类涉水工程活动是引起该处大型冲刷坑快速发育的主要驱动因素。     

The impact of the Parangana Dam on the River Mersey,Tasmania

By diverting the waters of the River Mersey into a neighbouring basin, the Parangana Dam has changed the hydrological character of the downstream river. The flow records of three gauging stations, located at distances of 10, 67 and 88 km below the dam, provide the basis for identifying the changes. Intermediate discharges have decreased the most and even the furthest downstream station are 50% lower than before. The flow extremes, at both ends of the scale, have been less affected, and particularly the less frequent flood discharges which are augmented by overspill. Indeed the highest flood on record, with a recurrence interval of over 500 years, occurred in the post-dam period. The entry of unregulated tributaries in the middle section separates a much changed upstream hydrology from a downstream one able to mitigate the worst effects of the dam except at intermediate discharges.Field survey, air and ground photograph analysis are used to assess the impact of impoundment on the downstream channel. The main changes involve the expansion of existing lateral bars and the growth of new ones, but such deposition and the consequent narrowing of the channel are rather localized. The invasion of bar surfaces by vegetation could accelerate the process, but the general coarseness of the channel bed and the lack of fine material for bank building will severely delay adjustment of the Mersey channel. The chemical and biological character of the river could be adversely affected by the altered flow regime, particularly in those reaches immediately below the dam.