What is Prototype Water and Sediment Regulation?
Prototype water and sediment regulation means to control and regulate the water and sediment effectively, to store and discharge in time, to regulate the natural water and sediment process, to turn the improper water and sediment process as harmonious as possible so as to transport silt and reduce the sedimentation of the lower channel to stop the riverbed from rising.
Why Conduct the First Prototype Water and Sediment Regulation Experiment of the Yellow River?
The main problem is the insufficient water and excessive sediment and the disequilibrium between water and sediment. The soil erosion on the Loess Plateau results in the sedimentation on the lower reaches of the Yellow River and the riverbed rises 0.1m per year, thus making the Yellow River a suspended river. Generally the riverbed is 3-5m above the ground and in some places, it can be as high as 10m. The frequent breaches of the lower reaches of the Yellow River and the damage in history had a close relationship with the suspended river . For a long time, the Yellow River will still be a river with much silt. Owing to the storage of the upper reaches reservoirs, the increased use of water for the upper and middle reaches agriculture, the contradiction of insufficient water and excessive sediment becomes more serious, the riverbed will be raised with sedimentation, the flood control situation will be more demanding. So it has been an urgent problem to deal with the sedimentation of the lower reaches of the Yellow River.
During the harnessing of the Yellow River, especially in its application in the Sanmenxia Project, people further realize that it plays an important role to build a series of large reservoirs on the Yellow River, to have a centralized dispatch for the effective control and regulation, for the reduction of the sedimentation on the lower channel, and for the prevention of the elevation of the riverbed and eventually for the safety of the river. So, we put forward the idea to harness the Yellow River by Prototype Water and Sediment Regulation in the Xiaolangdi Reservoir. The experiment is a great attempt to put this theory into practice.
Scientific Foundations for Prototype Water and Sediment Regulation
While studying the silt-transport features of the lower course, people found that in certain riverbed boundary, the silt carrying capacity in water is in direct ratio with the flow square and it has something to do with the silt content in the runoff. That is, in certain riverbed boundary and the unchanging runoff conditions, the more silt load in the runoff, the larger silt transport in the cross section in a certain time, and vise versa. It shows more silt load on the lower course, more silt discharge, less silt load, less silt discharge. The outstanding trait of the Yellow River is insufficient water and excessive sediment and the disequilibrium between water and sediment. So, the construction of reservoirs on the Yellow River should regulate both the main channel and the silt in order to have a good relation between water and silt and achieve a better effect for the discharge and reduction of the silt. It is the scientific foundation for Prototype Water and Sediment Regulation.
Some Schemes for the Prototype Water and Sediment Regulation Experiment
Prototype Water and Sediment Regulation has the following plans: (1) man-made flood peaks. The silt carrying capacity of water is nearly in direct ratio with the square flow. The natural runoff is regulated by reservoirs and discharged in the centralized form with a larger flow, and man-made flood peaks can be formed. This can improve the scouring capacity of the riverbed greatly. (2) Block the course sand and discharge the fine. Particles of less than 0.025mm in diameter on the lower reaches of the Yellow River can be transported into the sea generally and have little influence on the sedimentation. If we can block the course sand (larger than 0.05mm) that is harmful to the lower course by making reasonable use of the reservoirs, then the effect of the sedimentation reduction of the lower course can be increased by more than 50%. (3) Sediment regulation by detention. That is to discharge the silt of the non-flood season in the flood season and discharge the silt of the disadvantageous years with more silt in the advantageous years with less silt. (4) Store the clear water and discharge the sandy water. That is, the reservoirs store water and block the silt in flood season and lower the water level to discharge flood and silt.
Purpose of the Prototype Water and Sediment Regulation
Prototype Water and Sediment Regulation is an important project that marks the changes of the harnessing and regulating measures of the Yellow River. Its purpose is to have a reasonable water-silt process when the reservoir begins its actual performance, which is beneficial for the reduction of the sedimentation on the lower reaches. Through the observation and analysis of the prototypes, check the reasonability of the regulation standard in order to gain experience for improvement and have an application of the Prototype Water and Sediment Regulation centered on flood control and reduction of sedimentation. Meanwhile, the reduction of the sedimentation of the lower course by the application of the Prototype Water and Sediment Regulation of the Xiaolangdi Reservoir, the steady survey of the application of the 4-reservoir combination can stabilize the present river course for a long time, and prevent the riverbed from rising.
The Application of the Prototype Water and Sediment Regulation of the Xiaolangdi Reservoir on the Yellow River
According to the early application of reservoirs, we have two ways, i.e., gradual storing and central discharge and timely discharge the big flood to make flood peaks. Since the reservoir has a large capacity in the early 3-5 years and the silt transport mainly relies on the density flow, the Prototype Water and Sediment Regulation to a large extent lies in the regulation of the water. The regulation of the silt load lies in that when the upper and middle reaches areas have large runoff and silt content, control appropriately the applied water level before the dam and set the order of the discharge projects and dispatch the storage and discharge of the fine sand applied before the dam in the form of density flow.
The Important Positions of the Xiaolangdi Reservoir
Xiaolangdi Multi-purpose Project is located at the down-mouth of the last valley of the main course of the Yellow River. It is 130km away up from Sanmenxia Dam, 115 km down from the Zhengzhou Railway Bridge, over 30 km from Luoyang City in Henan Province. Its dominated drainage area is 694,000km, which takes up 92% of the total. It plays an important role in regulating the silt in the upper and middle reaches of the Yellow River. It is the only place on the main course of the Yellow River that can have a large storage of water from Sanmenxia downward, and it s also the only place that can be used to prevent flood, ice, sedimentation and for water supply, irrigation and generation of electricity. The Xiaolangdi Reservoir has a good effect for flood control and reduction of sedimentation. Its combined application with Sanmenxia, Luhun, Guxan Reservoir can raise the flood control standard up to once a thousand years from our present once a hundred years. It is not necessary for us to use the Beijindi Detention Area and thus get rid of the losses of 167,000 hectares of cultivated land and 1,400,000 people and Zhongyuan Oil Field in the area. It also plays a role to smooth other flood peaks, to lessen the flood control pressure downward Huayuankou and avoid the threat caused by the ice flood on the lower reaches. The total storage of the Xiaolangdi Reservoir is 126.5billion m , the consistent effective storage is 51billion m . It can block large quantity of silt and prevent the riverbed from elevating within 21 years. The large storage of Xiaolangdi reservoir can increase the quantities of water supply and soften the contradiction of water shortage caused by zero-flow of the lower reaches of the Yellow River. The power output of the Xiaolangdi Hydropower Station is 1,800,000kw and the annual average is 58.4billion kwh. It is quite effective for the generation of electricity and irrigation.
The Advancing of the Principle of Prototype Water and Sediment Regulation
The advancing of the principle of the Prototype Water and Sediment Regulation experienced a long process. It can be traced back to the 1940s. American scholar suggested in his preliminary report of harnessing the Yellow River in 1946 to control flood and generate electricity with Balihutong Reservoir, to build silt-discharge projects at the bottom of the dam and make empty silt discharge every year so as to reduce the sedimentation on the lower reaches of the Yellow River. When the silt problem in Sanmenxia Reservoir became apparent in the 1960s, the idea of re-regulating the silt with the Xiaolangdi Reservoir was suggested. In the later 1970s, the limitation of blocking on the upper course and discharging on the lower and the application of Sanmenxia Reservoir made people realize the important roles of the sedimentation on the lower reaches of the Yellow River caused by insufficient water and excessive sediment and the disequilibrium between water and sediment. The principle of the Prototype Water and Sediment Regulation was advanced once again. They assumed to build a series of large reservoirs on the Yellow River to dispatch and regulate the water and silt effectively, to change the disequilibrium between water and sediment, to discharge the flood and silt into the sea and to reduce even get rid of the sedimentation of the lower channel. Owing to the important position of the Xiaolangdi Reservoir and the demonstrations of many scholars and the hard work of the Yellow River Conservancy Commission and the officials concerned, they decided to build the Xiaolangdi Reservoir to conduct the experiment. On Jan. 1987, the State Council ratified the design of the Xiaolangdi Multi-purpose Project, which made a further step forward toward the harnessing of the Yellow River. After the construction of the Xiaolangdi Reservoir, through much research and practice in various ways, it is playing a very important role in the Prototype Water and Sediment Regulation.
Basic Principles of Prototype Water and Sediment Regulation
The basic principle of the Prototype Water and Sediment Regulation is to control the time and quantity of storage and discharge of the reservoir in a planned way, regulate the natural water and silt process, change the disequilibrium between water and sediment as harmonious as possible according to the capability of sand transport and the regulated storage of the reservoir. To be more specific, it means to shut the dam to store water and stop the discharge of the clear water and sedate some silt in the reservoir when the runoff of the coming water is less than 2,500m in the main flood seasons (July-September), and when the runoff is more than 2,500m , open the dam and discharge water and silt by making flood peaks to increase the scouring of the river channel to improve the riverbed, to increase the height difference and the flood-discharging and silt-transmitting capacities of the beach channel, to reduce the sedimentation of the lower reaches, and to regulate the runoff with the storage of the reservoir in the non-flood seasons to satisfy the need of water supply and the irrigation and increase the output of electricity.
Source:www.yellowriver.gov.cn Editor: HuangFeng
