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Prototype Water and Sediment Regulation of the Yellow River

Prototype Water and Sediment Regulation of the Yellow River

Write: Froth [2011-05-20]

General Director of the first prototype testing of water and sediment regulation

of the Yellow River

Director of Yellow River Conservancy Commission, the Ministry of Water Resources of China

(October 17, 2002)

In ancient books and records of China, the Yellow River was called Source of Four Ditches, Head of Hundred Rivers . It is world-notorious for a river channel which has a high silt load and is easily breached and changed. It is regarded as the most difficult river to be harnessed in the world.

From Pan Jixun of the Ming Dynasty, people have undertaken theoretical development and practical application of the Yellow River sediment harnessing continuously for several hundred years. As valuable experience has been gained, the measures of the Yellow River sediment harnessing are outlined as interception, discharge, drawing off, regulation and excavation . The interception, discharge, drawing off and excavation have been applied in varying degree. The regulation , however, has not undergone any real prototype testing in spite of the long time theoretical work.

1. Lower channel sedimentation of the Yellow River

The silt of the Yellow River is mainly from the soil erosion of the loess plateau.

The topography, geomorphy and physical features of the loess plateau have been formed under the neo-tectonic movement in this field since the post-Cenozoic era. The neo-tectonic movement turns the whole loess plateau into a state of an endlessly rising movement and results in a change of erosion level.

Therefore, there exists intensified slope erosion and activated gully erosion. In the meantime, due to the soil mass gravitation and the phreatic water effect, gravity erosion with unstable soil mass sloughing and sliding often takes place. In the humanity era, human activities also enhance soil erosion intensity in the loess plateau.

Under rainstorm conditions, the main channel and many branches of the Yellow River in the loess plateau become world-rare muddy streams with high silt loads.

The Yellow River with its large quantity of silts has been filling up the pale-epicontinental basin in North China, which is spread out to Bohai Sea and forms a new land North China Great Plain.

The stream route of the Yellow River had no constraints before levees appeared on the North China Great Plain. Originally, the river always found out low-lying route into the sea; and then it might trundle to another relatively low-lying route along with the sustained sedimentation. Repeated many times in this way, silts were spread over the alluvial fan of the Yellow River.

In the middle years of the Spring-and-Autumn Period, iron-wares arose and were extensively used to make large-scale dikes possible. Improved social productive forces, a developed economy, increased population, upgraded civilization and advanced technology all made the levee systems on the lower reaches of the river arise. The levees on the lower reaches of the river were formed on a fairly large-scale scale during the periods of the Warring States.

The levees restrain the river and, in the meantime, result in silt spreading over between two riverbanks so that the riverbed rises continuously. In light of the record riverbed rises above dwelling houses around Liyang (present Xunxian County, Henan Province) in the later stage of the Western Han Dynasty (the first year of Han Ai Emperor), the Yellow River at that time had become a suspended river .

When the suspended river grows up to a certain degree, river dike breach will happen, even river course changes sometimes. Record shows that, in 2540 years from 602 B.C. (the fifth year of Zhou Ding Emperor) to 1938 A.D., the years with breaches amount to 543, the number of breaching is 1590 times, and the number of changing course is 26 times. The distribution of the river stream routes is shaped like a fan extending northward to Tianjin, southward to the Huaihe River and the Changjiang River, and the area amounts to 250 thousands km2.

Since the founding of new China, the levee system on the lower stretches of the Yellow River has been entirely heightened and thickened four times, which supports the great achievement of no breaches in either summer or autumn floods for more than 50 years. Sludge deposit between the two riverbanks of the lower stretches at present reaches almost 10 109 t and makes the riverbed rise to 2~4 m.

This means that the riverbed of the lower course is generally 4~6 m higher than the land outside the river, in some part, even 10 m. It becomes a drainage divide between the Huaihe River and the Haihe River Basins. All cities alongside the lower course are below the riverbed, e.g., Xinxiang City 20 meters, Kaifeng City 13 meters, both in Henan Province, and Jinan City in Shandong Province 5 meters.

Since the 1990s, annual average deposit on the lower river course has reached 0.22 109 t. Continuously dry years and small discharge have resulted in severe sedimentation on the lower main river channel. According to the statistics, the deposit on the main lower course is 90% of that on the entire river section, and some section even 93%, for example, the section from Huayuankou to Gaocun.

Severe channel sediment makes the wetted cross section reduce so that the water level for the same discharge rises and the beach discharge reduces by a big margin. The flood in August of 1996 ( 8/96 flood in short) intensively proves this fact. The peak discharge of flood at Huayuankou cross section corresponded to 7600 m3/s only, but the water level approached el.

94.73 m, 0.91 m higher than that of 22300 m3/s on the same cross section in 1958. The beach discharges on some stretches reduce to about 3000 m3/s from 5000 m3/s in 1980s.

2. Origins of the lower channel sedimentation of the Yellow River

The lower channel sedimentation of the Yellow River lies in insufficient water and excessive sediment as well as disequilibrium between water and sediment .

2.1 Insufficient water and excessive sediment

The lower river course corresponds to an annual average runoff of 55.9 109 m3, with an annual average silt load of 1.6 109 t and an average silt content of 35 kg/m3. Comparison can be taken with some other great rivers. Annual runoff of the Changjiang River outnumbers the Yellow River seventeen to one, but its average silt load is just one third of the Yellow River.

Annual silt load of the Ganges in India and Bengal is 1.45 109 t, nearly equal to that of the Yellow River, but its runoff is about 371 109 m3 much larger than the Yellow River, and its silt content is 3.9 kg/m3 much less than the Yellow River. The silt content of the Colorado River is 27.5 kg/m3, less than the Yellow River, but its annual silt load is only 0.

135 109 t. It is true that the Yellow River lists on the first rank in all rivers both for annual silt load and average silt content.

2.2 Disequilibrium between water and sediment

2.2.1 Uneven distribution in space

The Yellow River flows over different natural geographical divisions and the topography, geology, precipitation and silt production have fairly great differences. This situation can be described as different sources of water and sediment . For example, the upper reach of the Yellow River controls a drainage area of 360 103 km2, 45 per cent of the entire river drainage area, but the runoff here is 53 per cent of the entire river.

Therefore, it is a reach with more water but less sediment and here the silt load is only 9 per cent of the total river and the annual average silt content is only 5.7 kg/m3. The middle river course between Hekou and Longmen, however, controls a drainage area of 130 103 km2, 16 per cent of the entire river drainage area.

Its runoff quantity is 15 per cent of the entire river, but its silt load is 56 per cent and annual average silt content is 128 kg/m3, the highest value along the river. Most silt is produced here. The stretch between Longmen and Tongguan controls a drainage area of 190 103 km2. Its runoff occupies 22 per cent of the entire river value, the silt load is 34 per cent, and the annual average silt content is 53.

8 kg/m3, next to the highest value mentioned above. The branch runoff of the Yiluo River and the Qinhe River below Sanmenxia occupies 11 per cent of the river runoff, but the silt load is 2 per cent and the annual average silt content is only 6.4 kg/m3. This is the second relatively clear water source after the upper reach.

In general, most water on the lower course comes from the upper course, but the sediment mainly from the middle course.

2.2.2 Uneven distribution in time

Besides, there exists an obviously uneven distribution during the year. Water volume in flood season (July to October) is 60% of the whole year. With the increased human actions, this percentage is being reduced. For example, since the project was commissioned in October 1986, the runoff of Longyangxia reservoir has just corresponded to 47% of the annual runoff.

The silt load takes more obvious disequilibrium in time. According to the statistics, more than 85 per cent of the annual silt load comes in flood seasons, and often concentrates in a few storm floods. On the stretch with the maximum silt load between Hekou and Longmen, for example, the annual silt load is 0.

91 109 t, in which 0.81 109 t is from the flood season. The silt load in flood season occupies 90 per cent of the annual total but the value in other periods is only 10 per cent. The region between Huangpuchuan and Tuweihe has the maximum erosion modulus in the loess plateau. The maximum silt load recorded in five days during a flood, at Kuyehe Wenjiachuang gauging station, exceeds 75 per cent of the annual value.

Considering a year time, it is insufficient water and excessive silts; the flood season intensifies the disequilibrium between water and silts. Considering year-to-year distribution, the variability coefficient of the river runoff is 0.22~0.25, in which the ratio of maximum to minimum is 3.1~3.4; the variability coefficient of the silt load is 0.

55, in which the ratio of maximum to minimum is 4~10. The maximum river silt load of 3.91 109 t was recorded in 1933, but the runoff in 1933 was 56.1 109 m3 which was not a maximum value in a long series of periods (86.1 109 m3 in 1964). The minimum silt load of 0.33 109 t was recorded in 1987, but the runoff in 1987 was 20.

4 109 m3 which approached the minimum value in a long series of periods (14.3 109 m3 in 1997). These imply a non-synchronicity of water and silt year-to-year distribution. This non-synchronicity, characterized by insufficient water and excessive silts, further intensifies the disequilibrium between water and sediment.

3. Alluvial patterns of the lower channels of the Yellow River

According to survey and analysis, the lower channels generally have sedimentation for a long period, but not one-phase sedimentation, i.e., depositing in some years and flushing in other years. Such alluvial character is closely related to the conditions of the runoff and silt load in the lower channels of the Yellow River.

In a year of more water and less silt, the lower channels hardly deposit but flush. For example, in 1952, the lower channels deposited 0.035 109 t only, while water volume was 39.6 109 m3, silt load 0.82 109 t, and average silt content 20.6 kg/m3. In 1955, the lower channels flushed 0.1 109 t, while water volume was 58.

1 109 m3, silt load 1.41 109 t, and average silt content 24.1 kg/m3. In 1961, the lower channels flushed 0.81 109 t, while water volume was 55.4 109 m3, silt load just 0.19 109 t, and average silt content 3.4 kg/m3. In all the years of less water and more silt, conversely, the lower channels deposited seriously.

For example, in 1969, the lower channels deposited 0.7 109 t, while water volume was 31.0 109 m3, silt load 1.4 109 t, and average silt content 45.1 kg/m3. In 1970, the lower channels deposited 0.82 109 t, water volume was 35.5 109 m3, silt load 2.09 109 t, and average silt content 58.9 kg/m3. In 1977, the lower channels deposited 0.

96 109 t, water volume was 30.1 109 m3 only, silt load and average silt content reached 2.07 109 t and 68.1 kg/m3 respectively.

Under natural conditions, there are different combinations of water and silts in the lower channels due to different precipitation in different fields. When water is mainly from the reach above Hekou or the branches the Yiluo River and the Qinhe River below Sanmenxia or both, the lower channels hardly deposit, sometimes even flush.

The flood records during 1960~1990 show that there were 76 floods (38.3 per cent of all the river floods) in the above two fields. Their average discharge exceeded 2000 m3/s and average silt content was 21.8 kg/m3, whereas lower channels flushed 1.59 109 t. If water was mainly from the stretch from Hekou to Longmen or the stretch from Longmen to Tongguan or both, in these years, the lower channels deposited fairly or extremely seriously.

There were 14 floods (7.1 per cent of all the river floods) in the field from Hekou to Longmen during 1960~1990. Their average discharge was 1775 m3/s, average silt content 174 kg/m3, and lower channels deposited 2.795 109 t. There were 108 floods (54.5 per cent of all the river floods) in the field from Longmen to Tongguan during same period.

Their average discharge was 2200 m3/s, average silt content 63.5 kg/m3, and lower channels deposited 4.783 109 t.

From the records of 145 floods in natural conditions during 1950~1960 and 1969~1985, it can be found that, when other factors remain unchanging, the lower channel sedimentation will reduce by 0.051 109 t if the silt load from Hekou to Longmen reduces by 0.1 109 t; the lower channel sedimentation will reduce by 0.

039 109 t if the silt load from Longmen to Tongguan reduces by 0.1 109 t. Moreover, the lower channel sedimentation reduces by 0.082 109 t if water volume above Hekou increases by 10 109 m3; the lower channel sedimentation reduces by 0.16 109 t if water volume of the Yiluo River and the Qinhe River below Sanmenxia increases by 10 109 m3.

According to the above statistics and analysis, it is apparent that there is a close relation between the annual average silt content in the lower course and the channel deposit per 100 million cubic meters water. Small average silt content corresponds to small channel deposit per 100 million cubic meters water, or to flushing; great average silt content corresponds to great channel deposit per 100 million cubic meters water.

From the inter-dependence relation between the annual average silt content and the channel deposit per 100 million cubic meters water, it is found that the channels attract deposition once the annual average silt content is greater than 20~25 kg/m3, and the channels incur flushing once the annual average silt content is smaller than 20~25 kg/m3.

Therefore, a threshold value of annual average silt content related to lower channel alluvium should be 20~25 kg/m3, which can be a simple criterion about the lower channel alluvium. If annual average silt content in channel water of the lower course is 35 kg/m3, greater than the threshold value of 20~25 kg/m3, for example, a certain channel sedimentation on the lower course can be predicted.

This threshold value of annual average silt content is suitable for a rough assessment of large-scale alluvial variation. For a specific flood, its discharge and lasted time should also be involved, besides the silt content. By means of the influence analysis between the flood factor and channel alluvial variation, based on 397 real floods in the lower channels since 1960, the following patterns are found:

a. If the silt content is smaller than 20 kg/m3, the discharge is 2600 m3/s and the lasted period is 6 days (water volume 1.35 109 m3), channel sedimentation on the lower course does not happen;

b. If the silt content is 20~40 kg/m3, the discharge is 2900 m3/s and the lasted period is 10 days (water volume 2.5 109 m3), channel sedimentation on the lower course does not happen;

c. If the silt content is 40~60 kg/m3, the discharge is 4000 m3/s and the lasted period is 11 days (water volume 3.8 109 m3), channel sedimentation on the lower course does not happen;

d. If the silt content is 60~80 kg/m3, the discharge is 4400 m3/s, the lasted period is 12 days (water volume 4.6 109 m3), and there is no bank overflowing on the stretches above Gaocun, channel sedimentation on the lower course does not happen;

e. If the silt content is 80~150 kg/m3, the discharge is 5600 m3/s, lasting 12 days (water volume 5.8 109 m3), and there is no bank overflowing above Gaocun, channel sedimentation on the lower course does not happen; if bank overflowing above Gaocun, but the discharge is 7000 m3/s and the lasted period is 11 days (water volume 6.7 109 m3), channel sedimentation on the lower course does not happen;

f. If the silt content is greater than 150 kg/m3 or belongs to a high silt load flood, the channels of the lower course generally incur severe sedimentation. The characters are bigger water, bigger discharge, bigger sediment in the lower channels. The more water and the higher silt load, the severer sedimentation in the lower channels. There are no clear critical values of water discharge and volume that make sedimentation not happen.

The deposited matter in lower channels is composed of three parts. The first is the coarse sands with particle diameter of greater than 0.05 mm. To stress its attribute, we call them coarse sands which are different from the coarse sand definition of 0.5 mm in soil particle classification. The second is the medium sands with particle diameter of greater than 0.

025 mm but less than 0.05 mm. The third is fine sands with a particle diameter of less than 0.025mm. Statistics show a group of data as follows: the silt load in the lower channels from September 1960 to June 1996 was 38.556 109 t containing coarse sands 8.907 109 t, medium sands 9.536 109 t and fine sands 20.

1 109 t. The sediment of above silt load in the lower channels was a total of 3.622 109 t containing coarse sands 2.935 109 t, medium sands 0.931 109 t and fine sands flushing 0.234 109 t. The sediment of coarse sands occupies 81 per cent of the above total sediment, in other words, coarse sands make up the main part of sedimentation.

Therefore, to reduce sediment efficiently in lower channels we have to consider reducing both the volume of silt load and coarse sands whose particle diameter is greater than 0.05 mm.

4. Creating harmonious relation of water and sediment water and sediment regulation

The alluvial patterns show that non-sedimentation in the lower channels can be completely realized once the unbalanced water and sediment in the lower channels is regulated to be a harmonious relationship. To regulate the unbalanced water and sediment relies on a reservoir with enough storage capacity that holds a source of the lower river course. Xiaolangdi reservoir, which was commissioned at the end of 2001, has a powerful regulation function for the unbalanced water and sediment.

Xiaolangdi reservoir is located at the mouth of the last gorge in the middle river reach, which is a key point for controlling water and sediment in the lower river channels. It controls 91 per cent of the Yellow River runoff and 100 per cent of the river sediment. The storage capacity is 12.65 109 m3, and long-term usable capacity is 5.

1 109 m3. The function of water and sediment regulation can be utilized for a long time. This is because the reservoir has enough storage capacity for water and sediment regulation during early operation, the water storage and silt interception period. After 30 years, when the reservoir s interception capacity has been filled up and turned into a normal operation period, this reservoir still has a usable capacity of 5.

1 109 m3 of which 1.05 109 m3 is prepared for water and sediment regulation.

Based on the alluvial patterns of the lower river channels, the water and sediment regulation operation of Xiaolangdi reservoir can be used in two ways:

a. Utilize three factors of water release silt content, discharge and lasted time

Through the combined operation of water release structures at different elevations, e.g., sediment tunnels, free flow tunnels, water release control factors to create a water and sediment relation suitable for sediment transport in the lower river channel, and to make the most the best possible use of sediment transport per unit of water for non-sedimentation or flushing;

b. Control silt gradation intercepting coarse sands and discharging fine silts

Since fine silts smaller than 0.025 mm can generally be transported to sea, it is not necessary to retard them in reservoir. Conversely, by means of operation choices, to intercept coarse sands that are greater than 0.05 mm and easily deposited is beneficial to both prolonging the operation life of silt interception and reducing sediment.

4.1 Decision of operational way for first testing of water and sediment regulation of the Yellow River

Xiaolangdi reservoir operation is divided into several stages. Firstly, it is water storage, silt interception and sedimentation in dead storage capacity below the starting level. Secondly, it is silt interception by gradually raising flood operational level. This stage is undertaken after the dead storage capacity is fully silted up.

The sediment surface before the dam in operation gradually reaches el. 245 m. The third stage is silt interception with high beach and deep trenches. It, after the beach surface before the dam reaches el. 245 m, will continue to raise beach surface to el. 254 m, then to flush the corroding trenches and lower them to el.

230 m in high flow years. There will appear a sediment profile of high beach and deep trenches. The fourth stage is water and sediment pluriennial regulation by using the trench storage capacity 1.05 109 m3 of the long-term usable capacity of 5.1 109 m3.

Xiaolangdi reservoir just went into operation. Now it is undergoing the stage of water storage and silt interception by dead storage capacity. The reservoir in this period has fairly great impounding volume and uneasily performs the intercepting coarse sands and discharging fine silts . The key of intercepting coarse sands and discharging fine silts , in fact, is only when the reservoir keeps fairly small impounding volume.

If the reservoir does keep such a volume, once water flows into the impounding volume, it roughly shows a feature of free flow silt transport and is beneficial to intercepting more coarse sands and discharging less fine silt. According to this condition, Xiaolangdi reservoir operation in the first testing must control three water release factors.

4.2 Decision of silt content, discharge and lasted time factors

4.2.1 Silt content

Xiaolangdi reservoir, during water storage and silt interception by dead storage capacity, for filling up the dead storage capacity below the starting level, definitely undergoes a period of relatively clear water discharge. During this period, the silt discharge of the reservoir is mainly by density flow.

Average silt transport ratio under different water silt condition is about 10~20%, a fairly small silt content. Therefore, an average silt content of less than 20 kg/m3 of flow-out in the testing has been decided, in view of the threshold value 20~25 kg/m3 of average silt content related to the lower channel alluvium.

4.2.2 Discharge

Statistical data shows the situation with a silt content of less than 20 kg/m3. When the discharge at Huayuankou cross section is 800 m3/s, the flushing of the lower river channels will be extended to Gaocun or above. When the discharge at Huayuankou cross section is 1700 m3/s, the flushing of the lower river channels will be extended to about Aishan.

If the discharge at Huayuankou is 2600 m3/s, the lower river channels are fully in flushing condition, which indicates a critical discharge value. When the discharge at Huayuankou cross section is 3700 m3/s, the flushing of the lower river channels has the greatest efficiency.

For testing it has been decided to confine the discharge at Huayuankou cross section to 2600 m3/s, meanwhile, the discharge at Aishan cross section is 2300 m3/s and at Lijin cross section 2000 m3/s.

There are reasons as follows:

a. As the first water and silt regulation testing, one of the goals is to find out the critical discharge value related to the lower channel alluvium. Previously, vast amounts of observed and statistical data have shown a critical discharge value of 2600 m3/s;

b. Since 1986, the discharge of the main flood in the lower river channels has been smaller than 3000 m3/s. Lower channels, especially the main river channel, have severe sedimentation. The beach discharges of some stretches, e.g., Gaocun or above, have reduced to 3000 m3/s or below;

c. In recent years, despite most river training works, they have not thoroughly improved the river outline with wandering channels on the lower river course. Physical model experiments show that, while Huayuankou cross section discharge is confined at 2900 m3/s, the outlines of some lower stretches change obviously. River training works on some reaches, however, have not undergone medium or great floods. The foundation of these runs a risk and may result in serious consequences.

4.2.3 Lasted time

From Huayuankou to the sea outfall, each cross-section has a critical discharge value of alluvium. If the lasted time of water discharging is too short, it will make the discharge weaken quickly and difficult to provide appropriate flushing discharges for the river reaches below.

Theoretical analysis shows that, while silt content is 20 kg/m3 and release discharge is 2600 m3/s, water current will last 6 days from Xiaolangdi to the sea outfall.

The lasted time originally decided is over 10 days with a release discharge of 2600 m3/s.

There are reasons as follows:

a. The lasted time of 6 days is advanced according to the calculation under the condition of none bank overflowing. Because there have been no great floods on the lower river channels in recent years, long-term small discharge has resulted in severe sedimentation in the main river channel of some reaches, and the beach discharge on some reaches reduces to 3000 m3/s or below.

2600 m3/s may, possibly, result in bank overflowing on some reaches. Therefore, the critical period of 6 days cannot ensure that the silts are carried by artificial flood peak into sea. On the contrary, it probably will result in severe sedimentation in some channels.

b. The storage of Xiaolangdi reservoir at the beginning of testing is at el. 236.42 m, 11.42 m higher than the flood limit of el. 225 m, which means an excess of storage volume 1.46 109 m3. In addition, the forecasted reservoir inflow is 1030 m3/s. If it is 6 days at the release discharge of 2600 m3/s, the reservoir storage level at the end of testing is higher than the flood limit still. If 10 days, at the end of testing, the reservoir storage level is at el.225.52 m. The lasted time of 10 days will make the reservoir level fall to the flood limit or below at the end of testing.

c. There have been 110 floods with silt content less than 20 kg/m3 on the lower river course from September 1960 to June 1996. They lasted a total of 937 days, on the average, 9.4 days for each. There have been 35 with a discharge of greater than 2500 m3/s, they lasted 342 days and flushed sediment totaled 2.158 109 t, on the average, about 10 days for each and the flushed sediment is 0.062 109 t for each.

4.3 Arrangement of measuring sections on Xiaolangdi reservoir and the lower channels

There are 197 measuring sections in the reservoir area, in which 174 sections are for measuring sedimentation, 2 for measuring water and silt factor, and 21 for measuring the funnel before the dam. There are 297 measuring sections from the dam foot to the sea outfall, in which 116 are for measuring sedimentation on the lower river channels and 81 for the topography of the coastal area.

4.4 Experimental process and results

The testing started from 9 o clock on July 4, 2002, with reservoir storage level of el. 236.42 m and the volume of 4.35 109 m3. Xiaolangdi reservoir ended discharging at 9 o clock on July 15, when the level had fallen to el. 223.84 m. Total release water is 2.61 109 m3, in which the compensation water into the reservoir is 1.

59 109 m3 and the compensation water above flood limit is 1.46 109 m3. In testing, the silt load into the reservoir is 0.1831 109 t, the silt load out of the reservoir 0.0319 109 t, and reservoir deposit 0.1512 109 t. Silt transport ratio is 17.4%, consistent with the designed values 10~20%.

4.4.1 Controlling experimental parameters

The average silt content on Huayuankou cross section is 13.3 kg/m3, while the designed value is 20 kg/m3;

Average discharge at Huayuankou cross-section is 2649 m3/s, the designed value 2600 m3/s;

The lasted time is 11 days, the designed value no less than 10 days.

4.4.2 Measuring

a. Reservoir area

w Riverbed sampling: 157 times

w Observation for funnel before the dam: 3 times, with an accumulative length of 90 km

w The accumulative measuring section length is 127 km for one observation of an entire process of density flow.

b. Lower river channels

w Discharge measuring: 310 times

w Water level measuring: 11290 times

w Flood report: 2850 times

w Silt transport ratio measuring: 115 times

w Silt load measuring: 1095 times

w Collected silt samples for grain analysis: 4700

w Wetted cross section measuring: 383

w Riverbed matter samples: 2000

c. Total 5200 thousand groups of measuring data have been obtained.

4.4.3 Experimental result

a. Total flushed sediment is 0.0362 109 t in the lower river channels.

According to the river sections, the section above Aishan flushes sediment 0.0137 109 t, including: the section above Jiahetan 0.0202 109 t, from Jiahetan to Sunkou 0.0082 109 t, from Sunkou to Aishan 0.0017 109 t. The section below Aishan flushes sediment 0.0225 109 t.

According to river beaches and channels, the beaches (only the section from Baihe to Huayuankou and from Jiahetan to Sunkou) flush sediment 0.02 109 t; river channels (entire lower course) flush sediment 0.0562 109 t.

b. Average depth of main river channel flushing

w Jiahetan above 0.16~0.18 m

w Jiahetan to Sunkou 0.24~0.26 m

w Sunkou to Aishan 0.07 m

w Aishan below 0.12~0.16 m

c. Increased discharging capacity of the main river channels

w Jiahetan above 240~300 cubic m/s

w Jiahetan to Sunkou 300~500 cubic m/s

w Sunkou to Aishan 90 cubic m/s

w Aishan to Lijin 80~90 cubic m/s

w Lijin below 200 cubic m/s

d. Adaptability inspection of the river training works

w There is a general trend towards changing well along the reach from Baihe to Jingguang Railway Bridge.

w Because of the incomplete river training works, in spite of a fairly small change of the river profile, the flow route of from Jingguang Railway Bridge to Dongbatou is obstructed, and the unfavorable river outline formed by small discharge for a long time has not been changed.

w Dongbatou below, the river outline is fairly clear and the flow route very stable.

e. Inspection of channel beach discharge

In recent years the inflow has been low, Xiaolangdi reservoir releases only a small discharge to meet the needs of industry and irrigation, which results in sediment and shrinkage of the lower river channels and greatly reduces the beach discharge. Beach discharge in a certain reach could not be easily accessed before.

In the present testing, Huayuankou cross-section average discharge is 2600 m3/s and the lasted time is 11 days, there appears an obviously high water level and bank overflowing along the reach from Jiahetan to Sunkou. For example, the level at Susizhuang cross section is even 0.28 m higher than that of 8/96 flood whose discharge is 6810 m3/s.

The situation of two-step suspended river of the reaches above and below Gaocun is severe, where beach discharge is reduced to about 2000 m3/s.

f. Inspection of flood process time

In the testing, the flood processing time lasted 15 days from the maximum release discharge of 3480 m3/s (10:54 on July 4) to the maximum sea outfall discharge of 2450 m3/s (10:00 on July 19), about twice as long as the ordinary processing time. Ordinarily at the reach from Jiahetan to Gaocun with 1800 m3/s the flood processing time is 30 h.

However, in the testing with 2500 m3/s it is up to 82 hours. At the reach from Gaocun to Sunkou with 1700 m3/s, ordinarily, it is 31 h. But with 2300 m3/s it is 118 h. The reasons are bank overflowing and reclaimed river beaches with great roughness after the long time small discharge flow.

g. Calibration bases of mathematical model and physical model

The present mathematical model and physical model are advanced based on the former statistics data. While the mathematical model and physical model are simultaneously applied in the testing, there appear many inconsistent data between simulation and prototype testing. This implies that it is necessary and possible to carry out parameter calibration for the mathematical model and physical model making use of the valuable data from the prototype testing.

Briefly speaking, the first testing of water and sediment regulation of the Yellow River has achieved its goal. The achievements are not only at the flushing deposit of 0.0362 109 t on the lower river channels but also at the vast amounts of data collected (total 5200 thousand groups). They can give us more knowledge on the riverbeds evolution as well as water and sedimentation patterns of the Yellow River.

Moreover, they can help us reset the mathematical model and physical model to be more consistent with the prototype of the Yellow River. They also help us further understand the complexity and formidability of harnessing the Yellow River.

The testing proves that water and sediment regulation by a reservoir is one of the effective ways of harnessing the Yellow River. The regulation can make non-harmonious relation between water and sediment into a harmonious one, which is quite beneficial to silt transport, reducing river channel sedimentation and even flushing river channels. It is worth further carrying out this kind of testing in future. Surely, most experimental parameters, the operational way of Xiaolangdi reservoir, and so on will take on some new changes.

Source:www.yellowriver.gov.cn Editor: HuangFeng