Elaborate on the ice in the lower reaches of the Yellow River
Since June, 5438+February, 2002, affected by two strong cold air, the lower reaches of the Yellow River have been closed twice. The first temperature drop was 65438+February 8 ~ 65438+March 3, and the first interception was made at Kenli 14 km on February 9. 65438+February 1 0.25km in February, the longest interception10.25km, and the upper end of interception is located at Yihe Dangerous Works1Dam in Kenli County. With the temperature rising, all the ice melted on June 5438+February 65438+February 8.
The second time, from 65438+February 22nd, the low temperature continued in the area along the Yellow River in Shandong, with the lowest temperatures in Heze, Jinan and Binzhou reaching-12℃,-1 1.6℃,-14.2℃ and 65438+February respectively. In the early morning of the 24th, the second river closure occurred in the estuary this year, and the number and length of river sections increased rapidly. By June 3rd, 2003, the 73rd section of the Yellow River in Shandong Province was 223.5km long, and it was first intercepted at 0.5km of No.9 Dam of Weizhuang Extension Project in Yuncheng County, Heze City. The freezing form is mostly flat sealing, with ice thickness of 3- 10 cm and maximum 15 cm. The ice thickness of Mo Lifeng reach is generally 7- 15cm, and the maximum ice thickness is 30cm. According to the temperature forecast, the temperature will continue to be low in the next few days, and the ice situation may develop further.
The closure of the lower Yellow River is a normal phenomenon. However, because the flow of the Yellow River during the ice flood this year is only about 28.6 cubic meters per second, the daily water supply flow to Tianjin is about 90 cubic meters per second, the flow below the mountain gate in Liaocheng is even smaller, and the flow at Lijin Station in Hekou is about 30 cubic meters per second. To ensure the safety of the Yellow River against ice and supply water to Tianjin, the Yellow River keeps flowing, which is very contradictory and difficult to control ice. According to the risk dispatching plan for ice flood prevention formulated before the ice flood, the Yellow River Flood Control Headquarters strengthened the water dispatching for ice flood prevention. Shandong River Affairs Bureau carefully analyzes the development and changes of water regime and ice conditions, and carefully dispatches floodgates to divert water, so as to ensure the smooth progress of water diversion from the Yellow River to Tianjin and the basically stable flow of Lijin Station. Although there are still some unfavorable factors, as long as observation and dispatching are strengthened, major disasters will generally not occur.
According to the requirements of the Yellow River Defense General, the provincial party committee and the provincial government, all levels along the Yellow River in Shandong Province are actively preparing for ice prevention. The province * * * organized 450,000 people in the Yellow River ice, 902 people in 25 ice blasting teams and 432 people in the10/ice observation group; Targeted anti-icing technical training was carried out; Revised and improved the yellow river ice plan; Measures to prevent ice jam during the period of diverting water from the Yellow River into Tianjin were formulated. Check and confirm the materials of anti-icing tools. At the beginning of June165438+1October, the provincial flood control office made a comprehensive deployment of flood control work. Since then, the provincial Yellow River Flood Control Office has issued five notices, which put forward further requirements for flood control work such as ice observation, water transfer and dispatching, pontoon bridge management, and water diversion from the Yellow River to Tianjin, and sent personnel to various places for inspection and guidance.
At present, the Yellow River affairs departments at all levels in Shandong Province have stepped up the duty of ice prevention, paid close attention to the development and changes of temperature, water regime and ice conditions, earnestly observed, analyzed and predicted the ice conditions (the river affairs departments participated in the observation and analysis of ice conditions for nearly 700 times every day), strictly controlled the diversion of water from culverts and gates, strengthened the management of pontoon bridges, assembled professional mobile rescue teams to stand by and prepare for ice blasting and defense and rescue. Once the floodplain is flooded and the dike safety is threatened, the Yellow River professional team and the mass flood control team will go to the dike to defend and rescue in time to ensure the flood control safety of the Yellow River.
The ice flood and ice flood situation of the Yellow River in history.
Historically, the ice flood in the lower reaches of the Yellow River is famous for its frequent breaches, serious harm and difficult prevention and control. Because of the latitude difference between the upper and lower reaches of the Yellow River, the upper reaches are wide and the lower reaches are narrow, and the temperature and flow change greatly, the ice situation in the lower reaches of the Yellow River is complicated. Since the people ruled the Yellow River, they have overcome many serious ice floods and reversed the sinister situation of two decisions in five years in history.
According to incomplete statistics in history, in the 54 years of 1883- 1936, there are 2 1 year in flood season, with an average of two breaches in five years. 195 1 and 1955 also burst due to serious icing, weak dikes and lack of experience. During the 40 years of 1950- 1990, it was frozen for 36 years (the river channel was not closed in 1952, 62, 65 and 75 years), of which it was frozen for 27 years below Lankao. The first one reached Siyi estuary in Xingyang, with a freezing length of 703km( 1969), and the shortest one was only sealed to Kenli 18 households, with a length of 25. 1km, with an average freezing length of 3 17km for many years and a maximum ice volume of140. The thickness of the ice sheet is generally 0.3-0.5m in the coastal reach and 0. 1-0.2m above Lankao. The earliest freezing date is 65438+February 12 (1972), and the latest is February 16 (1978), with an average of 1 March 3rd. The earliest thawing date is 1 4th of month (1989), and the latest is March18th (1969), with an average of 24th February. Generally, the Ling Feng flow of rivers increases gradually from top to bottom, with the maximum of 3430m3/s (Lijin Station, 1957). In freezing years, it is generally frozen and thawed once, and in some years it is frozen twice or thawed three times.
The lower reaches of the Yellow River belong to unstable frozen reach, and the change of ice conditions is much more complicated than stable freezing. This is mainly due to the specific geographical location, different river types, temperature and flow combinations in the lower reaches of the Yellow River. The longitudinal gradient of the estuary is small, and the bar sand is often formed due to the influence of tides. Generally, the river pattern is dispersed, with small flow and multiple streams flowing into the sea. Therefore, after the river flows in the cold season, a large amount of ice cannot be discharged freely, and it is easy to insert into Lingfeng River. Below Taochengbu in the lower reaches of the Yellow River, the rivers are mostly arc-shaped, with L-shaped and S-shaped sections. When the water flows through these sections, it is easy to form ice jam, backwater or ice due to the narrow bend of the river and the disorder of water flow potential.
As the lower reaches of the Yellow River flow from southwest to northeast, the latitude gradually rises, while the upper reaches of the Yellow River are cold late and warm early, and the duration of sub-zero temperature is short. The downstream is cold early, the temperature rises late, and the temperature below zero lasts for a long time. The corresponding ice change rules are: the upstream river channel is frozen late, thawed early, frozen for a short time and the ice is thin; The downstream freezes early, thaws late, freezes for a long time, and the ice is thick. The change of flow rate is closely related to ice conditions. The middle winter discharge of the lower Yellow River (65438+February to February of the following year) is the smallest, and the low water discharge is in the low temperature period, which is easy to freeze. After sealing, the underwater flow section is small. When the river starts, the upper part opens first, and the ice water flows together, which causes the lower part to burst and form the "Wukai River". At this time, ice jam, ice dam and other dangers are prone to occur. 90% of the downstream water comes from Sanmenxia in winter, and the downstream flow can be changed by using Sanmenxia Reservoir in ice season. According to the understanding of ice conditions and the experience of reservoir operation in recent decades, generally speaking, the flow rate of the downstream river is 500m3/s when it is intercepted, and it can be controlled between 300m3/s and 400m3/s during the freezing period. During the river opening period, according to the temperature forecast, considering the distance from Sanmenxia to Shandong, pay attention to the opportunity to gradually increase the flow.
What are the causes and hazards of ice flood?
Ice flood is a phenomenon that the water level of the river rises obviously due to the resistance of ice to water flow. The natural conditions of ice flood depend on the geographical location and channel shape of the river. In the alpine region, the river flows from low latitude to high latitude, and the shape of the river is wide and narrow at the bottom, so the probability of serious ice flood increases where the river bends and bends. This is because the freezing time in the lower section of the river is earlier than that in the upper section, and the thawing time in the lower section is later than that in the upper section. Moreover, the ice layer is thicker under the thickness and thinner at the top. When there is ice in the lower reaches of the river, part of the upstream water flow is blocked, which increases the water storage capacity of the river. When the ice melts to open the river, the water storage capacity of this river is released sharply, and the Ling Feng descends, and the ice water gathers more and more along the way, and the ice peak increases. When the ice water from the upstream spreads downstream, it will get stuck in a narrow reach or where the river turns, forming an ice dam, thus increasing the water level in the upstream. The severity of ice flood depends on the influence of river ice on water level. Usually, the water level will rise sharply only after serious ice or ice dam appears in the river, causing serious ice flood.
Ice flood has three main hazards:
First, the flood hazard caused by ice jam. It usually occurs in the freezing period, mostly at the backwater end of the reservoir with large slope change and relaxation, which lasts for a long time and the water level rises gradually, which is harmful to engineering facilities and human beings.
Second, the flood hazards caused by ice dams. Usually occurs during thawing. Most of them occur in the river sections with large differences between north and south latitudes, and the formation speed is fast. After the formation of the ice dam, the upstream water level of the ice dam rose sharply, the dike burst and the flood flooded.
Third, the harm caused by ice pressure. Ice pressure is the force that ice directly acts on buildings, including the dynamic pressure caused by the impact of flowing ice, the static pressure transmitted to buildings by wind and water shear on a large area of ice sheet and the static pressure caused by the expansion of the whole ice sheet. 1February, 929, the ice dam in Lijin County, Shandong Province blocked the river, causing a breach and flooding more than 60 villages in Lijin and Zhanhua counties.
What anti-icing measures are there?
The prevention and control measures of ice disasters are constantly improved on the basis of understanding the evolution law of ice conditions. Before the founding of the People's Republic of China, anti-icing measures were relatively simple. When ice blocks the river and floods the embankment, people are organized to defend the embankment. After the founding of People's Republic of China (PRC), the change law of ice flood was observed and discussed. With the increase of various anti-icing projects, anti-icing measures have been significantly improved in theory and practice, which has played a great role in ensuring the safety of ice flood.
In the 1950s, the main anti-icing measures were to break the ice during the river opening period, and to break the ice once the ice dam was formed before the river opening or in the narrow and curved river section where ice dams might occur. The methods of breaking ice include breaking ice, spreading soil, rocking ship (icebreaker), explosive blasting, shelling and plane bombing. When breaking the ice, the timing of breaking the ice should be selected according to the ice forecast and the icing condition of the river. It is also necessary to choose the ice-breaking river section and predict the river sections that may form ice plugs and ice dams. No icebreaking measures shall be taken in river sections with wide river and wide beach and high position. This simple method of breaking ice is passive and difficult to achieve the expected purpose. After the 1960s, summing up the experience of ice prevention over the years, we gradually realized that the main cause of ice disaster was water, and controlling the water storage capacity of the river during the river opening period was an effective way to prevent ice.
First, use reservoirs to prevent icing. First, control the river flow and reduce the threat of downstream ice flood; Secondly, the temperature of the discharged water from power generation in the reservoir rises, which affects the river course at a certain distance downstream of the reservoir and prevents it from freezing.
Second, break the ice. There are many methods, mainly including explosive charge, icebreaker, shelling, plane bombing, artificial ice beating and so on.
Third, divide water. Part of the water blocked by ice and stored in the river will be discharged in a planned way through coastal sluice or water diversion project to avoid ice water flooding. There are more than 70 sluices in the lower reaches of the Yellow River, which have certain water diversion conditions. For culvert gates that can divide water, it is necessary to choose a good outlet, make preparations in advance, and arrange drainage channels. Water diversion should be combined with spring irrigation as far as possible to achieve the goal of eliminating pests and promoting benefits simultaneously. However, the drainage holes of the Yellow River Diversion Project are generally small. Due to the influence of river regime and ice conditions, whether water can be divided as required in an emergency is of little guarantee rate.
Fourth, observe ice conditions, hydrology and meteorology. In order to master the development and change of river ice, study its development trend and take anti-icing measures as soon as possible. Since 1950s, the lower Yellow River has gradually established and improved the ice prevention observation system and specification requirements.
Fifth, strengthen defense. According to the requirements of flood control, establish and improve the anti-icing headquarters at all levels before the flood season, organize various anti-icing teams, and prepare anti-icing tools, materials and lighting equipment. After Lingshui leaned against the embankment, it was ordered to go to the embankment to defend.