Hanjiang plain?

A plain formed by alluvial deposits of the Yangtze River and the Han River. Located in the middle reaches of the Yangtze River. Together with Dongting Lake Plain, it is called Lianghu Plain. It is located in the south-central part of Hubei Province, starting from Zhijiang in the west, Wuhan in the east, Zhongxiang in the north and Dongting Lake Plain in the south. It is between 29 26 ′ ~ 310 ′ north latitude and1145 ′ ~1416 ′ east longitude. It covers an area of more than 30,000 square kilometers.

Geomorphic plain belongs to Jianghan fault depression of Yangtze paraplatform, with low and flat terrain. Except for the gentle slope about 50 meters above sea level and the low mountain above 100 meters above sea level, its altitude is below 35 meters. Generally, it is slightly inclined from northwest to southeast, with an altitude of about 35 meters in the northwest, below 25 meters in the southeast and only 23 meters in Hankou. Lakes are scattered all over the plain, and water networks and riverbanks are intertwined. The surface materials are mainly composed of modern river sediments and lake sediments, belonging to fine sand, silt and clay, and the tertiary red beds are only exposed at the edge of the plain.

The Yangtze River, Hanjiang River and Dongjing River are relatively high in terrain, generally 28-38 meters. The landform can be divided into two parts: ① Bund land located between riverbed and artificial dike, with strong modern alluvial effect and high terrain, mostly over 30 meters, and mostly sandy soil. (2) Generally, the plain in the embankment is 3 ~ 6m lower than the embankment, slightly inclined inward, and the soil is mostly thick silty loam.

The river is relatively low, forming a long concave land, mainly Tianmen River and Diaocha Lake concave land between hanbei river and Hanjiang River; Tongshun River and Paihu Depression between Hanjiang River and Dongjing River; Four lakes between the Dongjing River and the Yangtze River (Changhu, Sanhu, Baihu and Honghu); Songzi River and Wangjia Lake depression on the right bank of the Yangtze River. The elevation of the concave ground is mostly 25 ~ 28 meters, and the surface is mainly composed of clay. The groundwater level is generally 0.5 ~ 1.0 meters away from the surface, or even less than 0.5 meters. Every time it rains, it is easy to become waterlogged.

There are more than 300 lakes in Jianghan Plain, including Honghu Lake, Diaocha Lake, Changhu Lake, Paihu Lake, Datong Lake and Dasha Lake. Lakes are generally flat and shallow, and are the base of freshwater culture; It can also adjust the river water volume and reduce the drought and flood disasters in plain areas.

The climate plain belongs to the north subtropical monsoon climate, with an average annual sunshine hours of about 2,000 hours and an annual total solar radiation value of about 460-480 kJ/cm2. The frost-free period is about 240 ~ 260 days, the duration above 10℃ is about 230 ~ 240 days, and the active accumulated temperature is 5 100 ~ 5300℃. All parts of the plain are suitable for growing warm crops such as cotton and rice. The annual average precipitation is1100 ~1300mm, and the precipitation from April to September with high temperature accounts for about 70% of the annual precipitation. Hanjiang river basin is an important channel for cold air to go south, and Jianghan plain bears the brunt. Low humidity and rainy weather often occur in spring and autumn, which makes the probability of dry seedling rot and empty shell rate of late rice in the second season higher. In case of years with long plum rains and heavy rains, early summer is prone to floods; Midsummer is often controlled by subtropical ridge; There are many sunny days in autumn and many droughts in summer and autumn.

The Wan Li of the Yangtze River is long, and the dangerous section is in Jingjiang. First, when the water level is high in summer, the water surface of the Yangtze River is often several to ten meters higher than the plains on both sides. Second, the meandering reach of Jingjiang River is developed, the river course is curved and the water flow is not smooth. Since ancient times, the Han River has been called "a winding river", and its flood volume is not as good as that of the Yangtze River. However, the downstream channel is funnel-shaped, with a wide upper part and a narrow lower part. Every flood seriously threatens both sides of the river, especially when it meets the flood peak of the Yangtze River. When the flood season of the outer river coincides with the season when the water level of the inner lake rises and the groundwater level rises, the outer flood is waterlogged and the waterlogging is serious.

Before 1949, the plain water system was very chaotic and the flood disaster was serious. Jiang and Han dikes have been in disrepair for a long time, and they often burst in floods. During the more than 300 years from 1644 to 1949, Jingjiang levee burst 19 times, of which 193 1 year burst, and more than 333,000 hectares of fertile land in 9 counties were flooded,120,000. Since 1949, Jingjiang, Hanjiang and Dongjinghe dikes have been repaired and reinforced, and Jingjiang flood diversion project and Hanjiang Dujiatai flood diversion project were completed on 1952 and 1956 respectively. Especially after Danjiangkou Reservoir of Hanjiang River (see Danjiangkou Water Control Project) 1968 impounded for power generation, the flood in the upper reaches of Hanjiang River was effectively controlled. With the cooperation of the above dikes and flood diversion projects, the threat of flood to Jianghan Plain was greatly reduced. At the same time, Shangchewan and Zhongzhouzi projects were carried out in the lower Jingjiang reach, which increased the flood discharge and improved the flood control capacity.

Since 1949, the original water system has been greatly adjusted. From Weijiatai in Tianmen County in the west to Xingou Town in Hanyang County in the east, the Hanbei River with a length of nearly 100 km has been excavated. Main canal in Sihu area 126 km; Dozens of large and medium-sized backbone irrigation and drainage channels such as East-West Main Canal and Tianguan Canal. By the early 1980s, the plain irrigation and drainage system was initially formed, which reduced the drought and flood disasters.

Economic overview of Jianghan Plain Dry land accounts for about 52% of the total cultivated land, and paddy field accounts for about 48%. The dry land is concentrated in the plain in the dike, and the cotton fields in the plain in the dike account for 40 ~ 60% of the cultivated land area, and some areas are as high as 80% or more. After 1949, it became one of the high-yield and high-quality cotton regions in China. Paddy field is concentrated in the valley between rivers and the edge of the plain, and the commodity rate of grain is high. It is one of the important commodity grain bases in China. A large number of lakes have been reclaimed, and the area of lakes has increased, with more fields and less labor, extensive farming and low and unstable output per unit area. In recent years, returning farmland to lakes has been partially realized. Oil crops occupy an important position in the plain, mainly rape, sesame and peanut.

Jianghan Plain Lake area is a famous aquatic area in China, which is rich in grass, silver carp and bighead carp, and yif of carp, crucian carp, cinnamon, bighead carp and snakehead. It is also rich in shrimp, crab, shellfish, lotus, lotus root, water chestnut, reed and waterfowl. Among them, many aquatic products are important export commodities. With water conservancy construction and comprehensive management of rivers and lakes, aquatic products have changed from natural fishing to artificial breeding.