When the river flows into the ocean or lake, due to the decrease of velocity, a large amount of sediment is deposited and gradually develops into an alluvial plain. Delta, also known as estuary plain, looks like a triangle in plan, with the top pointing upstream and the bottom as its outer edge, so it is called delta. The delta has a large area, deep upper layer, dense water network, flat surface and fertile soil. For example, the Yangtze River Delta and Pearl River Delta in China. Delta can be divided into: ① pointed delta, such as the Yangtze River Delta in China; (2) Fan deltas, such as the Nile Delta in Africa; (3) Bird's Foot Delta, such as Mississippi River Delta in the United States. There are many famous deltas in the world, including Nile Delta, Mississippi Delta, Danube Delta, Mekong Delta, Ganges Delta and Yangtze Delta in China. Delta region is not only a good agricultural region, but also a region rich in oil, natural gas and other resources.
When the river is injected into the ocean or lake, the water flows outward, and the kinetic energy is obviously weakened, and the subsequent sediment accumulates, forming a flat land extending to the ocean or lake, which is often delta-shaped, so it is called delta.
Chu Chiang Delta
Formerly known as Yuejiang Plain. Located in the eastern coast of Guangdong Province, China, it is a delta complex with a radial estuary, which is the general name of the large delta formed by the simultaneous alluvial of Xijiang River and Beijiang River and the small delta formed by the alluvial of Dongjiang River. It is an inverted triangle, with the bottom line starting from Sanshui City in the west, Guangzhou City in the east, and Shilong, with the apex at Yamenwan. The area is about 1. 1 10,000 square kilometers. Alluvium is thin, generally 20 ~ 30 meters. The ground fluctuates greatly, surrounded by hills, mountains and islands, accounting for 30% of the area. The central part is plain, distributed in southern Guangzhou, northern Zhongshan, eastern Jiangmen and western Humen. The annual sediment transport capacity of the Pearl River system is more than 80 million tons, and the delta near the estuary is still extending to the South China Sea. In the estuary area, it can stretch 10 ~ 120 meters every year, which is one of the key reclamation areas in China. The delta has a subtropical climate, which is warm and humid all year round. The annual average temperature is 2 1 ~ 23℃, the coldest 1 monthly average temperature 13 ~ 15℃, and the hottest July average temperature is above 28℃. There are frequent typhoons from June to 10, with concentrated rainfall and the hottest weather. The annual average precipitation exceeds1500mm. The rainy season is synchronized with the high temperature season, with fertile soil and rivers, which is beneficial to agriculture. The yield per unit area of rice is among the best in China. Tropical and subtropical fruits include litchi, citrus, banana, pineapple, longan, carambola, mango, grapefruit and lemon. Three-dimensional agricultural structures such as mulberry-based fish ponds, fruit-based fish ponds and sugarcane-based fish ponds have been developed, which has become a model of ecological agriculture in China. There are sugar, silk, food, paper, machinery, chemicals, building materials, shipbuilding and other industries, known as the pearl of the South China Sea.
Physical and geographical characteristics of the Pearl River Delta
The Pearl River Delta is a tropical delta, because its geographical location is south of the Tropic of Cancer (for a small delta), and for a large delta, it is also between 23 40 ′-265 438+0 30 ′ north latitude, that is, most of it belongs to the tropical range. From the climate point of view, the big delta also belongs to the tropical region (see Zhu Kezhen et al. Phenology, 1962). Landform development also has this feature, and the vegetation landscape is more influenced by it, developing into tropical monsoon rainforest vegetation. Moreover, because the northern part of the delta is the mountainous area of northern Guangdong, it plays a barrier role to the cold current from the north, so that tropical vegetation can invade the mountainous area north of the Tropic of Cancer along the valley.
The Pearl River Delta region includes Guangzhou, Shenzhen, Zhuhai, Foshan, Jiangmen, Zhongshan, Dongguan and Huicheng, Huiyang, Huidong and Boluo in Huizhou, and Ruizhou, Dinghu, Gaoyao and Sihui in Zhaoqing. The whole area accounts for 23.4% of the total area of the province, and the population accounts for 31.4% of the total population of the province (1.994). In recent years, GDP has accounted for about 70% of the province's GDP. The Pearl River Delta is one of the fastest growing areas in China. With the rapid development of economy, the social development in this area presents the characteristics of high degree of rural industrialization and rapid process of urban-rural integration.
Seen from the topographic boundary of the Pearl River Delta, Luoping Mountain Range is the dividing line between the west and the north, that is, the Xijiang River Valley is west of Luoping Mountain Range, which is customarily called the western mountainous area of Guangdong. To the north of the mountain range is the Beijiang River system, or the mountainous area of northern Guangdong. Luofushan area in the east is the eastern boundary of the delta.