An example of ice flood

The section from the Yellow River to Lanzhou is the first end of the upper reaches of the Yellow River. Although the climate is cold and long, because the Yellow River passes through the mountains of the Qinghai-Tibet Plateau, the river slopes in different reaches are very different and the flow velocity changes greatly. Therefore, some river sections have both ice and frozen; Part of the river can only flow ice, but not freeze; Other river sections are often frozen under natural conditions, but after the completion of the reservoir, the thermal and hydraulic conditions have changed, resulting in many ice jams in the upstream of the reservoir, and the downstream of the reservoir has changed from freezing to thawing.

The reach from the Yellow River to Maqu is 9 1 1.6 km long, and the first glacial period usually occurs from the middle of 10 to the late of1/0/year, and the earliest is August 2 1 year (1960 The final ice date is generally from early April to late May of the following year, and the latest is June 29th (1956). It is the longest frozen section of the whole river. For example, the average freezing time of stations along the Yellow River is 160 days, the longest is 193 days, and the shortest is 128 days. The maximum ice thickness in the middle of the river is1.28m, and the average ice thickness is 0.93m.. The average freezing period of Maqu Station over the years is 105 days, with the longest being 1 18 days and the shortest being 95 days.

The 726-kilometer-long Maqu-Xunhua reach can only freeze because of the great hydrodynamic effect. The first glacial period occurred in late October of 165438+ 10, and the last glacial period occurred from late February to early March.

The total length of Xunhua-Lanzhou section is 2 1l km, and the first ice date generally appears in late October (1 1), and the last ice date is late February. In winter, due to the sudden drop of temperature, the density of flowing ice increases rapidly, and local freezing occurs over Lanzhou, and it often freezes near Lanzhou section. In the early 1960s, before the completion of the Yanguoxia Reservoir and Liujiaxia Reservoir, there were several serious ice jam disasters in Ada. The Lanzhou section below Yanguoxia Reservoir is not frozen, but there is sparse water flow. After Liujiaxia Reservoir 1968 was put into operation, due to its regulation of heat and water quantity, the ice flowing into the reservoir upstream was melted, and the water temperature discharged from the reservoir in winter was as high as 3 ~ 5℃, so there was no ice flow and freezing in Lanzhou reach. The Ningxia section of the Yellow River, with a total length of 397 kilometers, flows from south to north from the south long beach in Zhongwei County to the grasshopper ditch in Shizuishan. Heishan Gorge to Zaoyuan 135km is the canyon reach, and the river surface is 200 ~ 300 m wide. Because of its steep slope and fast current, this river can only be closed in cold winter, so it is called an ice-free reach. Zaoyuan is more than 260 kilometers below, and the river surface is 500 ~ 1 000 meters wide. Because of its gentle slope, low speed and low temperature, it is a normal frozen reach. In the cold winter, it is sealed to the downstream river, and in the warm winter, it does not exceed the jujube garden.

After Qingtongxia and Liujiaxia reservoirs were put into operation one after another, due to the increase of flow and water temperature in winter, the unsealed reach extended from Zaoyuan to Xintian for more than 20 kilometers. There is an unfrozen reach of 40 ~ 90km below Qingtongxia Dam, and the unfrozen reach is still below Panchang 100km above.

The flood disaster in Ningxia reach is not serious in general, but it can be caused by ice jam in some reaches under special circumstances.

Three ice jams and backwaters occurred continuously in the reach from Shikong to Zaoyuan in Zhongning County, 45 kilometers above the dam of Qingtongxia Reservoir, during the winter solstice of 1967 and the spring of 0968. The length of the ice jam is 16 km, the thickness of the ice sheet is 0.4 m, and the thickest ice flower under the ice sheet exceeds 1 m ... The maximum backwater level of the ice jam is 1.3m higher than the corresponding water level of 5240 m3/s in the normal season, resulting in ice flood disaster. The causes of the disaster are: first, a large amount of ice came from the upstream, and a steady stream of ice came from top to bottom, forming an ice jam in the Shikong reach; Second, after the river was cut off, the upstream inflow surged. On February 6th, 1967, 1967, the diversion tunnel gate of Liujiaxia Reservoir in the upper reaches of the Yellow River failed, and the flow increased by 300 ~ 750 m3/s compared with that when it was intercepted, which caused the water body above Shikong to burst, and a large number of floating ice swooped up and down in the jujube orchard, forming a serious ice jam. Third, the high water level in Qingtongxia Reservoir prevented the flowing ice from flowing down. From the end of February to the middle of1October, the water level of Qingtongxia Reservoir was 1967+ 1968, which was13m higher than the natural water level. Therefore, the ice jam can't move down, resulting in the flood disaster of ice jam in the reach from Shikong to Zaoyuan.

Ice disaster in Inner Mongolia

The Inner Mongolia section of the Yellow River, located at the northernmost part of the Yellow River, enters from Shizuishan City, Ningxia, Laseng Temple, Yikezhaomeng, Inner Mongolia, and exits from Mazha elm bay, Zhungeer Banner, Yikezhaomeng, with a total length of 840 kilometers and a total drop of only 162.5 meters. Although located in the upper reaches, the river slope from Zhaojun Tomb to Toudaoguai is close to the Yellow River estuary. The Yellow River is located in Inner Mongolia, with few tributaries and seasonal rivers of rain and flood, and almost no water supply during the ice age. Therefore, most of the water from Inner Mongolia during the ice age came from Lanzhou.

Inner Mongolia is located in the northernmost part of the Yellow River Basin, with an altitude of 1000 meters. It's far from the ocean, so it's difficult for warm air to reach. Often controlled by Mongolian high pressure, the continental climate has obvious characteristics. Winter is cold and long, and the temperature below zero lasts for 4-5 months, and the lowest temperature can reach 35℃ below zero. The freezing period of this river is 4-5 months, and most of them are stably frozen. Because the temperature in the upper reaches of the river is high in Gansu and Ningxia and low in Inner Mongolia from south to north, the river reaches its source, and the thawing and opening of the river is gradually developed from Gansu and Ningxia. Under natural circumstances, the freezing time of the river in Baotou, Inner Mongolia is often more than 20 days earlier than that in Lanzhou, but the thawing opening time is more than one month later.

In winter, the river flow in Inner Mongolia is generally above 400 cubic meters per second. The temperature in this section is low, the ice layer is thick, the flood peak is cracked, and a large amount of flowing ice is produced. In addition, due to the action of river regime, flowing ice blocks and dams intensively, which makes the water level of the river suddenly crack and rise, which easily leads to dike breach and flood.

According to incomplete statistics, during the thawing period in Inner Mongolia, disasters of different degrees occurred every year in history, once every two years on average. After Liujiaxia Reservoir 1968 in the upper reaches of the Yellow River was put into operation, the ice age adjusted the water quantity and heat of the river, significantly changed the ice flood in Inner Mongolia and greatly reduced the disaster. However, the situation of ice flood is complicated and there are many influencing factors. Under special circumstances, there is still the possibility of a major ice flood disaster, and the threat of ice flood in the Yellow River has not been completely lifted. Because the upstream reservoir is too far away from the downstream reach where the flood is serious, the operation of the upstream reservoir can not fundamentally alleviate the flood threat in Inner Mongolia, nor can it completely cut off the water supply during the thawing period according to the water demand of industrial and agricultural production. Moreover, the storage capacity of the reservoir is limited, so it is impossible to store water for a long time. Therefore, at this stage, it is necessary to comprehensively use a variety of anti-icing measures to alleviate or avoid the occurrence of ice disasters. The Yellow River, from Taohuayu in Henan to the estuary, is called the lower reaches, with a total length of 786 kilometers. Embankments are built on both sides and flow into Bohai Sea in Kenli County, Shandong Province. The lower reaches of the river are wide at the top and narrow at the bottom, and the river runs southwest and northeast. In winter, it is often attacked by cold waves. The daily average temperature of the upstream and downstream is between 3℃ and 4℃, which appears alternately. River flow is generally 200~400 cubic meters per second. Due to natural conditions such as river course, meteorology and hydrology, there is ice flood in the lower reaches every year, and ice jam and river closure often occur. Since the founding of New China, the river has been closed for more than 30 times, mostly from the mouth of the river and then gradually upward. Generally speaking, the total length of freezing is about 400 kilometers, the shortest is 40 kilometers and the longest is 703 kilometers. When the river is opened from top to bottom, ice water accumulates along the river, forming an obvious Ling Feng, which is easily blocked in shallow, sharp or narrow reaches, forming an ice dam, which makes the water level in the reach rise rapidly, threatening the safety of dikes and even causing ice disasters.

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. According to incomplete historical statistics, during the 54 years from 1883 to 1936, there were 2 1 year ice floods, with an average of two breaches in five years. Even in the early days of the founding of New China, there were still two breaches in the mouth of Shandong Province in the lower Yellow River. There is a saying in history that "the flood season is easy to rob, but the ice season is difficult to prevent" and "the ice season is broken, and the river official is innocent". After the founding of New China, the people in the lower reaches of the Yellow River, under the leadership of the Party and the government, overcame many severe ice floods, reversed the sinister situation of two breaches in history in five years, and made great achievements for 49 consecutive years.