悬移质单宽输沙率的计算

众所周知,悬移质泥沙运动的基本理论有两种:由维里卡诺夫根据能量守恒原理而创立的重力理论;由马卡维也夫根据施密特的紊动扩散概念而提出的扩散理论。这两种理论所导出的悬移质含沙量沿垂线的分布公式,都存在着一个共同的缺点,就是水面处的含沙量均为零。同时,重力理论所导出的公式,对于粗颗粒泥沙(沉降速度ω>3.0cm/s)在含沙量较小的水中应用比较适合,在能量方程的建立     

表面驻波作用下紊动射流运动特性的试验研究

对表面驻波作用下紊动射流运动进行了试验研究。应用多普勒激光测速仪(LDV)进行流速场量测,应用电容式波高仪测量表面波动特性。结果表明,在表面驻波作用下,紊动射流动量主导远区流速的横向变化仍然可以用高斯分布表达,横剖面上流速的等值线图由原来对称于轴心的圆形变形为椭圆形;表面波动增强了紊动射流的扩散能力。     

明渠收缩过渡段流速分布及紊动特性试验

受地形、地质等条件影响,明渠收缩过渡段在输水工程中十分常见,过渡段长度过短,会导致水面波动,水体紊动加剧。为研究明渠不同长度过渡段内纵向时均流速及紊动强度的分布规律,通过室内模型试验,利用二维电磁流速仪ACM2-RS测量了渠道内沿程中垂线不同深度处瞬时流速。试验结果表明:收缩段内,纵向时均流速沿程增加,紊动强度沿程降低,遵循涡旋的拉伸机制和线性扭曲理论;受二次流影响,最大流速位于水面以下,且最大流速的位置随二次流作用的增强而降低;不同长度过渡段对下游纵向流速分布和紊动强度影响不同,过渡段越短,下游水流紊动越强,但非渠底附近紊动强度沿垂向先减后增的规律不变。     

水动力学条件对复氧过程的影响研究

通过水槽实验对紊动水体复氧规律进行了研究.将氧通量理论应用于紊动水体复氧过程的研究,得到了紊动水体表面传质系数.数值模拟研究了实验流场分布和紊动特性,得出了紊动水体表面传质系数与流速和紊动动能的关系式.不同工况的实验资料验证表明了紊动复氧理论的合理性和可靠性.     

含淹没植物河流水流紊动强度最大值及其影响因素

根据含淹没植物河流水流紊动强度与流速和流速分布的关系,建立紊动强度经验公式,并数学推导证明了紊动强度垂向分布最大值的存在。根据实验数据,该紊动强度最大值的大小及出现位置受植物和水流条件的影响:植物的存在增加水流阻力,植物排列密度改变紊动强度最大值的大小;植物叶片的摆动形成水流紊动的主要干扰源,植物/水深相对高度控制紊动强度最大值的出现位置;断面平均流速的变化改变水流的稳定性和植物冠层的高度,对紊动强度最大值的大小和出现位置均有一定影响。     

淹没刚性植被明渠紊流沿程流动特性差异

淹没刚性植被通过改变水流结构,造成时均流速、紊动强度、雷诺应力等水力参数垂线分布不均匀和沿程差异化。采用声学多普勒测速仪(ADV)测量3种淹没度(3.0、4.0、5.0)下的流速,结合统计学方法,系统分析植被段内及其上、下游过渡段流速和紊动特性差异。结果表明：植被显著增强了水流紊动,且紊动特性取值与淹没度正相关;植被段内流速差异在低淹没度下的植被层内和高淹没度下的自由流动层内更加显著,而紊动特性沿程增强,且垂线分布具有相似性,最大值点位于冠层顶部附近;当淹没度满足KH涡的形成和发展条件时,随淹没度的增大,植被段内紊动特性垂线分布出现转折点(临近此点梯度急剧减小并趋于0)的断面数量增多,经验证,在充分发展的紊流区此点可作为KH涡的上边界点。     

一种改进的近岸波浪破碎数值模型

提出一种基于完全非线性Boussinesq方程的改进波浪破碎模型,用于模拟近岸浅水波浪破碎.模型借助水滚的概念,提出一种确定k方程紊动模式中紊动源项的计算公式,通过解k方程计算Boussinesq方程中的涡黏系数,实现对破碎波的模拟.岸边界采用窄缝法,使得模型可用于波浪爬坡的计算.用实验室实测波高和增减水资料对模型进行了验证,得到了一致的结果.紊动源、紊动动能以及紊动耗散率的计算结果表明:①在破波点处紊动源项值最大,随着波浪向岸边传播,逐渐减小;②破波点处,水平方向的对流和扩散在紊动能量输移中发挥重要作用;③岸边附近紊动源与紊动耗散接近平衡.     

温度和盐度分层流的数值模拟

以N-S方程和k-ε湍流模型为基础,针对水温和盐度分层流的流动特性,考虑了浮力对紊动的影响,建立了温度和盐度分层流的k-ε模型,对同时存在温度和盐度梯度的一类密度分层流进行了数值模拟计算,其中紊动平均量控制方程中的紊动项是由k-ε紊流模型计算,给出了速度、温度和盐度的分布。计算结果正确地反映了分层及紊动特征,与实测结果吻合较好。     

水流紊动对泥沙絮凝的影响

主要研究水流紊动对泥沙絮凝的影响。认为水处理方面的絮凝动力学理论可用于研究泥沙絮凝问题。根据试验实测资料及国外有关试验结果研究表明,在紊动状态下,泥沙絮凝存在两个阶段,每个阶段中紊动对泥沙絮凝的影响也有所不同。     

宽窄相间河道水流紊动特性试验研究

为了探索宽窄相间河道的水流紊动特性,以西南地区宝兴河上游宽窄相间河段为研究对象,基于室内概化模型试验,采用多普勒声学流速仪(ADV)测量了室内模型典型断面上的三维瞬时流速,分析典型断面上的纵向时均流速、紊动强度、雷诺切应力和紊动能的分布规律。试验结果显示:宽窄相间水槽中,扩散段边壁的紊动强度大于中心区域的紊动强度,最大值位于0.2倍水深处;扩散段两侧坡脚处紊动能最大;侧壁区的平面和立面雷诺切应力最大值出现在扩散段内,中心区域最大雷诺切应力位于两槽间的中间断面处;扩散段内水流紊乱,两侧出现旋涡和涡脱,易造成侧壁侵蚀加强,引起河道拓宽。深入分析了宽窄相间河道水流的紊动特性,可为山区河流治理和自然灾害防治提供参考。     

Sediment production and transport in a proglacial stream: Hilda Glacier, Alberta, Canada

Hilda Glacier, a small cirque glacier in the Canadian Rocky Mountains, yields two principal types of sediment: ablation till, deficient in fine material and produced by rockfalls and avalanches falling on to the glacier surface, and basal lodgement till, rich in fines and formed mainly by subglacial erosion. Recent recession from its Neoglacial maximum has exposed large areas of basal till with thin veneers of ablation till which, when combined with present subglacial and supraglacial debris, provide abundant material for erosion and transport by the mcltwatcr stream. Sediment transport measurements over two summers (1977–1978) showed that bed load and suspended load occur in approximately equal proportions and that dissolved loads are minor. Local source variations, especially bank slumps, are a major cause of scatter in sediment rating curves. Suspended-sediment concentrations are greater early in the melt season due to availability of loose sediment produced by freezing and thawing. Other contributors to scatter in suspended-sediment rating curves include rain showers and diurnal hysteretic effects. Although the distinction between bed load and suspended load is never sharp, available data suggest that the sand/ gravel grain-size boundary (-1ø) approximates the suspendcd-load/bed-load division for characteristic Hilda flows transporting gravel. This approximation, combined with till grain-size analyses, suspended-sediment measurements, and spatial distributions of till types, leads to the following computations of fluvial sediment sources: for suspended load - 6% supraglacial, 47% subglacial, 47% channel banks; for bed load - 46% supraglacial, 27% each subglacial and channel banks. Supraglacial debris provides only about one-fourth of all fluvial sediment, but nearly half of the bed load.     

On the dynamics of sediment suspension by residual Reynolds stresses—confirmation of Bagnold's theory

ABSTRACT Bagnold's dynamic theory for sediment suspension requires that the immersed weight of suspended grains over unit bed area is supported by an upward-directed residual Reynolds stress, τ_yy, arising from asymmetrical shear turbulence. The present paper presents an analysis of previously published turbulence data which confirms the existence of this residual stress and indicates its generation in the lowermost part of the buffer layer of turbulent shear flows. The magnitude of τ_yy is estimated as about 0.3τ_yx. Calculations from experimental data on suspended fine sand transport over upper phase beds reveals that τ_yy, is in approximate equilibrium with the weight stress due to the suspended load.     

Sediment suspension dynamics and a new criterion for the maintenance of turbulent suspensions

The vertical component of the turbulent flow acceleration term, , is used to determine the net positive vertical force that may support a suspended sediment load. A dimensionless criterion, Λ, is proposed for the maintenance of suspension, defined as the ratio of the maximum vertical turbulent stress to immersed weight of the suspended load above a unit bed area. In order that a suspension be maintained: where v ′ is instantaneous vertical turbulent velocity, σ and ρ are solid and fluid densities, respectively and m is the suspended load dry mass. The Λ criterion is dynamic, being a ratio of stresses and is analogous in this respect to Shields dimensionless stress criterion, θ, for the initiation of bedload motion. The new criterion is successful in predicting the maintenance of steady-state suspended sediment transport in open channel shear flow and deposition from non-uniform particulate density flows of wall jet type.     

Flow and sediment transport over large subaqueous dunes: Fraser River, Canada

Large symmetric and asymmetric dunes occur in the Fraser River, Canada. Symmetric dunes have stoss and lee sides of similar length, stoss and lee slope angles <8°, and rounded crests. Asymmetric dunes have superimposed small dunes on stoss sides, sharp crests, stoss sides longer than lee sides, stoss side slopes <3° and straight lee side slopes up to 19°. There is no evidence for lee side flow separation, although intermittent separated flow is possible, especially over asymmetric dunes. Dune symmetry and crest rounding of symmetric dunes are associated with high sediment transport rates. High near-bed velocity and bed load transport near dune crests result in crest rounding. Long, low-angle lee sides are produced by deposition of suspended sediment in dune troughs. Asymmetric dunes appear to be transitional features between large symmetric dunes and smaller dunes adjusted to lower flow velocity and sediment transport conditions. Small dunes on stoss sides reduce near-bed flow velocity and bed load transport, causing a sharper dune crest. Reduced deposition of suspended sediment in troughs results in a short, steep lee slope. Dunes in the Fraser River fall into upper plane bed or antidune stability fields on flume-based bedform phase diagrams. These diagrams are probably not applicable to large dunes in deep natural flows and care must be taken in modelling procedures that use phase diagram relations to predict bed configuration in such flows.     

Slurry-flow deposits in the Britannia Formation (Lower Cretaceous), North Sea: a new perspective on the turbidity current and debris flow problem

The Lower Cretaceous Britannia Formation (North Sea) includes an assemblage of sandstone beds interpreted here to be the deposits of turbidity currents, debris flows and a spectrum of intermediate flow types termed slurry flows. The term ‘slurry flow’ is used here to refer to watery flows transitional between turbidity currents, in which particles are supported primarily by flow turbulence, and debris flows, in which particles are supported by flow strength. Thick, clean, dish‐structured sandstones and associated thin‐bedded sandstones showing Bouma T_b–e divisions were deposited by high‐ and low‐density turbidity currents respectively. Debris flow deposits are marked by deformed, intraformational mudstone and sandstone masses suspended within a sand‐rich mudstone matrix. Most Britannia slurry‐flow deposits contain 10–35% detrital mud matrix and are grain supported. Individual beds vary in thickness from a few centimetres to over 30 m. Seven sedimentary structure division types are recognized in slurry‐flow beds: (M₁) current structured and massive divisions; (M₂) banded units; (M₃) wispy laminated sandstone; (M₄) dish‐structured divisions; (M₅) fine‐grained, microbanded to flat‐laminated units; (M₆) foundered and mixed layers that were originally laminated to microbanded; and (M₇) vertically water‐escape structured divisions. Water‐escape structures are abundant in slurry‐flow deposits, including a variety of vertical to subvertical pipe‐ and sheet‐like fluid‐escape conduits, dish structures and load structures. Structuring of Britannia slurry‐flow beds suggests that most flows began deposition as turbidity currents: fully turbulent flows characterized by turbulent grain suspension and, commonly, bed‐load transport and deposition (M₁). Mud was apparently transported largely as hydrodynamically silt‐ to sand‐sized grains. As the flows waned, both mud and mineral grains settled, increasing near‐bed grain concentration and flow density. Low‐density mud grains settling into the denser near‐bed layers were trapped because of their reduced settling velocities, whereas denser quartz and feldspar continued settling to the bed. The result of this kinetic sieving was an increasing mud content and particle concentration in the near‐bed layers. Disaggregation of mud grains in the near‐bed zone as a result of intense shear and abrasion against rigid mineral grains caused a rapid increase in effective clay surface area and, hence, near‐bed cohesion, shear resistance and viscosity. Eventually, turbulence was suppressed in a layer immediately adjacent to the bed, which was transformed into a cohesion‐dominated viscous sublayer. The banding and lamination in M₂ are thought to reflect the formation, evolution and deposition of such cohesion‐dominated sublayers. More rapid fallout from suspension in less muddy flows resulted in the development of thin, short‐lived viscous sublayers to form wispy laminated divisions (M₃) and, in the least muddy flows with the highest suspended‐load fallout rates, direct suspension sedimentation formed dish‐structured M₄ divisions. Markov chain analysis indicates that these divisions are stacked to form a range of bed types: (I) dish‐structured beds; (II) dish‐structured and wispy laminated beds; (III) banded, wispy laminated and/or dish‐structured beds; (IV) predominantly banded beds; and (V) thickly banded and mixed slurried beds. These different bed types form mainly in response to the varying mud contents of the depositing flows and the influence of mud on suspended‐load fallout rates. The Britannia sandstones provide a remarkable and perhaps unique window on the mechanics of sediment‐gravity flows transitional between turbidity currents and debris flows and the textures and structuring of their deposits.     

Textural trends in turbidites and slurry beds from the Oligocene flysch of the East Carpathians, Romania

Deep‐water sandstone beds of the Oligocene Fusaru Sandstone and Lower Dysodilic Shale, exposed in the Buz?u Valley area of the East Carpathian flysch belt, Romania, can be described in terms of the standard turbidite divisions. In addition, mud‐rich sand layers are common, both as parts of otherwise ‘normal’ sequences of turbidite divisions and as individual event beds. Eleven units, interpreted as the deposits of individual flows, were densely sampled, and 87 thin sections were point counted for grain size and mud content. S₃/T_a divisions, which form the bulk of most sedimentation units, have low internal textural variability but show subtle vertical trends in grain size. Most commonly, coarse‐tail normal grading is associated with fine‐tail inverse grading. The mean grain size can show inverse grading, normal grading or a lack of grading, but sorting tends to improve upward in most beds. Fine‐tail inverse grading is interpreted as resulting from a decreasing effectiveness of trapping of fines during rapid deposition from a turbidity current as the initially high suspended‐load fallout rate declines. If this effect is strong enough, the mean grain size can show subtle inverse grading as well. Thus, thick inversely graded intervals in deep‐water sands lacking traction structures do not necessarily imply waxing flow velocities. If the suspended‐load fallout rate drops to zero after the deposition of the coarse grain‐size populations, the remaining finer grained flow bypasses and may rework the top of the S₃ division, forming well‐sorted, coarser grained, current‐structured T_t units. Alternatively, the suspended‐load fallout rate may remain high enough to prevent segregation of fines, leading to the deposition of significant amounts of mud along with the sand. Mud content of the sandstones is bimodal: either 3–13% or more than 20%. Two types of mud‐rich sandstones were observed. Coarser grained mud‐rich sandstones occur towards the upper parts of S₃/T_a divisions. These units were deposited as a result of enhanced trapping of mud particles in the rapidly deposited sediment. Finer grained mud‐rich units are interbedded with ripple‐laminated very fine‐grained sandy T_c divisions. During deposition of these units, mud floccules were hydraulically equivalent to the very fine sand‐ and silt‐sized sediment. The mud‐rich sandstones were probably deposited by flows that became transitional between turbidity currents and debris flows during their late‐stage evolution.     

Prediction of daily suspended sediment load using wavelet and neurofuzzy combined model

This study investigated the prediction of suspended sediment load in a gauging station in the USA by neuro-fuzzy, conjunction of wavelet analysis and neuro-fuzzy as well as conventional sediment rating curve models. In the proposed wavelet analysis and neuro-fuzzy model, observed time series of river discharge and suspended sediment load were decomposed at different scales by wavelet analysis. Then, total effective time series of discharge and suspended sediment load were imposed as inputs to the neuro-fuzzy model for prediction of suspended sediment load in one day ahead. Results showed that the wavelet analysis and neuro-fuzzy model performance was better in prediction rather than the neuro-fuzzy and sediment rating curve models. The wavelet analysis and neuro-fuzzy model produced reasonable predictions for the extreme values. Furthermore, the cumulative suspended sediment load estimated by this technique was closer to the actual data than the others one. Also, the model could be employed to simulate hysteresis phenomenon, while sediment rating curve method is incapable in this event.     

Heavy metal flows in aquatic systems of the Don and Kuban river deltas

This paper presents the calculated heavy metal (Fe, Mn, Zn, Ni, Cu, Cr, Co, Cd, and Pb) flows in suspended and dissolved forms in the main navigable branches of the Don and Kuban river deltas during the low-water period of 2013–2014. This work is based on the data of field studies in which water and suspended matter samples were collected and the turbidity and water discharge in deltas were measured. A quantitative estimate of heavy metal inflows into the deltas of the Don and Kuban rivers is provided. Transformation of flows of suspended and dissolved metal forms from the delta top to the sea edge is discussed. The influence of localities (Rostov-on-Don, Temryuk) on the increase in heavy metal flows downstream is shown, and the heavy metal flows in the deltas of the Don and Kuban rivers are compared.

     

Methods of computation of suspended load from bed materials and flow parameters

Computation of the grain-size distribution of the suspended load above a sand bed must take into consideration: (1) sorting processes from the bed to the bed layer and (2) sorting between the bed layer and suspension. Grain-size distributions of the bed layers above sand beds of three different types have been computed in this work, both by the Einstein and the Gessler methods. Using these as references, suspended load distributions have been obtained in each case by the Rouse suspension equation. A new formula has also been developed in partial modification of Hunt's method for direct computation of bed load and suspended load from a bed's grain-size distribution and flow parameters. Comparison of the computed data with actual observations in laboratory flumes show that no one method is particularly superior to the others, but the present method is advantageous because it affords direct computation of the suspended load from a bed's grain-size distribution, without going through an intermediate stage (bed load). The possible sources of error in each of the methods have been discussed.     

The partitioning of the total sediment load of a river into suspended load and bedload: a review of empirical data

The partitioning of the total sediment load of a river into suspended load and bedload is an important problem in fluvial geomorphology, sedimentation engineering and sedimentology. Bedload transport rates are notoriously hard to measure and, at many sites, only suspended load data are available. Often the bedload fraction is estimated with ‘rule of thumb’ methods such as Maddock’s Table, which are inadequately field‐tested. Here, the partitioning of sediment load for the Pitzbach is discussed, an Austrian mountain stream for which high temporal resolution data on both bedload and suspended load are available. The available data show large scatter on all scales. The fraction of the total load transported in suspension may vary between zero and one at the Pitzbach, while its average decreases with rising discharge (i.e. bedload transport is more important during floods). Existing data on short‐term and long‐term partitioning is reviewed and an empirical equation to estimate bedload transport rates from measured suspended load transport rates is suggested. The partitioning averaged over a flood can vary strongly from event to event. Similar variations may occur in the year‐to‐year averages. Using published simultaneous short‐term field measurements of bedload and suspended load transport rates, Maddock’s Table is reviewed and updated. Long‐term average partitioning could be a function of the catchment geology, the fraction of the catchment covered by glaciers and the extent of forest, but the available data are insufficient to draw final conclusions. At a given drainage area, scatter is large, but the data show a minimal fraction of sediment transported in suspended load, which increases with increasing drainage area and with decreasing rock strength for gravel‐bed rivers, whereby in large catchments the bedload fraction is insignificant at ca 1%. For sand‐bed rivers, the bedload fraction may be substantial (30% to 50%) even for large catchments. However, available data are scarce and of varying quality. Long‐term partitioning varies widely among catchments and the available data are currently not sufficient to discriminate control parameters effectively.