PROGNOSIS OF AGGRADATION IN THE LOWER YELLOW RIVER BY HISTORIC ANALYSIS OF THE MORPHOLOGY OF ITS ABANDONED ANCIENT CHANNEL

1. INTROOUCnONFor a long time, the Lower Yellow River has been aggtading. As a result, the river bed becomesmuch higher than the adjacent land beyond the levees and poses a threat to the safety of the GreatNorthern Plain of China. Since the founding of the New China, great success has been achieved insafeguarding the levee for forty years. The trend of aggravation in lower reaches however is still Soingon and is at a rate even higher than before. That makes the flood control on the LO…     

黄河下游南四湖地区黄河河道变迁的湖泊沉积响应

黄河下游地区湖泊演化多与黄河河道变迁密切相关,进行高分辨率的湖泊沉积环境的研究,可揭示历史时期黄河下游的河道变迁,本文以南四湖ＤＳ孔为例,探讨河道变迁的湖泊沉响应。     

TWO－DIMENSIONAL MATHEMATICAL MODEL FOR STUDYING EROSION AND SEDIMENTATION OF A WANDERING STRETCH IN THE LOWER YELLOW RIVER

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IMPACTS OF FLOOD EVENTS IN COARSE SEDIMENT-PRODUCING AREAS ON CHANNEL SILTATION AND FLUVIAL PROCESS OF THE LOWER YELLOW RIVER

The method of multiple regression is used to analyze the influences of flood events from the coarse sediment producing areas on the channel siltation and fluvial process of the lower Yellow River based on the flood events from 1950 to 1985. The results showed that the flood events from the coarse sediment producing areas carry larger amounts of sediment load and coarser particle sizes than from other source areas, which increases deposition in the lower river channel. And there exist good correlations between channel siltation of the lower reaches of the Yellow River and the coming water and sediment of flood events from the coarse sediment producing areas. Through these correlations, the amounts of sediment deposition in the lower river channel could be roughly estimated based on the runoff and sediment load of flood events from the coarse sediment producing areas. The sediment deposition caused the fluvial process. There exists a complex response of channel form change to the coming water and sediment load of flood events from the coarse sediment producing areas. When the sediment concentration is smaller than 200kg/m3, the ratio between wide-depth ratio after flood and wide-depth ratio before flood((B/h)a / (B/h)b) will increase with the increase of the maximum sediment concentration; when the sediment concentration is near 200kg/m3, (B/h)a / (B/h)b reaches the maximum value; and when the sediment concentration reaches the limits of hyperconcentrated flow, (B/h)a / (B/h)b will decrease with the increase of the maximum sediment concentration. Generally, flood events from the coarse sediment producing areas made channel form of the lower Yellow River deeper and narrower, but a large amount of sediment deposition simultaneously occurs. So, the impacts of flood events from the coarse sediment producing areas on the channel of the lower Yellow River are lessened.     

ON THE SHRINKAGE OF RIVER CHANNEL

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The 1800-year variation of the lower Yellow River bank breachings in relation to the drainage basin vegetation reconstructed using cave stalagmite records

Rivers are closely related to climate, and the hydrogeomorphic features and stability of river channels respond sensitively to climatic change. However, the history of instrumental observations of climatic, hydrological and channel changes is short, notably limiting our ability to understand the complex river responses to long-term climate change and human activity. In this study, we show that cave stalagmite records reflected the variations in precipitation and temperature in the Yellow River basin, and the net primary productivity (NPP) of vegetation over the past 1800 years can therefore be reconstructed. We found that the reconstructed annual mean precipitation (P_m) and NPP closely related to the 1800-year variation of the lower Yellow River (LYR) channel instability indexed by the frequency of the LYR levee breaching events (LBEs) (F_b) derived from historical documents. The temporal variations in P_m, NPP and F_b exhibited an anti-phase relationship (negative correlation) and in-phase relationship (positive correlation), referred to as Type I and Type II relationships, respectively. The two types alternately appeared, dividing the studied period into several sub-periods. Type I occurred when the vegetation remained in a quasi-natural condition, and Type II occurred when the vegetation had been altered by humans to some degree. These features reflect complex river behaviours in response to climate change and human activity and may be explained by the interaction between climate, vegetation and human activity on the millennial timescale. © 2018 John Wiley & Sons, Ltd.     

GEOMORPHIC THRESHOLDS FOR CHANNEL EVOLUTION IN THE LOWER YELLOW RIVER

Channel evolution refers to boundary changes of rivers affected by fluvial actions. This paper provides an analysis of the development and formation of stream patterns in the lower Yellow River and presents intensive studies of several critical problems relating to channel evolution, including thresholds of channel gradient and longitudinal profile adjustment, channel surface morphology, response of channel pattern to boundary conditions, critical discrimination of cross sections and the discrimination of channel pattern changes using hydrologic parameters.     

Quantifying sediment storage on the floodplains outside levees along the lower Yellow River during the years 1580–1849

The lower Yellow River channel was maintained by artificial levees between 1580 and 1849. During this period, 280 levee breaches occurred. To estimate sediment storage on the floodplains outside the levees, a regression model with a decadal time step was developed to calculate the outflow ratio for the years when levee breaching occurred. Uncertainty analysis was used to identify the likely outflow ratio. Key variables of the model include annual water discharge, a proxy for levee conditions, and potential bankfull discharge of the channel before flood season. Uncertainty analysis reveals an outflow ratio of 0.35–0.56. We estimate that during this period, 18.8–30.1% of the total ~312 Gt of sediment load was deposited on the floodplains outside the levees. Human-accelerated erosion in the Loess Plateau caused a 4-fold increase in sediment delivery to the lower Yellow River, which could not be accommodated by channel morphodynamic changes. As a result, 21.2–27.5% of the total sediment load was deposited within the levees, creating a super-elevated channel bed that facilitated an uncommonly high breach outflow ratio. Hence, the factor of a large super-elevation relative to the mean main channel depth should be considered when designing diversions to restore floodplains. © 2018 John Wiley & Sons, Ltd.     

Wide river or narrow river: Future river training strategy for Lower Yellow River under global change

The choice of a river training strategy is extremely important for the Lower Yellow River (LYR). Currently, the wide-river training strategy applies in the training of the LYR. However, remarkable changes in the hydrological processes in the Yellow River basin, as well as immediate pressure from socio-economic development in the Yellow River basin, make it necessary to consider if there is a possibility to change the river training strategy from wide-river training to narrow-river training. This research investigates the impacts of different river training strategies on the LYR through numerical simulations. A one-dimensional (1-D) model was used to simulate the fluvial processes for the future 50 years and a three-dimensional (3-D) model was applied to study typical floods. The study focused on river morphology, the results show that if the present decreasing trend in both water discharge and sediment load persists, the deposition rate in the LYR will further decrease no matter what strategy is applied. Especially, narrow-river training can achieve the aim to increase the sediment transport capacity in the LYR compared with wide-river training. However, if the incoming water and sediment load recovers to the mean level of the last century, main channel shrinkage due to sedimentation inevitably occurs for both wide-river and narrow-river training. Most importantly, this study shows that narrow-river training reduces the deposition amount over the whole LYR, but it provides little help in alleviating the development of the “suspended river”. Instead, narrow-river training can cause aggradation in the transitional reach where the river pattern changes from highly wandering to meandering, further worsening the “hump deposition” there. Because of uncertainty regarding future changes in hydrological processes in the Yellow River basin, and the lack of feasible engineering measures to mitigate “suspended river” and “hump deposition” problems in the LYR, caution should be exercised with respect to changes in the river training strategy for the LYR.     

FLUVIAL PROCESSES IN THE LOWER JINGJIANG RIVER：IMPACT OF THE THREE GORGES RESERVOIR IMPOUNDMENT

Sediment supply to the lower Jingjiang River will be subject to substantial reduction after the impoundment of the Three Gorges Reservoir, which could result in an excess of carrying capacity and serious bank erosions in the downstream alluvial channel, threatening the bank protection works and the safety of the Jingjiang Dyke. This paper presents a summary of research works concerning the fluvial processes in the lower Jingjiang River and the possible impact of the Three Gorges Reservoir impoundment on the variation of its channel pattern. Three different predictions have been put forward by researchers: 1) the Jingjiang River will evolve towards a more sinuous, meandering channel pattern, with extensive bank erosion taking place along the river; 2) the river channel will be straightened and broadened because no point bar can be formed due to reduced sediment supply while bank erosion develops in the concave bank, and 3) this river reach will maintain its present channel pattern without significant change, although the sinuosity may be slightly reduced, since: a) the Three Gorges Reservoir mainly intercept sediment particles with sizes larger than 0.025mm, and b) the complex interaction between the Yangtze River and the Dongting Lake helps to reduce the negative effect of channel erosion through certain self-adjusting mechanism in fluvial processes. Discrepancy between these predictions shows that further research efforts are needed to understand the impact of Three Gorges Reservoir operation on the downstream fluvial processes. Meanwhile, there is an urgent need to closely monitor future development in the fluvial processes of the Jingjiang River and its influence on the safety of the Jingjiang Dykes.     

Impact of water diversion on the morphological development of the Lower Yellow River

In this paper we carry out a theoretical analysis based on the general one-dimensional morphodynamic model for rivers in order to show how the morphological equilibrium of a fiver is influenced by water and sediment diversion/supply along the river. The results of the analysis show that large scale water diversions, like those along the Lower Yellow River, can cause the development of a convex riverbed profile in the long-term. Deposition will take place along the whole reach of the river, with an increasing deposition depth from downstream to upstream. The slope of the river bed increases from upstream to downstream. Furthermore, an analysis on the morphological time scale shows that this development in the Lower Yellow River will take a time period on the order of decades to centuries. The results of the analysis have been compared with observations in the Lower Yellow River. Since the second half of the 1980＇s large scale water diversions from the Yellow River have been taking place. The observations show that this has indeed led to significant sedimentation along the river.     

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

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

CHARACTERISTICS AND REGULATION OF WANDERING RIVERS

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Erosion, sediment transportation and accumulation in rivers

The present paper analyses the interrelation between erosion, sediment transportation and accumulation proposed by N. I. Makkaveyev （1908-1983） and its further development in modem studies of river channel processes in Russia. Spatio-temporal linkages between erosion and accumulation are defined considering channel processes at different scales - river longitudinal profile, channel morphological patterns, alluvial bedforms （bars, dunes） and individual sediment particles. Relations between river geomorphic activity, flow transportation capacity and sediment budgets are established （sediment input and output; channel bed erosion and sediment entrainment into flow - termination of sediment transport and its deposition）. Channel planforms, floodplain segments separated by the latter and alluvial channel bedforms are shown to be geomorphic expressions of sediment transport process at different spatial and temporal scales. This paper is dedicated to the 100th anniversary of N. I. Makkaveyev, Professor of the Moscow State University, author of the book ＂River channel and erosion in its basin＂ （1955）. That book is regarded in Russia as the pioneering work which initiated the complex hydrological and geographical studies of channel processes and laid a basis for the theory of unified fluvial erosion-accumulation process.     

近1200 a来黄河下游梁山泊沉积记录的环境变迁

利用梁山泊670 cm柱状岩芯沉积物,基于精确的AMS-~(14)C年代测定,通过高分辨率的粒度、磁化率、总有机碳、C/N比值等环境代用指标的综合分析,并结合历史文献记载,初步揭示了1200 a来黄河下游地区平原湖泊沉积特征及环境演化历史.结果表明,梁山泊环境演化大致分为5个阶段:790-940 AD期间,为低湖面的沼泽沉积环境,气候冷干;940-1215 AD期间,屡次受到黄河决溢洪水影响,湖盆扩张,湖泊水位上升,为梁山泊极盛期,气候暖湿;1215-1310 AD期间,黄河夺淮入黄海,湖区淤积严重,湖泊萎缩减小;1310-1470 AD期间,再次受到黄河决溢洪水影响,水位上升,面积扩张,但逊于极盛期;1470 AD至现代,黄河河道进一步南移,远离梁山泊,湖盆淤积抬高,梁山泊最终消失,直到1855AD,黄河第6次大改道北移,湖泊再次受到黄河洪水影响,由于前期受到泥沙淤积抬高,该地区仅作为黄河泥沙承载区.在气候变化大背景下,黄河改道决溢是梁山泊演化的主因.     

RIVER MORPHOLOGY AND CHANNEL STABILIZATION OF THE BRAHMAPUTRA RIVER IN BANGLADESH

１ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅＢｒａｈｍａｐｕｔｒａＲｉｖｅｒｏｒｉｇｉｎａｔｅｓｆｒｏｍｔｈｅＪｉｍａｙａｎｚｈｏｎｇｇｌａｃｉｅｒａｔｔｈｅｎｏｒｔｈｆｏｏｔｏｆｔｈｅＨｉｍａｌａｙａＭｏｕｎｔａｉｎｓｉｎＳｏｕｔｈＴｉｂｅｔ,Ｃｈｉｎａ．Ｉ...     

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.     

Variation in reach‐scale thalweg‐migration intensity in a braided reach of the lower Yellow River in 1986–2015

Thalweg migration of an alluvial river plays a key role in channel evolution, which may influence the effect of existing river training works and biodiversity on floodplains, and cause losses in riparian land and property. The braided reach of the Lower Yellow River underwent continuous channel aggradation during the period from 1986 to 1999, and then remarkable channel degradation in 1999–2015 owing to the state of operation of the Xiaolangdi Reservoir in 1999. Here we quantify associated thalweg migration changes and identify the key influencing factor in the braided reach. Thalweg‐migration distances and intensities at section‐ and reach‐scales were calculated during the past 30 years from 1986 to 2015, in order to investigate the characteristics of thalweg migration in the reach. There was a 47% reduction in the reach‐scale thalweg‐migration distance and a 35% reduction in the corresponding migration intensity after the reservoir operation. It is also revealed that fluvial erosion intensity is a dominant factor in controlling the thalweg migration, based on the investigation into various influencing factors in the study reach. The thalweg‐migration intensity of the braided reach can be expressed as a power function of the previous four‐year average fluvial erosion intensity. The calculated thalweg‐migration intensities in 1986–2015 using the proposed relation generally agree with the observed data. Copyright © 2017 John Wiley & Sons, Ltd.     

Two-thousand years of debates and practices of Yellow River training strategies

Throughout the history of China, the Yellow River has been associated with flood disasters and changes in the course of its lower reaches because of sedimentation. From 602 B.C. to 1949 the river experienced 1593 levee bursts, flooding vast areas, and claiming millions of human lives. The river shifted its main course by avulsion 26 times with the apex around Zhengzhou, resulting in devastating calamities and numerous old channels. Training of the Yellow River has a history of more than 3000 yr. Levee construction has been the major strategy for flood control. Two extremely different strategies has been proposed and practiced in the past 2000 yr, i.e. the "wide river and depositing sediment" strategy and the "narrow river and scouring sediment" strategy. This paper analyzes the levee breaches and flood disasters in the past 2000 yr and compares the results of the two extremely different strategies. The "narrow river and scouring sediment" strategy has only short term effects on levee breach control and flood mitigation. The "wide river and depositing sediment" strategy can essentially mitigate flood disasters and reduce levee breaches for a long term period of time. The "wide river and depositing sediment" strategy has been used and no levee breach has occurred in the past 67 yr, which has been the only periods of more than 50 yr with no levee breaches in the history of the Yellow River since 700 A.D.Modern flood and sedimentation management methods have also been introduced, and the strategy of applying the ' "widen the river and enhance the levees" approach for the upper and lower reaches management is proposed.     

SEDIMENT LOAD AND ITS INFLUENCE ON CHANNEL PROCESSES OF SOME LARGE RIVERS IN RUSSIA AND CHINA~1

I INTRODUCTIONThe volume and regime of sediment load are the most important factors, which are responsible for theformation, direction and deformation rate of the river channels. Despite the long history of study anddevelopment of sediment load calculation methodology, there are still numerous problems that remain tobe solved such as river pattern and sediment movement and so on (Wang et al, 1997).In this respect, the comparative analysis of sediment load and river channel processes of la…