Flood Formation, Types, and Flood Disasters in China

First, how is the flood formed?

Flooding (flood) by the heavy rains, flash melting of snow, ice, or a rapid increase in the water level rose rapidly in the amount of sea water phenomenon rivers, lakes, storm surges and other natural causes, often submerged embankment beach, even diffuse embankment flooded.

The word "flood" was first seen in China's "Book of Shu". According to legend, during the Yuxia period (around the 20th century BC), there was a continuous flood in the Yellow River valley. The book records that: “ Tang Tang flooded and cut the hills and hills, and it was a vast expanse of land, and it was under the masses . ” The floods of Haotian submerged the vast plains and surrounded the hills and hills. The floods returned year after year and brought untold suffering to the people.

The elements describing the flood include the peak discharge (water level), the peak discharge (level), the total flood volume, and the flood course. When runoff from heavy rain or melting snow occurs in the basin, they are gathered together at the exit section of the river channel. When the nearby runoff arrives, the flow of the river begins to increase and the water level rises accordingly, at which point the flood rises. When most of the high-intensity surface runoff is collected in the export section, the maximum flow of river water is called the peak flow, and the corresponding maximum water level is called the flood peak level. At a certain time after the rainstorm stopped, when the surface runoff of the river basin and the amount of water stored in the ground, surface soil and river network all flowed out of the outlet section, the river flow and water level fell back to the original state. The curve connecting the entire process of the flood rising from the peak to the fall is called the flood process line, and the total amount of water flowing out is called the total amount of flood.

Second , how to quantitatively describe the flood?

Due to heavy rain, drastic melting of snow, reservoir dams, storm surges, etc., rivers, lakes and oceans have increased their water flow or the water level has risen above a certain limit, threatening people’s lives and property or causing differences The degree of disaster, this natural phenomenon, is generally called a flood. The indicators for quantitatively describing floods include peak discharge, peak water level, flood course, total flood volume (flood flow), and flood frequency (or return period).

Peak flow refers to the instantaneous maximum flow value of a flood through a section of a river, in units of cubic meters per second ( m3/s ); the peak water level corresponding to the peak flow is called the peak flood level and is measured in meters ( m ).

Taking the time as the abscissa and the water level or flow of the river as the ordinate, the entire process curve of the flood from rising to peak and falling back to the original state can be drawn, which is called the flood process line.

The total flow (water volume) of a section of a river through a flood is called the flood of the flood. It is often measured in units of millions of cubic meters. The hydrology usually uses the maximum amount of water in a certain period of time during a flood. Comparing the size of floods, such as maximum 3 days, 7 days, 15 days, 30 days, 60 days, etc.

Third , what types of floods in China?

Floods are natural phenomena in which the rapid increase of water volume in rivers and the rapid rise in water levels. The formation of floods is often affected by natural factors such as climate and underlying surface and human activities. According to regions, there are six kinds of river floods, snowmelt floods, floods of flooded rivers, ice floods, floods mixed with rain and snow, and dam-break floods.

The major floods in China's rivers are mostly rainstorms and floods, occurring mostly in summer and autumn. Some areas in the south may also occur in the spring. Divided by regions, storm floods dominate the central and eastern regions of China, and floods and snow and snow mix floods in the northwestern region. The '98 Great Flood of the Yangtze River ' and the '98 Nenjiang River and the Songhua River's catastrophic flood were all formed by storm floods.

4. What major flood disasters have occurred in China in the past 100 years?

Ten floods in China are frequent, and the major floods that occurred in China in the past hundred years are as follows.

1915 : Zhujiang Dashui. Guangdong, Guangxi flooded farmland 947,000 hm2, the affected population of 600 million people, flooded the Pearl River Delta, Guangzhou City flooded 7th.

1931 : The Yangtze River and the Huaihe River. The floods throughout the year spread throughout 16 provinces. The worst disasters were in the lower reaches of the Yangtze River and in the Huaihe River Basin. Eight provinces of Hunan, Hubei, Fujian, Zhejiang, Jiangsu, Jiangsu, Shandong, Shandong, and Guizhou were affected by farmland . The affected area was 9.73 million hm2 . The affected population was 51.27 million, accounting for 1/1 of the total population in the eight provinces at the time. 4 , 220,000 people died . The mainstream of the Yangtze River runs west from Shashi City in Hubei Province. The cities along the Yangtze River to Shanghai are flooded. Wuhan City was flooded for 100 days.

1932 : Songhuajiang Dashui. The affected farmer was 1.9 million hm2 , and 20,000 people died . The Harbin urban area was flooded for as long as a month.

1933 : Yellow River flood. In the lower reaches of the Yellow River, there were more than 60 joint breaches on both sides of the river, with an area of 6,600 km 2 inundated , 2.73 million people affected , and 12,700 people were killed .

1935 : Yangtze River. The flooded agricultural lands in the four provinces of Dashui, Hubei, Fujian, and Fujian were 1.509 million hm2 , with more than 10 million affected people and 142,000 deaths.

1939 : Haihe River. H 3.467 million square meters of farmland flooded, affected population of over 800 million people, 1.33 million people died, Tianjin flooded for up to a half months, the downtown streets depth of 1m ~ 2m.

1951 : Liaohe Dashui. Liaoning and Jilin provinces flooded farmland h 434,000 square meters, the affected population of 87.6 million people, the death of 3100 people.

1954 : The Yangtze River and the Huaihe River. Yangtze River flooded farmland 3.17 million hm2, by 1888 the population of people, killed three thousand people. In the Huaihe River Basin, 400.82 million hm2 of disaster- prone farmland have occurred .

1858 : Yellow River. The largest flood occurred since the measured data occurred at the Huayuankou Station of the Yellow River, and the floodplain and the Dongping Lake were flooded.

1963 : Haihe Dashui. In the south of Henan Province, a major flood occurred, with 4.4 million hm2 of farmland flooded , and the Beijing-Guangzhou Railway was suspended.

1975 : Huaihe River. In early August the upper reaches of the Huaihe a rare rainstorm, Henan Biyang rain forest village 3 amounted to 1605.3mm, located in the central area of the storm wrecked two large reservoirs, Henan Province, 820 million people, 1.06 million square meters of arable land h Severe floods caused 5.6 million collapsed houses and 26,000 deaths.

1981 : The upper reaches of the Yangtze River. 138 counties and cities in Sichuan Province are affected.

1982 : Yellow River Dashui.

1991 : Huaihe River and Taihu Lake. 4.01 million hm2 Huaihe River flooded arable land, the affected population of 5423 million people, 1.96 million houses collapsed.

1994 : Xijiang Dashui.

1995 : Changjiang, Liaohe and Songhua Rivers. In the year, the flooded farmland in the four provinces of the Yangtze River, Hunan, Hubei, and Chongqing was 3.214 million square meters, and the population was 85.26 million people. Northeast Liaoning, Jilin and Heilongjiang provinces farmland flooded 2.232 million hm2, the affected population 1078.6 million.

1996 : Pearl River, Yangtze River, Haihe River. In the same year, various provinces (autonomous regions and municipalities directly under the Central Government) suffered floods and floods to varying degrees, and more than half of the provinces (regions) were seriously affected. There were 311 cities above the county level that flooded the country, with an area of 11.8233 million ha affected by floods and 267 million people affected by the floods . The direct economic loss was 220.86 billion yuan.

In 1998 : The Yangtze River, Nenjiang River, Songhua River, Pearl River, and Lancang River were flooded.

Judging from the time-series distribution of the flood, China has had three periods of frequent flooding in the past 100 years. The first frequency was from 1930 to 1939 , and the second frequency was from 1949 to 1963 . In the frequent occurrence period, almost all major rivers in the seven major rivers have been flooded, and some rivers have even experienced large floods. After entering the 1990s , China was in the third high-frequency period of floods. The Huaihe River and the Taihu Lake in 1991 , the Xijiang River in 1994 , the Yangtze River, the Liaohe River, and the Songhua River in 1995 , and the middle reaches of the Yangtze River, the Pearl River, and the Haihe River in 1996 . Dashui, the Yangtze River, Nenjiang River, and the Songhua River in 1998 . Therefore, in the future, we must also be particularly vigilant against the occurrence of catastrophic floods in the valleys of the Yangtze River, the Yellow River, the Huaihe River, and the Haihe River.