黄河下游游荡段排沙比对水沙条件与断面形态的响应

提高黄河下游游荡段的输沙能力是河道治理的主要任务,而河道输沙效率（排沙比）受到来水来沙条件和河床边界条件的共同影响。本文基于1971—2016年花园口—高村河段（简称花高段）的实测水沙及地形资料,计算了花高段的平均河相系数及水沙条件（来沙系数和水流冲刷强度）,从汛期和场次洪水2个时间尺度,定量分析了排沙比与水沙条件及前一年汛后主槽形态之间的响应关系。分析结果表明：① 汛期和场次洪水排沙比与来沙系数呈负相关,与水流冲刷强度呈正相关,临界的汛期不淤来沙系数为0.012 kg?s/m ⁶,场次洪水排沙比与来沙系数及水量比的决定系数为0.76;② 游荡段排沙比与河相系数呈负相关,当河相系数大于15 /m ^0.5时,河段排沙比基本小于1;③ 以来沙系数与河相系数为自变量的汛期排沙比计算式的决定系数为0.82,计算精度较高,对于场次洪水排沙比而言,断面形态的影响权重大于来沙系数。这些排沙比计算公式能够反映游荡段的输沙特点,有助于定量掌握断面形态及水沙条件对河道输沙能力的影响。     

黄河下游河道断面形态参数变化及其水沙过程响应

基于1965—2015年黄河下游花园口、高村、泺口站的逐年水文和汛前河道断面的实测资料,分析了河道断面形态参数（河道断面面积,河道宽深比等）的变化,以及对河道断面形态与来水来沙间的关系做出定量化分析。结果表明：主槽断面形态参数与水沙搭配以及前期断面形态密切相关,沿程3个断面形态参数调整方式存在显著差异。河宽调整幅度沿程减小,辫状河段变幅最大,尤其在1986—1999年,辫状河段萎缩程度最为严重,其次为弯曲河段,顺直河段横向调整幅度最小。受到前期断面形态的影响,辫状河段河道断面调整方式既有横向展宽（萎缩）又有垂直加深（淤积）;弯曲河段河道宽深比与流量呈较弱的正相关关系,具有横向和垂向的调整方式;而顺直河段的宽深比与流量呈负相关关系,与来沙系数呈正相关关系,河道以垂直加深（淤积）为主。     

Prediction of alluvial channel pattern of perennial rivers

Purely braided, meandering and straight channels can be considered as end-members of a continuum of alluvial channel patterns. Several researchers have succeeded in separating channel patterns in fields defined by flow related parameters. However, the discriminators of the principal channel patterns derived from these diagrams all require some a priori knowledge of the channel geometry. In this paper a method is presented which enables prediction of the equilibrium conditions for the occurrence of braided and high sinuosity meandering rivers in unconfined alluvial floodplains. The method is based on two, almost channel pattern independent, boundary conditions: median grain size of the river bed material, and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient. This can be regarded as a potential maximum of the available flow energy corresponding to the minimum sinuosity condition, P = 1. Based on an analysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that separates the occurrence of braided rivers and meandering rivers with P > 1.5. The function applies to equilibrium conditions of rivers that neither incise nor show rapid aggradation, with a bankfull or mean annual flood discharge above 10 m³/s and a median bed material grain size between 0.1 and 100 mm.     

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。     

黄河上游内蒙古段河床演变及其与水沙变化的关系

对黄河内蒙古段河道大断面进行了连续4 a的测量,分析了断面泥沙冲淤与形态调整的变化过程;通过对河床形态指标变化与水沙条件的相关分析,揭示了河床调整主要的影响因素。结果显示：近4 a内不存在河槽萎缩的现象,整个河段河道存在总的冲刷降低的趋势,继承了自2004年以来该段河道以深度加大为主,河槽逐渐缓慢扩大的变化方向。整个河段平均从2011年汛后至2014年汛后,全断面冲刷了64 m²,河槽河底降低了0.16 m,河槽断面面积增加了4.4%,平均深度增加了4.9%,河槽宽度只增加了0.88%,河槽宽深比减小了4.8%。河槽冲刷和形态调整主要发生在2011年汛后至2012年汛后期间,与2012年较大的洪峰有关。分析河槽冲淤和断面形态变化与水沙条件的关系,结果显示滩唇高度、河槽过水面积、平均深度及宽深比变率与流量大小关系密切。滩唇高度、河槽过水面积、平均深度随着流量的增大而增加,宽深比随着流量的增大而减小。相反,河床断面面积和主槽宽度的变化与水沙条件的关系不显著。除了滩唇高度与平均含沙量有关外,平均含沙量和来沙系数与河床冲淤以及河槽形态变化之间关系都不显著。揭示出近年来内蒙河道主槽以垂向冲淤为主,并且流量变化控制着河槽冲淤与形态调整过程。     

1986-2015年小浪底水库运行前后黄河下游主槽调整规律

Based on the measured discharge,sediment load,and cross-sectional data from 1986 to 2015 for the lower Yellow River,changes in the morphological parameters(width,depth,and cross-sectional geomorphic coefficient)of the main channel are analyzed in this paper.The results show that before the operation of the Xiaolangdi Reservoir(XLDR)from 1986 to 1999,the main channel shrunk continually,with decreasing width and depth.The rate of reduction in its width decreased along the river whereas that of depth increased in the downstream direction.Because the rate of decrease in the width of the main channel was greater than that in channel depth,the cross-sectional geomorphic coefficient decreased in the sub-reach above Gaocun.By contrast,for the sub-reach below Gaocun,the rate of decrease in channel width was smaller than that in channel depth,and the cross-sectional geomorphic coefficient increased.Once the XLDR had begun operation,the main channel eroded continually,and both its width and depth increased from 2000 to 2015.The rate of increase in channel width decreased in the longitudinal direction,and the depth of the main channel in all sub-reaches increased by more than 2 m.Because the rate of increase in the depth of the main channel was clearly larger than that of its width,the cross-sectional geomorphic coefficient decreased in all sub-reaches.The cross-sectional geometry of the main-channel of the lower Yellow River exhibited different adjustment patterns before and after the XLDR began operation.Before its operation,the main channel mainly narrowed in the transverse direction and silted in the vertical direction in the sub-reach above Aishan;in the sub-reach below Aishan,it primarily silted in the vertical direction.After the XLDR began operation,the main channel adjusted by widening in the transverse direction and deepening in the vertical direction in the sub-reach above Aishan;in the sub-reach below it,the main channel adjusted mainly by deepening in the vertical direction.Compared with the rates of decrease in the width and depth of the main channel during the siltation period,the rate of increase in channel width during the scouring period was clearly smaller while the rate of increase in channel depth was larger.After continual siltation and scouring from 1986 to 2015,the cross-sectional geometry of the main-channel changed from wide and shallow to relatively narrow and deep.The pattern of adjustment in the main channel was closely related to the water and sediment conditions.For the braided reach,the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with suspended sediment concentration(SSC)during the siltation period.By contrast,the cross-sectional geomorphic coefficient was positively correlated with discharge and negatively correlated with SSC during the scouring period.For the transitional and meandering reaches,the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with SSC.     

黄河下游游荡段河床萎缩的影响因素分析

黄河下游河床萎缩典型地表现为平滩水位下河床断面面积的趋势性减小,本文根据黄河下游实测断面和水沙资料采用相关分析方法研究了游荡段河床萎缩的主要影响因素。1960~1997年游荡段河床平滩水位下断面面积经历了1960~1964年和1974~1985年的扩张时期及1965~1973年和1986~1997年的萎缩时期,这种变化是多种因素共同作用的结果。在来水来沙中,年径流量是主要因素,洪峰流量和年平均含沙量是较次要的因素;本文所讨论的其它4个因素中,花园口以上引水量影响最大,降雨量影响次之,兰州以上水库的调节作用对河床断面面积的变化也有较明显的影响;三门峡水库三种不同的使用方式对下游河床有不同的影响,采取"蓄清排浊"方式后对下游河床的影响较小。     

GIS技术支持下的洪水模型建模

在复杂区域建立洪水模型时,计算网格的手工生成方法容易出错甚至不可行,自动生成算法则可大大节省计算网格生成的工作量。洪水模型中的计算网格与GIS栅格数据及不规则三角网空间数据结构非常相似,因此,GIS中成熟的网格自动生成算法可用于生成洪水模型计算网格。文章详细讨论了GIS支持下的洪水模型自动建立步骤,并以黄河下游花园口～夹河滩河段为例,利用地形图、土地利用图、水利工程设施分布、水文站点图等资料,通过自动生成网格及其空间拓扑关系,建立了洪水过程数值模拟模型,并详细解释了计算网格数据格式。     

三门峡水库影响渭河下游河道横向演变的研究

多沙河流修建水库影响库区河道演变,建库前后河道遵循不同的演变规律,兴建三门峡水库后的15年间赤水河河口至陈村河段发生了7次自然裁弯,三门峡水库改建后20年间却没有发生一次自然裁弯,这是一个非常有趣的现象。文中利用渭河下游河道的实测资料,对比兴建三门峡水库前后以及三门峡改建前后渭河下游河道的横向演变,得到如下几点认识:(1)侵蚀基准面的变化是引起渭河下游河道横向摆动的主要因素;(2)洪水比降变平,相应河道弯曲系数变大,河道由稳定型向摆动型发展;洪水比降变陡,相应河道弯曲系数变小,河道由摆动型向稳定型发展;(3)滩地的泥沙组成代表河岸的可动性。河岸可动性增大,河道由稳定型向摆动型发展,河岸可动性变小,河道由摆动型向稳定型发展;(4)河道断面形态的调整是对基准面变化和来水来沙变化的复杂响应过程;(5)来水来沙影响渭河下游河道横向演变。     

The relationship between water level change and river channel geometry adjustment in the downstream of the Three Gorges Dam

In this study, data measured from 1955-2016 were analysed to study the relationship between the water level and river channel geometry adjustment in the downstream of the Three Gorges Dam (TGD) after the impoundment of the dam. The results highlight the following facts: (1) for the same flow, the low water level decreased, flood water level changed little, lowest water level increased, and highest water level decreased at the hydrological stations in the downstream of the dam; (2) the distribution of erosion and deposition along the river channel changed from “erosion at channels and deposition at bankfulls” to “erosion at both channels and bankfulls;” the ratio of low-water channel erosion to bankfull channel erosion was 95.5% from October 2002 to October 2015, with variations between different impoundment stages; (3) the low water level decrease slowed down during the channel erosion in the Upper Jingjiang reach and reaches upstream but sped up in the Lower Jingjiang reach and reaches downstream; measures should be taken to prevent the decrease in the channel water level; (4) erosion was the basis for channel dimension upscaling in the middle reaches of the Yangtze River; the low water level decrease was smaller than the thalweg decline; both channel water depth and width increased under the combined effects of channel and waterway regulations; and (5) the geometry of the channels above bankfulls did not significantly change; however, the comprehensive channel resistance increased under the combined effects of riverbed coarsening, beach vegetation, and human activities; as a result, the flood water level increased markedly and moderate flood to high water level phenomena occurred, which should be considered. The Three Gorges Reservoir effectively enhances the flood defense capacity of the middle and lower reaches of the Yangtze River; however, the superposition effect of tributary floods cannot be ruled out.     

The braided Milk River, northern Montana, fails the Leopold–Wolman discharge-gradient test

The Milk River, the northernmost tributary to the Missouri–Mississippi River system, exhibits an anomalous sand-bed braiding reach in an otherwise meandering system. Shortly after leaving Alberta and entering Montana the river suddenly changes to braiding and maintains this pattern for 47 km before entering Fresno Reservoir. Measured stream gradient and bankfull discharge in the braiding reach severely fail the Leopold and Wolman [U.S. Geol. Surv. Prof. Pap. 282B (1957) 39] slope–discharge test for differentiating channel patterns. While channel slope has long been regarded as one of the primary variables associated with braiding, our data from the sand-bed Milk River do not support this relationship. Instead, the data show that the braiding reach has a lower channel slope (0.00047) than the meandering reach (0.00055). Coupled with a constant discharge the unit length stream power is comparable between the two reaches. At the morphologic transition between meandering and braiding, a dramatic reduction in channel bank strength occurs where the sampled silt–clay content declines from 65% in the meandering reach to 18% in the braiding. This enables channel widening which is reflected in a 60% reduction in unit area stream power in the braiding reach. Thus, sediment transport capacity declines and channel bars are deposited. During waning flows, these bars are dissected, producing a braiding morphology. We suggest that for sand-bed braiding rivers the silt–clay percentage in the channel banks may be more important than slope. A review of the original Leopold and Wolman [U.S. Geol. Surv. Prof. Pap. 282B (1957) 39] dataset, and many subsequent analyses, reveals that most braided rivers studied were gravel-bed. As a result, causal variables associated with braiding in sand-bed environments may need a thorough evaluation.     

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。     

河道糙率系数变化对全新世古洪水流量计算的影响研究

洪水流量计算中河道糙率是一个重要的灵敏度参数。以汉江上游郧县尚家河台地前沿记录的四期古洪水流量计算为例,研究河道糙率系数在比降-面积法和HEC-RAS模型中对古洪水流量计算结果的影响。结果表明：其他水文参数一定时,河道糙率系数以±15%变幅,比降-面积法重建的古洪水流量变幅在-13.04%～17.65%,HEC-RAS模型计算的流量变幅在-4.32%～4.57%;若河道糙率系数以±25%变幅,比降-面积法和HEC-RAS模型计算的流量变幅分别为-20%～33.33%和-7.79%～9.18%,说明采用HEC-RAS模型重建古洪水流量,可减少河道糙率系数对计算结果的影响,使古洪水流量计算结果更为可靠。此外,假定其他参数不变,主河槽和左、右岸糙率系数依次变幅±25%,主河槽糙率系数变化对流量计算结果影响最大,说明洪水流量计算时应准确选取主河槽的糙率系数。该结果对水利工程建设具有重要的现实意义。     

Geomorphic Controls on Historical Channel Planform Changes on the Lower Pages River,Hunter Valley,Australia

Historical planform changes in a 14.7 km reach of the lower Pages River were determined to assess whether they were autogenic (inherent in the river regime) or allogenic (driven by external changes) in nature so as to better focus river management activities and river restoration works. A pattern metamorphosis or complete change in river morphology occurred during the February 1955 flood. The peak discharge of this event exceeded the slope and grain size (intrinsic) threshold for braiding, converting the narrow, slightly sinuous stream to a wide, braided-like river. Five subsequent intrinsic threshold-exceeding floods did not cause further bar development because an over-widened channel already existed. Autogenic channel planform changes included sinuosity variations due to lateral migration and pattern metamorphosis due to the exceedance of a discharge–slope–grain size geomorphic threshold. Allogenic channel planform changes included: (1) realignment/channel straightening and artificial cutoffs by river training works; (2) lateral migration by increased bank erodibility due to riparian vegetation clearing; (3) lateral migration by the operation of a transitive geomorphic threshold involving the onset of a flood-dominated regime after 1946 and increased catchment runoff after 1830 due to large-scale clearing of catchment vegetation; and (4) the occurrence of a large flood in February 1955. Multiple forcing factors have clearly caused historical channel planform changes of the lower Pages River, making the design of river management and restoration works a complex matter outside the scope of simple formulaic protocols.     

VARIABILITY OF IN-CHANNEL SEDIMENT STORAGE WITHIN A SMALL SEMIARID DRAINAGE BASIN

This study determines the spatial and temporal variability of in-channel storage within a small semiarid drainage basin in equatorial East Africa, and establishes a tentative sediment budget for coarse (>200 μm) in-channel sediments. Detailed measurements of in-channel sediment storage (mass) within third and fourth-order ephemeral channels were obtained using channel-pit excavations and probing with metal rods. Eighty-seven monumented cross-sections were established in February 1986 and resurveyed in December 1986, following the last runoff event of the year. These provided data on change in sediment storage on a 30-m channel reach basis. In addition, measurements of bankfull channel width, mean depth, cross-sectional area, wetted perimeter, hydraulic radius, channel slope and distance from the basin outlet were measured at each cross section. Total in-channel sediment storage was approximately 8640 t with 83% of this total stored within the Main (fourth-order) Channel. Stepwise multiple regression of In-transformed data indicated that bankfull channel width and distance from the outlet (which is strongly related with slope) were significantly related to in-channel storage. The variation in the ratio of stream power:critical power along the Main Channel may explain the distribution of in-channel sediments. Net aggradation of 50 to 60 t during 1986 was minor in relation to the total in-channel storage reservoir, but indicates that a static equilibrium condition cannot be assumed. Bedload output during 1986 was approximately 125 t, and the computed input of coarse sediments to the major channels within the basin was approximately 185 t. The sediment delivery ratio for the coarse material was approximately 68%, which indicates a relatively efficient transport system. [Key words: geomorphology, sediment budget, in-channel sediment storage, semiarid, drainage basin.]     

黄河下游河道泥沙存贮-释放及其临界条件

确定了黄河下游河道处于泥沙存贮-释放临界状态的水沙临界条件。当场次洪水平均含沙量小于31.68 kg/m³,或者来自中游多沙粗沙区场次洪水来沙量小于4 543×10⁴ t,下游河道将由泥沙存贮状态变为泥沙释放状态。当河口镇以上清水区径流占场次洪水总径流量比率大于0.70时,也会由泥沙存贮状态变为泥沙释放状态。场次洪水泥沙输移比随洪水平均流量的增到而增大,流量为4 000 m³/s(相当于平滩流量)时达到峰值,此后有所减少。这表明,平滩流量时泥沙存贮最少,低于平滩流量和高于平滩流量时泥沙存贮均增大。     

黄河内蒙古段淤积泥沙洪水冲刷效应

为了探讨黄河内蒙古段淤积泥沙的洪水冲刷效应,于2012年对其三湖河口水文站河道监测断面汛期（7-10月）流量、悬移质泥沙含量以及洪水期间（2012年8月20日-2012年10月1日）悬移质泥沙含量、粒度百分含量的垂直变化特征与流量的关系进行了统计和分析。结果表明：（1）该次洪水具有峰高量大、洪峰过程在河段内持续时间长、洪水起涨和消退缓慢、峰形矮胖的特点;（2）洪水过程中,小于0.05 mm的细颗粒泥沙在2 000 m³·s^-1左右的流量下就能输移通过,在2 000～2 400 m³·s^-1时输沙强度最大,对河道淤积泥沙可以达到输沙最优的效果;而粒径大于0.05 mm的泥沙输移的效果不好。     

河流地貌系统的过程响应模型实验

本文讨论了河流地貌系统的过程响应模型的基本原理、设计步骤、模型砂料配制以及实验数据的系统分析,并给出了设计实例和某些分析成果。     

Response of bankfull discharge to discharge and sediment load in the Lower Yellow River

This paper presents a study on the response of bankfull discharge to incoming discharge and sediment load based on long-term hydrological and bankfull discharge data measured on the lower reaches of the Yellow River. The analysis indicated that the bankfull discharge was a function of the preceding 5 to 6 years' flow regimes, revealing that bankfull channel dimensions were a result of the accumulative effect of several consecutive years' flow discharge and sediment load conditions. In other words, the mean relaxation time was about 5 to 6 years for channel adjustment. Theoretical methods for the prediction of bankfull discharge were developed, in which the response time or the relaxation time was fully considered. Testing of the methods using data observed at five hydrologic stations in the lower reaches of the Yellow River from 1960 to 2003 showed that the proposed methods can predict the variation of bankfull discharge in response to changes in the incoming discharge and sediment load. The proposed methods hold promise for predicting the magnitude and trend of channel response to other rivers undergoing aggradation or degradation from changes in hydrologic or sediment regime.     

Framing realistic river rehabilitation targets in light of altered sediment supply and transport relationships: lessons from East Gippsland, Australia

Since European settlement, the Cann River in East Gippsland, Victoria has experienced a 700% increase in channel capacity, a 150-fold increase in the rate of lateral channel migration, a 45-fold increase in bankfull discharge and a 860-fold increase in annual sediment load. Over the last century, and primarily the last 40 years, channel incision has removed the equivalent of around 1500 years of floodplain deposition. A numerical floodplain evolution model is presented which suggests that under a best case scenario, infilling the incised channel trench will take 31,000 years and this is predicated on the full recovery of the immediate riparian vegetation and the in-channel loading of woody debris. The asymmetry in the recovery time following rapid channel change, compared with the original deposition of the material, is explained by a combination of the sediment-starved character of the catchment and the altered hydraulic conditions within the channel, principally associated with the role of woody debris. These factors have major implications for geomorphic recovery potential, constraining what can be realistically achieved in river rehabilitation.