What are the conditions for ice flood?

There are three conditions for the occurrence of ice flood; Rivers have a certain ice age; Rivers flow from low latitude to high latitude; The time of occurrence is the freezing and thawing period.

Analysis of the conditions for the occurrence of ice flood The natural conditions for the occurrence 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 there are more chances of serious ice flood in the place where the river pattern is wide and narrow. Usually, opening a frozen river and "waking up" is called talking. However, not all river ice is thawed in a gentle way, so that the river can be unblocked. Sometimes the thaw comes quickly, especially when the temperature rises sharply or the water level rises sharply, and large pieces of ice surge down, which is easy to cause ice flooding.

Scientists have given interesting names to these two ways of opening rivers. For slow thawing, it is called "Kevin River", and for rapid thawing, it is called "Wukai River". It is not difficult to see that the flow direction of the river from south to north is a specific geographical factor that causes the "Wukai River". In winter, the downstream temperature drops early and freezes first. After the downstream icing, the ice layer has the function of blocking water, and the cross section of water decreases, which affects the discharge capacity. In this way, part of the water is trapped in the upstream channel, and the water level rises accordingly. In spring, the temperature rises early in the upper reaches of low latitudes, and the river starts from top to bottom. When the ice water from the upstream spreads to the downstream, it often gets stuck in a narrow river or bend, while the hard and thick ice layer that is still sleeping downstream makes the ice accumulate horizontally along the river, just like a river dam (called an ice dam), which intercepts a large amount of ice water and makes the water level rise rapidly, leading to flooding. Ice depends on water, and water helps ice. The ice outpost is like a giant bulldozer, which is unstoppable and will seriously damage the downstream dike and its nearby buildings and cultivated land, especially the ice poses the greatest threat to the pier. Therefore, from the point of view that the edge of ice flood is warmer from downstream than upstream, ice flood often occurs in late winter and early spring. In China, the Yellow River and some big rivers north of it are likely to have ice flood in late winter and early spring.

The upper reaches of the Yellow River extend from Ningxia to Inner Mongolia, and the lower reaches of the Yellow River enter the sea in Shandong. Due to the northward flow of the reach, ice floods often occur. During the 63 years from 1875 to 1938, there were 74 ice floods in the Shandong section of the Yellow River, which caused great disasters to people on both sides.

Songhua River is the second river with ice flood in China. Ice dams appear almost every year below Yilan County, and 30%-50% of the highest water level over the years occurs during the ice flood.

It is not difficult to see that the change of temperature is the fundamental reason for the formation of ice flood. Therefore, making a good weather forecast and preparing for the prevention of ice flood in advance according to the forecast can reduce or avoid the losses caused by ice flood.

What is the reason for the flood of ice? 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 channel is wide and narrow, so there are more opportunities for serious ice flood where the river channel bends into a ring. This is because the lower section of the river freezes earlier than the upper section, and the upper section thaws earlier than the lower section. And the thickness of the ice sheet is thicker in the lower section and thinner in the upper section. 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. In short:

1, ice age river. (especially rivers below zero)

2. From the lower latitude to the higher latitude, there is an obvious north-south flow direction. The Yellow River in China has ice flood in Ningxia and Shandong, and the rivers in the northeast will also have ice flood when the above conditions are met.

The occurrence of ice flood is closely related to the geographical location of rivers. Generally speaking, the higher the latitude of the river, the greater the possibility of serious ice flood. According to statistics, the probability of serious ice flood in the river north of 50 N in Russia is 80%, and the basin area exceeds 654.38+10,000 km. The latitudes of Luogu hydrological station in the upper reaches of Heilongjiang and Yilan hydrological station in Songhua River are 53 27' N and 4618' n, respectively. According to the data of 26 years, the probability of severe ice flood in the former is 67%, and that in the latter is about 50%. At the same time, the river flows from low latitude to high latitude, which is an important factor of ice flood. The upper and lower reaches of the Yellow River in Runing (Ningxia) and Inner Mongolia all flow from low latitude to high latitude, and the latitude difference between the upper and lower reaches is 4 37 ′ and 3 00 ′ respectively. Ergon River, a tributary of Heilongjiang, flows from the source of the river to the estuary where it joins Heilongjiang, with a latitude difference of about 7. After the river thaws, it branches first and then dries up, and "Wukai River" often appears. The Elbe River in Europe also flows from low latitude to high latitude, and ice dams often appear in Hamburg, Germany, just downstream, causing disasters. In some mid-latitude areas, the strong cold wave process also has a great influence on the ice flood. For example, during the flood season in the lower reaches of the Yellow River 1968~ 1969, the daily average temperature rose and fell four times on the basis of about 0℃, resulting in three times of freezing and three times of thawing. On the eve of river thawing, a heavy rainfall will also accelerate the melting of ice, leading to rapid thawing and rapid release of river water, forming Ling Feng.

River morphology has a great influence on ice flood. The river section with narrow bend, many beaches in the middle of the river, gentle longitudinal slope of riverbed and large bend radius is easy to get stuck in ice and raise the water level.

The amount of ice flowing in the river is also the main factor to form the ice flood. According to statistics, ice flood rarely occurs in rivers with ice flow below 100 m/s, and the change of ice flow is mainly manifested in the increase of water storage capacity in the channel, which is an important factor for the Ling Feng. Once there are suitable temperature conditions, it is easy to produce Ling Feng, form ice dams and cause disasters.

Ice flood can be divided into melting flood, ice jam flood and ice dam flood according to the causes.