Shaping and maintaining a medium-sized main channel in the Lower Yellow River

This paper studies relations between bankfull discharge,lateral cross section variation and the incoming flow and sediment condition in the Lower Yellow River using measured data from 1950 to 2003.Since 1950 the bankfull discharge has obviously decreased and the ratio of channel width to flow depth has increased.The critical annual average incoming sediment coefficient（defined as the ratio of sediment concentration to discharge） and discharge at the Huayuankou station are approximately 0.012 and 1,850 m³s^-1,respectively,for no accumulative deposition occurring in the reach from Huayuankou to Lijin.On this basis,a mathematical model is used to study the scale of the main channel in the Lower Yellow River and its corresponding bankfull discharge under possible incoming flow and sediment conditions in the near future.The main factors influencing the scale of the main channel are analyzed,and measures to shape and maintain a medium-sized channel are discussed.The results show the effect of various water and sediment combinations released from the Xiaolangdi Reservoir on the shaping of the main channel and suggest that under recent incoming flow and sediment conditions,it is possible to shape and maintain a medium-sized channel with a bankfull discharge of approximate 4,000 m³ s^-1.     

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.     

Influences of retrogressive erosion of reservoir on sedimentation of its downstream river channel——A case study on Sanmenxia Reservoir and the Lower Yellow River

Retrogressive erosion, a widespread phenomenon of sediment transport in reservoirs, often impacts on both the reservoir capacity and the sedimentation in the downstream river channel. Based on field data from the Sanmenxia Reservoir and the Lower Yellow River over the past decades, three courses of ret-rogressive erosion with distinctive features were analyzed. The results indicate that retrogressive erosion, especially caused by rapid reduction in the water level till the reservoir is empty, often results in the serious siltation of the lower Yellow River and threatens the safety of the flood control in the Lower Yellow River. Unreasonable operation of the reservoir and incoming hyperconcentrated floods accom-panied by retrogressive erosion also aggravate the siltation of the main channel of the river. However, a reasonable operation mode of the reservoir so named"storing the clear (low sediment concentration) water in the non–flood season, and sluicing the muddy(high sediment concentration) water in the flood season" was found, which might mitigate the deposition in both the reservoir and the Lower Yellow River. This operation mode provides important experience for the design and operation of large reser-voirs in other large rivers carrying huge amounts of sediment.     

SHRINKAGE OF THE ESTUARINE CHANNELS OF THE HAIHE DRAINAGE SYSTEM AND ITS INFLUENCES ON FLOOD HAZARD

1INTRODUCTIONTheHaiheRiverBasinislocatedinNorthChinawithareaof262.6km2.Itisaquicklydevelopedareawithmanyimportantcitiesandindustrialhubs,includingBeding,Tianjin,Tangshan,Cangzhou,DezhouandHuanghua.Theareawatchedfastprogressesinurbanizationinthepastdecades,andhumanactivitieshaveresultedingreatinfluencesontheenvironment,riverhydrologyandsedimentbudget.Theareaisprojectedtobemoreprosperouswithmoreoilandgasfields,chemicalindustrybases,anddenserrailwaysandexpresshighwaysinthenextcent'Ury.T…     

CHARACTERISTICS OF SEDIMENT TRANSPORT ALONG A RIVER REACH WITH A RESERVOIR

Based on long-term measurements at three gauging stations, Toudaoguai, Fugu and Hequ, and one meteorological station, this article discusses the features of discharge (Q) and sediment concentration (Cs) of a river reach of the Yellow River with a reservoir located in the Loess Plateau. The impacts of the local sub-watershed between Toudaoguai and Fugu gauging stations on sediment budget to the Yellow River have been analyzed. In addition, the deposition processes in the Tianqiao Reservoir have been investigated. Results show over 80% of the precipitation that falls in the local subwatershed is unable to contribute to the Yellow River runoff process. It is found that the annualmaximum sediment concentration is usually less than 30 kg/m^3 during flood seasons at Toudaoguai Gauging Station, but the sediment concentration varies dramatically at Fugu Gauging Station. About 35% of the sediment eroded in the sub-watersheds between Toudaoguai and Fugu gauging stationswas produced from the Huangfuchuan sub-watershed which has a drainage area accounting only for 10% of the drainage area between Toudaoguai and Fugu gauging stations. The Tianqiao Reservoir generally has deposition during the summer flood season, and scouring during the non-flood season.On average, over 85% of deposited sediment in the reservoir occurs in the 12 km long lower reservoir reach. The volume of annual deposition in the reservoir mainly depends on the volume of water from the local region between Hequ and Fugu gauging stations.     

THE OPERATION MODE OF "STORING THE CLEAR WATER AND DISCHARGING THE MUDDY FLOW" FOR RESERVOIRS BUILT ON HEAVILY SILT-LADEN RIVERS--A CASE STUDY OF THE SANMENXIA RESERVOIR

Observation of the operation of the Sanmenxia Reservoir on the Yellow River has led to the conclusion that to preserve a certain effective storage volume for reservoirs built on heavily silt-laden rivers is feasible if the reservoir is operated according to the principle known as "storing the clear water and discharging the muddy flow". The relative stability of the bed elevation at the end of the backwater and the reservoir's erosion and deposition equilibrium depend on the compatibility of the pool level maintained in non-flood seasons with the conditions of flow and sediment load during flood seasons. Operating the reservoir to regulate the flood and sediment load during flood seasons can reduce the rate of aggradation in the Lower Yellow River. The basic condition for applying the operation mode of "storing the clear water and discharging the muddy flow" is that a sufficient amount of water should be used for discharging sediment during flood seasons. Under the condition of extremely low flow years, reservoir sedimentation cannot be avoided even if this operation mode is adopted.     

REGULATION OF FLOW AND SEDIMENT LOAD IN THE YELLOW RIVER

Small runoff, large sediment load, and incompatible relationship of flow and sediment load are very important characteristics of the Yellow River. They are also the crux of the most prominent problems of the Yellow River. To solve these problems, the regimes of flow and sediment load have to be improved by increasing water, reducing sediment load, and by using reservoirs to regulate flow and sediment load. The results of experiments for regulating the flow and sediment load in the last three years by the Xiaolangdi Reservoir have indicated that this measure is a realistic and effective way to mitigate the prominent problems in flood control of the Lower Yellow River at present and in the near future. However, the regulation system is still imperfect. It is advisable to speed up the pace of research and construction of the system for regulating flow and sediment load.     

FLUVIAL PROCESSES AND SEDIMENT SCOUR RATE OF THE YELLOW RIVER UNDER ACTION OF UNSTEADY FLOWS

1 wrsoooCTIoxThe Yeuow mver crtes a huge amoun of sedimcht and the noods often cause raPid and severeerosinn and dePOsihon. The channl bed of the YelOw mver often exPeriences degIadation in the mainchannel during fioods. In some cases vigorous erosion uP to l0 meters takes place in a shOrt Period oftiIn. Such phenomenon usually occurs in the ndddie reaChs of the Yelow mver and its tributaries suchas the Wdse mVer the Beiluohe mver etc. For examPle, th6 hyPenconcentraed nood in July l…     

Recent changes of water discharge and sediment load from Feiyun River in Zhejiang Province,China

In-depth studies of water and sediment fluxes from rivers into the sea are very important for understanding the interactions between land and sea. This paper is concerned with identifying the changes in the time series of water and sediment fluxes from Feiyun River in Zhejiang Province, China. Inter- and intraannual variability in the water discharge and sediment load of the Feiyun River into the sea are analyzed using the observed data of runoff (1956–2008) and sediment (1957–2008) at Xuekou Station, which is in the main channel. The results show that there is a good peak–valley correlation between the water discharge and sediment load, and there are obvious seasonal variations, with a 65.7% water discharge and 89.2% sediment load during the flooding periods. Water discharge is mainly controlled by natural rainfall, but the construction of the upstream reservoirs in 1997 increased the discharge amount in the dry season and decreased the amount in the flooding season. Sediment loads were reduced after a huge flood in 1990 and construction of upstream reservoirs, while the latter also decreased the sediment load during the typhoon flooding period. Furthermore, the correlation between water discharge and sediment load is also affected by the flood and reservoir construction. There are some differences in the regression equations of sediment load and water discharge for 1957–1989, 1991–1996, and 1997–2008.     

Implications of climate change in the twenty‐first century for simulated magnitude and frequency of bed‐material transport in tributaries of the Saint‐Lawrence River

More frequent extreme flood events are likely to occur in many areas in the twenty‐first century due to climate change. The impacts of these changes on sediment transport are examined at the event scale using a 1D morphodynamic model (SEDROUT4‐M) for three tributaries of the Saint‐Lawrence River (Québec, Canada) using daily discharge series generated with a hydrological model (HSAMI) from three global climate models (GCMs). For all tributaries, larger flood events occur in all future scenarios, leading to increases in bed‐material transport rates, number of transport events and number of days in the year where sediment transport occurs. The effective and half‐load discharges increase under all GCM simulations. Differences in flood timing within the tributaries, with a shift of peak annual discharge from the spring towards the winter, compared to the hydrograph of the Saint‐Lawrence River, generate higher sediment transport rates because of increased water surface slope and stream power. Previous research had shown that channel erosion is expected under all GCMs' discharge scenarios. This study shows that, despite lower bed elevations, flood risk is likely to increase as a result of higher flood magnitude, even with falling base level in the Saint‐Lawrence River. Copyright © 2010 John Wiley & Sons, Ltd.     

INFLUENCE OF THE UPSTREAM RESERVOIRS ON THE ADJUSTMENT OF DOWNSTREAM ALLUVIAL CHANNEL

I. INTRODUCTIONThe Yellow River is a heavily sediment--laden river. The sediment load of the Yellow River ranks the first in the world while its annual runoff is only of medium size. Toharness the river, it is necessary to build reservoirs for regulating runoff to meet the demands of economic development. Since the founding of PRC in 1949, I S4 large and medium--sized reservoirs have been constructed on the main stem and the tributaries with atotal storage capacity of 84.5 billion m3.…     

Peak discharge increase in hyperconcentrated floods

The peak of river floods usually decreases in the downstream direction unless it is compensated by freshwater inflow from tributaries. In the Yellow River (China) the opposite is regularly observed, where the peak discharge of river floods increases in the downstream direction (at a rate far exceeding the contribution from tributaries). This flood peak discharge increase is probably related to rapid morphological changes, to a modified bed friction, or to a combination of both. Yet the relative role of these processes is still poorly understood. This paper aims to analyze the relative contribution of bed erosion and friction change to the peak discharge increase, based on available data and a recently developed numerical model. Using this high-resolution, fully coupled morphodynamic model of non-capacity sediment transport, two hyperconcentrated floods characterized by downstream peak discharge increase are numerically reproduced and analyzed in detail. The results reveal that although erosion effects may contribute to the downstream discharge increase (especially in case of extreme erosion), for most cases the increase must be mainly due to a reduction in bed friction during peak discharge conditions. Additionally, based on the concept of channel storage reduction, the effects of decreasing bed friction and (very strong) bed erosion can be integrated in explaining the peak discharge increase.     

Recent variation in reach‐scale bankfull discharge in the Lower Yellow River

Bankfull discharge is a key parameter in the context of river engineering and geomorphology, as an indicator of flood discharge capacity in alluvial rivers, and varying in response to the incoming flow and sediment regimes. Bankfull channel dimensions have significantly adjusted along the Lower Yellow River (LYR) due to recent channel degradation, caused by the operation of the Xiaolangdi Reservoir, which has led to longitudinal variability in cross‐sectional bankfull discharges. Therefore, it is more representative to describe the flood discharge capacity of the LYR, using the concept of reach‐averaged bankfull discharge. Previous simple mean methods to estimate reach‐scale bankfull discharge cannot meet the condition of flow continuity or account for the effect of different spacing between two sections. In this study, a general method to calculate cross‐sectional bankfull discharge using the simulated stage‐discharge relation is outlined briefly, and an integrated method is then proposed for estimating reach‐scale bankfull discharge. The proposed method integrates a geometric mean based on the log‐transformation with a weighted average based on the spacing between two consecutive sections, which avoids the shortcomings of previous methods. The post‐flood reach‐scale bankfull discharges in three different channel‐pattern reaches of the LYR were estimated annually during the period from 1999 to 2010 using the proposed method, based on surveyed post‐flood profiles at 91 sedimentation sections and the measured hydrological data at seven hydrometric sections. The calculated results indicate that: (i) the estimated reach‐scale bankfull discharges can effectively represent the flood discharge capacity of different reaches, with their ranges of variation being less than those of typical cross‐sectional bankfull discharges; and (ii) the magnitude of the reach‐scale bankfull discharge in each reach can respond well to the accumulative effect of incoming flow and sediment conditions. Finally, empirical relationships for different reaches in the LYR were developed between the reach‐scale bankfull discharge and the previous four‐year average discharge and incoming sediment coefficient during flood seasons, with relatively high correlation coefficients between them being obtained, and the reach‐scale bankfull discharges in different reaches predicted by the delayed response model were also presented for a comparison. These relations for the prediction of reach‐scale bankfull discharges were validated using the cross‐sectional profiles and hydrological data measured in 2011. Copyright © 2013 John Wiley & Sons, Ltd.     

Variations of Amur water chemistry during the historical 2013 flood

Water chemistry in the Amur R. at Khabarovsk was studied during the historical 2013 flood. The concentrations of dissolved substances were shown to vary significantly over both time and space, because of the difference between the discharge and chemistry in the main flood-forming tributaries. The ion runoff, nutrient runoff, and microelement runoff were estimated for the flood peak and all over flood period.     

2-D NUMERICAL MODEL FOR FLOOD FORECAST IN RIVERS WITH HEAVILY SEDIMENT LADEN FLOW

I.INTRODUCTIONTwo-dimensionalnumericalmodelisaPOwerfoltoolforengineersandriVermanagerstopredictfloodhydxaulics,identifyareasofinundation,anddesignoptionsforfloodcontrollingstructures.SomespecialproblemswithheavilysedimentladenflowriVershouldbecarefullyconsideredforthenumericalmodeldesigning;1.theplaneformofariVerisusuallybraidedanditsmainchannelshiftsoften.Themainchannelandbarreplaceeachotherseveraltimesinonefloodevent.Atagivenlocationthewaterdepthmaychangefromover10meterstoseveralcenhm…     

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.     

CHARACTERISTICS OF SEDIMENT TRANSPORT AND CHANNEL FORMATION BY FLOODS AT HYPERCONCENTRATIONS OF SEDIMENT IN THE YELLOW RIVER

1. INTRODUCTIONThe Yellow River is a heavily sediment--laden river. Floods at Hyperconcentrationso f sediment (hereinafter simply referred to as hyperconcentrated flood) frequently occurring in the main river and its tributaries possess different characteristics of sedimenttransport. Sometimes they cause severe deposition whereas at other times they are capable of carrying substantial amount of sediment over long distances. The study on the lawof sediment transport is of significance to …     

Decadal trends and causes of sedimentation in the Inner Mongolia reach of the upper Yellow River,China

Using hydrological and sediment data, this study investigated decadal trends in sediment erosion/deposition in the Inner Mongolia reach of the upper Yellow River. The calculated yearly sediment erosion/deposition show that the reach was dominated by aggradation, degradation, and aggradation successively in three periods with the years around 1961 and 1987 as break‐points. By constructing relations between water discharge and sediment load, the contributions of key factors to the changes in sediment erosion/deposition in the reach were quantified. Results show that the sediment retention behind the main stem dams, the increase of natural runoff, and the decrease of sediment inputs from tributaries and upstream watershed were the main factors causing the transition from aggradation during 1955–1961 to degradation during 1962–1987. The reduction of natural runoff, the decrease of sediment retention behind dams, and the rise of sediment supply from tributaries were the key causes of the reversal from degradation in 1962–1987 to aggradation in 1988–2003. Water diversion has played an important role in the long‐term aggradation of the Inner Mongolia reach. The main stem dams had functioned to alleviate siltation after 1961, but their effects on siltation reduction had been gradually diminishing since the 1990s. Copyright © 2015 John Wiley & Sons, Ltd.     

基于SWAT模型的淮河上游流域设计洪水修订

变化环境下洪水序列的一致性遭到破坏,引发基于统计原理计算的设计洪水可靠性下降,亟需开展非一致性条件下的设计洪水修订研究.以淮河上游流域为研究区域,运用Pettitt检验法和滑动t检验法综合检测年最大洪峰流量序列突变点,在此基础上,采用SWAT分布式水文模型对变异前的洪峰与洪量序列进行还现,利用径流深的模拟结果修订设计洪...     

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 were selected;these floods had a complete evolution of the flood process from the Xiaolangdi to the Lijin hydrological stations.For five hydrological stations(Xiaolangdi,Huayuankou,Gaocun,Aishan,and Lijin),a correlation was first established for floods of different magnitudes between the average sediment transport rate at a given station and the average sediment concentration at the closest upstream station.The results showed that the sediment transport rate at the downstream station was strongly correlated with the inflow(upstream station) sediment concentration during a flood event.A relation then was established between sedimentation in the LYR and the average sediment concentration at the Xiaolangdi station during a flood event.From this relation,the critical sediment concentrations were obtained for absolute erosion,sedimentation equilibrium,and absolute deposition during floods of different magnitudes in the LYR.The results of the current study contri b ute to a better understanding of the mechanisms of sediment transport and the regularity of sedimentation in the LYR during floods,and provide technical support to guide the joint operation of reservoirs and the regulation of the LYR.