Regularity of sediment transport and sedimentation during floods in the lower Yellow River,China

The flood season is the main period of flow,sediment transport,and sedimentation in the lower Yellow River(LYR).Within the flood season,most of the flow,sediment transport,and sedimentation occurs during flood events.Because of the importance of floods in forming riverbeds in the LYR,the regularity of sediment transport and sedimentation during floods in the LYR was studied.Measured daily discharge and sediment transport rate data for the LYR from 1960 to 2006 were used.A total of 299 floods wer...     

Predictability of sediment transport in the Yellow River using selected transport formulas

This paper evaluates the applicability of the sediment transport methods developed by Engelund and Hansen, Ackers and White, Yang et al., and van Rijn, together with the Wuhan methods developed in China, to the Yellow River, which has highly concentrated and fine-grained sediment. The sediment data includes over 1000 observations from the Yellow River, 32 sets of data from a canal, and 266 sets of data from laboratory flumes. The best predictions were obtained by the Yang 1996 method, the Wuhan method, and the modified Wuhan method by Wu and Long, while reasonably good predictions were also provided by the van Rijn 2004 method. The Engelund and Hansen, the Ackers and White, and the van Rijn 1984 methods in their original forms are not applicable to the Yellow River. The predicted results for total load concentrations were as good as for bed-material concentrations, even though the total load includes a large portion of wash load.     

Macroinvertebrates in the bed sediment of the Yellow River

Extensive agricultural,industrial and urban development in the Yellow River,China,have modified the sediment-water balance,flow and inundation regimes,longitudinal connectivity,integrity of riparian vegetation,and water quality.Macroinvertebrate assemblages in the bed sediment of main channel and major reservoirs of the Yellow River are described in detail for the first time.A total of 74 taxa comprising 17 taxa of oligochaetes,48 taxa of aquatic insects,5 taxa of molluscs,and 4 taxa of other animals were recorded.A range of feeding guilds were represented,including, collector-gatherers(32 taxa),predators(17 taxa),scrapers(16 taxa),shredders(6 taxa)and collector-filterers(2 taxa).Both the mean density and biomass of macroinvertebrates were significantly higher in sites located in the artificial reservoirs compared with the main river channel. Assemblages varied spatially;Oligochaetes dominated assemblages in upper reaches,insects dominated in middle reaches and other animals(e.g.Crustacea)dominated in lower reaches. Collector-gatherers were dominant throughout the entire river.Classification analysis identified five site-groups on the basis of macroinvertebrate presence/absence:downstream of reservoirs;vegetated sites;reservoir sites;polluted sites,and;lower-reach sites.Lower macroinvertebrate richness,density and biomass,compared with other similar large rivers,were attributed to modification of the sediment-water balance and associated disturbance of benthic habitats.Pollution,stability of sediment and sediment concentration combined to influence the distribution of macroinvertebrates.This knowledge will substantially benefit the recent focus on the health and environmental water requirements of the Yellow River.     

Comprehensive evaluation method for sediment allocation effects in the Yellow River

Scientific evaluation of the sediment allocation effects in the Yellow River plays an important role in the comprehensive harnessing of the Yellow River. A new evaluation index system for sediment allocation has been established using the Analytic Hierarchy Process, and six main evaluation indexes have been selected for this study. The calculation methods and evaluation criteria of each evaluation index are proposed. The evaluation criterion of bankfull discharge in the upper reach is 2,000 m³/s, that of Tongguan elevation in the middle reach is 325.7 m, and that of bankfull discharge in the lower reach is 4,000 m³/s. The evaluation criteria of water volume and sediment volume into the Yellow River are 25 billion m3/a and 300 million t/a, respectively, and that of sediment volume into the sea to maintain stability of the estuary is 130–260 million t/a. The comprehensive evaluation method and grade index are proposed, and the effect of sediment allocation in the Yellow River from 1960 to 2015 is evaluated. The comprehensive evaluation grades in different periods are determined. The evaluation results objectively reflect the situation of sediment allocation in the Yellow River, and the new comprehensive evaluation method can be applied to evaluate the sediment allocation scheme of the Yellow River in the future.     

Analyses of trends and causes for variations in runoff and sediment load of the Yellow River

Due to the impacts of globe climate change and human activities, dramatic variations in runoff and sediment load were observed for the Yellow River. Analyses of nearly 65 years' data measured at main hydrologic-stations on the Yellow River from 1950 to 2014 indicated that, except for the Tangnaihai station in the head region, sharp downward trends existed in both the annual runoff and annual sedi-ment load according to the Mann–Kendal trend test;and their abrupt changes occurred in 1986 and in 1980, respectively, according to the rank sum test. Factors affecting the changes in the runoff and sediment load were very complicated. Results indicated that the reducing precipitation and the increasing water consumption were the main causes for the runoff decline, while the impoundment of the Longyangxia Reservoir and its combined operation with the Liujiaxia Reservoir exerted a direct bearing on the abrupt change in the annual runoff. In addition to the sediment load decrease associated with the runoff reduction, the reduced storm intensity, the conducted soil erosion control, and the constructed dam buildings all played an important role in the trends and abrupt changes of sediment load decline.     

Characteristics and influencing factors of sediment deposition-scour in the Sanhuhekou-Toudaoguai Reach of the upper Yellow River,China

The annual changes of sediment deposition-scour on the riverbed in the Sanhuhekou-Toudaoguai Reach of the upper Yellow River during the years 1952-2010 were investigated based on runoff and sediment transport observations from the Sanhuhekou and Toudaoguai hydrological stations. Multiple influencing factors such as reservoir operations, tributary inflows, as well as runoff and sediment loads from the Shidakongdui area were analyzed. The results show that even though the sediment loads from the major sources, the Shidakongdui area as well as the upstream tributaries such as the Qingshui River and the Zuli River have reduced especially since the 2000 s as a result of enhanced water-soil conservation measures and improvement of vegetation cover, the study reach was still generally in a status of cumulative aggradation. This is mainly due to the joint operations of the Liujiaxia Reservoir and the Longyangxia Reservoir, which significantly reduced the annual runoff and sediment loads at the Sanhuhekou Crosssection. The reservoirs also remarkably altered the summer flood characteristics of the study reach, inducing the shape of the annual flow curve changing from a 'single-peak' into a 'doublepeak'. These alternations sharply decreased the sediment transport capacity of flooding in the summer flood season which yields more than 90% of the sediment loads, leading to an unbalanced relation between the water and sediment. In addition, the estimated incoming sediment coefficient of the Sanhuhekou Crosssection ranged from 0.003 to 0.014 kg s/m~6, of which 0.004 kg s/m~6 was suggested as a rough critical value to determine the scour or deposition status of the study reach.     

Equilibrium relations for water and sediment transport in the Yellow River

The equilibrium relations for water and sediment transport refer to the relative balance of sediment transport and the relative stability of river courses formed by the automatic adjustment of riverbeds.This is the theoretical basis for the comprehensive management of sediment in the Yellow River.Based on the theories of sediment carrying capacity and the delayed response of riverbed evolution,in this study,the equilibrium relations for water and sediment transport in the Yellow River are established.These relations include the equilibrium relationships between water and sediment transport and bankfull discharge in the upper and lower Yellow River and between water and sediment transport and the Tongguan elevation in the middle Yellow River.The results reveal that for the Ningmeng reach,the Tongguan reach,and the lower Yellow River,erosion and deposition in the riverbeds are adjusted automatically,and water and sediment transport can form highly constrained equilibrium relationships.These newly established equilibrium relationships can be applied to calculate the optimal spatial allocation scheme for sediment in the Yellow River.     

Changes in sediment transport in the Kuye River in the Loess Plateau in China

In this paper, the changes in sediment transport over 51 years from 1955 to 2006 in the Kuye River in the Loess Plateau in China are assessed. Key factors affecting sediment yield and sediment transport, such as precipitation depth, discharge, and human activities are studied. To investigate the changes in sediment yield in this watershed, a trend analysis on sediment concentration, precipitation depth, and discharge is conducted. Precipitation depths at 2 Climate Stations （CSs）, as well as discharge and sediment transport at 3 Gauging Stations （GSs） are used to assess the features of sediment transport in the Kuye River. The rtmoff modulus （defined as the annual average discharge per unit area, L/（s·km^2）） and the sediment transport modulus （defined as the annual suspended sediment transport per unit area, t/（yr km^2）） are introduced in this study to assess the changes in runoff and sediment yield for this watershed. The results show that the highest average monthly discharge during the study period in the Kuye River is 66.23 m^3/s in August with an average monthly sediment concentration of 88.9 kg/m^3. However, the highest average monthly sediment concentration during the study period in the Kuye River is 125.34 kg/m^3 and occurs in July, which has an average discharge of 42.6 m^3/s that is much less than the average monthly discharge in August. It is found that both the runoff modulus and sediment transport modulus at Wenjiachuan GS on the Kuye River has a clear downward trend. During the summer season from July to August, the sediment transport modulus at Wenjiachuan GS is much higher than those at Toudaoguai and Longmen GSs on the Yellow River. The easily erodible loess in the Kuye River watershed and the sparse vegetation are responsible for the extremely high sediment yield from the Kuye River watershed. The analyses of the grain size distribution of suspended load in the Kuye River are presented. The average monthly median grain size of suspended load in the Kuye River is largest in February and then decreases until June. In July, the average monthly median grain size of suspended load approaches another peak and decreases until September. Then, the median grain size of suspended load starts to increase until February of the following year. However, the average monthly median grain size of suspended load in the Yellow River at Toudaoguai and Longmen GSs is the smallest between early summer and late fall The median grain size in the Yellow River starts to increase in November and approaches the largest size in January.     

Using sediment rating parameters to evaluate the changes in sediment transport regimes in the middle Yellow River basin,China

This study analyses the changes in sediment transport regimes in the middle Yellow River basin (MYRB) using sediment rating parameters. Daily streamflow and suspended sediment concentration data were collected at 35 hydrological stations from the 1950s to 2016, which can be divided into three periods based on the type and intensity of human activities: the base stage before 1970, the restraining stage from 1971 to 1989, and the restoration stage after 2002. Data within each period were fitted by log‐linear sediment rating curves and the sediment rating parameters were utilized to analyse the spatial and temporal variations in sediment transport regimes. The results show that sediment rating parameters are indicative of sediment transport regimes. In the base stage and the restraining stage, the hydrological stations can be categorized into four groups based on their locations on the rating parameter plot. The stations with small drainage basins were characterized by the highest sediment transport regime, followed by those located in the coarse‐particle zone, the loess zone, and the mountainous/forest zone. In the restoration stage, the difference in sediment transport regimes between different geomorphic zones became less distinguishable than in previous stages. During the transition from the base stage to the restraining stage, sediment rating parameters showed no significant changes in sediment transport regimes in all four geomorphic groups. During the transition from the restraining stage to the restoration stage, significant changes were observed in the coarse‐particle zone and the mountain/forest zone, indicating that the revegetation programme and large reservoirs imposed a stronger influence on sediment transport regimes in these two zones than in the rest of the MYRB. This study provides theoretical support for evaluating sediment transport regimes with sediment rating parameters.     

Comparison of sediment transport computations using hydrodynamic versus hydrologic models in the Simiyu River in Tanzania

This paper presents the results of a study that compares the sediment routing of the Simiyu River using the hydrologic model, Soil and Water Assessment Tool (SWAT) and the 1D hydrodynamic simulation software for Rivers and Estuaries (SOBEK-RE) model. Routing in SWAT is completed using the simplified Bagnold’s equation and in the SOBEK-RE model is undertaken using the Saint Venant equation. The upstream boundary conditions for the routing modules were derived from the subcatchments sediment yields that were estimated by SWAT using the Modified Universal Soil Loss Equation (MUSLE). The sediment loads extrapolated or interpolated from the sediment rating curve for the catchment outlet were used for calibration and validation purposes. The SWAT model predicted an erosion rate of 2.09 Mt/yr. The total sediment load transported to the main outlet of the catchment simulated by the SWAT and SOBEK-RE models was equal to 2.94 and 2.72 Mt/yr, respectively. Thus the models computed a net erosion in the channels of 0.84 Mt/yr (SWAT) and 0.63 Mt/yr (SOBEK-RE). When comparing the results of the models for the different reaches of the main channel and main tributaries, the models showed different results both in magnitude and in sign (erosion/deposition). However, in a situation where data is scarce (such as grain size, channel geometry), the more complex hydrodynamic model does not necessarily lead to more reliable results.     

Decreasing trend of sediment transfer function of the Upper Yellow River,China, in response to human activity and climate change

Abstract

An index (F_s) for sediment transfer function is introduced, based on the sediment budget at the channel scale. The purpose of this study is two-fold: to gain a deeper insight into how F_s is influenced by natural and human factors, and to provide some new knowledge for decision making in the management of the Upper Yellow River, China. Since 1960, the F_s of the Lanzhou to Toudaoguai reach of the Upper Yellow River shows a decreasing trend. At the drainage basin level, the decreased F_s can be explained by changes in precipitation and air temperature, as well as by a number of variables describing human activity, such as reservoir regulation, water diversion, and soil and water conservation. The higher temperature reduces the transfer function, while the larger runoff coefficient increases it. At the channel level, the decreased F_s can be explained by a number of variables of flow and sediment input. Three countermeasures for restoration of the F_s are suggested.

Editor Z.W. Kundzewicz     

Sediment retention by check dams in the Hekouzhen-Longmen Section of the Yellow River

Coarse sediment retention by check dams is analyzed for five typical catchments in the Hekou-Longmen section of the midstream of the Yellow River, which is an area of high .coarse sediment concentration. The catchments are the Huangfuchuan, Kuye, Wuding, Sanchuan and Qiushui River Basins. The amount of coarse sediment retained by check clams in these areas for different periods was measured. Sediment reduction due to check clams is compared with other soil conservation measures and the results show that check clams are the most effective to rapidly reduce the amount of coarse sediment entering the Yellow River. If the average percentage of the drainage area with check clams for the five typical catchments reaches 3.0%, the average sediment reduction ratio can reach 60%. Therefore, to rapidly and effectively reduce the amount of sediment, especially coarse sediment, entering the Yellow River, the area percentage of check clams in the Hekou-Longmen section should be kept around 3%. The Kuye and Huangfuchuan River Basins are the preferred main catchments in which such water conservation measures are implemented.     

现代黄河三角洲沉积物磁性地层年代框架及环境磁学研究

本文对黄河三角洲Z07孔沉积物进行了系统的磁性地层学和环境磁学研究.通过结合沉积速率和古地磁长期变化数据,我们为该孔建立了较为精确可信的年代框架（1999-03-2006-06 A.D.）.环境磁学结果表明黄河三角洲沉积物与中国黄土的磁学特征相似,主要载磁矿物为单畴（SD）磁铁矿,超顺磁颗粒（SP）含量也较高.整体上,该孔沉积物磁学参数的变化主要受粒度和含量控制.岩芯磁性参数在2003年前后发生了系统变化.我们认为,黄河自2002年起进行调水调沙工程,黄河下游河道冲刷加剧,形成新的物质来源,河流输入的沉积物粒度变粗,输沙量增加,这一新的物质来源是造成Z07钻孔磁性参数发生显著变化的主因.

     

Chemical characterization of naturally weathered oil residues in the sediment from Yellow River Delta, China

With its close proximity to Shengli Oilfield, China’s second largest oilfield, the Yellow River Delta is at high risk for crude oil contamination. The massive oil discharge in oilfield may offer a chance for a natural experiment to investigate compositional changes of oil residues and study the stability of source- and weathering-dependent molecular parameters in oil residues after spills. The results demonstrate that the conventional diagnostic ratios, such as C₂₉20S/(20S + 20R), C₂₉/C₃₀H, C₃₀βα/αβ, C₃₁22S/(22S + 22R), C₂-DBTs/C₂-PHENs, C₃-DBTs/C₃-PHENs, DBT/MCHRY, CHRY/PHENs, are also valid for oil source identification even after extensive weathering of spilled oils in terrestrial environment, although some exceptions were encountered for extensively weathered sample. Moreover, the ratios of selected specific biomarkers (the oleanane index, the gammacerane index) have been developed and assessed as source indicators. Finally, we find that some maturity parameters based on alkyl naphthalenes and methyl phenanthrenes in petroleum geochemistry, such as the methylnaphthalene ratios (TMNr, TeMNr, PMNr), the methylphenanthrene ratios (MPI-1, MPDF), can be applied for the source identification and correlation at their lightly to moderately weathered stage.     

Modelling hyperconcentrated flow in the Yellow River

A large amount of the total sediment load in the Chinese Yellow River is transported during hyperconcentrated floods. These floods are characterized by very high suspended sediment concentrations and rapid morphological changes with alternating sedimentation and erosion in the main channel, and persistent sedimentation on the floodplain. However, the physical mechanisms driving these hyperconcentrated floods are still poorly understood. Numerical modelling experiments of these floods reveal that sedimentation is largely caused by large vertical concentration gradients, both in the channel during the rising stage of the flood, as well as on the floodplains, during a later stage of the flood. These vertical concentration gradients are large because the turbulent mixing rates are reduced by the increased sediment‐induced density gradients, resulting in a positive feedback mechanism that produces high deposition rates. Erosion prevails when the sediment is largely held in suspension due to hindered settling, and is strengthened by the reduced wetted cross‐section caused by massive sedimentation on the floodplain. Observed patterns of erosion and sedimentation during these floods can be qualitatively reproduced with a numerical model in which sediment‐induced density effects and hindered settling are included. Copyright © 2009 John Wiley & Sons, Ltd.     

Delayed response model for bankfull discharge predictions in the Yellow River

Delayed response means that channels cannot achieve a new equilibrium state immediately following disruption;the channel requires a response time or relaxation time to reach equilibrium.It follows that the morphological state of fluvial system represents the cumulative effects of all previous disturbances and environmental conditions.A unique feature of the delayed response model for bankfull discharge is that the model is capable of representing the cumulative effects of all previous flow conditions when applied to predict the path/trajectories of bankfull discharge in response to altered flow regimes.In this paper,the delayed response model was modified by readjusting the weight for the initial boundary conditions and introducing a variableβwith respect to time.The modified model was then applied to the bankfull discharge calculations for three selected river reaches of the Yellow River,with each reach having different geomorphic settings and constraints. Results indicated that the modified model can predict accurately the bankfull discharge variation in response to changes in flow discharge and sediment load conditions that have been dramatically altered in the past.Results also demonstrated the strong dependence of current bankfull discharge on the previous years’ flow conditions,with the relaxation time varied from 2 to 14 years,meaning that the bankfull discharge was not only affected by the flow discharge and sediment load in the current year,but also by those in previous 1 to 13 years.Furthermore,the relaxation time of bankfull discharge adjustment was inversely proportional to the long-term average suspended sediment concentrations,and this may be explained by fact that high sediment concentrations may have a high potential to perform geomorphic work and there is more sediment readily available to shape the channel boundary and geometry.     

Multiple temporal scale relationships of bankfull discharge with streamflow and sediment transport in the Yellow River in China

This paper presents a study on the characteristics of multiple time scales of bankfull discharge and its delayed response to changes of flow conditions using continuous wavelet analysis for data from selected hydrological stations in the Yellow River basin. Results showed that bankfull discharge series had one or two dominant time scales. For example, the Huayuankou station in the lower reach of the Yellow River had two dominant time scales of 19-20 years and 545 years. The dominant time scales of the bankfull discharge series were generally consistent with the dominant time scales of water discharge and sediment concentration series, indicating that the channel morphology inherits the characteristics of the hydrological system in terms of multiple time scales. In addition, the wavelet coefficients of the bankfull discharge series had a phase difference in relation to those of the sediment concentration series, with a delay time that varied from 3 to 16 years at different sites. This delay time or relaxation time is a result of the delayed response of bankfull discharge to flow conditions, which was significant for channel adjustments in response to changes of flow conditions. The findings of the multiple time scales and the delayed response are of importance for further study of channel morphology of fluvial systems.     

River adjustment to changes in sediment load: The effects of tin mining on the Ringarooma River,Tasmania, 1875–1984

The mining of alluvial tin in the Ringarooma basin began in 1875, reached a peak in 1900–20, and had virtually ceased by 1982. During that time 40 million m³ of mining waste were supplied to the main river, quickly replacing the natural bed material and requiring major adjustments to the channel. Based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load, the river's transport history is reconstructed using a mass-conservation model. Because of the lengthy time period (110 years) and river distance (75 km) involved, the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream. Peak storage is predicted in that part of the river where braiding and anastomosis are best developed. Aggradation was most rapid in the upper reaches close to major supply points, becoming slower and later with distance downstream. Channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common. Bridges had frequently to be replaced. While bed levels were still rising in lower reaches, degradation began in upper ones, notably after 1950, and by 1984 had progressed downriver over 30 km. Rates of incision reached 0·5 m yr^?1, especially in the early 1970s when record high flows occurred. As a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions. Also a narrower unbraided channel has developed. The river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris.     

Quantifying the suspended sediment discharge to the ocean from the Markham River,Papua New Guinea

The Markham River is a small river draining a tropical mountain range with altitudes between 1000 and 3000 m and discharges directly into a submarine canyon, the head of which is at 30 m depth and reaches depths of 500 m only 4 km from the shore. As such, the Markham discharge system serves as a possible analogue for rivers discharging onto margins during low stands of sea-level. Located in a tectonically active area and with high rainfall, sediment supply is high and episodic and is sometimes related to catastrophic mountain landslides. The river has an estimated sediment load of 12 Mt yr⁻¹. Occasionally, high energy flows are generated at the river mouth which is evident from the channel morphology and sediment distribution. Profiles of salinity and suspended sediment concentrations (SSC) show that sediment is dispersed via a plume with components at both the surface, intermediate depth along isopycnal surfaces and near the sea bed. The dispersal pattern of the surface freshwater plume is largely determined by the buoyancy force. The surface plume is very thin with salinity gradients 15 ppt m⁻¹ while a Richardson number greater than unity suggested that the mixing zone is highly stratified. Estimates of the horizontal sediment flux gradient of the surface plume along the estuary axis suggest that about 80% of the sediment discharged is lost from the plume within a distance of 2 km from the river mouth. Particle fall velocities estimated from the vertical flux indicate values less than those of flocculated material. Layers of sediment with SSCs between 500 and 1000 mg l⁻¹ were observed at intermediate depths and near the seabed during periods of both high and intermediate discharge. The mass of sediment in a SSC layer at intermediate depths between 150 and 250 m within the canyon channel was estimated to be equivalent to an average of 2 to 3 days of Markham sediment discharge. SSCs near the seabed of between 250 and 750 mg l⁻¹ suggest that layers of significantly elevated density exist near the seabed, moving under the influence of gravity down steep seabed slopes of the Markham canyon.     

Migration rate of river bends estimated by tree ring analysis for a meandering river in the source region of the Yellow River

Meandering rivers have dynamic evolution characteristics of lateral migration and longitudinal creeping movement, and studies on the migration rate of meandering rivers have both scientific and practical significance for understanding the evolution process. A river source region often is sparsely populated and lacks long-term monitoring data, making it difficult to estimate the migration rate of river bends. In the source region of the Yellow River, located in the northeastern part of the Qinghai-Tibet Plateau, China, meandering rivers have extensively developed. Combined with field investigation and sampling in the source region in 2016 and 2017, 9 river bends in the middle Baihe River were selected to attempt estimation of migration rates of the river bends using tree ring analysis. The tree core and disc samples were collected using an increment borer and a crosscut saw, and the ages of the trees were estimated based on tree ring analysis. A method for estimating the migration rate of river bends based on the relation between positions and ages of trees grown on the point bars in inner banks is proposed. The estimated migration rates of the 9 river bends of the Baihe River ranged 0.38–6.10 m/yr, and the migration rates were found to be related to the flow rate, channel slope, height of the outer bank, and width of the river valley. The maximum migration rate was determined to be at the No. 9 River Bend where the ratio of the meander-bend radius to the channel width (R/W) was 2.31, which is consistent with previous findings that the bend migration is most rapid in the ‘migration phase’. The proposed method for estimating the migration rate of river bends provides a potential alternative option for future study on the morphodynamic process of a meandering river.