The Healthy Yellow River: Essence, Indicators and Approach 黄河的健康：实质，

紫露草

The Healthy Yellow River: Essence, Indicators and  Approach
黄河的健康：实质，指标和方法

Liu Xiaoyan

Department of International Cooperation Science and Technology, Yellow River Conservancy Commission, Zhengzhou, China, 450003

The Yellow River has ever brought serious disasters of floods and drought in history. In recent 50 years, along with the changes of nature conditions and social development, the flood and drought problem have been alleviated, but the Yellow River is subject to a series of new challenges, i.e. shrinking river channel, suspended river and secondary suspended river, water scarcity, water pollution and degraded river ecosystem etc. All the above mentioned phenomena indicate that the health status of the Yellow River was a very significant problem.

How to restore and sustain the health life of the Yellow River so as to support regional social economic development? It becomes the focus of people’s concern at present. In this circumstance, the Yellow River Conservancy Commission (YRCC) puts forward a new concept of river management as “Keeping Healthy Life of the Yellow River”. And this paper aims at expounding the essence, criteria, indicators and methodologies to build a healthy Yellow River, which provides theoretic guidelines to  implement the new river management concept.

1 River’s Life and River’s Health
The river is the main channel of substance and energy exchange between land and ocean, and the river system is the main path of water circulation in land. River’s life is a process of hydrologic cycle which is carried out under certain direction and path, and represented by continuous flow in the river channels. Therefore, river’s life embodies at least three aspects, namely, existing river channel, complete drainage system and continuous surface runoff. Continuous water circulation is the key to keep the life of river, it enables incessant renewal of water resources in land, which results in the formation of riverbed and river system, and development of river ecosystem.

The river may have different health status, it depends on climate and ground condition which also affect each other and restrict each other. The change of climate and ground condition come from the natural movement of the universe and the earth on the one hand, and human activities on the other, actually the latter is playing a more important role along with the improvement of the human productivity. The significant change of hydro regime of the Yellow River in the past decades reflects the combined impacts by both global climate change and human activities. Unfortunately, the natural resources can not be used directly by human at many situations, and even river in its natural condition frequently brings disaster to human. Under the pressure of survival and development, human needs to change the ground surface, such as cleanup natural vegetation, build reservoirs and dykes etc. so as to get water, food, raw materials and social services. At the same time, the activities will change the life status of river, thereby, many rivers in the world appear unheard-of crises just like the Yellow River.

The crisis of river life brought stress and menace to the survival and development of human, urged people to reconsider and appraise the attitude and manner of their behavior towards river in the past century, and thereby put forward the concept of “River Health” in about 1990s. But up to now, there is no clear and recognized definition for river health. The River Health program of the South Africa chose invertebrate, fish, riverside vegetation belt and the shape of river as the appraise indexes of river health. In Europe, the river Rhine hope the salmon can be back to the upper reaches. Danube River takes biodiversity and the size of species as the indexes of river health.

River health is the description of river life status, which is under the precondition of the existence of river life, and it is a concept of social attribute. In remote antiquity of flood era, without intervention of human, every river will go through the evolution process of formation, development and decline which is just like the life process of a man. The rivers will experience flood and drought, which depends on the precipitation is more or less, and form natural landscape. But for the most rivers in the world today, rivers are not only natural rivers, but also social rivers. When the services offered by rivers cannot satisfy the requirements of human, for example, flood and drought severely affects the survival and development of human, the issue of unhealthy river in original meaning will come into being, and harnessing of river on purpose will come into practice. So, the river health conditions reflects human’s judgments on river‘s contributions to human society, or if the river could function well to meet the requirement of people.

Generally speaking, the river functions include two main types, i.e. social function and natural function. The social function of river reflects the support extent of river to social economy system. It’s the original intention and meaning of maintaining the healthy life of river. The natural function of river is the support extent to river ecosystem which will develop or wither along with the runoff more or less. It’s important indexes of river life vitality, and will finally affect the sustainable development of society and economy. Possessing both normal social function and natural function at the same time is obviously the basic index of river health. But, because of different social, economic and environmental background, the river function expected certainly exist clear characteristics of times. In the forepart of human history, flood is the main problem of river health. Along with the rapid development of society and economy, water shortage becomes important embodiment of river unhealthiness. After having enough food and clothes, people began to pay attention to living quality, then the river pollution and its ecosystem shrink becomes the focus of attention. The concept of river health came into being in the western developed countries when their main challenge is ecology protection. So, in a long period, river health is mainly considered from ecology point of view. The concept of river health and its appraisal indexes are mainly the reflection of health indexes of river ecosystem. But , along with the development and deepening of this concept, people pay more attention to the integrated requirements of society, economy and nature. For example, Australia puts forward the concept of “Health Working River” and “Living Murry”, its purpose is to provide a standard, which can be identified by society, for compromising between river ecosystem protection and water resources utilization. In a word, in different times and different area, the essence of river health reflects the contradiction between the economy development and the natural environment protection, reflects the values of people under the correspond background. The standard of river health is the balance or compromise of human’s benefit and other biology’s benefit in corresponding times and river reaches. Today, the era with greatly human activities, river health can only be a relative health. The standard of river health under different background is actually a choice of society and its judgment indexes should be dynamic and changeable.

A healthy river should at least have the following 5 abilities: (1) to keep natural hydrologic circulation and the basic drainage system; (2) adequate floods safety; (3) to ensure water resources supply for certain level of society and economy development; (4) to maintain a favorable river ecosystem; (5) to bear certain degree of pollution. Thus, the symbols of river health are the viewable images that can fulfill the above mentioned requirements, includes shape, water quantity and water quality etc., and follows the basic principles of socially acceptable, economically viable and environmentally sustainable.

2 The Essence of the Healthy Yellow River
Different from the western countries where the River Health concept came into being, the concept of Maintaining the Healthy Life of the Yellow River was born in the situation of flood thread still exists, suspended river and secondary suspended river exacerbate, the main channel severely shrink, riverbed frequently dries up, water quality tends to become worsen daily and ecology degenerates. Thereby, the essence and criteria of the Yellow River healthy must reflect the characteristics and current contradictions of the Yellow River. This paper discusses mainly the health standard of the Yellow River at present phase (before 2050).

2.1 Keep the River alive
Being alive is the precondition of the health. To maintain the existence of the life, the Yellow Rive at least has the following two basic conditions.

One is to maintain certain amount of runoff from the source to the estuary, and from the branches to the mainstream. This is the limit for keeping the healthy hydrologic cycle in the Yellow River basin. The continuous water circulation is the core of the existence of the Yellow River life. But, from 1970s, the quick development of economy and society increases water consumption greatly, and then the runoff of the river decrease greatly. That not only damaged the river’s cycle, but also results in frequently drying up.

Another one is to maintain an unblocked riverbed. It’s the basis for the river to realize its function of substance transportation. Whether the riverbed of the Yellow River is smooth or not depends on the extent of sedimentation and the activities on the floodplain. In recent years, immoderate water resources development and unreasonable flood control methods caused the flood frequency and flood peak reduced greatly, the runoff process flatten in big extent, the sediment concentration increased sharply, which decrease the momentum of sediment transporting and riverbed modeling. Together with the increase of population and human activities, the main channel has shrunk greatly.

2.2 Keep the River working
The discharge capacity should basically satisfy with the requirements of the human’s safe habitation. The Yellow River is called as China’s sorrow, and the flood control is always a great event for each government. According to the record, in the 2500 years start from the Qin dynasty, the Yellow River breached 1590 times altogether, changed its course 26 times and the flood basin area was 250,000 km2. Once dykes Breaching, the water and sediment came down together from the riverbed, and that cause other rivers silted and farmland desertification, thus, brought considerable tragedy to the people. At present, the flood basin area is about 130,000 km2 and 100 million people live there. Therefore, it is the first expectation of the people from the Yellow River that the Yellow River should possess enough discharge ability. The indicates of the so called enough discharge capacity should be embodied in the following two aspects: (1) The water level of flood, which is smaller than the defended flood, is lower than that of the defended flood at the same year, the flow velocity on the floodplain along the dykes is not rapid, and the main flow does not clash the dykes directly. (2) The enough sediment transportation capacity should be reflected in the big proportion of sediment discharge, the small sediment deposition in the main channel. The key of realizing the above requirements is to maintain an unblocked and safe channel for water and sediment transport.

Water quality should basically satisfy with the requirements of the human’s health. The importance of water quality to human is evident. The water quality of a healthy river should satisfy with the requirements of human production and life; satisfy the requirements of survival and breeding of aquatic and riverside organisms. At present, the water quality at the reaches above Lanzhou is good, but the water quality in most reaches below Lanzhou is Ⅳ, Ⅴ even worse than Ⅴ. The deterioration of water quality not only affects directly the healthy survival of human, but also aggravates water resources shortage.

Water quantity should basically satisfy the requirements of economy development. Water is the basic condition of human survival and development. Economy development often relies on the guaranteed extent of water quantity. But the water supply ability of one river is limited; especially the river like Yellow River, people can not expect it to satisfy their unlimited requirements. From 1986 to 2003, water consumption annually 29.6 billion m3. Considering the water taking from groundwater, branches, floodplain and the unmeasured water, the actual water consumption from the Yellow River has possibly reached 35 billion m3, but the annual average natural runoff at the same period is only 46 billion m3. The fact of the deteriorating of the Yellow River health shows that the demands of human has exceeded the limitation of water supply of the Yellow River at the same period. In the interest of regional sustainable development of economy and society, the demands of human for the runoff of the Yellow River in the future must be cut down and controlled strictly.

2.3 Keep the River living
When the river is basically satisfying the requirements of human, protecting river ecosystem and maintaining the ecological function of rivers have become common understanding of the river basin managers in the world. The purpose is to maintain the normal succession of biology community and the normal circulation of the food chain. But under the background of present economy and society, to restore the river ecosystem to the aboriginality status is impossible. Protecting the river ecosystem is not protecting all the species. From the point of view of society and biodiversity, the protection is to protect the biology sight with the most native value, such as special wetlands, lakes and species with the most special meaning, so as to maintain its long term productivity ability and ecology service function.

The Yellow River ecosystem is an inter-active system of the aquatic biology and their habitates. The required services from the river include water quality and water quantity. The possible target scale of ecosystem protection largely rest with the water quality status and runoff conditions that are possibly provided by the Yellow River. The requirements of species for water quality are consistent with that of human, but in middle and low water years, the requirements of river species for water quantity are often conflict sharply with the water usage requirements of human.

2.4 Criteria of a healthy Yellow River
The symbols of the healthy Yellow River is, under the precondition of the existence of the life, the expectation of people from the river’s main functions such as flood discharge function, purifying function, water supply function and ecological function etc. Sum up the analyses above, the health criteria of the Yellow River can be summarized as the following 5 points: (1) continuous flow; (2) free-and-safe riverbed; (3) favorable water quality; (4) sustainable river ecosystem; (5) suitable water supply capacity to satisfy sustainable social economic development. The first point is the important basis of the Yellow River life existence, it includes the continuous flow of the mainstream, and the hydrologic link between main branches and mainstream. The second point not only reflects the existence requirements of river life, but also embodies the hope of human for safe flood prevention, and it is the basic condition to ensure the economy and society move on the rails. The third point is the needs of both human and other species. The fourth and fifth points embodied respectively the natural functions and social functions of river, and they are related to the sustainable development of economy and society, but their relationship is competitive, which is reflected in the requirement and demand contradiction for the runoff.

3. Health Indicators of the Yellow River
3.1 Continuous flow
Continuous flow, suitable runoff and perfect river system are important symbols of the YR life, which is the base of YR healthy life. The continuous flowing and suitable runoff means that certain discharge must be maintained from river resource to the sea; in addition, the hydrological relations between main tributaries and the mainstream must be maintained, which means the main tributaries must be maintained with certain level of discharge entering into the YR.

In theory, only if discharge is greater than zero, it means YR and its tributaries realize the minimum runoff condition for life. But the functional drying up exists in practice if the flow is too low to support the river ecosystem well. So the minimum threshold runoff of the YR should meet not only the demands of water circling and river system, but also the demands of domestic water, minimum ecological flow, self-purification and sediment transportation. The water demand for self-purification is affected greatly by economic development and the capacity of sewage processing. The water demand for sediment transportation depends on the sediment load and the acceptable deposition in the main channel. The minimum water amount for sediment transportation is very difficult to be determined. So the domestic water and river ecosystem should be mainly taken account for the minimum threshold runoff of the YR.

It is predicted that the population in the YR basin will be up to 126 million in 2020 and 132 million in 2050 respectively, and the domestic water demands will be 4 billion m3 and 4.9 billion m3 respectively. Taking account of water supply for other river basins, the domestic water demands will reach 4.4 billion m3 and 5.0 billion m3 respectively in year 2020 and 2050. The water utilization will reach 2.2 billion m3 and 2.5 billion m3 respectively. The water utilization of 2.5 billion m3 is regarded as the benchmark to estimate the minimum threshold runoff of the YR and its tributaries in this paper.



The minimum ecological flow is the water amount corresponding with the ecosystem protecting objective. Since the research of the relationship between ecosystem protecting objective and the river flow will need a long period, Tannant method is adopted here. According to this method, 10% of the observed discharge of the base series at some cross section on the river can be regarded as the minimum ecological flow. The data series between 1956~1985 is adopted for calculating minimum ecological flow.

With the boundary condition of domestic water demand, minimum ecological water demand in key cross sections of Yellow River mainstream and tributaries, continuous flow in the whole river and complete river system, fully taking into account natural infiltration, evaporation and runoff supply in different reaches, the minimal flow of Yellow River mainstream in different time can be deduced out from river mouth to river source. For example, the monthly minimal flow is 50~260 m3/s in the estuary and 120~330 m3/s in Huayuankou station. During recent 6 years, the time of the Upper and Lower YR being maintained with a minimum threshold discharge accounts for 3~7% and that of the estuary reaches over 60%.

The minimal flow of the main tributaries entering into the YR are based on that of the mainstream, and calibrated with the observed monthly average discharge from 1956 to 1985. The minimum threshold discharge of Weihe River is 20~120 m3/s.

3.2 Riverbed
3.2.1 Riverbed Cross Section
Riverbed means the waterway of the long-strip concave ground or formed by dike system. Its cross section can be described by width, depth and area etc. In general, the maximum capacity for flood conveyance and detention are used to describe the riverbed cross section, which is the maximum peak flow that could be discharged or stored in the river course in safety.   

The large flood and typical large flood are generated from rainstorm of the middle YR and occur mostly during the period from July to August. This kind of floods is characterized by high peak discharge, short duration, hyper-concentration, and rising and falling rapidly due to the frequent rainstorm with high intensity and short duration. So enough space for corresponding flood is necessary to ensure the safety of flood control in the lower YR.

The maximum flood peak discharge 22,300 m3/s was observed in 1958 at Huayuankou (HYK) station. The flood volume of 12 days amounts to 8.88 billion m3. In addition, it is estimated from the historical records that the maximum peak discharge at HYK station is 33,000 m3/s, which occurred in 1843, and the flood volume of 12 days is 13.6 billion m3. Dyke system in the LYR has been fortified to prevent dyke breaching with flood of 22,000m3/s, and had been heightened and strengthened 4 times since the founding of new China. During recent 30 years, the occurring frequency of medium and ordinary flood in the middle YR has reduced because of water conservation project and medium and small reservoirs. But the relationships among rainfall, runoff and sediment transportation have not changed under heavy rainstorm or especially heavy rainstorm (1). It means that the occurring frequency of large flood has not changed. Therefore, taking account of the flood regime in the future, the importance of ensuring the safety of flood control to social safety and economical development, and the demands of prompting China into an affluent society in the 21st century, the standard of flood control of the LYR afore-mentioned should be maintained.

The flood defense standard in the reach from Ningxia to Inner Mongolia is to prevent a 20~50 year flood, corresponding flood peak of which ranges between 5600~5900m3/s. This discharge can be regarded as the necessary capacity of flood discharging and detention in the reach.

3.2.2 Main-channel Cross Section
River main-channel can be represented by width, ratio of width to depth, and crosssection area etc. However, bank-full discharge is usually adopted to express the main-channel cross section. The method to determine the rational main channel in the future by bank full discharge is introduced as the following.

1. Optimized main-channel for scouring and sediment transportation

The main channel in the LYR should be the way of flood routing and sediment transportation. It is to conquer bed resistance for sediment transportation and erosion. The energy is proportioned with velocity square and quality. So the discharge is a main factor to determine sediment transportation and scouring efficiency. The flood discharge which will not cause floodplain and owns the largest efficiency of sediment transportation or scouring need to be demonstrated and taken as proof of selecting objective bankfull discharge.

Based on the observed data sets of 168 floods since 1974, the most suitable discharge of 3500 m3/s for sediment transportation effectively is proposed. The concentration responding to this discharge is 75 kg/m3 and the sediment transportation rate is 16.6m3/t. But the silting rate is about 13.5% for the LYR (2).

According to the observed data since 1986, the relationship between discharge and the sediment transportation ratio, which is the ratio of sediment load at Lijin station to coming sediment load of the LYR, is analyzed. It can be found that the sediment transportation ratio increases with the discharge increasing. But after the discharge exceeds 3000 m3/s, the increase of sediment transportation ratio reduces greatly or keeps no changing basically. This result is agreed with the velocity changing law at different discharges in main channel. In similar, after the discharge exceeds 3000 m3/s, the increase of velocity reduces greatly. According to the formula of sediment transportation by Zhangruijin, the sediment transportation capacity is proportioned with velocity. So the increase of sediment transportation capacity will reduce greatly with the velocity increase reducing.

Relationship between the discharge of Sanmenxia, Heishiguan and Xiaodong and erosion of per cubic water in the LYR is analyzed and it is found that the erosion of per cubic water almost reaches the maximum value at the discharge of about 3500 m3/s. After the discharge exceeds 3500 m3/s the erosion per cubic water does not increase obviously.

By the afore-mentioned analysis, if the bank-full discharge reaches 3500 m3/s, the sediment transportation and scouring are in higher efficiency and it does not increase obviously with the discharge increasing later. The discharge with maximum sediment transportation efficiency does not mean the corresponding sediment load is the largest. The sediment load of flood is proportioned with the discharge and flood duration. The larger the discharge is and the longer the duration is, the more of sediment load carried by flood is. But because the lack of water resource in the YR is very serious at present, and the future possible bankfull discharge is close to the above mentioned discharge with largest sediment transportation efficiency, there is no doubt to select the discharge as objective bankfull discharge is optimum.

2. Favorable discharge capacity of main-channel in long run

Yellow River runoff changed greatly in past 50 years. Taking HYK station as example, the observed average annual runoff is 46 billion m3 in years from 1950 to 1985 and average runoff in flood season is 26 billion m3. But in the period from 1986 to the end of flood season in 1999(prior to Xiaolangdi operation)， the observed annual runoff reduced 40% and flood season runoff reduced 50%. It is analyzed by precipitation and water utilization that the annual runoff of the LYR will be about 27 billion m3 and 13 billion m3 in flood season in the future without cross-river basin water diversion. Regarding the water saved in dry season, the water for people and ecosystem in flood season, and the effective regulation of the Xiaolangdi reservoir, the flood water which can be used to transport sediment or scour the riverbed will be not more than 8~10 billion m3.

Flood regime has changed greatly. Since 1986 the average annual maximum peak flow at HYK station has decreased to lower than 5000 m3/s and the average daily discharge of 4000 m3/s has been prevailed in the Middle and Lower YR. At present it is difficult to predict the precipitation accurately. But the precipitation may not increase greatly. In the future the average daily peak flow will be lower than 5000 m3/s in most case though the water transfer from other basins can increase the runoff.

The sediment load entering into the YR has reduced greatly. The annual sediment load of the YR is about 1.6 billion ton in average under natural condition. After the extensive harness to the soil erosion in the Loess Plateau, the annual sediment load has reduced to about 1.1 billion ton with the same precipitation as before. But the sediment concentration corresponding to the discharge of 2500~5500 m3/s has nearly doubled. As estimated, Prior to year 2020, the sediment load entering into the YR will reduce to 0.9~1.0 billion ton. Taking account of the Xiaolangdi reservoir operation for coarse sediment retaining and discharging fine sediment as well as the warping in the Middle YR, the coming sediment load of the LYR will be controlled about 0.5 billion ton in the early period and less than 0.7 billion ton for late period. In 2050, the sediment load will reduced at about 0.8 billion ton.

The flood is main hydrodynamic force for channel-forming. Flood kinetic energy is proportioned with its velocity square and quality. So flood hydrodynamic force depends on discharge and flood volume. The index (W0.32Q0.37) of relationship between main channel area and hydrodynamic force are analyzed with the observed data since year 1952 at Gaocun station except year 1977 when the typical flood with high sediment content occurred. From this relation, if no ex-water join in YR, a main channel with the section area 1800~2000 m2 can be formed future by the effective regulation of Xiao Langdi reservoir , and which is corresponding to the bank-full discharge of 4000~5000 m3/s. If maintaining a natural runoff ( no regulation), from the relations between the flood season volume and bank-full discharge, runoffs for flow discharge greater than 2000 m3/s in flood season and bank-full

discharge at HYK station, the bank-full discharge in the LYR can be maintained at 3500~3700 m3/s basically.It must be pointed out that the sediment deposition is annually more than 0.15 billion ton in the LYR during the data period above used. In the future, the frequency of flood causing floodplain will reduce and the most deposition will take place in the main channel. So the bank-full discharge which can be maintained will be less than the above-mentioned discharge under the same runoff in the LYR.

Whether or not the main channel will wither for long time depends on whether the water for sediment transportation can be ensured due to the heavy sediment-laden flow of the YR. After operation of the Xiaolangdi reservoir, inflows of the LYR are basically clear water during the periods of non-flood season and non-flood period in flood season. Only a few of sediment load carried by flow are mainly from bed material supplementary. The annual sediment transportation concentrates in flood period. So the concept of water demand for sediment transportation is introduced here. It means the water for certain sediment load transported to the estuary by natural or man-made flood under the condition that the main channel can be maintained without withering. The effective water should be calculated according to the compatible relation of flow and sediment. The flood of 4000 m3/s will often occurred in the future and the corresponding critical sediment content for deposition and erosion is about 50 kg/ m3. So the discharge of 4000 m3/s and sediment content 50 kg/ m3 can be used to calculate the water demand for sediment transportation with different coming water and sediment condition (3)(4)(5). Then, in the year before 2020, there are some difficult to keep the main-channel no shrinking, especially in about 2020, because there is no enough water for transporting such a large quantity of sediment load. After year 2020, the western line project of Water Transfer from South to North and other projects will take effect, and the runoff of the YR will increase to 10 billion m3. The sediment load entering into the YR will reduce to about 0.8 billion ton, and the regulation of water and sediment by Xiaolangdi reservoir will be improved greatly. So the main channel of the LYR can be maintained with the bank full discharge larger than 4000 m3/s.

3. Impacts of main-channel discharges capacity on flood conveyance and floodplains

According to above analysis, the bank-full discharge in the LYR can be maintained about 4000 m3/s. So it is necessary to research whether or not the bank full discharge can meet the flood control and floodplain safety in the future.

The water levels of the flood of 22,000 m3/s are compared for different bank-full discharges. Though the bankfull discharge can influence the water levels to some extent, the difference of the water levels of the flood of 22,000m3/s corresponding the bank-full discharge of 6000 m3/s and 4000 m3/s respectively are only 21cm, because the area of river cross section is much bigger than that of main channel, in addition, the dyke system is designed with 2~2.5 m higher than flood prevention water level. So the difference of 21 cm can only affect the dyke system slightly.

The floodplain in the LYR is very special. After the dykes breaching at Tongwaxiang in 1855, many people had to live in YR floodplains. Since 1949, the floodplains have been flooded more than 30 times. Flooding floodplains frequently has impeded the inhabitants from developing into an affluent society. The floodplains are important parts of the river course of the YR, especially during large flood period. The floodplains can play a remarkable role on flood and sediment detention. During the flood periods in 1954, 1958, 1977 and 1982, the peak reducing rates in reaches above Ai’san are more than 50%. In years from 1950 to 1998, the deposition in the LYR are 9.2 billion ton and the deposition in the floodplains constituted 69% of that. If the floodplains cannot realize the function of sediment and flood detention, LYR will face much bigger pressure of dealing flood and sediment. So the floodplains have to be flooded by certain level of flood. To determine the bank-full discharge, which can meet the flood control and inhabitants in the floodplain, is very difficult. But for many years the peak discharges greater than 4000 m3/s in Huayuankou station have been regarded as the registered floods. So the objective bank-full discharge should be above 4000 m3/s.

Based on aforementioned analysis, the bank-full discharge of about 4000m3/s and more than 4000m3/s is regarded as the discharge capacity restoration objective in 2020 and 2050 respectively.

3.2.3 Longitudinal and transversal slope
The deposition in the main channel is inevitable due to the incompatible water and sediment flow of the YR. The sediment silts up firstly near the lip of floodplain for over bank flood. So the transverse slope of the floodplain is also difficult to be avoided even without dyke system. In the period prior to the 1970s, the transverse slope of the floodplain is not remarkable because that the main flow shifted and over bank flood occurred frequently. Since 1970s, sediment deposition in the main channel and near lips of the floodplain have increased because that the frequency of over bank flooding occurrence decreased, sediment concentration increased, the scope of main flow shifting reduced and the flow resistance increased. Thus the transverse slope has increased. Taking account of the safety of livelihood and production in the floodplains, we have to accept transverse slope to certain extent. On the other hand, when dykes have been heightened and strengthened, transverse slope of certain extent in the floodplain of the LYR is acceptable.

The acceptable slope relates to the anti-scouring capacity of the dyke system and floodplain roughness. The roughness ranges from 0.012 to 0.016 in the main channel of the YR and from 0.03 to 0.035 in floodplain. During recent 20 years, the floodplain roughness has increased with the economic development. According to Chezy formula of V=R2/3j1/2/n, the floodplain transverse slope which is 6~9 times that of the longitudinal slope is acceptable. But transversal and lateral river are usually caused by the ditches in the floodplain. The ditch roughness is much less than the average of the floodplain and is generally 2 times less than that that of mainstream, so the critical floodplain transversal slope is within 4 times that of longitudinal slope. Thus the transverse slope should be controlled less than 4 times of the longitudinal slope to safeguard against the flood in the LYR. At present the transversal slope of the floodplain is 4~10 times the longitudinal slope in floodplain of Dongbatou-Taochengpu. Whether or not the transverse slope of the floodplain can be reduced to within 4 times the longitudinal slope depends on warping intensity in the floodplain in the future, due to the reduction of the frequency of over bank flood. Recently the transverse slope can be controlled by regulating small over bank flood and silting up the ditches near the dikes in the floodplains. With the improvement of the warping technology and the standard of flood control in the floodplains, and the realizing of the inundation compensation policy, the transverse slope of the floodplain can be reduced gradually.  

The reduction of longitudinal slope will lower flow velocity and reduce the sediment carrying and channel forming capacity. So it is necessary to control the river extension in the estuary, and reduce the longitudinal slope to keep the maim channel without withering. In the early period of impoundment of Xiaolangdi reservoir, the annual coming sediment load of the LYR can amount to 0.5~0.6 billion ton. So the river path extension in the estuary can be controlled completely. In the late period, the sediment load will reach 0.7~1 billion ton. Thus it is very difficult to control river path extension. But we can reduce the development of river path extension by changing the river course in the estuary of the YR.

3.3 Water Quality
The water resources protection goal of the Yellow River firstly depends on water functions of each reach. For instance, to provide domestic water is the main function in Huayuankou reach, so its water quality should be class Ⅲ, but water for agriculture can be lowered gently. According to The Water Functional Partition of China, the Yellow River mainstream is classified into 18 first-level water functional areas and 50 second-level water functional areas. Based on the water functional demands, the reaches down Lanzhou should meet class Ⅲ and the reach above Lanzhou should be maintained at class Ⅱ.

                               
登录/注册后可看大图

The goal is also restricted by the river flow in the future. In other words, whether water demand for self-purification could be met or not. The paper has calculated the flow of self-purification as following table, which take class Ⅲ as the goal and, chose CODcr and NH3-N as pollution control factors, adopte 1-D water quality model, with the premising of “the sewage into the main watercourse of Yellow River entirelymeet national standards, and the bayou of branches into the main watercourse of Yellow River meet the demand of water quality”.





Through comparing month discharges in typical section from 2000 to 2004, it is found out that the flow demand of self-purification is not met all the time in every reach except Xiaochuan and Lanzhou. The time with insufficient self-purification in the reach above Longmen accounts for 15% of the whole year and the reach down Tongguan accounts for 25%. But , the problem that the flow demand of self-purification is not meet can be settled if the volume of water supplemented is 0.6~1.0 billion m3 by eastern line and middle line projects of Water Transfer from South to North, and the water quality goal of Xiaheyan-Tongguan is lowered to class IV.

Because the sewage discharged into mainstream and tributaries scarcely meet the national standard, the water quality in reach down Lanzhou is below the national standard to a serious extent in a long time. At present, more than 10 standards have been constituted, and it should be followed by the enterprise concerned. Most of the Yellow River Basin are economically disadvantaged area, so it is very difficult to make the sewage discharged meeting the national standards. According to the experiences of the developed country, when the living condition of the people is greatly bettered they should think much of the environment protection, and the prevention of water pollution will be strengthened. So it is impossible for the sewage discharged to meet national standards with the present economical development of the Yellow River Basin.

In a sum, the water quality in reach down Lanzhou in the mainstream of Yellow River should meet class III, of which, Xiaoheyan～Sanmenxia reach seriously polluted is properly lowered to class III～IV before 2020; the reach up Lanzhou should strive to maintain present class II.

紫露草

3.4 River Ecosystem
3.4.1 Wetlands

According to cause of formation of wetlands,wetlands alongside Yellow River include natural wetlands, artificial wetlands and semi-artificial wetlands.Plateau wetlands Yellow River source area, the wetland in Yellow River estuarine Delta, and the watercourse wetlands, with Yellow River wetlands in Henan province as a representative of it, are the natural wetlands of Yellow River, and with typical natural features, plenty of rare species, and high ecology value. TheSanmenxia reservoir and the region alongside the reservoir, the Shahu lake in Ningxia Autonomous Region and the Wuliangsuhai lake in the Inner Mongolia Autonomous Region belong to artificial wetlands and semi-artificial wetlands. For the Yellow River Basin lies in arid and semi-arid zones, the survival of animals and plants needs water, so these artificial wetlands have been the habitats of some rare species at present.

People have agreed on protecting wetlands, so the wetland protection is the vital goal of river management. From the view of river managers, it is vital to provide sufficient water with suitable quality, in order to protect the area and size of wetlands. By analyzing the relation between wetlands and the flow of Yellow River, it is found out that the wetlands in the Yellow River basin depends on the water of Yellow River and is one of the competitor of water except the wetland in Yellow River source area. The rivalrousness exists not only between the wetlands and the human, but also between the upside and the downside. In the late years, with the promotion of ecology protection, the provincial governments alongside the Yellow River have paid more attention to wetlands protection, plotted out the wetland conservation reserving area and taken some relevant measures. The objective includes not only natural wetlands but also artificial wetlands. As far as some province, the wetlands maintaining can give rise to the ecological or eco-social benefits, but the inordinate protection will result in the harm to other ecological units in the downstream, in addition, destroy the natural ecological balance in the local. It is obvious that the wetlands protection must be integrated into the plan of water resource management in the Yellow River Basin, on the basis of thinking much of the value of wetlands alongside the Yellow River, reasonably rank the priority, scale and layout of wetlands alongside the Yellow River in term of total ecological benefits of river ecosystem. According to the pilot study, the wetland in Yellow River source area and the wetland in Yellow River estuarine Delta should be reserved with highest priority. The watercourse wetland formed by floodplain has a very high ecological value and should be listed in the wetlands protected. But the reservation scale of other wetlands should be demonstrated comprehensively.

There are plenty of lakes and marshes distributed in Yellow River source area, in which some have been listed in the national wetlands conservation plan. Among them, Ruoergai wetland with some dozens of endangered, rare and endemic species is the largest and most typical plateau wetland and the largest plateau wetland and peatland wetland in the world.Wetlands in the source area have not only ecological value but also the significance to maintaining the water resources of the Yellow River and sustaining Yellow River flow, which is the main water source of wetlands alongside the Yellow River, so it must be rehabilitated with much effort.

   The swamp of river mouth delta is formed by multifarious swing of river channel of YR in the estuary and floodplain. It is the biggest, most-quickly-increasing neonatal swamp in China, as well as in the world. And it is the important district to connect the terrestrial ecosystems with the ocean ecosystems. At the same time, it is the home of many precious plants (such as wild soybean, reed, Chinese tamarisk etc.), and is the protective gene storage of plant. And it is also a station for rare migratory birds, a habitat for living through the winter, and a breeding place for rare birds in the world. Now, the swamp has been listed in the national wetland nature reservation. The freshwater swamp and particularly the aquatic vegetation cover among them is the region where estuarine land area, fresh water body and the oceanic ecosystem unit joint and transit into each other. It is the key of maintaining the equilibrium of estuarine system and protecting the biodiversity. It is also the core district of estuarine ecosystem and the important protected object. According to satellite image, before the middle of 1980s, the estuarine freshwater swamp is about 2 million hm2 in a long time, and the area of aquatic vegetation cover in the main area reaches 1.60 million hm2, of which, the area directly depending on the surface water of Yellow River is over 0.2 million hm2. Since the 1990s, the speed of freshwater swamp getting salinized rises quickly. Till the beginning of the 21st century, the area of freshwater swamp reduces roughly 1.00 million hm2; the area of aquatic vegetation cover descends to 0.48 million hm2; the stability of estuarine delta is threatened. Due to the restriction of embankment, the possibility of relying on natural over bank flooding to supply water is very small. Therefore, the special facilities for water diversion have already been set up in the nature reservation of estuarine delta. Now the freshwater area which is directly supplied by Yellow River has reached 79,000 hm2, and that is the most important protection area at present. Making use of water supplied by other rivers in the future, the wetland finally should recover to the level of late 1980s.

3.4.2 Aquatic ecosystem

Due to high sediment content, low transparency and unstable riverbed, the Yellow River mainstream biologic structure is simple, and biologic kinds and amount are very less. Its phytoplankton is average 0.411mg/L, zooplankton 0.128mg/L and benthon 2.44 mg/m2. Fishes quantity is also very limited, mainly being made up of cyprinidae. Migratory fishes are mainly coilia ectenes, eel and coreius hetreodon; economy fishes are mainly cyprinoid, coilia ectenes, coreius hetreodon and catfish.

Aquatic ecological protection does not protect all living creatures in the river, but realize the biology diversity in the Yellow River mainstream by protecting the key species in the aquatic ecosystem. The most reliable method of recognizing key species is to do some removing experiments, and then observe the reaction of species combinations inside the system. But these experiments are not feasible at present. Key indices method is adopted in this paper. The method of recognizing the key species is to divide Yellow River into three reaches such as reach above Lanzhou, Lanzhou-Huayuankou and Huayuankou-Lijin according to the difference of climate and ecology characteristic, and then compare various kinds of key index of species in the aquatic ecosystem. The results show that fishes’ key index is the biggest, so fishes are key species in the Yellow river aquatic ecosystem.

There are many kinds of fishes in different reaches. It needs to define which kind of fish is the key species to be protected. The selection of fishes to be protected chiefly follows the aspects: ecological significance, local value, special value and endangered degree. According to the results of the method, the protection coefficient of Gymnocypris eckloni is the highest in reach above Lanzhou, it is the representative original fish living in cold water in the source area; in reach of Lanzhou-Huayuankou, the protection coefficient of coreius hetreodon is the highest, so the coreius hetreodon is key species in this reach; the second is Yellow River carp, it should also be included in the key species in this reach; the protection coefficient of coilia ectenes is the highest in reach of Huayuankou-Lijin, therefore coilia ectenes is the key species of this reach. To the manager of river water resource, protecting these key fishes, the core is to protect their major spawn places, major habitats and the important migratory channel.

3.5 Water for human
Human water demand includes domestic, industrial and agricultural water demands.

According to national controlling objective of population, the population will not increase till the middle of the 21st century. Consulting related achievements, in 2020 and 2050, domestic water demand of YR basin will reach respectively 4 billion m3 and 5 billion m3. Water consumption nearly reach 2 billion m3 and 2.5 billion m3.



Agricultural water demand is the total of water resources for farmland, forest, grassland, fishery and etc. With the improvement of the urbanization rate, adjustment of the industrial structure and popularization of agricultural water-saving technology, the agricultural water demand will be reduced gradually, and will maintain a certain level finally. According to calculating result, after 2010, the agricultural water demand of YR basin keeps about 42 billion m3 basically, among which, water consumption is about 35.7 billion m3 basically after 2020.

According to the goal of developing into an affluent society put forward on the 16th National People’s Congress of China, combining relevant national industrial policies and regional economy development characteristic, and referring to relevant achievements, industrial water demand will change from 6.3 billion m3 in 2000 to 11.2 billion m3 in 2020 and 12.6 billion m3 in 2050 in the Basin; Water consumption reaches 5.6 billion m3 and 6.3 billion m3 correspondingly .

As eastern line project of Water Transfer from South to North takes effect gradually, under the condition that the health of lower Yellow River has already worsened seriously, water consumption out of the Yellow River basin should be basically controlled within the water allocation plan (12 billion m3) issued by State Council, and should reduce to 10～11 billion m3 after 2020.

According to analysis above, in 2020 and 2050, water demand for the area supplied by the YR will be 69.4 billion m3 and 69.6 billion m3 respectively; water consumption will be 53.4 billion m3 and 54.5 billion m3 respectively. The groundwater that can be exploited in the Yellow River Basin is 11 billion m3. Because there are some areas where groundwater is over exploited, water requirement increase in the future should be met with surface water mainly, namely, surface human water demand is 42.4 billion m3 and 43.5 billion m3 respectively in 2020 and 2050.

4 Approaches towards a healthy Yellow River
Indices of the Yellow River health are the integrated reflection of human activities in the whole river basin. The activities may be various. However, only the activities possible to change water and sediment into the Yellow River (including runoff, flood, grain size, their quantity, temporal and spatial distribution, water quality and other factors) are those elements having notable impact on healthy life of the Yellow River. In order to make all the indices of healthy Yellow River reach standards, human activities involving water and sediment in the whole river basin or related regions must be adjusted and normalized so that the flood, water and sediment matching, runoff, sediment runoff and sediment grain size, water quality and etc. can benefit the healthy Yellow River. The key approaches are to increase water, reduce sediment and scientifically regulate water and sediment relation.

4.1 Water resources management
4.1.1 The Flow needed by Healthy Yellow River
Water demand of Yellow River healthy life is the water amount needed to keep the Yellow River healthy. It is the total river flow to satisfy environmental water demand and human water demand.

The environmental water demand includes ecological water demand, self-purification water demand (see the table above), and water demand for sediment transportation and river channel-forming. Water demands for various functions being coupled spatially and temporally is the environmental water demand.

Ecological water demand is the water condition needed to realize the reservation goals of Yellow River ecological system (including certain scale of wetland and fishes). It needs to firstly analyze the relation between the change of ecological reserving goals and the supply of Yellow River fresh water. However, it is hard to analyze the relationship because the above data was not systematically observed previously. The paper adopts Tennant method to estimate ecological water demand. The observed data series during 1956-1985 is adopted as ecological benchmark. 20% of the benchmark flow is set as the calculation standard of ecological water demand. In reach where owns special ecological significance, the standard value during April to June, the important multiplication period for creatures, adopts 40% of average discharge.

Water demand for sediment transportation is calculated with the method referred in 3.2.1. In 2050, annual sediment into the Yellow River is about 0.8 billion ton. Taking into account reservoir regulation, warping in the middle stream and other factors, sediment in the downstream which need to be transported to estuary by flood can be supposed as 0.7 billion ton. Based on it, and under the precondition of preventing the mainstream from shrinking, the water demand for effective sediment transportation in the downstream is 14 billion m3 or so. It needs to be clarified that the result is obtained with supposing Xiaolangdi reservoir can regulate natural flood with disharmonious water and sediment relation into flood with a balanced relation. However, at present, there are still difficulties in realizing this object. According to observed data, under the condition of natural flood and that coming sediment is 0.7 billion ton in the downstream, the siltation ratio in the river bed is about 15%, therefore, after Xiaolangdi reservoir is put into use, the siltation ratio can be supposed as 10%. In Lijing cross section of the lower Yellow River, the ecological discharge of flood season and low flow season is 500 m3/s and 200 m3/s respectively. Based on the average of many years, annual sediment transportation can reach 0.06 billion ton or so. After the Xiaolangdi reservoir is put into use, in 2050, water demand for sediment transportation is 14 billion m3; however, it is still hard to avoid slight siltation in the mainstream.

In order to maintain the bankfull discharge of Ningxia-Inner Mongolia reach above 2500 m3/s, with taking into account the results of the 4 water and sediment regulation experiments, the water amount with flood peak larger than 2000m3/s should be more than 2.5 billion m3.  

    Compared above-referred monthly water demand for various functions, the maximum is environmental discharge of Yellow River mainstream (The detailed data is omitted here). For example, in Lijin cross section, monthly environmental discharge ranges between 100~530 m3/s; discharge in sediment transportation period is 4000 m3/s and annual environmental water demand is 22 billion m3. In Huayuankou cross section, annual environmental water demand is about 24.5 billion m3.

In 2050, human water demand (only surface water) is about 43.5 billion m3. After it is coupled with environmental water demand, the water demand of Yellow River healthy life is 65.5 billion m3(Lijin). Human water demand accounts for 66% of it. Presently Yellow River runoff is only 53.5 billion m3, and the difference reaches 12 billion m3. The water shortage mainly reflects in flood season.            

4.1.2 Increase water supply by all the possible means
Focusing on Yellow River water allocation plan of normal and dry years. The present Yellow River water allocation plan is based on average annual runoff, which integrates the situation of rich year, normal year and dry year. In fact, normal and dry years with relatively less precipitation are the years with outstanding water contradiction. Yellow River water is always over used during these years. Therefore, the idea of Yellow River water allocation should be modified and the average annual natural runoff of normal and dry years should be the basis for water allocation plan.



Clarifying the water right allocation plan of Yellow River tributaries and the ground water. The present Yellow River water allocation plan is for average annual natural runoff of the whole river basin. In practical water allocation, it mainly depends on observed runoff in key reaches of the mainstream. When water is abstracted in tributaries of the Yellow River or from ground water, the surface runoff into the Yellow River is sure to be reduced. However, the reduction is hard to be reflected objectively in water consuming record of users. Hence, in order to reasonably allocate Yellow River water resources, water right of tributaries and ground water must be scientifically and reasonably allocated based on the basis of provincial total water quantity control.

Attaching high importance to water saving mechanism and policies. To improve water using value through water allocation and transfer in industry and agriculture; exploring water saving potential to the maximum through updating water saving establishments, improving water price and other policies; making agricultural water use have high value through adjusting economic structure especially agricultural planting structure; controlling saline lands through developing irrigation with both wells and canals; realizing the water-saving cost sharing, drainage monitoring and drainage re-allocation through controlling ground water level, drainage reclaiming and other measures. The monitoring and assessing methods of human water use should be innovated to realize a real water consumption record. Evaporation, leakage, observation error and other wastage are unavoidable, and it should be jointly born by all stakeholders in the Yellow River basin and all related provinces.

Reserving Yellow River water sources. The source area of the Yellow River is with massive lakes and marshes. With an area of 122,000 km2, it accounts for 16% of the basin area. Average annual natural runoff here is 20.5 billion m3, accounting for 38% of natural runoff of the Yellow River. In the past 20 years, pasture and marshes in source area has severely degraded and runoff also decreases largely. In order to protect marshes in source area and reserve the water sources, we must scientifically control the amount of livestock and their breeding pattern in different seasons, strictly control the drainage establishment and structure building in marshes. In addition, we should explore to use creatures or other measures to mitigate rat disaster, strictly regulate mining, drug-picking and other activities in source area. At the same time, we should build monitoring network in source area with advanced technology. In addition, suitably lengthen the duration of flood in areas with severe ground water funnel to recharge ground water, under the precondition of ensuring the safety of flood control.

Implementing cross-river basin water transfer. It is to consider transferring water from other river basins to supply Yellow River runoff. The present plans under argumentation includes western line project of Water Transfer from South to North and Water Transfer From XiaoJiang River. The former can meet the demand of healthy life of the upstream and the middle stream. The latter can meet the discharge demand of Weihe River health. Both of them need further argumentation. Due to the severe shortage of ecological discharge in reach below Lijin, during a short period, we should consider to use eastern line project of Water Transfer from South to North to provide water to the Yellow River, and to transfer water from other rivers to replace the Yellow River to provide water for agricultural irrigation in the lower reach.  

Strictly control pollutant discharged into the Yellow River. To make Yellow River water meet standards, the key is to adjust water use mode in the river basin, arouse environmental protection consciousness and the consciousness of the upper reach and the lower reach to work together. Relevant departments should put efforts on exploring mechanism of water pollution information publication and information sharing, mechanism of responding on urgent water pollution events, to form a set of cross-jurisdiction water quality management mechanism and relevant policies. With the demand on restricting pollutant discharged into the Yellow River being guide line, through economic, administrative, legal, technological measures and etc. relevant provinces should urge people to adjust economic structure, change production pattern, strengthen pollution fathering and develop green industries.           

4.2 Soil erosion Control
4.2.1 Thresholds of Sediment load for the healthy Yellow River
The discharge capacity of the river channel is a major indicator of healthy Yellow River, it is also one of the most significant challenges. The discharge capacity is very much depend on the total flushing water to transport the sediments, which was closely related to total sediments load and silt’s size distribution. To reduce every 100 million ton of sediment load, it will save 2000 million ton of flushing water. According to the laboratory analysis, the coarse sand (refers to particles bigger than 0.05 mm) amounts to 23% of the total sediment load in the river, however, it amounts to 51% of the total deposition in the lower reach river bed. Which means the key issues for sediment control is to reduce the sediment load, especially the coarse sand.

Before the fully operation of the National South-North water transferring project, the remained flow for sediment transportation other than environment and human water demand is some 800-1000 million m3, which is able to transport maximal sediment conveyance of 500 million ton, that is the threshold of sediment load of Yellow River at this stage. During a long period, other river basin is very likely to supply water to the Yellow River, however, due to the restriction of water transfer cost, reducing sediment into the Yellow River and saving water for sediment transportation should be primarily considered.

4.2.2 To Control the Soil Erosion by all the best
The area of heavy sediment yield and coarse sediment source is the key harnessing area of soil erosion area. In loess plateau, soil erosion area reaches 454,000 km2, however, medium or coarse sediment with grain size larger than 0.025 mm is mainly from the area of heavy sediment yield and coarse sediment of the middle reach, which is about 78,600 km2, average annual sediment load of which reaches about 62.8% of the total sediment load of the Yellow River, and runoff of which is only 6% of the runoff of the Yellow River. Sediment load of medium or coarse sediment with grain size larger than 0.025 mm is 0.622 billion ton, which accounts for 65.5% of that of the Yellow River during the same period; sediment load of coarse sediment with grain size larger than 0.05 mm is 0.319 billion ton, which accounts for 72.5% of that of the Yellow River during the same period. In 786,000 km2 excessive and coarse sediment area, the main source area of coarse sediment is only 18,800 km2, accounting for 23.9% of the area, however, regarding the coarse sediment with grain size larger than 0.05 mm, which is most harmful to the main channel of the lower Yellow River, its yielding accounts for 47.6% of that of the area of heavy sediment yield and coarse sediment source. Hence, the harnessing of soil erosion in Loess Plateau should focus on the area of heavy sediment yield and coarse sediment source, especially the main source area of coarse sediment.

Making harnessing measures of soil erosion play the role of erosion reduction and sediment trapping in a sustainable way. The practices have proved how to realize sustainable and stable erosion reduction and sediment trapping is the main challenge facing presently. During the early period of warping dam construction, sediment-trapping result is obvious. For example, in the 1970s and the 1980s, sediment-retention dam contributes about 70% to the sediment trapping. With the capacity being silted completely, its sediment trapping function reduces gradually. Till the middle 1990s, its contribution had reduced to below 50%. In order to push warping dam construction effectively, we must aim at sustainable and stable sediment trapping in the future, deeply study amount of different scale of sediment-detention dam in the dam system and their functional cooperation, the dam construction procedure and operation, using pattern of lands reclaimed, management and protection of a sediment-retention dam system and other issues. It is hard to realize the goal of sustainable sediment reduction only relying on gullies measures. In the future, we should follow the principle of taking into account both ecological benefit and economic benefit, objectively establish slope improving measures and policy suitable to various areas.     

4.3 Sediments regulation through artificial floods
4.3.1 Optimized floods regime to improve river morphology
Demands of healthy water and sediment transportation channel on Yellow River runoff and sediment process mainly reflect in the demands on quantity, duration and sediment content of floods in flood season of preventing main channel from shrinking.

The forming of main channel is a process during which floods fight the resistance of riverbed. From the relationship between downstream main-channel-forming and flood power, it can be found that to form a main channel with certain cross section, flood power W0.32Q0.37 needed is definite. If discharge is large, flood runoff could be small. However, if the discharge is larger than discharging capacity of the main channel, the sediment carrying ability of the flow will be reduced. Taking into account sediment transportation efficiency, scouring efficiency of floods and practical discharging capacity of main channel and etc., the floods in the lower reaches should be regulated in alternative ways of discharging at about 4000 m3/s or with large-scale floodplain respectively.  

Under the condition of discharge being about 4000 m3/s, sediment content is a key factor influencing deposition in main-channel. Based on studies, regarding normal sediment grain size, the critical sediment content corresponding to the discharge is about 50 kg/m3. If the ratio of fine sediment rises 10%, the critical sediment content will increase 10 kg/m3 or so.  

Water amount of preventing main-channel from shrinking is related to sediment entering into the downstream during a flood. If coming sediment load of the flood which will not cause floodplain inundated is 0.4 billion ton, water requirement should reach 8 billion m3. However, if Xiaolangdi reservoir can change the grain size of coming sediment, water amount needed can be reduced.   

4.3.2 Key factors of water and sediment regulation
After 1986, in Tongguan station, floods over 5500 m3/s reduced largely; the sediment concentration of floods ranging between 2500~5500 m3/s increases obviously; from July to October, the days on which discharge is less than 2000 m3/s accounts for about 84%, the runoff during which accounts for over 2/3 of the total water amount 13 billion m3. It shows the chance of relying on flood to inundate floodplain area and to scour main-channel will be quite few, and once sediment deposition occurs, it will be in the main channel. Therefore, the natural flood must be regulated by the joint operation of reservoirs in the middle reach so that the downstream main-channel is maintained not to shrink.

Sediment concentration and its grain size is key elements when regulating flood and sediment. It is simple to regulate the discharge of the downstream, however, it is very hard to regulate the flood with demanded sediment concentration. The involved technologies include combining operation scheme of sluice gates in Xiaolangdi reservoir, joint operation of Xiaolangdi reservoir and reservoirs in the middle reach, artificial density flow technology and etc. These issues have been explored in previous practices on water and sediment regulation; however, they could not fully meet the demands. In addition, how to make Xiaolangdi reservoir play the role of sediment trapping effectively and lastly through silting coarse sediment and discharging fine sediment, is a challenge facing in the future.

Constructing Yellow River water and sediment regulating system is the basis of realizing flood and sediment regulation. Till 2050, annual sediment load of the Yellow River is still high to 0.8 billion ton. Under the precondition of preventing the downstream main-channel from shrinking, at least 14 billion ton water is needed. Supposed corresponding flood procedure for sediment transportation can be realized in 1~3 stages based on the situation of natural floods and artificial floods, because flood control capacity of Xiaolangdi reservoir is 5.05 billion m3, and the capacity for water and sediment regulation is only 1 billion m3, it is hard to realize harmonious relationship between water and sediment only relying on Xiaolangdi reservoir when the sediment deposition in the reservoir reaches certain degree. The regulation of sediment content of reservoir outflow must rely on joint operation of reservoirs. Hence, in order to realize the goal of no shrinkage of the main-channel and lengthen the duration of sediment trapping of the reservoir, it is imperative to build a water and sediment regulating system in the middle reach with Guxian reservoir, Sanmenxia reservoir and Xiaolangdi reservoir being the main component.  

Dealing with and settle sediment by various ways. Due to the restriction of limited water for sediment transportation, and the present technologies, which could not precisely control sediment concentration of outflow of Xiaolangdi reservoir, therefore, even if coming sediment can be controlled less than 0.8~1 billion ton and water for sediment transportation can be ensured, it is not sure there will be no sediment deposition in the main-channel. Therefore, various ways have to be used to deal with and settle sediment such as warping in floodplain area, shifting the mouth ways entering sea, water and sediment diversion, storing sediment in reservoirs, dredging and etc.

Establishing flood management polices for floodplain area (or beach) as soon as possible. Floodplain area is important space for sediment deposition in the lower reach, and also area for flood detention. When it is inundated, we should make compensation according to national compensation policies for flood detention area, so that floodplain area can be flooded and its inundation is deserved. the pre-warming system construction in floodplain area should be strengthen, so that people can be evacuated timely and effectively. At the same time, people in floodplain area should adjust economic structure and develop livestock farming based on characteristics of floodplain area.

4.4 Integrated water and sediment management
The practice of keeping healthy life of the Yellow River is related to not only the natural features of a river basin, but also human activities in related regions. On the one hand, a river basin is an integrated geography unit, is a complex of economy, society and environment. Its inner elements are interrelated. Unceasing water circulation in a river system links the following together: land utilization, resources utilization, economic activities, ecological system and other activities in the river basin. Activities to meet certain demands of human being in one aspect, or unilateral measures to maintain healthy life of the Yellow River are possible to do harm on healthy life of the Yellow River in other aspects. On the other hand, keeping healthy life of the Yellow River, realizing the Yellow River water resources sharing by human being, the river itself and other species is a re-adjusting process of interests of stakeholders. The core is to maximize comprehensive benefits of economy, society and ecology, through improving management and development of water, land and other sources in Yellow River basin, and under the precondition of avoiding doing harm on Yellow River itself. The process is always at the cost of sacrificing local interest of some stakeholders. Therefore, putting the new concept of keeping healthy life of the Yellow River into practice, must harmonize the relation between human activities in the river basin and protecting a healthy life of the Yellow River through integrated water and sediment management in the river basin. The integrated water and sediment management in the river basin means a process of maximizing economic and social benefits, which are through cooperative cross-department and cross-jurisdiction management, prompt harmony development and management of water, land and relevant resources in a fair way, and under the condition of maintaining the sustainable development of important ecological system. The integrated referred here should reflects the harmonious relations among a natural system, such as both freshwater body and offshore, both land and water, both green water and blue water, both surface water and ground water, both water quantity and water quality, relation between the upper reach and the lower reach and etc. and take into account the balance of relations in human system, such as relation among different departments, different industries, different groups and etc.

Yellow River management agency with the river basin as a unit is the basis of boosting integrated water and sediment management in a river basin. Water resources management, water and soil loss fathering, ecology recovering in river source, ecological protection of a river or water quality improvement, will inevitably involve the cooperation of benefits, activities and supervision of different provinces (municipalities) or departments. Therefore, a river basin management and decision-making agency, which is authoritative, has obvious functions and responsibilities and involves central government, provincial (municipal) governments and relevant experts, should be built gradually. In addition, with the principle of balancing concentration and deconcentration, relevant provinces (municipalities) are authorized to carry out management within their jurisdiction, to form a mechanism of combining river basin management with regional management and to ensure the execution of river basin integrated management.  

Reasonable and effective management mechanism is the guarantee of boosting integrated water and sediment management. In order to form a mechanism that all stakeholders involve in decision-making of important water events and provide a platform for their participation, we should put efforts to improve the environment for public participation, build information publication system, improve capabilities of stakeholders to take part in river basin management, continually improve the cooperation capability of river basin agency to realize the separation of rights for decision-making, execution and supervision.

Laws and stipulations are compulsive norms to restrict human activities. In order to bring the concept keeping healthy life of the Yellow River into effect, the existing laws regarding river basin management should be modified to reduce the conflicts in it. River basin laws and stipulations must clarify rights and obligations of stakeholders in river basin management, clarify responsibilities and rights of river basin agency, definite the norms which human activities must observed in the river basin, to provide powerful legal guarantee for river basin integrated water management.

Establishing Yellow River comprehensive plan is an important measure of boosting integrated water and sediment management in a river basin. We should integrate the concept keeping healthy life of the Yellow River into the plan, harmonize the objectives, contradicts and measures of water resources development, water and soil loss fathering, ecological protection and water quality protection and etc. clarify the long-term and short-term objectives of keeping healthy life of the Yellow River, the Yellow River water and sediment regulating system, water management system and water and soil loss fathering system in the river basin which are built to meet the demand of the concept, to maximize the comprehensive benefits in the river basin, based on taking into account special regions or special situations.

Sounded information and scientific and technological basis is an important support of implementing integrated water and sediment management in a river basin. We should make full use of advanced technologies, construct water information monitoring and processing system over the whole river basin, build water circulation model and water and sediment routing model of the Yellow River basin to provide scientific and technological support for establishing river basin comprehensive plan, through researching Yellow River water and sediment movement rules and regulation technologies.

Forming harmonious social environment with much effort. Keeping healthy life of the Yellow River needs the support, participation and cooperation of all stakeholders in the whole river basin and related regions. We should cultivate the society to own a healthy psychology through all kinds of measures, so that most people can consciously realize the harmonious relation instead of the opposite, and won’t try to sacrifice others interests or future interests to seek their own interests, when they deal with the relation with the Yellow River.

5 Conclusions
The healthy Yellow River means its runoff can basically meet the demands of healthy ecological system while ensuring the safety of human society and economic development. The main Symbols of healthy Yellow River in 2050 are as following: continuous flow, free-and-safe riverbed, favorable water quality, acceptable river ecosystem and certain water supply capacity. Besides, minimal flow, bank-full discharge capacity, wetlands area, water quality and others altogether 9 elements are main indicators of healthy Yellow River. Ensuring the life of the Yellow River and the safety of human being is the minimal requirement on keeping the Yellow River healthy. Therefore, safeguard the minimal environment flow in tributaries and mainstream of the Yellow River, and ensure the maximum flood discharging capacity in important reaches is of high priorities in Yellow River health indicators. Making the river function well in sediment transportation, self-purification, ecological, water supply, etc., are the expectation on healthy Yellow River from human being. Hence, we should put efforts to restore main-channel discharge capacity, control longitudinal and transverse slope in the important reaches, basically meet water demand of social and economic development, and reserve important scenic spots and bio-diversity. The key-influencing factor is Yellow River runoff and sediment load, which is hard to have fundamental change before the completion of National South to North Water Transferring Project, therefore, relative lower standards should be applied before 2020.  

The process of keeping healthy life of the Yellow River is a process of human being adjusting activities on the Yellow River. Through scientifically using Yellow River water and sediment movement rules and suitably regulating runoff and sediment, the balance of benefits of human being, Yellow River itself and ecology, namely, the balance of nature and society, is achieved.   

The essence, criteria, indicator system and action plans of healthy life of the Yellow River are based on present understanding of river health. The indicators matrix based on which is just a interim standards. With the restoration of healthy life of the Yellow River and rapid social economic development, significant conflicts of the river system will also change. Hence, criteria and indicators of healthy Yellow River should develop with the time.

Source:  www.yellowriver.gov.cn

刘秀

好吧，我也要好好学习英文了，很多单词都不记得什么意思了，惭愧啊惭愧……

飞天

算了，不研究了，太长了，看到一些语法错误。

紫露草

啊，有语法错误，好吧！仔细看看，尽快修改！

冷月-无声

英语退化了啊。。。好多术语都没看懂