Yellow River's Research and Management Strategy

Forward of My Book "Sediment Transport Potentials of the Lower Yellow River Channel and Development of the High Efficient Flood Discharge and Sediment Transport Channel". 

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The Yellow River is the cradle of Chinese nationalities, and it is famous for its abundant sediment in the world. Due to the severe soil losses from the middle reach, a great amount of sediment is washed away by flood, and deposits in the channel of the lower reach. This process has resulted in a “suspended river” and frequent levee breaches, which brought grave disasters to people living in this region.

As early as in 1955, a comprehensive plan on Controlling the Flood and Developing the Water Resources of the Yellow River was passed in the 2^nd Session of the First National People’s Congress. After half century’s research and engineering development, great achievements attracting worldwide attentions have been made. However, sediment problems of Yellow River have not been completely resolved. In the lower Yellow River, issues such as aggraded river bed due to siltation, secondary suspended river, transversal/diagonal river and floodplain inundation are still great threats. Flood protection remains a concern with potentially severe consequences. Seeking a strategy that can radically eliminate flood hazards becomes a high priority task.

Siltation is the main reason for flood hazard in the lower Yellow River. In the early days of the foundation of P.R. China, based on the planning principles of “store water and trap sediment by reaches”, a comprehensive plan on the Yellow River was proposed. This goal was trying to keep all the sediment in the upper and middle reaches, which could thus alleviate the sediment deposition and flood threats in the lower reach. As the preliminary results in reality showed, the effect of Water and Soil Conservation Project of Losses Plateau and management of sediment-laden tributaries to reduce sediment was not so obvious. Sanmenxia Reservoir was forced to be reconstructed twice, and its function was altered from “store water and trap sediment” to “detent flood and release sediment”. In the book published in 1987 entitled “My River Management Practices”, the famous river training expert Mr. Huayun Wang pointed out during his conclusions of the experiences gained on managing the Yellow River, “In the past, it was always thought that managing the Yellow River should focus on issues related with the upper and middle reaches. Once those issues are resolved, so are the issues related with lower reach. From the failures and frustrations, I have learned that to manage the Yellow River, we should not solely focus on upper and middle reaches, but rather on all reaches as a long and painstaking task, also on the lower reach (page 200).” In the preface of this book, he also pointed out “The thinking of water and sediment regulation is still in the developing stage, and the experiences gained are not completed yet. But in my opinion, this approach is more scientific, and meets the realistic situation better. In the future development, great breakthroughs can be achieved from this aspect.

There are more than 10 major water conservancy projects on the main stem of the Yellow River. The total flood control capacities of Longyangxia Reservoir, Liujiaxia Reservoir, Sanmenxia Reservoir and Xiaolangdi Reservoir reach 15.62 billion m³. On the major tributaries, there are also many big reservoirs, such as Luhun Reservoir on Yihe River,  and Guxian Reservoir on Luhe River, with flood control capacity of 0.677 billion m³ and 0.698 billion m³, respectively. Once in 1,000 year flood at Huayuankou Hydrologic Station has reduced the peak discharges from 42,300 m³/s to 22,500 m³/s. Once in 100 year flood has reduced from 29,200 m³/s to 15,700 m³/s. If the 1958 flood of 22,300 m³/s happened today, the peak discharge would be reduced to 9,620 m³/s. After the 1982 flood of 15,300 m³/s, for almost 30 years, peak discharges at Huayuankou have never exceeded 8,100 m³/s, which means the flood is under fully control. The key issue of managing the floodplains of the lower Yellow River is how to achieve the non-aggregation of the river bed.

Due to the combined operations of Longyangxia Reservoir and Liujiaxia Reservoir, and the increased industrial and agricultural water demand, the amount of water flowing into the lower Yellow River has been reduced significantly. The peak discharges have also been reduced, which weakens the bed-shaping function of a flood, and the conflicts between less water and more sediment are more and more severe. The planned function of Sanmenxia Reservoir, “store clear water and release muddy water” now faces more and more challenges, and the limitation is more and more obvious.  There are new situations and tasks emerging for the flood protection of the lower Yellow River.

In the past, people always concluded the main reason for the severe depositions on the lower Yellow River as “less water and more sediment” in general. Compared with other major rivers in the world, the average annual sediment of 1.6 billion ton with the discharge of only 50 billion m³ should really be called “less water and more sediment”. However, does a heavily sediment-laden river always lead to a “bad” river? The answer is “no”. As an example of the major tributaries like Weihe River and Beiluohe River in the middle Yellow River reach, sediment-laden rivers do not necessarily lead to a severely deposited meandering river.

As the research on hyperconcentrated flow initialized by Prof Ning Qian demonstrates, the reason for the huge sediment carrying capacities by hyperconcentrated flow is due to the existence of fine particles which change the characteristics of the fluid. With the dramatic increase of the flow viscosity, and the decrease of fall velocity for coarse particles, even the coarse particles are easier to be transported in the hyperconcentrated flow. The resistance force of the river bed to flow does not increase accordingly, which can still be calculated by Manning’s equation. Under the conditions of same slope and water depth as the clear water flow, the velocity of hyperconcentrated flow will not be decreased. Therefore, sediment transport by using the characteristics of hyperconcentrated flow in Yellow River is really an economic and ideal technical measure.

Mme Zhengying Qian, member of the Chinese Academy of Engineering, has paid great expectations on the research of the hyperconcentrated flow and its application on the Yellow River. She has emphasized the importance of related research many times during her speeches, and wished its applications on managing the Yellow River.

As early as in 1988, she pointed out, “Concerning the river training issues, I feel that there is a great breakthrough in understanding the lower Yellow River channel.   Besides the levees can be strengthened by siltation inside and outside of the banks, researchers from the Yellow River Institute of Hydraulic Research proposed sediment transport by using hyperconcentrated flow and management of medium and small discharges to reduce siltation, which deserves in-depth studies and analysis. If there is a breakthrough in research, the amount of water needed for sediment transport, and the sediment carrying capacity of the channel will likely to change dramatically. The amount of water needed for sediment transport, from some reference I have read, ranges from 10 m³/ton to 30 m³/ton. That means, for transporting every 100 million tons of sediment to sea, some people think 3 billion m³ of water is needed, while some other people think only 1 billion m³ is needed. Now the planned water quantity for sediment transport is 20-24 billion m³, and 8-10 billion m³ during non-flood season. We should really pay attention to different opinions about water needed for sediment transport, and the sediment carrying capacity of the channel. I hope in the future plan, there are evaluative comments about those opinions, and the future work direction should be proposed.”

On April 15, 1992, during the working conference with the Yellow River Conservancy Commission, she pointed out “Yellow River is the most challenging river to manage in China, possibly even in the world. During the past years, we achieved great accomplishments with the efforts from generations of researchers and engineers. For future plans, we need to keep up the good spirits, and try to combine the diligent work on current issues with early explorations based on reality and innovative thinking. That is from my personal experience. Since every year there is a realistic flood protection task, we need to accomplish this task first with great performance. However, only finishing the flood protection task, but no future explorations based on reality and innovative thinking, is not enough. That is to say, both tasks are important to us, and we need to combine them closely to manage the Yellow River.

In 1993, when she wrote the preface for my book entitled “The Dynamic Principles of Hyperconcentrated Flow in the Yellow River and Its Applications”, she said “The Yellow River is the most sediment-laden river in the world, and it is the most difficult river to manage. With the construction of big reservoirs like Longyangxia Reservoir and Liujiaxia Reservoir in the upper river, the amount of water flowing into the main stem has been reduced significantly. The conflicts between less water and more sediment become more and more prominent. The Yellow River flows through the most arid region like Northwest China and North China, which needs urgent compensation by more water sources. How to make full use of the limited water resources of the river, and try to furthest satisfy water demands, becomes the most important issue in developing and managing the Yellow River.

This book emphasizes on illustrating the fundamental research on the rheological properties, dynamics and sediment transport characteristics of the hyperconcentrated flow. Based on the field surveyed data, the principle of sediment transport theory was studied, and the conclusion was the narrow and deep channel has significant sediment transport capacity. Make full use of the channel to transport sediment to sea, reduce the deposition on the river bed, save water needed for sediment transport, can be very worthy research topics to be explored.

Initialized by Prof. Ning Qian in the 1950’s, it has been several decades for the basic research on hyperconcentrated flow in the Yellow River. The research topics gradually evolve from pure theories to engineering practices. Active researches are now focusing on how to regulate the water and sediment more scientifically with the current and future projects on the Yellow River. I hope both the old and young colleagues in the water resources engineering field can cooperate to achieve greater accomplishments in developing the theories and practices of hyperconcentrated flow.”

The Yellow River is the most sediment-laden river in the world, and it is perhaps the most difficult river to be managed. However, it is also a promising river to be harnessed. After several generations’ research and engineering practice in our country, there is a major breakthrough in the knowledge and understanding on sediment transport of the Yellow River, i.e. the high flood discharge and sediment transport capacity of the narrow and deep channels can be used to transport sediment to sea. Ministry of Water Resources proposed the overall management objectives for the Yellow River in 21^st century, “no embankment breaching, no river course running dry, no pollution over standard, and no river bed rising”. The most difficult objective is to achieve “no river bed rising”. For the new situations emerged since October 1999, after the Xiaolangdi Reservoir began operations for trapping sediment and creating a flood to scour downstream channel, the Yellow River Conservancy Commission also proposed detailed technical measures for managing the downstream channel, “stabilize the main channel, regulate the water and sediment, widen the river and strengthen the levees, and compensate the flood inundation”. Among the five major sediment managing measures, “trap, discharge, regulate, release and dredge”, “regulate” is the most important component. Only when the sediment is regulated to be transported during flood season, the transport characteristics of the narrow and deep channel called “more sediment coming in, and more sediment will be transported” can be fully used to transport more sediment to sea. Only when the sediment concentration in the flow is regulated to a certain high level, the water required for sediment transport can be reduced. As conclusion, constructing a straight narrow channel with certain sediment discharge capacities can form an efficient flood discharge and sediment transport corridor in lower Yellow River. By using the multi-year sediment regulation operation of Xiaolangdi Reservoir and sediment discharge capacity of the narrow and deep channel, the deposition on the main channel can be controlled, and the non-aggradations of the river bed in the lower Yellow River can be achieved.

Located just upstream of the lower reach of the Yellow River, Xiaolangdi Reservoir is the last big valley-type reservoir with large regulation capacity. After its operation, better conditions can be provided for improving the flood protection, silt reduction and water supply for residents living in the vicinity. Thus, how to make full use of its advantages to regulate water and sediment more wisely, transform the channel shape from shallow and wide to narrow and deep, make full use of the sediment carrying capacities of the channel, and save the water needed for sediment transport, have great strategic significances for managing the middle and lower reaches of the Yellow River. There are two major criteria to judge the pros and cons of the water and sediment regulation rules of a reservoir: 1) how much sediment can be regulated to be transported during flood season; 2) how much water can be utilized through the reservoir regulation.

Based on the understanding of the flood discharge and sediment transport principles of the narrow and deep channel of the Yellow River, this book proposes the future direction of managing the meandering reaches. Stabilizing the main channel and developing a narrow channel can secure the flood protection, and the sediment transport capacity of the channel can thus be increased. As a result, the sediment transport capacity during flood season can be fully used to transport more sediment to sea. From this perspective, developing a narrow and deep channel with certain flood discharge and sediment transport capacities should be the major objectives for managing the meandering reaches. The increased of flow capacity of the main channel will reduce the opportunity of overtopping flood on the floodplain, which will develop a harmony relationship between the people living in the floodplain with the nature. The 1.8 million people living in the floodplain can be totally free of worries, and 3.59 million mu of farmland can be fully used. From the people-oriented, scientific development point of view, the management method introduced in this book is the objective requirement for managing the lower Yellow River. Only when the channel is regulated to narrow, deep, straight, smooth and stable with high efficient flood and sediment discharge capacity, the objectives of the non-aggregation of the river bed can be achieved. The problems of water resources shortage, secondary suspended river and its floodplain, sediment of the bayou, etc. can thus be resolved properly. What will appear in front of us is a deep main channel with floodplain at high elevations. The strategic objectives of non channel bed rising can then be accomplished.

Since October, 1999, the Xiaolangdi Reservoir began operations for trapping sediment, creating flood to scour downstream channel, and regulating medium and small discharges to reduce the siltation in the channel downstream of Aishan.  The total amount of scoured sediment in the downstream channel has reached 1.3 billion m³. Channels upstream of Gaocun and downstream of Aishan have all been scoured. Between Huayuankou and Jiahetan, for the discharge around 2000 m³/s, the water depth reduced about 1.8 m. This value also reduced 1 m in the channel downstream of Aishan. Bankfull discharge at Gaocun station has reached 5,300 m³/s or more. With the effect from the production dikes, average flood will not overtop the levee. But the reach upstream of Jiahetan is still shallow and wide, with an average width of 2,000 m to 3,000 m, which needs two-bank regulation urgently.

After the sand fills the sediment-regulation volume of Xiaolangdi Reservoir, regulate the sediment on a multi-year basis, release the sediment at the right moment, transport most sediment during flood season, can all contribute to the non-rising of the river bed, or even scoured river bed. Since every time when hyperconcentrated flood occurs, the main channel is always scoured, and the sediment transport characteristics can be described as “scour during the rising of flood and deposition during the falling of the flood”. Release clear water from Xiaolangdi Reservoir at the initial stage, regulate sediment on a multi-year basis after the sediment fills the sediment-regulation volume, release the sediment at the right moment, can be successfully combined to achieve the non-aggradations of the river bed.

The traditional opinions believe the extended siltation at the bayou is the main reason for aggradations of the channel in the lower reach. The only solution is to reduce sediment source. The impact of the optimal incoming flow and sediment condition on scour and deposition in the channel of the bayou has greater effect than that of sediment deposition and extension in the bayou on the upstream channel. The sediment transport potential could be fully utilized to transport more sediment to sea during flood season, and bed-shaping function of flood and sediment transport capacity can also be increased. The impact on the upstream channel can be adjusted by varying the river width to reach the new equilibrium of sediment transport.

Sediment transport by flood will create density current at bayou, and the sediment will be deposited in a larger area. By using the wave dynamics from the ocean along the coastline, sediment can be transported to open sea. The flow path in bayou will not extend any more, and the negative impact on channels in the upper reach can be mitigated.

Proposed by Senior Engineer Mr. Zegang Li, a flood and sediment diversion project at bayou should be constructed. By making full use of the wave dynamics of the ocean and storage capacity of the sediment in the sea area, and the better incoming flow and sediment condition henceforth, impact of the extended siltation at the bayou on the channel of the lower reach can be minimized, and non-aggradations of the river bed will be achieved.

The publication of this book clarifies the critical issues of managing the channel of the lower reach, and it will continue to contribute to the process of eliminating the flood-hazard and developing the water resources. With the implementation of bayou management and regulations of the lower reach channel, multi-year sediment regulations and constructing the high efficient sediment transport corridor are proposed by the author of this book. The flood hazard will not occur again in the future as it was in history, and people will enjoy their peaceful life forever.

The main reason that the understandings of managing the Yellow River can not be reconciled at present can be concluded as the following. Traditional river managers do not want to recognize the flood discharge and sediment transport potentials of the lower Yellow River channel. Everyone saying “less water with more sediment” is the crucial issue of this river. But if we do admit the findings in this book, the major management issues of the Yellow River will change. The understandings of this river and the regulation strategies will also have significant improvements. The process of how I researched the Yellow River will be introduced in the postscript of this book.