Why can't you dig the sediment of the Yangtze River?

Because the bottom of the river bed is uneven, there will be large and small gyrations under the action of water flow, which will affect shipping and increase insecurity. When the river sand is dug away, it will strengthen the scouring effect of water flow on the riverbed, increase the speed of water flow and increase the scouring on both banks.

The geographical distribution of drought and flood disasters in the Yangtze River basin is very strong, and the drought and flood disasters in different regions vary greatly. The average frequency of severe drought is 5.55%, and the probability of drought in the middle and lower reaches is higher than that in the upper reaches. The drought frequency in the Yangtze River Delta, the middle and lower reaches of the main stream and Dongting Lake is as high as 9.0%, which is the highest in the whole flow area.

Followed by the upper reaches of Jialing River, the highest drought frequency in the middle is above 7.0%. The average frequency of flood disasters in the basin is 7.97%, which is obviously higher than that of drought. The regional distribution of flood disasters is basically consistent with drought, that is, the middle and lower reaches are generally higher than the upper reaches.

There is an east-west high-frequency flood disaster zone in the main stream and the middle and lower reaches of the two lakes, in which the northern part of Poyang Lake and the middle reaches of Yuanjiang River and Lijiang River to Dongting Lake are two high-frequency central areas of flood disaster, and the central frequency is as high as 12.0%.

Jialing River and Hanjiang River in the upper reaches of the Yangtze River are the third largest high-frequency flood areas. The above-mentioned flood high-frequency zones and centers are basically consistent with the Meiyu zone in the middle and lower reaches of early summer, the concentrated rain zone in the upper reaches of midsummer and the main rainstorm centers in the basin.

Extended data:

The southeast monsoon and southwest monsoon, which come from the Pacific Ocean and the Indian Ocean respectively and carry a lot of water vapor, prevail in the Yangtze River basin in summer and around summer, and precipitation is formed in the process of monsoon advance and retreat and cold and warm airflow confrontation.

In mid-June, the ridge line of the subtropical high jumped to 20 ~ 25 north latitude, and the middle and lower reaches entered the rainy season. In mid-July, it jumped to the north, plum blossoms appeared in this area, and it entered the summer drought weather. In winter and around winter, dry and cold air from polar regions and high latitudes in Asia prevails in the basin, with little precipitation.

The average annual precipitation in the Yangtze River basin is nearly 1 100 mm ... April to 10 is the rainy season, and its precipitation can account for 85% of the annual precipitation. Except White in Jinsha River and Luhuo in Yalong River, there are occasional rainstorms in the remaining 6,543,800 km.

There are mainly two areas with high rainstorm value in the basin: one is centered in northeast Jiangxi, including northern Hunan, southern Anhui and southern Hubei, with annual average precipitation1800 ~ 2000 mm;

Second, the Ya 'an area in western Sichuan, including eastern Sichuan, northern Sichuan, southwestern Shaanxi, western Hubei and northwestern Yunnan, has an average annual precipitation of about 2,000 mm ... The daily rainstorm coverage in the basin is about 40,000 ~10.5 million km, with a maximum of 210.3 million km.

The precipitation of each tributary is: 600-800 mm in the upper reaches of Yalong River and 900-1800 mm in the middle and lower reaches; 370 ~ 600 mm in the upper reaches of Dadu River and 652 ~ 1949 mm in the middle and lower reaches;

The upper reaches of Tuojiang River 1200 ~ 1400 mm, Longmen Mountain is a rainstorm area, and the middle and lower reaches are 900 ~1000 mm; Jialing river basin 1494 mm, and the southern foot of Daba mountain is a rainstorm area; Wujiang river basin1163mm;

Qingjiang river basin 1400 mm, Enshi and Wufeng are the rainstorm centers in western Hubei; Hanjiang river basin 700 ~ 1 100 mm; Zishui River Basin 1200 ~ 1800 mm, Liuduzhai, Zhexi to Taojiang are rainstorm areas;

Yuanjiang river basin 1 100 ~ 1800 mm; Lishui river basin 1300 ~ 1800 mm, Wufeng and Hefeng are rainstorm areas; Ganjiang river basin 1400 ~ 1800 mm.