Where is the lower reaches of the Yangtze River?

The Yangtze River enters the lower reaches after receiving the Poyang Lake system at Hukou, Jiangxi Province. The lower reaches of the Yangtze River pass through Jiangxi, Anhui and Jiangsu, accept the Huangpu River, the last tributary in Shanghai, and then flow into the East China Sea, with a total length of about 835 kilometers. * * * The basin covers an area of about 6.5438+0.3 million square kilometers, which is the largest section of the Yangtze River and the richest area in the whole basin.

? The northern part of the lower reaches of the Yangtze River is bounded by Dabie Mountain and Jianghuai Hills, adjacent to the Huaihe River Basin. The southern part is bounded by Huangshan Mountain and Tianmu Mountain, adjacent to Qiantang River Basin. There are more than 200 kilometers between the north and south watershed, most of which are plain depressions and lakes. The hills are low and scattered, most of them are located on the south bank, and there are few mountains and mountains. The river is wider than the middle reaches, and the water volume is also large.

? The main stream of the lower reaches of the Yangtze River belongs to a relatively stable bifurcated river, with many and large Jiang Xinzhou, which divides the river into many parallel tributaries. Because the main flow swings to the south bank, and the south bank has control "nodes" formed by natural rock heads and mountains every ten or twenty kilometers, as well as the constraints of river works such as dikes, the river is basically stable, and only tributaries flow.

? Below Jiangyin, the Yangtze River enters the sea. The width of the river gradually widened from 1. 1 km to more than 5 km, reaching the south branch and the north branch separated by Chongming Island. The river width between the north and south banks is close to 100 km, which is an inseparable sight between the river and the sea. Chongming Island covers an area of 1000 square kilometers, and there are several along the coast of China. It is also the largest sandbar island in China, with a history of 1300 years. The south branch and the north branch on both sides of Chongming Island have been alternately used as the main floods of the Yangtze River since its formation. Due to the abundance of water and sand in the south branch, many open sands and hidden islands have been deposited, and nearly 100 sandbars have surfaced. The two largest sandbars are Changxing Island and hengsha island. They further separated Nangang Branch from Nangang Branch and Beigang Branch. In recent years, the main flood has gradually turned to the north trough. This change is endless. If the dike is not diverted, the main stream of the Yangtze River will return to the north branch one day.

? In order to stabilize the river regime, prevent the bank from collapsing, maintain the main flood of the south branch and prevent the Yangtze River route from being far away from Shanghai Port, a large number of dike projects, revetment projects and dredging projects have been set up in the lower reaches of the Yangtze River since the Ming and Qing Dynasties. In recent decades, the engineering quantity is the largest and the effect is the most remarkable. Due to the low terrain and many lakes on the north shore, most of the downstream dikes are still located on the north shore. Such as Tong Tong in Susong, Wangjiang and Huaining counties and Wuwei levee with a length of175km in Wuwei county. Among them, Wuwei levee is the most important, which is the safety barrier of 8 counties 1 city in Chaohu Lake Basin, and ranks as two key levees of the Yangtze River together with Jingjiang levee in the middle reaches. In addition, Subei seawall (Funing to Qidong, length 1 km, commonly known as Gongfandi) is located in the Yangtze River Delta.

Since 1997, thousands of dikes have been built in Jiangsu Province. After 1998 flood, Jiangxi, Anhui and other provinces also carried out large-scale dike construction.

The main tributaries in the lower reaches of the Yangtze River are Qingyi River, Shuiyangjiang River and Taihu Lake formed by Dongtiaoxi River, Xitiaoxi River, Wusongjiang River and Huangpu River in the south bank, and Anhe River, Chuhe River and Chaohu Lake in the north bank. These tributaries are short and small, with limited water. In addition, the main stream is mostly tidal reach, which is often affected by tidal jacking. Therefore, Datong, Anhui Province has always been regarded as the control section of the whole river to calculate water and sediment. The annual inflow of the Yangtze River through Datong is 65.438+0.36 billion cubic meters in the highest year, 637 billion cubic meters in the lowest year, and the multi-year average is 96.5438+0./kloc-0.00 billion cubic meters, but it is usually 654.38+0 trillion cubic meters. The amount of sediment discharged into the sea is 472 million tons, or 500 million tons.

? The shipping in the lower reaches of the Yangtze River is more developed than that in the upper and middle reaches. The main stream can pass 3000-ton ships, 5000-ton oil tankers and mineral barges from Hankou to Nanjing, and 15000-ton seagoing ships can pass below Nanjing. There are thousands of tributaries and artificial canals, with a total navigation mileage of nearly 20 thousand kilometers. The main waterways are Qingyi River, Shuiyangjiang River, Hefei-Wuhu Line and Jiangnan.

The North-South Grand Canal, which meets the Yangtze River near Zhenjiang, runs through Hebei, Shandong, Jiangsu and Zhejiang provinces, and connects the five major water systems of Haihe River, Yellow River, Huaihe River, Yangtze River and Qiantang River. The greatest water conservancy project in ancient times reached Beijing in the north and Hangzhou in the south, with a total length of 1794 km, of which the Li Canal and the Jiangnan Canal were in the Yangtze River basin. It starts in Zhenjiang and ends in Hangzhou. It is about 400 kilometers long. Along the way, it passes through Jiangnan water network area and famous tourist cities such as Changzhou, Wuxi, Suzhou and Jiaxing. The Grand Canal dug by the ancients has been playing a role for more than 1000 years. After the founding of New China, after more than 30 years of intermittent dredging, shiplocks and docks were built, which changed the old appearance and played an increasingly important role in prospering the economy, developing transportation and tourism along the line.

Although there are 39 1 10,000 kilowatts of hydropower resources in the lower reaches of the Yangtze River, the inundation loss caused by dam construction is too great and lacks practical significance. In fact, only about 490,000 kilowatts of tributaries can be developed, including 470,000 kilowatts in Anhui, 3600 kilowatts in Jiangsu and 0/0.4 million kilowatts in Zhejiang/KLOC. At present, about 220,000 kilowatts have been developed, of which 80% are in Qingdao.

In addition to the above dikes, revetment works, waterway dredging and port construction, water conservancy construction in the lower reaches of the Yangtze River has also done many projects in water diversion irrigation, flood discharge and drainage in the plain.

The scale of water diversion irrigation in Jianghuai area of Anhui Province is the largest and the prospect is the most impressive. There are many rivers and lakes in the Yangtze River, but few in the Huaihe River, with low watershed and many gaps. This is an ideal route to divert water from the Yangtze River to the Huaihe River. The largest projects are Fenghuangjing Water Diversion Hub and Simashan Irrigation Project. The main body of Fengjing Project is to open a new river from Zongyang to Chaohu Lake and transfer water to the east of Chaohu Lake and the tributary of Huaihe River. It also supplies water to Hefei, Huainan, Bengbu and other cities. At present, it is gradually expanding northward. The Sima Mountain project mainly includes the 27-kilometer waterway of the Wujiang River Diversion Hub, dredging in the upper reaches of the Chuhe River, multi-stage sluices, substations and pumping stations, and irrigates 3.55 million mu of dry land in the Jianghuai area with water sources such as Jiang Shui, Chuhe River and Chihe River, a tributary of the Huaihe River (at present, the initial project can irrigate 6.5438+0 million mu). Jiangdu Water Control Project, located near Yangzhou City, Jiangsu Province, is the leading project of the East Route of South-to-North Water Transfer Project. The whole project consists of four large pumping stations, seven sluices and three shiplocks, which is magnificent.